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Human Physiology/The male reproductive system

Introduction
In simple terms, reproduction is the process by which organisms create descendants. This miracle is a characteristic that all living things have in common and sets them apart from nonliving things. But even though the reproductive system is essential to keeping a species alive, it is not essential to keeping an individual alive.

In human reproduction, two kinds of sex cells or gametes are involved. Sperm, the male gamete, and a secondary oocyte (along with first polar body and corona radiata), the male gamete must meet in the female reproductive system to create a new individual. For reproduction to occur, both the female and male reproductive systems are essential. It is a common misnomer to refer to a woman's gametic cell as an egg or ovum, but this is impossible. A secondary oocyte must be fertilized by the male gamete before it becomes an "ovum" or "egg".

While both the female and male reproductive systems are involved with producing, nourishing and transporting either the oocyte or sperm, they are different in shape and structure. The male has reproductive organs, or genitals, that are both inside and outside the pelvis, while the female has reproductive organs entirely within the pelvis.

The male reproductive system consists of the testes and a series of ducts and glands. Sperm are produced in the testes and are transported through the reproductive ducts. These ducts include the epididymis, vas deferens, ejaculatory duct and urethra. The reproductive glands produce secretions that become part of semen, the fluid that is ejaculated from the urethra. These glands include the seminal vesicles, prostate gland, and bulbourethral glands.

Testes
The testes (singular, testis) are located in the scrotum (a sac of skin between the upper thighs). In the male fetus, the testes develop near the kidneys, then descend into the scrotum just before birth. Each testis is about 1 1/2 inches long by 1 inch wide. Testosterone is produced in the testes which stimulates the production of sperm as well as give secondary sex characteristics beginning at puberty.

Scrotum

The two testicles are each held in a fleshy sac called the scrotum. The major function of the scrotal sac is to keep the testes cooler than thirty-seven degrees Celsius (ninety-eight point six degrees Fahrenheit). The external appearance of the scrotum varies at different times in the same individual depending upon temperature and the subsequent contraction or relaxation of two muscles. These two muscles contract involuntarily when it is cold to move the testes closer to the heat of the body in the pelvic region. This causes the scrotum to appear tightly wrinkled. On the contrary, they relax in warm temperatures causing the testes to lower and the scrotum to become flaccid. The temperature of the testes is maintained at about thirty-five degrees Celsius (ninety-five degrees Fahrenheit), which is below normal body temperature. Temperature has to be lower than normal in order for spermatogenesis (sperm production) to take place.

The two muscles that regulate the temperature of the testes are the dartos and cremaster muscles:

 * Dartos Muscle

The dartos muscle is a layer of smooth muscle fibers in the subcutaneous tissue of the scrotum (surrounding the scrotum). This muscle is responsible for wrinkling up the scrotum, in conditions of cold weather, in order to maintain the correct temperature for spermatogenesis.

 * Cremaster Muscle

The cremaster muscle is a thin strand of skeletal muscle associated with the testes and spermatic cord. This muscle is a continuation of the internal oblique muscle of the abdominal wall, from which it is derived. Seminiferous Tubules

Each testis contains over 100 yards of tightly packed seminiferous tubules. Around 90% of the weight of each testes consists of seminiferous tubules. The seminiferous tubules are the functional units of the testis, where spermatogenesis takes place. Once the sperm are produced, they moved from the seminiferous tubules into the rete testis for further maturation.

Interstitial Cells (Cells of Leydig)

In between the seminiferous tubules within the testes, are instititial cells, or, Cells of Leydig. They are responsible for secreting the male sex hormones (i.e., testosterone).

Sertoli Cells

A Sertoli cell (a kind of sustentacular cell) is a 'nurse' cell of the testes which is part of a seminiferous tubule.

It is activated by follicle-stimulating hormone, and has FSH-receptor on its membranes.

Its main function is to nurture the developing sperm cells through the stages of spermatogenesis. Because of this, it has also been called the "mother cell." It provides both secretory and structural support.

Other functions During the Maturation phase of spermiogenesis, the Sertoli cells consume the unneeded portions of the spermatazoa.

Efferent ductules

The sperm are transported out of the testis and into the epididymis through a series of efferent ductules.

Blood Supply

The testes receive blood through the testicular arteries (gonadal artery). Venous blood is drained by the testicular veins. The right testicular vein drains directly into the inferior vena cava. The left testicular vein drains into the left renal vein.

Epididymis
The seminiferous tubules join together to become the epididymis. The epididymis is a tube that is about 2 inches that is coiled on the posterior surface of each testis. Within the epididymis the sperm incomplete their maturation (full maturation occur in female genital tract) and their flagella become mobile. This is also a site to store sperm, nourishing them until the next ejaculation. Smooth muscle in the wall of the epididymis propels the sperm into the ductus deferens. Vasa efferentia from the rete testis open into the epididymis which is a highly coiled tubule. The epididymis has three parts- 1)head or caput epididymis- it is the proximal part of the epididymis. It carries the sperms from the testis. 2)body or corpus epididymis- it the highly convoluted middle part of the epididymis 3)tail or cauda epididymis- it is the last part that takes part in carrying the sperms to the vas deferens. The cauda epididymis continues to form less convoluted vas deferens.

Ductus Deferens
The ductus (vas) deferens, also called sperm duct, or, spermatic deferens, extends from the epididymis in the scrotum on its own side into the abdominal cavity through the inguinal canal. The inguinal canal is an opening in the abdominal wall for the spermatic cord (a connective tissue sheath that contains the ductus deferens, testicular blood vessels, and nerves. The smooth muscle layer of the ductus deferens contracts in waves of  peristalsis during ejaculation.

Seminal Vesicles
The pair of seminal vesicles are posterior to the urinary bladder. They secrete fructose to provide an energy source for sperm and alkalinity to enhance sperm mobility. The duct of each seminal vesicle joins the ductus deferens on that side to form the ejaculatory duct.

Ejaculatory Ducts
There are two ejaculatory ducts. Each receives sperm from the ductus deferens and the secretions of the seminal vesicle on its own side. Both ejaculatory ducts empty into the single urethra.

Prostate Gland
The prostate gland is a muscular gland that surrounds the first inch of the urethra as it emerges from the bladder. The smooth muscle of the prostate gland contracts during ejaculation to contribute to the expulsion of semen from the urethra.

Bulbourethral Glands
The bulbourethral glands also called Cowper's glands are located below the prostate gland and empty into the urethra. The alkalinity of seminal fluid helps neutralize the acidic vaginal pH and permits sperm mobility in what might otherwise be an unfavorable environment.

Penis
The penis is an external genital organ. The distal end of the penis is called the glans penis and is covered with a fold of skin called the prepuce or foreskin. Within the penis are masses of erectile tissue. Each consists of a framework of smooth muscle and connective tissue that contains blood sinuses, which are large, irregular vascular channels.

Urethra
The urethra, which is the last part of the urinary tract, traverses the corpus spongiosum and its opening, known as the meatus, lies on the tip of the glans penis. It is both a passage for urine and for the ejaculation of semen.

Composition of human semen
The components of semen come from two sources: sperm, and "seminal plasma". Seminal plasma, in turn, is produced by contributions from the seminal vesicle, prostate, and bulbourethral glands.

Seminal plasma of humans contains a complex range of organic and inorganic constituents.

The seminal plasma provides a nutritive and protective medium for the spermatozoa during their journey through the female reproductive tract. The normal environment of the vagina is a hostile one for sperm cells, as it is very acidic (from the native microflora producing lactic acid), viscous, and patrolled by immune cells. The components in the seminal plasma attempt to compensate for this hostile environment. Basic amines such as putrescine, spermine, spermidine and cadaverine are responsible for the smell and flavor of semen. These alkaline bases counteract the acidic environment of the vaginal canal, and protect DNA inside the sperm from acidic denaturation.

The components and contributions of semen are as follows:

A 1992 World Health Organization report described normal human semen as having a volume of 2 ml or greater, pH of 7.2 to 8.0, sperm concentration of 20x106 spermatozoa/ml or more, sperm count of 40x106 spermatozoa per ejaculate or more and motility of 50% or more with forward progression (categories a and b) of 25% or more with rapid progression (category a) within 60 minutes of ejaculation.

Hormone Regulation
Hormones which control reproduction in males are:

Gonadotropin-Releasing Hormone (GnRH): Luteinizing Hormone (LH): Follicle-Stimulating Hormone (FSH): Testosterone:
 * The hypothalamus secretes this hormone into the pituitary gland in the brain.
 * There are two gonadotropic hormones, FSH and LH.
 * The pituitary gland secretes this hormone after receiving a GnRH signal from the hypothalamus.
 * LH stimulates Leydig cells, in the testes, telling them to produce testosterone.
 * The pituitary gland also secretes this hormone.
 * Testosterone helps FSH run through the bloodstream to make Sertoli cells, located in the seminiferous tubules of the testes, to make immature sperm to mature sperm.
 * Also known as "the male hormone" and "androgen".
 * Testosterone is vital for the production of sperm.

Erection
The erection of the penis is its enlarged and firm state. It depends on a complex interaction of psychological, neural, vascular and endocrine factors. The term is also applied to the process that leads to this state.

A penile erection occurs when two tubular structures that run the length of the penis, the corpora cavernosa, become engorged with venous blood. This is a result of parasympathetic nerve induced vasodilation. This may result from any of various physiological stimuli. The corpus spongiosum is a single tubular structure located just below the corpora cavernosa, which contains the urethra, through which urine and semen pass during urination and ejaculation, respectively. This may also become slightly engorged with blood, but less so than the corpora cavernosa.

Penile erection usually results from sexual stimulation and/or arousal, but can also occur by such causes as a full urinary bladder or spontaneously during the course of a day or at night, often during erotic or wet dreams. An erection results in swelling and enlargement of the penis. Erection enables sexual intercourse and other sexual activities (sexual functions), though it is not essential for all sexual activities.

