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Human Physiology/The endocrine system

Introduction To The Endocrine System
The endocrine system is a control system of ductless glands that secrete hormones within specific organs. Hormones act as "messengers," and are carried by the bloodstream to different cells in the body, which interpret these messages and act on them.

It seems like a far fetched idea that a small chemical can enter the bloodstream and cause an action at a distant location in the body. Yet this occurs in our bodies every day of our lives. The ability to maintain homeostasis and respond to stimuli is largely due to hormones secreted within the body. Without hormones, you could not grow, maintain a constant temperature, produce offspring, or perform the basic actions and functions that are essential for life.

The endocrine system provides an electrochemical connection from the hypothalamus of the brain to all the organs that control the body metabolism, growth and development, and reproduction.

There are two types of hormones secreted in the endocrine system: Steroidal (or lipid based) and non-steroidal, (or protein based) hormones.

The endocrine system regulates its hormones through negative feedback, except in very specific cases like childbirth. Increases in hormone activity decrease the production of that hormone. The immune system and other factors contribute as control factors also, altogether maintaining constant levels of hormones.

Types of Glands

Exocrine Glands are those which release their cellular secretions through a duct which empties to the outside or into the lumen (empty internal space) of an organ. These include certain sweat glands, salivary and pancreatic glands, and mammary glands. They are not considered a part of the endocrine system.

Endocrine Glands are those glands which have no duct and release their secretions directly into the intercellular fluid or into the blood. The collection of endocrine glands makes up the endocrine system.

 * 1, The main endocrine glands are the pituitary (anterior and posterior lobes), thyroid, parathyroid, adrenal (cortex and medulla), pancreas and gonads.

 * 2, The pituitary gland is attached to the hypothalamus of the lower forebrain.

 * 3, The thyroid gland consists of two lateral masses, connected by a cross bridge, that are attached to the trachea. They are slightly inferior to the larynx.

 * 4, The parathyroid glands are four masses of tissue, two embedded posterior in each lateral mass of the thyroid gland.

 * 5, One adrenal gland is located on top of each kidney. The cortex is the outer layer of the adrenal gland. The medulla is the inner core.

 * 6, The pancreas is along the lower curvature of the stomach, close to where it meets the first region of the small intestine, the duodenum.

 * 7, The gonads (ovaries and testes) are found in the pelvic cavity.

Hormones and Types
A hormone is a type of chemical signal. They are a means of communication between cells.

The endocrine system produces hormones that are instrumental in maintaining homeostasis and regulating reproduction and development. A hormone is a chemical messenger produced by a cell that effects specific change in the cellular activity of other cells (target cells). Unlike exocrine glands (which produce substances such as saliva, milk, stomach acid and digestive enzymes), endocrine glands do not secrete substances into ducts (tubes). Instead, endocrine glands secrete their hormones directly into the surrounding extra cellular space. The hormones then diffuse into nearby capillaries and are transported throughout the body in the blood.

The endocrine and nervous systems often work toward the same goal. Both influence other cells with chemicals (hormones and neurotransmitters). However, they attain their goals differently. Neurotransmitters act immediately (within milliseconds) on adjacent muscle, gland, or other nervous cells, and their effect is short-lived. In contrast, hormones take longer to produce their intended effect (seconds to days), may affect any cell, nearby or distant, and produce effects that last as long as they remain in the blood, which could be up to several hours.

In the following table there are the major hormones, their target and their function once in the target cell.

Hormones can be chemically classified into four groups:
 * 1) Amino acid-derived: Hormones that are modified amino acids.
 * 2) Polypeptide and proteins: Hormones that are chains of amino acids of less than or more than about 100 amino acids, respectively. Some protein hormones are actually glycoproteins, containing glucose or other carbohydrate groups.
 * 3) Steroids: Hormones that are lipids synthesized from cholesterol. Steroids are characterized by four interlocking carbohydrate rings.
 * 4) Eicosanoids: Are lipids synthesized from the fatty acid chains of phospholipids found in plasma membrane.