Ejaculation
Emission is the term used when sperm moves into the urethra. Ejaculation is the term used when sperm is forced out of the urethra and the penis. These are both stimulated by sympathetic nerves.

Sperm Production
A spermatozoon or spermatozoan (pl. spermatozoa), from the ancient Greek σπέρμα (seed) and ζῷον (living being) and more commonly known as a sperm cell, is the haploid cell that is the male gamete.

Spermatagonia divides several times during the process of sperm development. The entire process of sperm formation and maturation takes about 9-10 weeks. The separate divisions that take place and what happens in each are as follows:

 * First division: The first division is done by mitosis, and ensures a constant supply of spermatocytes, each with the diploid number of chromosomes.

 * Second division: Spermatocytes then undergo a series of two cell divisions during meiosis to become secondary spermatocytes.

 * Third division: Secondary Spermatocytes finally become spermatids.  Spermatids, which are haploid cells, mature slowly to become the male gametes, or sperm.

The sperm is the main reproductive cell in males. The sperms differ in that each carry a set of chromosomes dividing each into either a male, or female sperm. The females differ in that they carry a X gene, while the male sperm carry a Y gene. The female sperm also differ phenotypically in that they have a larger head in comparison to the male sperms. This contributes to the male sperm being lighter, and therefore faster and stronger swimmers than their female counterparts (although statistically there is still a 50% chance of an either XY or XX embryo forming.

Spermatozoan stream lines are straight and parallel. The tail flagellates, which we now know propels the sperm cell (at about 1-3 mm/minute in humans) by rotating like a propeller, in a circular motion, not side to side like a whip. The cell is characterized by a minimum of cytoplasm. During fertilization, the sperm's mitochondria gets destroyed by the egg cell, and this means only the mother is able to provide the baby's mitochondria and mitochondrial DNA, which has an important application in tracing maternal ancestry. However it has been recently discovered that mitochondrial DNA can be recombinant.

Spermatozoa are produced in the seminiferous tubules of the testes in a process called spermatogenesis. Round cells called spermatogonia divide and differentiate eventually to become spermatozoa. During copulation the vagina is inseminated, the spermatozoa move through chemotaxis (see glossary) to the ovum inside a Fallopian tube or the uterus.

Sperm Pathway
Spermatogenesis takes place inside a male’s testes, specifically in the walls of the seminiferous tubules. The epididymis is a tortuously coiled structure topping the testis, it receives immature sperm from the testis and stores it for several days. When ejaculation occurs, sperm is forcefully expelled from the tail of the epididymis into the ductus deferens. Sperm travels through the ductus deferens and up the spermatic cord into the pelvic cavity, over the ureter to the prostate behind the bladder. Here, the vas deferens joins with the seminal vesicle to form the ejaculatory duct, which passes through the prostate and empties into the urethra. Upon the sperm's exit from the testes, into the vas deferens, muscular movements take over. When ejaculation occurs, rhythmic muscle movements of peristalsis propel the sperm forward. This continues throughout the remainder of the sperm's journey through the male reproductive system.

Sperm cells become even more active when they begin to interact with the fertilizing layer of an egg cell. They swim faster and their tail movements become more forceful and erratic. This behavior is called "hyper activation."

A recent discovery links hyper activation to a sudden influx of calcium ions into the tails. The whip-like tail (flagellum) of the sperm is studded with ion channels formed by proteins called CatSper. These channels are selective, allowing only calcium ion to pass. The opening of CatSper channels is responsible for the influx of calcium. The sudden rise in calcium levels causes the flagellum to form deeper bends, propelling the sperm more forcefully through the viscous environment.

The sperm use their tails to push themselves into the epididymis, where they complete their development. It takes sperm about 4 to 6 weeks to travel through the epididymis. The sperm then move to the vas deferens, or sperm duct. The seminal vesicles and prostate gland produce a whitish fluid called seminal fluid, which mixes with sperm to form semen when a male is sexually stimulated.

The penis, which usually hangs limp, becomes hard when a male is sexually excited. Tissues in the penis fill with blood and it becomes stiff and erect (an erection). The rigidity of the erect penis makes it easier to insert into the female's vagina during sexual intercourse, and the extended length allows it to reach deeper into the female's oviduct, the passage from the ovaries to the outside of the body (allowing a shorter travel distance for the spermatozoa).

When the erect penis is stimulated to orgasm, muscles around the reproductive organs contract and force the semen through the duct system and urethra. Semen is pushed out of the male's body through his urethra - ejaculation. The speed of the semen is about 70 mph when ejaculation comes and it can contain 100 to 600 million sperm cells. When the male ejaculates during intercourse, semen is deposited into the fornix at the base of the female's vagina, near the cervix. From the fornix, the sperm make their way up through the cervix and move through the uterus with help from uterine contractions.

Sperm hyperactivity is necessary for breaking through two physical barriers that protect the egg from fertilization. The first barrier to sperm is made up of so-called cumulus cells embedded in a gel-like substance made primarily of hyaluronic acid. The cumulus cells develop in the ovary with the egg and support it as it grows.

The second barrier coating the oocyte is a thick shell formed by glycoproteins called the zona pellucida. One of the proteins that make up the zona pellucida binds to a partner molecule on the sperm. This lock-and-key type mechanism is species-specific and prevents the sperm and egg of different species from fusing. There is some evidence that this binding is what triggers the acrosome to release the enzymes that allow the sperm to fuse with the egg.

When a sperm cell reaches the egg the acrosome releases its enzymes. These enzymes weaken the shell, allowing the sperm cell to penetrate it and reach the plasma membrane of the egg. Part of the sperm's cell membrane then fuses with the egg cell's membrane, and the sperm cell sinks into the egg (at which point the sperm tail falls off).

Upon penetration, the egg cell membrane undergoes a change and becomes impenetrable, preventing further fertilization.

The binding of the sperm to an ovum is called a zygote. A zygote is a single cell, with a complete set of chromosomes, that normally develops into an embryo.

Puberty
In addition to producing sperm, the male reproductive system also produces sex hormones, which help a boy develop into a sexually mature man during puberty. When a baby boy is born, he has all the parts of his reproductive system in place, but it isn't until puberty that his reproductive organs mature and become fully functional. As an newborn FSH and LH levels are high and after a few weeks levels drop to extremely low. When puberty begins, usually between the ages of 10 and 14, the pituitary gland - which is located in the brain - secretes hormones that stimulate the testicles to produce testosterone. The production of testosterone brings about many physical changes. Although the timing of these changes is different for each individual male, the stages of puberty generally follow a set sequence.

 * First stage: the scrotum and testes grow larger, the apocrine glands develop (see explanation of apocrine glands in glossary).

 * Second stage: the penis becomes longer, and the seminal vesicles and prostate gland grow. Hair begins to grow in the pubic region. Reproductive capacity has usually developed by this stage.
 * Third stage: hair begins to appear on the face and underarms. During this time, a male's voice also deepens. Fertility continues to increase.

Testicular size, function, and fertility
In boys, testicular enlargement is the first physical manifestation of puberty (and is termed gonadarche). Testes in prepubertal boys change little in size from about 1 year of age to the onset of puberty, averaging about 2–3 cc in volume and about 1.5-2 cm in length. Testicular size continues to increase throughout puberty, reaching maximal adult size about 6 years later. While 18-20 cc is reportedly an average adult size, there is wide variation in the normal population.

The testes have two primary functions: to produce hormones and to produce sperm. The Leydig cells produce testosterone (as described below), which in turn produces most of the changes of male puberty. However, most of the increasing bulk of testicular tissue is spermatogenic tissue (primarily Sertoli and interstitial cells). The development of sperm production and fertility in males is not as well researched. Sperm can be detected in the morning urine of most boys after the first year of pubertal changes (and occasionally earlier).

Genitalia
A boy's penis grows little from the fourth year of life until puberty. Average prepubertal penile length is 4 cm. The prepubertal genitalia are described as stage 1. Within months after growth of the testes begins, rising levels of testosterone promote growth of the penis and scrotum. This earliest discernible beginning of pubertal growth of the genitalia is referred to as stage 2. The penis continues to grow until about 18 years of age, reaching an average adult size of about 10-16 cm.

Although erections and orgasm can occur in prepubertal boys, they become much more common during puberty, accompanied by development of libido (sexual desire). Ejaculation becomes possible early in puberty; prior to this boys may experience dry orgasms. Emission of seminal fluid may occur due to masturbation or spontaneously during sleep (commonly termed a wet dream, and more clinically called a nocturnal emission). The ability to ejaculate is a fairly early event in puberty compared to the other characteristics, and can occur even before reproductive capacity itself. In parallel to the irregularity of the first few periods of a girl, for the first one or two years after a boy's first ejaculation, his seminal fluid may contain few active sperm.

If the foreskin of a boy does not become retractable during childhood, it normally begins to retract during puberty. This occurs as a result of the increased production of testosterone and other hormones in the body.

Genital Erection
The penis contains two chambers called the corpora cavernosa, which run the length of the organ. A spongy tissue, full of muscle, veins, arteries, etc. fills these chambers. The corpora cavernosa are surrounded by a membrane, called the tunica albuginea. Erection begins with sensory or mental stimulation, or both. Impulses from the brain and local nerves cause the muscles of the corpora cavernosa to relax, allowing blood to flow in and fill the spaces. The blood creates pressure in the corpora cavernosa, making the penis expand. The tunica albuginea helps trap the blood in the corpora cavernosa, thereby sustaining erection. When muscles in the penis contract to stop the inflow of blood and open outflow channels, erection is reversed.

Pubic hair in boys
Pubic hair often appears on a boy shortly after the genitalia begin to grow. As in girls, the first appearance of pubic hair is termed pubarche and the pubic hairs are usually first visible at the dorsal (abdominal) base of the penis. The first few hairs are described as stage 2. Stage 3 is usually reached within another 6 to 12 months, when the hairs are too numerous to count. By stage 4, the pubic hairs densely fill the "pubic triangle." Stage 5 refers to spread of pubic hair to the inner thighs and upward towards the umbilicus as part of the developing abdominal hair.

Sexual Homology

In short, this is a known list of sex organs that evolve from the same tissue in a human life.

Aging
For most men, testosterone secretion continues throughout life, as does sperm production, though both diminish with advancing age. Probably the most common reproductive problem for older men is prostatic hypertrophy, enlargement of the prostate gland. This causes the urethra to compress and urination becomes difficult. Residual urine in the bladder increases the chance of urinary tract infections. Prostate hypertrophy is usually benign, but cancer of the prostate is one of the more common cancers in elderly men. A TURP is commonly used to correct this problem if the symptoms do not improve in response to home treatment and medication.

Erectile dysfunction (ED) is another common problem seen in aging males. In older men, ED usually has a physical cause, such as disease, injury, or side effects of drugs. Any disorder that impairs blood flow in the penis or causes injury to the nerves has the potential to cause ED. Although it is not an inevitable part of aging, incidences increases with age: About 5 percent of 40-year-old men and between 15 and 25 percent of 65-year-old men experience ED. As discouraging as Erectile dysfunction may be, it is treatable at any age, and awareness of this fact has been growing. More men have been seeking help and returning to normal sexual activity because of improved, successful treatments for ED.

Things that can go wrong with the male reproductive system
Boys may sometimes experience reproductive system problems. Below are some examples of disorders that affect the male reproductive system (Disorders of the Scrotum, Testicles, or Epididymis). Conditions affecting the scrotal contents may involve the testicles, epididymis, or the scrotum itself.

 * Testicular trauma. Even a mild injury to the testicles can cause severe pain, bruising, or swelling. Most testicular injuries occur when the testicles are struck, hit, kicked, or crushed, usually during sports or due to other trauma. Testicular torsion, when 1 of the testicles twists around, cutting off the blood supply, is also a problem that some teen males experience - although it's not common. Surgery is needed to untwist the cord and save the testicle.

 * Varicocele. This is a varicose vein (an abnormally swollen vein) in the network of veins that run from the testicles. Varicoceles commonly develop while a boy is going through puberty. A varicocele is usually not harmful, although in some people it may damage the testicle or decrease sperm production, so it helps for you to take your child to see his doctor if he is concerned about changes in his testicles.

 * Testicular cancer. This is one of the most common cancers in men younger than 40. It occurs when cells in the testicle divide abnormally and form a tumor. Testicular cancer can spread to other parts of the body, but if it's detected early, the cure rate is excellent. Teen boys should be encouraged to learn to perform testicular self-examinations.
 * Epididymitis is inflammation of the epididymis, the coiled tubes that connect the testes with the vas deferens. It is usually caused by an infection, such as the sexually transmitted disease chlamydia, and results in pain and swelling next to 1 of the testicles.
 * Hydrocele. A hydrocele occurs when fluid collects in the membranes surrounding the testes. Hydroceles may cause swelling of the testicle but are generally painless. In some cases, surgery may be needed to correct the condition.
 * Inguinal hernia. When a portion of the intestines pushes through an abnormal opening or weakening of the abdominal wall and into the groin or scrotum, it is known as an inguinal hernia. The hernia may look like a bulge or swelling in the groin area. It can be corrected with surgery.

Disorders of Penis
Disorders of the Penis Disorders affecting the penis include the following:

 * Inflammation of the penis. Symptoms of penile inflammation include redness, itching, swelling, and pain. Balanitis occurs when the glans (the head of the penis) becomes inflamed. Posthitis is foreskin inflammation, which is usually due to a yeast or bacterial infection.

 * Hypospadias. This is a disorder in which the urethra opens on the underside of the penis, not at the tip.

 * Phimosis. This is a tightness of the foreskin of the penis and is common in newborns and young children. It usually resolves itself without treatment. If it interferes with urination, circumcision (removal of the foreskin) may be recommended.
 * Paraphimosis. This may develop when a boy's uncircumcised penis is retracted but doesn't return to the unretracted position. As a result, blood flow to the penis may be impaired, and your child may experience pain and swelling. A doctor may try to use lubricant to make a small incision so the foreskin can be pulled forward. If that doesn't work, circumcision may be recommended.
 * Ambiguous genitalia. This occurs when a child is born with genitals that aren't clearly male or female. In most boys born with this disorder, the penis may be very small or nonexistent, but testicular tissue is present. In a small number of cases, the child may have both testicular and ovarian tissue.
 * Micro penis. This is a disorder in which the penis, although normally formed, is well below the average size, as determined by standard measurements.

 * Sexually transmitted diseases. Sexually transmitted diseases (STDs) that can affect boys include human immunodeficiency virus/acquired immunodeficiency syndrome (HIV/AIDS), human papillomavirus (HPV, or genital warts), syphilis, chlamydia, gonorrhea, genital herpes, and hepatitis B. They are spread from one person to another mainly through sexual intercourse.

 * Erectile dysfunction. E.D. is the inability to get or keep an erection firm enough for sexual intercourse. This can also called impotence.  The word "impotence" may also be used to describe other problems that can interfere with sexual intercourse and reproduction, such as problems with ejaculation or orgasm and lack of sexual desire. Using the term erectile dysfunction clarifies that those other problems are not involved.

Contraceptive for Men
Vasectomy: In the procedure the vas deferens of each testes is cut and tied off to prevent the passage of sperm. Sperm is still produced and stored in crypt sites causing inflammation. Because of this inflammatory response the immune system acts on them destroying them and then having antisperm antibodies. This causes a lower possibility if the vasectomy is reversed to becoming fertile again.

Condoms: A device, usually made of latex, or more recently polyurethane, that is used during sexual intercourse. It is put on a man's penis and physically blocks ejaculated semen from entering the body of a sexual partner. Condoms are used to prevent pregnancy, transmission of sexually transmitted diseases (STDs - such as gonorrhea, syphilis, and HIV), or both.

Review Questions

 * Answers for these questions can be found here

1. This is needed to make immature sperm mature
 * A) FHS
 * B) LH
 * C) FSH
 * D) HL

2. These become engorged with blood in an erection
 * A) corpora cavernosa
 * B) fibrous envelope
 * C) septum pectiniforme
 * D) integument
 * E) dorsal veins

3. The difference between male and female sperm
 * A) female sperm have a larger head
 * B) male sperm are lighter
 * C) female sperm are faster
 * D) male sperm are weaker
 * E) A and B
 * F) C and D

4. The entire process of sperm formation takes about
 * A) 5-6 weeks
 * B) 7-8 weeks
 * C) 3-4 weeks
 * D) 9-10 weeks

5. Hyper Activation occurs when
 * A) the sperm are introduced into the urethra
 * B) the sperm are ejaculated into the vaginal canal
 * C) the sperm begin to interact with the fertilizing layer of an egg cell
 * D) the sperm reach the cervix

6. It takes sperm ___________ weeks to travel through the epididymis
 * A) 6-8
 * B) 1-3
 * C) 2-4
 * D) 4-6

7. While singing in the choir, Ben suddenly notices his voice is constantly cracking. This is caused by
 * A) androgens
 * B) LH
 * C) FSH
 * D) Ben’s inability to sing

8. In sexual homology, the glans penis in the male is equal to _____________ in the female
 * A) clitoral hood
 * B) clitoris
 * C) clitoral glans
 * D) clitoral crura

9. In sexual homology, the ___________ in the male is equal to the fallopian tubes in the female
 * A) testis
 * B) appendix testis
 * C) vas deferens
 * D) seminal vesicle
 * E) efferent ducts

10. Joe has a bulge in the groin area that seems to get worse when he lifts things. This most likely is
 * A) epididymitis
 * B) testicular cancer
 * C) varicocele
 * D) hydrocele
 * E) inguinal hernia

Glossary
Androgen: The generic term for any natural or synthetic compound, usually a steroid hormone, that stimulates or controls the development and maintenance of masculine characteristics in vertebrates by binding to androgen receptors. This includes the activity of the accessory male sex organs and development of male secondary sex characteristics. They are also the precursor of all estrogens, the female sex hormones. The primary and most well-known androgen is testosterone.

Apocrine Glands: Apocrine sweat glands develop during the early to mid puberty ages approximately around the age of 15 and release more than normal amounts of sweat for approximately a month and subsequently regulate and release normal amounts of sweat after a certain period of time. They are located wherever there is body hair. These glands produce sweat that contains fatty materials. Mainly present in the armpits and around the genital area, their activity is the main cause of sweat odor, due to the bacteria that break down the organic compounds in the sweat.

Bulbourethral Glands: male accessory sex glands that secrete mucus for lubrication

Chemotaxis: Chemotaxis is a kind of taxis, in which bodily cells, bacteria, and other single-cell or multicellular organisms direct their movements according to certain chemicals in their environment. This is important for bacteria to find food (for example, glucose) by swimming towards the highest concentration of food molecules, or to flee from poisons (for example, phenol). In multicellular organisms, chemotaxis is critical to development as well as normal function. In addition, it has been recognized that mechanisms that allow chemotaxis in animals can be subverted during cancer metastasis.