Hormones circulating in the blood diffuse into the interstitial fluids surrounding the cell. Cells with specific receptors for a hormone respond with an action that is appropriate for the cell. Because of the specificity of hormone and target cell, the effects produced by a single hormone may vary among different kinds of target cells.

Hormones activate target cells by one of two methods, depending upon the chemical nature of the hormone.

 * Lipid-soluble hormones (steroid hormones and hormones of the thyroid gland) diffuse through the cell membranes of target cells. The lipid-soluble hormone then binds to a receptor protein that, in turn, activates a DNA segment that turns on specific genes.  The proteins produced as result of the transcription of the genes and subsequent translation of mRNA act as enzymes that regulate specific physiological cell activity.

 * Water-soluble hormones (polypeptide, protein, and most amino acid hormones) bind to a receptor protein on the plasma membrane of the cell. The receptor protein, in turn, stimulates the production of one of the following second messengers:

Cyclic AMP (cAMP) is produced when the receptor protein activates another membrane-bound protein called a G protein. The G protein activates adenylate cyclase, the enzyme that catalyzes the production of cAMP from ATP. Cyclic AMP then triggers an enzyme that generates specific cellular changes.

Inositol triphosphate (IP3) is produced from membrane phospholipids. IP3, in turn, triggers the release of CA2+ from the endoplasmic reticulum, which then activates enzymes that generate cellular changes.

Endocrine glands release hormones in response to one or more of the following stimuli:
 * 1) Hormones from other endocrine glands.
 * 2) Chemical characteristics of the blood (other than hormones).
 * 3) Neural stimulation.

Most hormone production is managed by a negative feedback system. The nervous system and certain endocrine tissues monitor various internal conditions of the body. If action is required to maintain homeostasis, hormones are released, either directly by an endocrine gland or indirectly through the action of the hypothalamus of the brain, which stimulates other endocrine glands to release hormones. The hormones activate target cells, which initiate physiological changes that adjust the body conditions. When normal conditions have been recovered, the corrective action - the production of hormones - is discontinued. Thus, in negative feedback, when the original (abnormal) condition has been repaired, or negated, corrective actions decrease or discontinue. For example, the amount of glucose in the blood controls the secretion of insulin and glucagons via negative feedback.

The production of some hormones is controlled by positive feedback. In such a system, hormones cause a condition to intensify, rather than decrease. As the condition intensifies, hormone production increases. Such positive feedback is uncommon, but does occur during childbirth, where hormone levels build with increasingly intense labor contractions. Also in lactation, hormone levels increase in response to nursing, which causes an increase in milk production. The hormone produced by the hypothalamus causing the milk let down and uterine contraction is oxytocin.

Pituitary gland
The hypothalamus makes up the lower region of the diencephalons and lies just above the brain stem. The pituitary gland (hypophysis) is attached to the bottom of the hypothalamus by a slender stalk called the infundibulum. The pituitary gland consists of two major regions, the anterior pituitary gland (anterior lobe or adenohypophysis) and the posterior pituitary gland (posterior lobe or neurohypophysis). The hypothalamus also controls the glandular secretion of the pituitary gland.

The hypothalamus oversees many internal body conditions. It receives nervous stimuli from receptors throughout the body and monitors chemical and physical characteristics of the blood, including temperature, blood pressure, and nutrient, hormone, and water content. When deviations from homeostasis occur or when certain developmental changes are required, the hypothalamus stimulates cellular activity in various parts of the body by directing the release of hormones from the anterior and posterior pituitary glands. The hypothalamus communicates directives to these glands by one of the following two pathways: The pituitary gland is found in the inferior part of the brain and is connected by the pituitary stalk. It can be referred to as the master gland because it is the main place for everything that happens within the endocrine system. It is divided into two sections: the anterior lobe (adenohypophysis) and the posterior lobe (neurohypophysis). The Anterior pituitary is involved in sending hormones that control all other hormones of the body.