Corpora Cavernosa: one of a pair of a sponge-like regions of erectile tissue which contain most of the blood in the male penis during erection

Ductus Deferens: epididymal ducts from each testis converge to form a large, thick walled, muscular duct

Ejaculatory Ducts: two ducts, receive sperm from the ductus deferens and secretions from the seminal vesicle; the ducts then empty into the urethra

Epididymis: comma shaped and loosely attached to the rear surface of each testis

Erectile Tissue: smooth muscle and connective tissue inside the penis that contain blood sinuses; large, irregular vascular channels

Erection: the penis at its enlarged and firm state; occurs when the corpora cavernosa become engorged with venous blood

Flagellum: the whip-like tail of a sperm, propels the sperm towards the egg in hopes of achieving fertilization

Follicle-Stimulating Hormone (FSH): hormone that stimulates production of sertoli cells, to make immature sperm to mature sperm

Glans Penis: distal end of the penis, covered with the foreskin

Gonadotropin-Releasing Hormone (GnRH): hormone secreted by the hypothalamus into the pituitary gland; two types, FSH and LH

Libido: In its common usage, it means sexual desire; however, more technical definitions, such as those found in the work of Carl Jung, are more general, referring to libido as the free creative—or psychic—energy an individual has to put toward personal development, or individuation.

Luteinizing Hormone (LH): hormone that stimulates Leydig cells in the testes to produce testosterone

Oviduct: the passage in females from the ovaries to the outside of the body.

Penis: external genital organ of the male

Prostate Gland: male accessory sex gland that secretes an alkaline fluid, which neutralizes acidic vaginal secretions

Puberty: the period of maturation and arousal of the dormant and nonfunctional reproductive system; usually occurs in males between the ages of 10 and 15

Scrotum: skin covered sac that houses the male testicles; keeps the testicles away from the body so that they can stay a few degrees cooler than the body, for better sperm production

Seminal Vesicle: male accessory sex glands that supply fructose to ejaculated sperm and secrete prostaglandins

Seminiferous Tubules: highly coiled tubules within the testes that produce spermatozoa

Sertoli Cell: A Sertoli cell (a kind of sustentacular cell) is a 'nurse' cell of the testes which is part of a seminiferous tubule.

It is activated by follicle-stimulating hormone, and has FSH-receptor on its membranes.

Its main function is to nurture the developing sperm cells through the stages of spermatogenesis. Because of this, it has also been called the "mother cell." It provides both secretory and structural support.

Sexual Homology: sex organs that evolve from the same tissues in both male and females

Sperm: main reproductive cell in males

Spermatogenesis: sperm production

Testes: located in the scrotum, produces testosterone which stimulates production of sperm

Testosterone: male sex hormone secreted by the leydig cells of the testes, vital for the production of sperm

TURP: transurethral resection of the prostate. During TURP, an instrument is inserted up the urethra to remove the section of the prostate that is blocking urine flow. This is most commonly caused by benign prostatic hyperplasia (BPH). A TURP usually requires hospitalization and is done using a general or spinal anesthetic. It is now the most common surgery used to remove part of an enlarged prostate.

Urethra: the last part of the urinary tract; in males, it is the passage for both urine and sperm

Varicocele: varicose vein of the testicles, sometimes a cause of male infertility

Vasectomy: most common sterilization procedure in males; small segment of each ductus deferens is surgically removed after it passes from the testis

Summary
Both male and female reproductive systems may seem somewhat isolated from other body systems in that their purpose is to create new life and not just to maintain existing life. There are however significant relationships between the reproductive system and other body systems. All systems relate in one way or another to help our bodies maintain homeostasis.


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Human Physiology/The respiratory system

The Respiratory System is vital to every human being. Without it, we would cease to live outside of the womb. Let us begin by taking a look at the structure of the respiratory system and how vital it is to life. During inhalation or exhalation air is pulled towards or away from the lungs, by several cavities, tubes, and openings.

The organs of the respiratory system make sure that oxygen enters our bodies and carbon dioxide leaves our bodies.

The respiratory tract is the path of air from the nose to the lungs. It is divided into two sections: Upper Respiratory Tract and the Lower Respiratory Tract. Included in the upper respiratory tract are the Nostrils, Nasal Cavities, Pharynx, Epiglottis, and the Larynx. The lower respiratory tract consists of the Trachea, Bronchi, Bronchioles, and the Lungs.

As air moves along the respiratory tract it is warmed, moistened and filtered.

Functions
In this chapter we will discuss the four processes of respiration. They are:

 * 1) BREATHING or ventilation
 * 2) EXTERNAL RESPIRATION, which is the exchange of gases (oxygen and carbon dioxide) between inhaled air and the blood.
 * 3) INTERNAL RESPIRATION, which is the exchange of gases between the blood and tissue fluids.
 * 4) CELLULAR RESPIRATION

In addition to these main processes, the respiratory system serves for:
 * REGULATION OF BLOOD pH, which occurs in coordination with the kidneys, and as a
 * DEFENSE AGAINST MICROBES
 * Control of body temperature due to loss of evaporate during expiration

Breathing and Lung Mechanics
Ventilation is the exchange of air between the external environment and the alveoli. Air moves by bulk flow from an area of high pressure to low pressure. All pressures in the respiratory system are relative to atmospheric pressure (760mmHg at sea level). Air will move in or out of the lungs depending on the pressure in the alveoli. The body changes the pressure in the alveoli by changing the volume of the lungs. As volume increases pressure decreases and as volume decreases pressure increases. There are two phases of ventilation; inspiration and expiration. During each phase the body changes the lung dimensions to produce a flow of air either in or out of the lungs.

The body is able to stay at the dimensions of the lungs because of the relationship of the lungs to the thoracic wall. Each lung is completely enclosed in a sac called the pleural sac. Two structures contribute to the formation of this sac. The parietal pleura is attached to the thoracic wall where as the visceral pleura is attached to the lung itself. In-between these two membranes is a thin layer of intrapleural fluid. The intrapleural fluid completely surrounds the lungs and lubricates the two surfaces so that they can slide across each other. Changing the pressure of this fluid also allows the lungs and the thoracic wall to move together during normal breathing. Much the way two glass slides with water in-between them are difficult to pull apart, such is the relationship of the lungs to the thoracic wall.

The rhythm of ventilation is also controlled by the "Respiratory Center" which is located largely in the medulla oblongata of the brain stem. This is part of the autonomic system and as such is not controlled voluntarily (one can increase or decrease breathing rate voluntarily, but that involves a different part of the brain). While resting, the respiratory center sends out action potentials that travel along the phrenic nerves into the diaphragm and the external intercostal muscles of the rib cage, causing inhalation. Relaxed exhalation occurs between impulses when the muscles relax. Normal adults have a breathing rate of 12-20 respirations per minute.

The Pathway of Air
When one breathes air in at sea level, the inhalation is composed of different gases. These gases and their quantities are Oxygen which makes up 21%, Nitrogen which is 78%, Carbon Dioxide with 0.04% and others with significantly smaller portions.

In the process of breathing, air enters into the nasal cavity through the nostrils and is filtered by coarse hairs (vibrissae) and mucous that are found there. The vibrissae filter macroparticles, which are particles of large size. Dust, pollen, smoke, and fine particles are trapped in the mucous that lines the nasal cavities (hollow spaces within the bones of the skull that warm, moisten, and filter the air). There are three bony projections inside the nasal cavity. The superior, middle, and inferior nasal conchae. Air passes between these conchae via the nasal meatuses. Air then travels past the nasopharynx, oropharynx, and laryngopharynx, which are the three portions that make up the pharynx. The pharynx is a funnel-shaped tube that connects our nasal and oral cavities to the larynx. The tonsils which are part of the lymphatic system, form a ring at the connection of the oral cavity and the pharynx. Here, they protect against foreign invasion of antigens. Therefore, the respiratory tract aids the immune system through this protection. Then the air travels through the larynx. The larynx closes at the epiglottis to prevent the passage of food or drink as a protection to our trachea and lungs. The larynx is also our voicebox; it contains vocal cords, in which it produces sound. Sound is produced from the vibration of the vocal cords when air passes through them.

The trachea, which is also known as our windpipe, has ciliated cells and mucous secreting cells lining it, and is held open by C-shaped cartilage rings. One of its functions is similar to the larynx and nasal cavity, by way of protection from dust and other particles. The dust will adhere to the sticky mucous and the cilia helps propel it back up the trachea, to where it is either swallowed or coughed up. The mucociliary escalator extends from the top of the trachea all the way down to the bronchioles, which we will discuss later. Through the trachea, the air is now able to pass into the bronchi, bronchioles and finally alveoli before entering the pulmonary capillaries. There is lots of oxygen and then there is less carbon dioxide when the air comes in, but when it diffuses, the amounts exchange. All of this happens in seconds.

Inspiration
Inspiration is initiated by contraction of the diaphragm and in some cases the intercostals muscles when they receive nervous impulses. During normal quiet breathing, the phrenic nerve stimulates the diaphragm to contract and move downward into the abdomen. This downward movement of the diaphragm enlarges the thorax. When necessary, the intercostal muscles also increase the thorax by contacting and drawing the ribs upward and outward.

As the diaphragm contracts inferiorly and thoracic muscles pull the chest wall outwardly, the volume of the thoracic cavity increases. The lungs are held to the thoracic wall by negative pressure in the pleural cavity, a very thin space filled with a few millilitres of lubricating pleural fluid. The negative pressure in the pleural cavity is enough to hold the lungs open in spite of the inherent elasticity of the tissue. Hence, as the thoracic cavity increases in volume the lungs are pulled from all sides to expand, causing a drop in the pressure (a partial vacuum) within the lung itself (but note that this negative pressure is still not as great as the negative pressure within the pleural cavity--otherwise the lungs would pull away from the chest wall). Assuming the airway is open, air from the external environment then follows its pressure gradient down and expands the alveoli of the lungs, where gas exchange with the blood takes place. As long as pressure within the alveoli is lower than atmospheric pressure air will continue to move inwardly, but as soon as the pressure is stabilized air movement stops.

Expiration
During quiet breathing, expiration is normally a passive process and does not require muscles to work (rather it is the result of the muscles relaxing). When the lungs are stretched and expanded, stretch receptors within the alveoli send inhibitory nerve impulses to the medulla oblongata, causing it to stop sending signals to the rib cage and diaphragm to contract. The muscles of respiration and the lungs themselves are elastic, so when the diaphragm and intercostal muscles relax there is an elastic recoil, which creates a positive pressure (pressure in the lungs becomes greater than atmospheric pressure), and air moves out of the lungs by flowing down its pressure gradient.

Although the respiratory system is primarily under involuntary control, and regulated by the medulla oblongata, we have some voluntary control over it also. This is due to the higher brain function of the cerebral cortex.

When under physical or emotional stress, more frequent and deep breathing is needed, and both inspiration and expiration will work as active processes. Additional muscles in the rib cage forcefully contract and push air quickly out of the lungs. In addition to deeper breathing, when coughing or sneezing we exhale forcibly. Our abdominal muscles will contract suddenly (when there is an urge to cough or sneeze), raising the abdominal pressure. The rapid increase in pressure pushes the relaxed diaphragm up against the pleural cavity. This causes air to be forced out of the lungs.

Another function of the respiratory system is to sing and to speak. By exerting conscious control over our breathing and regulating flow of air across the vocal cords we are able to create and modify sounds.

Lung Compliance
Lung Compliance is the magnitude of the change in lung volume produced by a change in pulmonary pressure. Compliance can be considered the opposite of stiffness. A low lung compliance would mean that the lungs would need a greater than average change in intrapleural pressure to change the volume of the lungs. A high lung compliance would indicate that little pressure difference in intrapleural pressure is needed to change the volume of the lungs. More energy is required to breathe normally in a person with low lung compliance. Persons with low lung compliance due to disease therefore tend to take shallow breaths and breathe more frequently.

Determination of Lung Compliance Two major things determine lung compliance. The first is the elasticity of the lung tissue. Any thickening of lung tissues due to disease will decrease lung compliance. The second is surface tensions at air water interfaces in the alveoli. The surface of the alveoli cells is moist. The attractive force, between the water cells on the alveoli, is called surface tension. Thus, energy is required not only to expand the tissues of the lung but also to overcome the surface tension of the water that lines the alveoli.

To overcome the forces of surface tension, certain alveoli cells (Type II pneumocytes) secrete a protein and lipid complex called ""Surfactant””, which acts like a detergent by disrupting the hydrogen bonding of water that lines the alveoli, hence decreasing surface tension.

Central control
The medulla oblongata is the primary respiratory control center

Its main function is to send signals to the muscles that control respiration to cause breathing to occur.

Peripheral control
CO2 is converted to HCO3; most CO2 produced at the tissue cells is carried to lungs in the form of HCO3
 * CO2 & H2O form carbonic acid (H2CO3)
 * changes to H CO3 & H+ ions
 * result is H+ ions are buffered by plasma proteins

Respiratory System: Upper and Lower Respiratory Tracts
For the sake of convenience, we will divide the respiratory system in to the upper and lower respiratory tracts:

Upper Respiratory Tract
The upper respiratory tract consists of the nose and the pharynx. Its primary function is to receive the air from the external environment and filter, warm, and humidify it before it reaches the delicate lungs where gas exchange will occur.

Air enters through the nostrils of the nose and is partially filtered by the nose hairs, then flows into the nasal cavity. The nasal cavity is lined with epithelial tissue, containing blood vessels, which help warm the air; and secrete mucous, which further filters the air. The endothelial lining of the nasal cavity also contains tiny hairlike projections, called cilia. The cilia serve to transport dust and other foreign particles, trapped in mucous, to the back of the nasal cavity and to the pharynx. There the mucus is either coughed out, or swallowed and digested by powerful stomach acids. After passing through the nasal cavity, the air flows down the pharynx to the larynx.

Lower Respiratory Tract
The lower respiratory tract starts with the larynx, and includes the trachea, the two bronchi that branch from the trachea, and the lungs themselves. This is where gas exchange actually takes place.

The larynx (plural larynges), colloquially known as the voice box, is an organ in our neck involved in protection of the trachea and sound production. The larynx houses the vocal cords, and is situated just below where the tract of the pharynx splits into the trachea and the esophagus. The larynx contains two important structures: the epiglottis and the vocal cords.
 * 1) Larynx

The epiglottis is a flap of cartilage located at the opening to the larynx. During swallowing, the larynx (at the epiglottis and at the glottis) closes to prevent swallowed material from entering the lungs; the larynx is also pulled upwards to assist this process. Stimulation of the larynx by ingested matter produces a strong cough reflex to protect the lungs. Note: choking occurs when the epiglottis fails to cover the trachea, and food becomes lodged in our windpipe.

The vocal cords consist of two folds of connective tissue that stretch and vibrate when air passes through them, causing vocalization. The length the vocal cords are stretched determines what pitch the sound will have. The strength of expiration from the lungs also contributes to the loudness of the sound. Our ability to have some voluntary control over the respiratory system enables us to sing and to speak. In order for the larynx to function and produce sound, we need air. That is why we can't talk when we're swallowing.

 * 1) Trachea
 * 2) Bronchi
 * 3) Lungs

Homeostasis and Gas Exchange
Homeostasis is maintained by the respiratory system in two ways: gas exchange and regulation of blood pH. Gas exchange is performed by the lungs by eliminating carbon dioxide, a waste product given off by cellular respiration. As carbon dioxide exits the body, oxygen needed for cellular respiration enters the body through the lungs. ATP, produced by cellular respiration, provides the energy for the body to perform many functions, including nerve conduction and muscle contraction. Lack of oxygen affects brain function, sense of judgment, and a host of other problems.

Gas Exchange
Gas exchange in the lungs and in the alveoli is between the alveolar air and the blood in the pulmonary capillaries. This exchange is a result of increased concentration of CO2, and a decrease of oxygen. This process of exchange is done through diffusion.

External Respiration
External respiration is the exchange of gas between the air in the alveoli and the blood within the pulmonary capillaries. A normal rate of respiration is 12-25 breaths per minute. In external respiration, gases diffuse in either direction across the walls of the alveoli. Oxygen diffuses from the air into the blood and carbon dioxide diffuses out of the blood into the air. Most of the carbon dioxide is carried to the lungs in plasma as bicarbonate ions (HCO3-). When blood enters the pulmonary capillaries, the bicarbonate ions and hydrogen ions are converted to carbonic acid (H2CO3) and then back into carbon dioxide (CO2) and water. This chemical reaction also uses up hydrogen ions. The removal of these ions gives the blood a more neutral pH, allowing hemoglobin to bind up more oxygen. De-oxygenated blood "blue blood" coming from the pulmonary arteries, generally has an oxygen partial pressure (pp) of 40 mmHg and CO2 pp of 45 mmHg. Oxygenated blood leaving the lungs via the pulmonary veins has an O2 pp of 100 mmHg and CO2 pp of 40 mmHg. It should be noted that alveolar O2 pp is 105 mmHg, and not 100 mmHg. The reason why pulmonary venous return blood has a lower than expected O2 pp can be explained by "Ventilation Perfusion Mismatch".

Internal Respiration
Internal respiration is the exchanging of gases at the cellular level.

The Passage Way From the Trachea to the Bronchioles
There is a point at the inferior portion of the trachea where it branches into two directions that form the right and left primary bronchus. This point is called the Carina which is the keel-like cartilage plate at the division point. We are now at the Bronchial Tree. It is named so because it has a series of respiratory tubes that branch off into smaller and smaller tubes as they run throughout the lungs.

Right and Left Lungs
The Right Primary Bronchus is the first portion we come to, it then branches off into the Lobar (secondary) Bronchi, Segmental (tertiary) Bronchi, then to the Bronchioles which have little cartilage and are lined by simple cuboidal epithelium (See fig. 1). The bronchi are lined by pseudostratified columnar epithelium. Objects will likely lodge here at the junction of the Carina and the Right Primary Bronchus because of the vertical structure. Items have a tendency to fall in it, where as the Left Primary Bronchus has more of a curve to it which would make it hard to have things lodge there.

The Left Primary Bronchus has the same setup as the right with the lobar, segmental bronchi and the bronchioles.

The lungs are attached to the heart and trachea through structures that are called the roots of the lungs. The roots of the lungs are the bronchi, pulmonary vessels, bronchial vessels, lymphatic vessels, and nerves. These structures enter and leave at the hilus of the lung which is "the depression in the medial surface of a lung that forms the opening through which the bronchus, blood vessels, and nerves pass" (medlineplus.gov).

There are a number of terminal bronchioles connected to respiratory bronchioles which then advance into the alveolar ducts that then become alveolar sacs. Each bronchiole terminates in an elongated space enclosed by many air sacs called alveoli which are surrounded by blood capillaries. Present there as well, are Alveolar Macrophages, they ingest any microbes that reach the alveoli. The Pulmonary Alveoli are microscopic, which means they can only be seen through a microscope, membranous air sacs within the lungs. They are units of respiration and the site of gas exchange between the respiratory and circulatory systems.

Cellular Respiration
First the oxygen must diffuse from the alveolus into the capillaries. It is able to do this because the capillaries are permeable to oxygen. After it is in the capillary, about 5% will be dissolved in the blood plasma. The other oxygen will bind to red blood cells. The red blood cells contain hemoglobin that carries oxygen. Blood with hemoglobin is able to transport 26 times more oxygen than plasma without hemoglobin. Our bodies would have to work much harder pumping more blood to supply our cells with oxygen without the help of hemoglobin. Once it diffuses by osmosis it combines with the hemoglobin to form oxyhemoglobin.

Now the blood carrying oxygen is pumped through the heart to the rest of the body. Oxygen will travel in the blood into arteries, arterioles, and eventually capillaries where it will be very close to body cells. Now with different conditions in temperature and pH (warmer and more acidic than in the lungs), and with pressure being exerted on the cells, the hemoglobin will give up the oxygen where it will diffuse to the cells to be used for cellular respiration, also called aerobic respiration. Cellular respiration is the process of moving energy from one chemical form (glucose) into another (ATP), since all cells use ATP for all metabolic reactions.