Posterior pituitary
Communication between the hypothalamus and the posterior pituitary occurs through neurosecretory cells that span the short distance between the hypothalamus and the posterior pituitary. Hormones produced by the cell bodies of the neurosecretory cells are packaged in vesicles and transported through the axon and stored in the axon terminals that lie in the posterior pituitary. When the neurosecretory cells are stimulated, the action potential generated triggers the release of the stored hormones from the axon terminals to a capillary network within the posterior pituitary. Two hormones, oxytocin and antidiuretic hormone (ADH), are produced and released this way. Decreased ADH release or decreased renal sensitivity to ADH produces a condition known as diabetes insipidus. Diabetes insipidus is characterized by polyuria (excess urine production), hypernatremia (increased blood sodium content) and polydipsia (thirst). Oxytocin is secreted by paraventricular nucleus and a small quantity is secreted by supraoptic nucleus in the hypothalamus. Oxytocin is secreted in both males and females. In females, oxytocin acts on the mammary glands and uterus. In males, oxytocin facilitates release of sperm into the urethra by causing contraction of vas deferens.

The posterior lobe is composed of neural tissue [neural ectoderm] and is derived from hypothalamus. Its function is to store oxytocin and antidiuretic hormone. When the hypothalamic neurons fire these hormones are release into the capillaries of the posterior lobe.

The posterior pituitary is, in effect, a projection of the hypothalamus. It does not produce its own hormones, but only stores and releases the hormones oxytocin and antidiuretic hormone. ADH is also known as arginine vasopressin (AVP) or simply vasopressin.

Anterior pituitary
The anterior lobe is derived from oral ectoderm and is composed of glandular epithelium. Communication between the hypothalamus and the anterior pituitary (adenohypophysis) occurs through hormones (releasing hormones and inhibiting hormones) produced by the hypothalamus and delivered to the anterior pituitary via a portal network of capillaries. It consists of three divisions: 1. pars distalis, 2. pars tuberalis, 3. pars intermedia. The releasing and inhibiting hormones are produced by specialized neurons of the hypothalamus called neurosecretory cells. The hormones are released into a capillary network or primary plexus, and transported through veins or hypophyseal portal veins, to a second capillary network or secondary plexus that supplies the anterior pituitary. The hormones then diffuse from the secondary plexus aunshine into the anterior pituitary, where they initiate the production of specific hormones by the anterior pituitary. Many of the hormones produced by the anterior pituitary are tropic hormones or tropins, which are hormones that stimulate other endocrine glands to secrete their hormones.

The anterior pituitary lobe receives releasing hormones from the hypothalamus via a portal vein system known as the hypothalamic-hypophyseal portal system.

The anterior pituitary secretes:
 * thyroid-stimulating hormone (TSH)
 * adrenocorticotropic hormone (ACH)
 * prolactin
 * follicle-stimulating hormone (FSH)
 * luteinizing hormone (LH)
 * growth hormone (GH)
 * endorphins
 * and other hormones

It does this in response to a variety of chemical signals from the hypothalamus, which travels to the anterior lobe by way of a special capillary system from the hypothalamus, down the median eminence, to the anterior lobe. These include:
 * thyrotropin-releasing hormone (TRH)
 * corticotropin-releasing hormone (CRH)
 * dopamine (DA), also called 'prolactin inhibiting factor' (PIF)
 * gonadotropin-releasing hormone (GnRH)
 * growth hormone releasing hormone (GHRH)

These hormones from the hypothalamus cause release of the respective hormone from the pituitary. The control of release of hormones from the pituitary is via negative feedback from the target gland. For example homeostasis of thyroid hormones is achieved by the following mechanism; TRH from the hypothalamus stimulates the release of TSH from the anterior pituitary. The TSH, in turn, stimulates the release of thyroid hormones form the thyroid gland. The thyroid hormones then cause negative feedback, suppressing the release of TRH and TSH.