It is in the mitochondria of the cells where oxygen is actually consumed and carbon dioxide produced. Oxygen is produced as it combines with hydrogen ions to form water at the end of the electron transport chain (see chapter on cells). As cells take apart the carbon molecules from glucose, these get released as carbon dioxide. Each body cell releases carbon dioxide into nearby capillaries by diffusion, because the level of carbon dioxide is higher in the body cells than in the blood. In the capillaries, some of the carbon dioxide is dissolved in plasma and some is taken by the hemoglobin, but most enters the red blood cells where it binds with water to form carbonic acid. It travels to the capillaries surrounding the lung where a water molecule leaves, causing it to turn back into carbon dioxide. It then enters the lungs where it is exhaled into the atmosphere.

Lung Capacity
The normal volume moved in or out of the lungs during quiet breathing is called tidal volume. When we are in a relaxed state, only a small amount of air is brought in and out, about 500 mL. You can increase both the amount you inhale, and the amount you exhale, by breathing deeply. Breathing in very deeply is Inspiratory Reserve Volume and can increase lung volume by 2900 mL, which is quite a bit more than the tidal volume of 500 mL. We can also increase expiration by contracting our thoracic and abdominal muscles. This is called expiratory reserve volume and is about 1400 ml of air. Vital capacity is the total of tidal, inspiratory reserve and expiratory reserve volumes; it is called vital capacity because it is vital for life, and the more air you can move, the better off you are. There are a number of illnesses that we will discuss later in the chapter that decrease vital capacity. Vital Capacity can vary a little depending on how much we can increase inspiration by expanding our chest and lungs. Some air that we breathe never even reaches the lungs! Instead it fills our nasal cavities, trachea, bronchi, and bronchioles. These passages aren't used in gas exchange so they are considered to be dead air space. To make sure that the inhaled air gets to the lungs, we need to breathe slowly and deeply. Even when we exhale deeply some air is still in the lungs,(about 1000 ml) and is called residual volume. This air isn't useful for gas exchange. There are certain types of diseases of the lung where residual volume builds up because the person cannot fully empty the lungs. This means that the vital capacity is also reduced because their lungs are filled with useless air.

Stimulation of Breathing
There are two pathways of motor neuron stimulation of the respiratory muscles. The first is the control of voluntary breathing by the cerebral cortex. The second is involuntary breathing controlled by the medulla oblongata.

There are chemoreceptors in the aorta, the carotid body of carotid arteries, and in the medulla oblongata of the brainstem that are sensitive to pH. As carbon dioxide levels increase there is a buildup of carbonic acid, which releases hydrogen ions and lowers pH. Thus, the chemoreceptors do not respond to changes in oxygen levels (which actually change much more slowly), but to pH, which is dependent upon plasma carbon dioxide levels. In other words, CO2 is the driving force for breathing. The receptors in the aorta and the carotid sinus initiate a reflex that immediately stimulates breathing rate and the receptors in the medulla stimulate a sustained increase in breathing until blood pH returns to normal.

This response can be experienced by running a 100-meter dash. During this exertion (or any other sustained exercise) your muscle cells must metabolize ATP at a much faster rate than usual, and thus will produce much higher quantities of CO2. The blood pH drops as CO2 levels increase, and you will involuntarily increase breathing rate very soon after beginning the sprint. You will continue to breathe heavily after the race, thus expelling more carbon dioxide, until pH has returned to normal. Metabolic acidosis therefore is acutely corrected by respiratory compensation (hyperventilation).

Regulation of Blood pH
Many of us are not aware of the importance of maintaining the acid/base balance of our blood. It is vital to our survival. Normal blood pH is set at 7.4, which is slightly alkaline or "basic". If the pH of our blood drops below 7.2 or rises above 7.6 then very soon our brains would cease functioning normally and we would be in big trouble. Blood pH levels below 6.9 or above 7.9 are usually fatal if they last for more than a short time. Another wonder of our amazing bodies is the ability to cope with every pH change – large or small. There are three factors in this process: the lungs, the kidneys and buffers.

So what exactly is pH? pH is the concentration of hydrogen ions (H+). Buffers are molecules which take in or release ions in order to maintain the H+ ion concentration at a certain level. When blood pH is too low and the blood becomes too acidic (acidosis), the presence of too many H+ ions is to blame. Buffers help to soak up those extra H+ ions. On the other hand, the lack of H+ ions causes the blood to be too basic (alkalosis). In this situation, buffers release H+ ions. Buffers function to maintain the pH of our blood by either donating or grabbing H+ ions as necessary to keep the number of H+ ions floating around the blood at just the right amount.

The most important buffer we have in our bodies is a mixture of carbon dioxide (CO2) and bicarbonate ion (HCO3). CO2 forms carbonic acid (H2CO3) when it dissolves in water and acts as an acid giving up hydrogen ions (H+) when needed. HCO3 is a base and soaks up hydrogen ions (H+) when there are too many of them. In a nutshell, blood pH is determined by a balance between bicarbonate and carbon dioxide.

Bicarbonate Buffer System. With this important system our bodies maintain homeostasis. (Note that H2CO3 is Carbonic Acid and HCO3 is Bicarbonate)

CO2 + H2O <---> H2CO3 <---> (H+) + HCO3

 * If pH is too high, carbonic acid will donate hydrogen ions (H+) and pH will drop.
 * If pH is too low, bicarbonate will bond with hydrogen ions (H+) and pH will rise.

Too much CO2 or too little HCO3 in the blood will cause acidosis. The CO2 level is increased when hypoventilation or slow breathing occurs, such as if you have emphysema or pneumonia. Bicarbonate will be lowered by ketoacidosis, a condition caused by excess fat metabolism (diabetes mellitus).

Too much HCO3 or too little CO2 in the blood will cause alkalosis. This condition is less common than acidosis. CO2 can be lowered by hyperventilation.

So, in summary, if you are going into respiratory acidosis the above equation will move to the right. The body's H+ and CO2 levels will rise and the pH will drop. To counteract this the body will breathe more and release H+. In contrast, if you are going into respiratory alkalosis the equation will move to the left. The body's H+ and CO2 levels will fall and the pH will rise. So the body will try to breathe less to release HCO3. You can think of it like a leak in a pipe: where ever there is a leak, the body will "fill the hole".

Problems Associated With the Respiratory Tract and Breathing
The environment of the lung is very moist, which makes it a hospitable environment for bacteria. Many respiratory illnesses are the result of bacterial or viral infection of the lungs. Because we are constantly being exposed to harmful bacteria and viruses in our environment, our respiratory health can be adversely affected. There are a number of illnesses and diseases that can cause problems with breathing. Some are simple infections, and others are disorders that can be quite serious.

Carbon Monoxide Poisoning: caused when carbon monoxide binds to hemoglobin in place of oxygen. Carbon monoxide binds much tighter, without releasing, causing the hemoglobin to become unavailable to oxygen. The result can be fatal in a very short amount of time.

 * Mild Symptoms: flu like symptoms, dizziness, fatigue, headaches, nausea, and irregular breathing
 * Moderate Symptoms: chest pain, rapid heart beat, difficulty thinking, blurred vision, shortness of breath and unsteadiness
 * Severe Symptoms: seizures, palpitations, disorientation, irregular heart beat, low blood pressure, coma and death.

Pulmonary Embolism: blockage of the pulmonary artery (or one of its branches) by a blood clot, fat, air or clumped tumor cells. By far the most common form of pulmonary embolism is a thromboembolism, which occurs when a blood clot, generally a venous thrombus, becomes dislodged from its site of formation and embolizes to the arterial blood supply of one of the lungs.

 * Symptoms may include difficulty breathing, pain during breathing, and more rarely circulatory instability and death. Treatment, usually, is with anticoagulant medication.

Upper Respiratory Tract Infections
The upper respiratory tract consists of our nasal cavities, pharynx, and larynx. Upper respiratory infections (URI) can spread from our nasal cavities to our sinuses, ears, and larynx. Sometimes a viral infection can lead to what is called a secondary bacterial infection. "Strep throat" is a primary bacterial infection and can lead to an upper respiratory infection that can be generalized or even systemic (affects the body as a whole). Antibiotics aren't used to treat viral infections, but are successful in treating most bacterial infections, including strep throat. The symptoms of strep throat can be a high fever, severe sore throat, white patches on a dark red throat, and stomach ache.

 * Sinusitis:An infection of the cranial sinuses is called sinusitis. Only about 1-3% of URI's are accompanied by sinusitis. This "sinus infection" develops when nasal congestion blocks off the tiny openings that lead to the sinuses. Some symptoms include: post nasal discharge, facial pain that worsens when bending forward, and sometimes even tooth pain can be a symptom. Successful treatment depends on restoring the proper drainage of the sinuses. Taking a hot shower or sleeping upright can be very helpful. Otherwise, using a spray decongestant or sometimes a prescribed antibiotic will be necessary.

 * Otitis Media:Otitis media in an infection of the middle ear. Even though the middle ear is not part of the respiratory tract, it is discussed here because it is often a complication seen in children who has a nasal infection. The infection can be spread by way of the 'auditory (Eustachian) tube that leads form the nasopharynx to the middle ear. The main symptom is usually pain. Sometimes though, vertigo, hearing loss, and dizziness may be present. Antibiotics can be prescribed and tubes are placed in the eardrum to prevent the buildup of pressure in the middle ear and the possibility of hearing loss.

 * Tonsillitis:Tonsillitis occurs when the tonsils become swollen and inflamed. The tonsils located in the posterior wall of the nasopharynx are often referred to as adenoids. If you suffer from tonsillitis frequently and breathing becomes difficult, they can be removed surgically in a procedure called a tonsillectomy.

 * Laryngitis:An infection of the larynx is called laryngitis. It is accompanied by hoarseness and being unable to speak in an audible voice. Usually, laryngitis disappears with treatment of the URI. Persistent hoarseness without a URI is a warning sign of cancer, and should be checked into by your physician.