The heart, gastrointestinal tract, the placenta, the kidneys and the skin, whose major function is not the secretion of hormones, also contain some specialized cells that produce hormones.

In addition, all cells, except red blood cells secrete a class of hormones called eicosanoids. These hormones are paracrines, or local hormones, that primarily affect neighboring cells. Two groups of eicosanoids, the prostaglandins (PGs) and the leukotrienes (LTs), have a wide range of varying effects that depend upon the nature of the target cell. Eicosanoid activity, for example, may impact blood pressure, blood clotting, immune and inflammatory responses, reproductive processes, and the contraction of smooth muscles.

Antagonistic Hormones
Maintaining homeostasis often requires conditions to be limited to a narrow range. When conditions exceed the upper limit of homeostasis, specific action, usually the production of a hormone is triggered. When conditions return to normal, hormone production is discontinued. If conditions exceed the lower limits of homeostasis, a different action, usually the production of a second hormone is triggered. Hormones that act to return body conditions to within acceptable limits from opposite extremes are called antagonistic hormones. The two glands that are the most responsible for homeostasis is the thyroid and the parathyroid.

The regulation of blood glucose concentration (through negative feedback) illustrates how the endocrine system maintains homeostasis by the action of antagonistic hormones. Bundles of cells in the pancreas called the islets of Langerhans contain two kinds of cells, alpha cells and beta cells. These cells control blood glucose concentration by producing the antagonistic hormones insulin and glucagon.

Beta cells secrete insulin. When the concentration of blood glucose raises such in after eating, beta cells secret insulin into the blood. Insulin stimulates the liver and most other body cells to absorb glucose. Liver and muscle cells convert glucose to glycogen, for short term storage, and adipose cells convert glucose to fat. In response, glucose concentration decreases in the blood, and insulin secretion discontinues through negative feedback from declining levels of glucose.

Alpha cells secrete glucagon. When the concentration of blood glucose drops such as during exercise, alpha cells secrete glucagon into the blood. Glucagon stimulates the liver to release glucose. The glucose in the liver originates from the breakdown of glycogen. Glucagon also stimulates the production of ketone bodies from amino acids and fatty acids. Ketone bodies are an alternative energy source to glucose for some tissues. When blood glucose levels return to normal, glucagon secretion discontinues through negative feedback.

Another example of antagonistic hormones occurs in the maintenance of Ca2+ ion concentration in the blood. Parathyroid hormone (PTH) from the parathyroid glands increases Ca2+ in the blood by increasing Ca2+ absorption in the intestines and reabsorption in the kidneys and stimulating Ca2+ release from bones. Calcitonin (CT) produces the opposite effect by inhibiting the breakdown of bone matrix and decreasing the release of calcium in the blood.

Thyroid gland
The Thyroid gland is one of the largest endocrine glands in the body. It is positioned on the neck just below the Larynx and has two lobes with one on either side of the trachea. It is involved in the production of the hormones T3 (triiodothyronine) and T4 (thyroxine). These hormones increase the metabolic activity of the body‘s cells. The thyroid also produces and releases the hormone calcitonin (thyrocalcitonin) which contributes to the regulation of blood calcium levels. Thyrocalcitonin or calcitonin decreases the concentration of calcium in the blood. Most of the calcium removed from the blood is stored in the bones.

The thyroid hormone consists of two components, thyroxine and iodine. This hormone increases the metabolism of most body cells. A deficiency of iodine in the diet leads to the enlargement of the thyroid gland, known as a simple goiter. Hypothyroidism during early development leads to cretinism. In adults, it produces myxedema, characterized by obesity and lethargy. Hyperthyroidism leads to a condition known as exophthalmic goiter, characterized by weight loss as well as hyperactive and irritable behavior.