Lower Respiratory Tract Disorders
Lower respiratory tract disorders include infections, restrictive pulmonary disorders, obstructive pulmonary disorders, and lung cancer.

Lower Respiratory Infections

 * Acute bronchitis:An infection that is located in the primary and secondary bronchi is called bronchitis. Most of the time, it is preceded by a viral URI that led to a secondary bacterial infection. Usually, a nonproductive cough turns into a deep cough that will expectorate mucus and sometimes pus.
 * Pneumonia:A bacterial or viral infection in the lungs where the bronchi and the alveoli fill with a thick fluid. Usually it is preceded by influenza. Symptoms of pneumonia include high fever & chills, with headache and chest pain. Pneumonia can be located in several lobules of the lung and obviously, the more lobules involved, the more serious the infection. It can be caused by a bacteria that is usually held in check, but due to stress or reduced immunity has gained the upper hand.

Restrictive Pulmonary Disorders

 * Pulmonary Fibrosis:Vital capacity is reduced in these types of disorders because the lungs have lost their elasticity. Inhaling particles such as sand, asbestos, coal dust, or fiberglass can lead to pulmonary fibrosis, a condition where fibrous tissue builds up in the lungs. This makes it so our lungs cannot inflate properly and are always tending toward deflation. Pulmonary fibrosis can be synonymous with interstitial lung disease (ILD), or interstitial pneumonia or pneumonitis.

Obstructive Pulmonary Disorders

 * Asthma:Asthma is a respiratory disease of the bronchi and bronchioles. The symptoms include wheezing, shortness of breath, and sometimes a cough that will expel mucus. The airways are very sensitive to irritants which can include pollen, dust, animal dander, and tobacco. Even being out in cold air can be an irritant. When exposed to an irritant, the smooth muscle in the bronchioles undergoes spasms. Most asthma patients have at least some degree of bronchial inflammation that reduces the diameter of the airways and contributes to the seriousness of the attack.

 * Emphysema:Emphysema is a type of chronic obstructive pulmonary disease. Typically characterized by a loss of elasticity and surfactant in the alveoli, a loss of surface area decreases the gas exchange in the lungs. These patients have difficulty with too little expiratory pressure, not retaining inspired air long enough for sufficient gas exchange to happen.

 * Chronic Bronchitis:Another type of chronic obstructive pulmonary disease, Chronic Bronchitis is caused by overproduction of mucus in the airways, causing an inadequate expiration of inspired air. Retention of air in the lungs reduces gas exchange at the alveoli, and can lead to a hypoxic drive. These patients are known as "blue bloaters", vulnerable to cyanosis and often have increased thoracic diameters.

Respiratory Distress Syndrome
At birth the pressure needed to expand the lungs requires high inspiratory pressure. In the presence of normal surfactant levels the lungs retain as much as 40% of the residual volume after the first breath and thereafter will only require far lower inspiratory pressures. In the case of deficiency of surfactant the lungs will collapse between breaths, this makes the infant work hard and each breath is as hard as the first breath. If this goes on further the pulmonary capillary membranes become more permeable, letting in fibrin rich fluids between the alveolar spaces and in turn forms a hyaline membrane. The hyaline membrane is a barrier to gas exchange, this hyaline membrane then causes hypoxemia and carbon dioxide retention that in turn will further impair surfactant production.
 * Pathophysiology

Type two alveolar cells produce surfactant and do not develop until the 25th to the 28th week of gestation, in this, respiratory distress syndrome is one of the most common respiratory disease in premature infants. Furthermore, surfactant deficiency and pulmonary immaturity together leads to alveolar collapse. Predisposing factors that contribute to poorly functioning type II alveolar cells in a premature baby are if the child is a preterm male, white infants, infants of mothers with diabetes, precipitous deliveries, cesarean section performed before the 38th week of gestation. Surfactant synthesis is influenced by hormones, this ranges form insulin and cortisol. Insulin inhibits surfactant production, explaining why infants of mothers with diabetes type 1 are at risk of development of respiratory distress syndrome. Cortisol can speed up maturation of type II cells and therefore production of surfactant. Finally, in the baby delivered by cesarean section are at greater risk of developing respiratory distress syndrome because the reduction of cortisol produced because the lack of stress that happens during vaginal delivery, hence cortisol increases in high stress and helps in the maturation of type II cells of the alveoli that cause surfactant.
 * Etiology

Today to prevent respiratory distress syndrome are animal sources and synthetic surfactants, and administrated through the airways by an endotracheal tube and the surfactant is suspended in a saline solution. Treatment is initiated post birth and in infants who are at high risk for respiratory distress syndrome.
 * Treatment

Sleep Apnea
Sleep apnea or sleep apnoea is a sleep disorder characterized by pauses in breathing during sleep. These episodes, called apneas (literally, "without breath"), each last long enough so one or more breaths are missed, and occur repeatedly throughout sleep. The standard definition of any apneic event includes a minimum 10 second interval between breaths, with either a neurological arousal (3-second or greater shift in EEG frequency, measured at C3, C4, O1, or O2), or a blood oxygen desaturation of 3-4 percent or greater, or both arousal and desaturation. Sleep apnea is diagnosed with an overnight sleep test called polysomnogram. One method of treating central sleep apnea is with a special kind of CPAP, APAP, or VPAP machine with a Spontaneous Time (ST) feature. This machine forces the wearer to breathe a constant number of breaths per minute.

(CPAP), or continuous positive airway pressure, in which a controlled air compressor generates an airstream at a constant pressure. This pressure is prescribed by the patient's physician, based on an overnight test or titration.

Nutrition for COPD (Chronic Obstructive Pulmonary Disease) Patients
Nutrition is particularly important for ventilator-dependent patient. When metabolizing macronutrients carbon dioxide and water are produced. The respiratory quotient (RQ) is a ratio of produced carbon dioxide to amount consumed. Carbohydrates metabolism produces the most amount of carbon dioxide so they have the highest (RQ). Fats produce the least amount of carbon dioxide along with proteins. Protein has a slightly higher RQ ratio. It is recommended that this kind of patient not exceed a 1.0 respiratory quotient (RQ). Lowering carbohydrates and supplementing fat or protein in the diet might not result in maintaining the desired outcome because, excess amounts fat or protein may also result in a respiratory quotient (RQ) higher than 1.0.
 * Please reference source and fact accuracy. It seems like by definition, it is impossible to exceed a respiratory quotient (RQ) of 1.0. *

Case Study
Cystic Fibrosis

This disease is most common in Caucasians and will happen to 1 in every 2500 people. It is most known for its effects on the respiratory tract although it does effect other systems as well. The respiratory passages become clogged with a thick mucus that is difficult to expel even with vigorous coughing. Breathing becomes difficult and affected individuals run the risk of choking to death on their own secretions unless strenuous effort is made to clear the lungs multiple times every day. Victims frequently will die in the 20's of pneumonia. All of us secrete mucus by certain cells in the epithelium that line the respiratory passageways. In normal cases the cells also secrete a watery fluid that will dilute the mucus making it easier to pass through the airways. In cystic fibrosis that secretion of watery fluid is impaired. This makes the mucus thicker and difficult to clear from the passageways. A 1989 discovery found that cystic fibrosis is caused by defects in a type of anion channel found in apical membranes of epithelial cells in the respiratory system and elsewhere. The defects directly impede the chloride ion transport, which will then indirectly effect other exchanges of ions in the cells. This causes the epithelium to not create the osmotic gradient necessary for water secretion. It has been known for a long time that cystic fibrosis is caused by a recessive gene inheritance. This gene codes for the chloride channel protein, which can malfunction in a variety of ways, each with specific treatment required.

External Resources

 * Eastern Kentucky University Gary Ritchison Lecture Notes: Human Respiration (includes videos)
 * In depth anatomy and physiology of the pulmonary system.

Fisiologia/Sistema respiratório

title: Human Physiology/The respiratory system


text:
Hebrew/Aleph-Bet

The 1,400 years old zodiac mosaic of Bet Alfa

Lessons
You really should know, before you learn the Hebrew alphabet, that the average Israeli needs to know how to read words without niqqud, and that to read an Israeli newspaper you have to know about 2000 words without niqqud.
 * Introduction: The aim of this level, what you will learn in it and how the lessons are structured.
 * Lesson 1: The letters Aleph, Bet and Tav , the niqqud symbols Pataħ and Shva.
 * Lesson 2: The letters Vet, He , Nun and Nun Sofit , the niqqud symbols Qamats  and Tsere.
 * Lesson 3: The letters Mem, Mem Sofit , Shin and Sin , the niqqud symbols Segol  and Ħiriq.
 * Lesson 4: The letters Lamed and Vav, the niqqud symbols Ħolam  and Shuruq.
 * Lesson 5: Review, the letters Dalet, Resh and Yod , the niqqud symbol Qubbuts.
 * Lesson 6: The letters Gimmel, Zayin and Ħet , the niqqud symbols Ħataf-Pataħ  and Ħataf-Qamats.
 * Lesson 7: The letters Tet, Kaf , Khaf and Khaf Sofit , dagesh, the niqqud symbol Ħataf-Segol.
 * Lesson 8: The letters Samekh, Qof , full writing (ktiv malei).
 * Lesson 9: Review, the letters ‘Ayin, Pe , Fe and Fe Sofit.
 * Lesson 10: The letters Tsadi, Tsadi Sofit and the Hebrew numerical system (gematria).
 * Review: Complete review of this level, alphabet and niqqud tables, extra notes regarding pronunciation, transliteration and shape.
 * Test: Tests what you've learned this level.

title: Hebrew/Aleph-Bet


text:
LaTeX/Print version

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= Contents = If you have saved this file to your computer, click on a link in the contents to go to that section.