The thyroid gland is a two-lobed gland that manifests a remarkably powerful active transport mechanism for up-taking iodide ions from the blood. As blood flows through the gland, iodide is converted to an active form of iodine. This iodine combines with an amino acid called tyrosine. Two molecules of iodinated tyrosine then combine to form thyroxine. Following its formation, the thyroxine becomes bound to a polysaccharide-protein material called thyroglobulin. The normal thyroid gland may store several weeks supply of thyroxine in this bound form. An enzymatic splitting of the thyroxine from the thyroglobulin occurs when a specific hormone is released into the blood. This hormone, produced by the pituitary gland, is known as thyroid-stimulating hormone (TSH). TSH stimulates certain major rate-limiting steps in thyroxine secretion, and thereby alters its rate of release. A variety of bodily defects, either dietary, hereditary, or disease induced, may decrease the amount of thyroxine released into the blood. The most popular of these defects is one that results from dietary iodine deficiency. The thyroid gland enlarges, in the continued presence of TSH from the pituitary, to form a goiter. This is a futile attempt to synthesize thyroid hormones, for iodine levels that are too low. Normally, thyroid hormones act via a negative feedback loop on the pituitary to decrease stimulation of the thyroid. In goiter, the feedback loop cannot be in operation - hence continual stimulation of the thyroid and the inevitable protuberance on the neck. Formerly, the principal source of iodine came from seafood. As a result, goiter was prevalent amongst inland areas far removed from the sea. Today, the incidence of goiter has been drastically reduced by adding iodine to table salt.

Thyroxine serves to stimulate oxidative metabolism in cells; it increases the oxygen consumption and heat production of most body tissues, a notable exception being the brain. Thyroxine is also necessary for normal growth. The most likely explanation being that thyroxine promotes the effects of growth hormone on protein synthesis. The absence of thyroxine significantly reduces the ability of growth hormone to stimulate amino acid uptake and RNA synthesis. Thyroxine also plays a crucial role in the closely related area of organ development, particularly that of the central nervous system.

If there is an insufficient amount of thyroxine, a condition referred to as hypothyroidism results. Symptoms of hypothyroidism stem from the fact that there is a reduction in the rate of oxidative energy-releasing reactions within the body cells. Usually the patient shows puffy skin, sluggishness, and lowered vitality. Other symptoms of hypothyroidism include weight gain, decreased libido, inability to tolerate cold, muscle pain and spasm, and brittle nails. Hypothyroidism in children, a condition known as cretinism, can result in mental retardation, dwarfism, and permanent sexual immaturity. Sometimes the thyroid gland produces too much thyroxine, a condition known as hyperthyroidism. This condition produces symptoms such as an abnormally high body temperature, profuse sweating, high blood pressure, loss of weight, irritability, insomnia and muscular pain and weakness. It also causes the characteristic symptom of the eyeballs protruding from the skull called exophthalmia. This is surprising because it is not a symptom usually related to a fast metabolism. Hyperthyroidism has been treated by partial removal or by partial radiation destruction of the gland. More recently, several drugs that inhibit thyroid activity have been discovered, and their use is replacing the former surgical procedures. Unfortunately thyroid conditions require lifetime treatment and because of the body's need for a sensitive balance of thyroid hormone both supplementing and suppressing thyroid function can take months or even years to regulate.