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 * 12) Page Layout
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 * 15) Footnotes and Margin Notes
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title: LaTeX/Print version


text:
Hebrew/Aleph-Bet/1

 Aleph-Bet Lesson 1 —

Welcome to the first lesson in the Hebrew alphabet! In this lesson you will learn the first two and most basic Hebrew letters - and the last letter,, and the first two niqqud symbols - pataħ and shva.

Important note: Hebrew words and sentences, unlike English words and sentences, are read from right to left.

Letters
The Hebrew alphabet has no vowel letters. The letters only mark consonants, which means that when you look at a word you would have no idea how it is pronounced. Such alphabets are known as "abjads". The vowels would be explained immediately after this section. But we will begin with the two, first consonants.

Aleph

The first letter in the Hebrew alphabet is Aleph. It has 3 uses:
 * 1) It makes a consonant called "glottal stop", as in "co’operate" or "re’enact".

 * }
 * 2. When at the beginning of a word, it means the word starts with a vowel.
 * 3. When preceded by any "a" vowel, when at the end of a word (there are exceptions) and in foreign words (because in most texts there are no marked vowels) it makes the "a" sound (IPA: /a/, "a" as in "spa").
 * }
 * 2. When at the beginning of a word, it means the word starts with a vowel.
 * 3. When preceded by any "a" vowel, when at the end of a word (there are exceptions) and in foreign words (because in most texts there are no marked vowels) it makes the "a" sound (IPA: /a/, "a" as in "spa").

Bet

The second letter in the Hebrew alphabet is Bet. It makes the "b" sound (IPA: /b/, "b" as in "ball"). When there is no dot in the middle, the letter makes a different sound, "v", so make sure to remember the dot.

Tav

The last letter in the Hebrew alphabet and the third you will learn is Tav. It makes the "t" sound if there is a dot in it. (IPA: /t/, "t" as in "tomato"). Sometimes if it does not have a dot in it, it is pronounced "s", but most of the time it is pronounced "t". Now you've learned the first three letters! But all you have is consonants. In order to be actually able to pronounce words, you need vowels.

Vowels
In Hebrew, vowels appear as dots and bars above, beneath or to the left of letters. This system of dots and lines is known as niqqud, a Hebrew word which means "applying dots". It was devised by a group of early Medieval Jewish scribes and Bible scholars known as the Masoretes (masoret means "tradition" in Hebrew). They invented the niqqud to make sure that the "correct" pronunciation of the Bible would not be lost.

You would eventually have to learn to read without niqqud. It might seem daunting, but with a little exercise you would learn to recognize words and know how to pronounce them. But until then, you must learn the niqqud symbols first. Now you learn the first two:

Pataħ
The pataħ is the line under the Bet.

The pataħ produces the "a" sound (IPA: /a/, "a" as in "spa").

Shva
The shva is the two vertical dots under the Bet.

Shva does two things:
 * 1) Shva naħ (resting Shva): placed under a consonant to mark the end of a syllable.
 * 2) Shva na‘ (moving Shva): when shva is at the beginning of a syllable, it produces the "ə" sound (IPA: /ə/, "a" as in "about"). Many Israelis pronounce it as "e".

Words
Now that we have three consonants and two vowels, we can produce words!

Vocabulary:

This word or bat is pronounced closer to the second syllable in the English word robot (American pronunciation) than the English word bat (the animal, or the thing you use to hit a baseball or cricket ball). Similarly, the word or at, is pronounced as in the word attraction. (notice - it is not pronounced like the English word that is spelled as at.)

Try to read these words out loud. Remember that Hebrew is read from right to left!

Notes about these letters
A common phrase that English speakers may know is Bat Mitzvah. This phrase is usually translated as Daughter of the Commandments and is used to refer to a young, Jewish woman, who is old enough to be morally responsible for her actions. This would be at age 12 or 13 depending on the Jewish denomination.

A very simple sentence is which means "you are a daughter" or "you are a girl". (We'll explain in later lessons about the "to be" verbs like are and the article a.)

The English word for our letters, alphabet, comes from aleph-bet, the first two letters in the Hebrew language.

Each Hebrew letter also has a numeric value. Those are explained separately. The letter Aleph has the value of 1. The letter Bet has the value of 2. The letter Tav is the 22nd and last letter of the Hebrew Aleph-Bet; it has the value of 400.

Exercises
Remember the letters you have learned: Aleph, Bet and Tav. Also remember the vowels you have learned: Pataħ and Shva. With this knowledge, you can make six possible combinations:

Assign each letter to the sound it makes:

Now do the opposite. Assign each sound to the equivalent Hebrew letter:

How do you spell each of the following words (most of which are fictional)? Example: Aleph-pataħ Bet-shva

How do you pronounce each of the following words? Example: Ab

Next lesson: Aleph-Bet 2 >>>

title: Hebrew/Aleph-Bet/1


text:
Diplomacy/Stabs

Stabs
A stab (short for backstab) is when a power breaks an agreement with another power. Stabs are one of the most recognizable and most dangerous strategies in Diplomacy. A stab involves betraying an ally for the chance to increase one's own strength. Indeed, the stab is more art than strategy. In order for the stab to be successful, the target must not suspect anything or, save that, be unable to mount an effective defense in time. The stab is by far the riskiest move a player can make. While the rewards can be big, a betrayed ally can become a powerful enemy. In addition, if one stabs too often, he or she may find it difficult to find allies in the current or future games.

Types of stabs
There are several types of stabs, some of which are listed below.

Enter a territory which was previously agreed upon as demilitarized zone
This is one of the least aggressive stabs, and will sometimes be forgiven directly afterwards, especially if the stabber aids the victim in some other way. It is often a preparation for an attack though.

Failing to support an ally's attack
This is often a subtle stab, but may not gain much. The chance of the stabbed player turning directly on the stabber is reduced, especially in the early game, since the stabbed player is already involved in a war (hence his original attack, which the stabber failed to support).

Failing to support an ally's defence
This kind of stab is often on the same scale as attacking the ally, especially if the failure to support leads to the ally having to retreat.

Attacking an ally
A very blunt and overt stab. Attacking an ally will almost always lead to war.

Enter an ally's supply centre
This is probably the most profitable type of stab. Always beware of it, and look out for opportunities to do it.

Normally the stabber plans to take more than just one supply centre from their ex-ally. The stabber has to make sure the stab-ee cannot recover in anything close to a timely fashion. The key point is that you gain centres at the same time your opponent is forced to disband units. If both you and your ally have six units each when you take the opportunity to stab them in the Fall, you want to make sure that you can steal at least two of his centres. If you do, the balance of power shifts from parity to eight vs four. It doesn't much matter how angry the stab-ee now is, they are half your size and (all other things being equal) will not last much longer in the game.

Opponents don't forgive this type of stab easily, so be very aware that once you have guided your dagger between the ribs, it is no time to stop attacking or to think about patching things up. You are best advised to rain blow after blow on your opponent until they are totally broken.

The Strategic Stab
This is where you take a key centre of strategic importance off your ally. A good example is when England steals St. Petersburg from Russia. England is a naval power and removing Russia's ability to build any more fleets in the North is of great worth to England.

How to react when you get stabbed
It can hurt. You feel betrayed. (You have been betrayed!). You want revenge. If your ally has stabbed you at the right time you may be too weak to take him on. Your best approach is to send a message to the person that stabbed you, something like "Ouch! That really hurt! An impressive stab - you got me there! But I see that our neighbors are looking threatening. I am happy to forgive and forget. Let's deal with the REAL enemy"

If you can get back on good terms, you can survive and grow - then you can time your counter-stab when it does the most harm.

Stabbing and secret alliances
Alliances which are kept secret and intended as a surprise, are especially susceptible to stabs since the only player who will know of the stab is the stabbed player, and the player's reputation might remain intact. It is not uncommon for players to make alliances or non-aggression pacts with all their neighbors during the first spring, and when they have no more neutrals to expand into whichever of their alliances is most opportune.

title: Diplomacy/Stabs


text:
User:CocoaZen

Working on...
I'm currently working on the Hebrew book. Unfortunately, I'm not fluent. Help please...

changes to pages in the Hebrew category (30 days)

Reading or using...

 * Spanish
 * Muggles' Guide to Harry Potter
 * Music Theory, Music Theory/Scales and Intervals

Hebrew templates
The Hebrew templates are doing odd things on my Mac, so playing with it here to correct...
 * 1) עִבְרִית
 * 2) עִבְרִית
 * 3) עִבְרִית
 * 4) עִבְרִית
 * 5) עִבְרִית

title: User:CocoaZen


text:
Circuit Theory/Cover

Circuit Theory Wikibooks: The Free Library

title: Circuit Theory/Cover


text:
Talk:Circuit Theory/Cover

This is just a crapy cover page that I threw together for use in the print version. We need to get a better cover image, and maybe some other stuff. --Whiteknight (talk) (projects) 02:12, 20 July 2006 (UTC)

title: Talk:Circuit Theory/Cover


text:
Circuit Theory/Resources

Wikibooks

 * Wikibooks: Electronics
 * Wikibooks: Signals and Systems
 * Wikibooks: Digital Circuits
 * Wikibooks: Circuit Idea

The following Wikibooks list Circuit Theory as a prerequisite: category=Circuit Theory/Prerequisite namespace=Main suppresserrors=true

Other Resources

 * Horowitz and Hill, The Art of Electronics, Second Edition, Cambridge University Press, 1989. ISBN 0521370957
 * US Navy, Basic Electrity, Dover, 1970. ISBN 0486209733
 * US Navy, Basic Electronics, Dover, 1973. ISBN 0486210766
 * Comer and Comer, Fundamentals of Electronic Circuit Design, John Wiley & Sons, 2003. http://www.wiley.com/college/comer/ ISBN 0471410160
 * Dorf and Svoboda, Introduction to Electric Circuits, Sixth Edition, John Wiley & Sons, 2004. ISBN 0471447951

title: Circuit Theory/Resources