T3 and T4 Function within the body
Iodine and T4 stimulate the spectacular apoptosis (programmed cell death) of the cells of the larval gills, tail and fins Transforming the aquatic, vegetarian tadpole into the terrestrial, carnivorous frog with better neurological, visuospatial, olfactory and cognitive abilities for hunting. Contrary to amphibian metamorphosis, thyroidectomy and hypothyroidism in mammals may be considered a sort of phylogenetic and metabolic regression to a former stage of reptilian life. Indeed, many disorders that seem to afflict hypothyroid humans have reptilian-like features, such as dry, hairless, scaly, cold skin and a general slowdown of metabolism, digestion, heart rate and nervous reflexes, with lethargic cerebration, hyperuricemia and hypothermia ( Venturi, 2000). ]] The Production of T3 and T4 are regulated by thyroid stimulating hormone (TSH), released by the pituitary gland, a bean shape node in the brain. TSH Production is increased when T3 and T4 levels are too low. The thyroid hormones are released throughout the body to direct the body's metabolism. They stimulate all cells within the body to work at a better metabolic rate. Without these hormones the body's cells would not be able to regulate the speed at which they performed chemical actions. Their release will be increased under certain situations such as cold temperatures when a higher metabolism is needed to generate heat. When children are born with thyroid hormone deficiency they have problems with physical growth and developmental problems. Brain development can also be severely impaired.

The significance of iodine
Thyroid hormone cannot be produced without an abundant source of iodine. The iodine concentration within the body, although significant, can be as little as 1/25th the concentration within the thyroid itself. When the thyroid is low on iodine the body will try harder to produce T3 and T4 which will often result in a swelling of the thyroid gland, resulting in a goiter.

Extrathyroidal iodine
Iodine accounts for 65% of the molecular weight of T4 and 59% of the T3. 15–20 mg of iodine is concentrated in thyroid tissue and hormones, but 70% of the body's iodine is distributed in other tissues, including mammary glands, eyes, gastric mucosa, the cervix, and salivary glands. In the cells of these tissues iodide enters directly by sodium-iodide symporter (NIS). Its role in mammary tissue is related to fetal and neonatal development, but its role in the other tissues is unknown. It has been shown to act as an antioxidant in these tissues.

The US Food and Nutrition Board and Institute of Medicine recommended daily allowance of iodine ranges from 150 micrograms /day for adult humans to 290 micrograms /day for lactating mothers. However, the thyroid gland needs no more than 70 micrograms /day to synthesize the requisite daily amounts of T4 and T3. These higher recommended daily allowance levels of iodine seem necessary for optimal function of a number of body systems, including lactating breast, gastric mucosa, salivary glands, oral mucosa, thymus, epidermis, choroid plexus, etc. Moreover, iodine can add to double bonds of docosahexaenoic acid and arachidonic acid of cellular membranes, making them less reactive to free oxygen radicals.

Calcitonin
Calcitonin is a 32 amino acid polypeptide hormone. It is an additional hormone produced by the thyroid, and contributes to the regulation of blood calcium levels. Thyroid cells produce calcitonin in response to high calcium levels in the blood. This hormone will stimulate movement of calcium into the bone structure. It can also be used therapeutically for the treatment of hypercalcemia or osteoporosis. Without this hormone calcium will stay within the blood instead of moving into bones to keep them strong and growing. Its importance in humans has not been as well established as its importance in other animals.

Parathyroid gland
There are four parathyroid glands. They are small, light-colored lumps that stick out from the surface of the thyroid gland. All four glands are located on the thyroid gland. They are butterfly-shaped and located inside the neck, more specifically on both sides of the windpipe. One of the parathyroid glands most important functions is to regulate the body's calcium and phosphorus levels. Another function of the parathyroid glands is to secrete parathyroid hormone, which causes the release of the calcium present in bone to extracellular fluid. PTH does this by depressing the production of osteoblasts, special cells of the body involved in the production of bone and activating osteoclasts, other specialized cells involved in the removal of bone.

There are two major types of cells that make up parathyroid tissue:
 * One of the major cells is called oxyphil cells. Their function is basically unknown.
 * The second type are called chief cells. Chief cells produce parathyroid hormone.

The structure of a parathyroid gland is very different from that of a thyroid gland. The chief cells that produce parathyroid hormone are arranged in tightly-packed nests around small blood vessels, quite unlike the thyroid cells that produce thyroid hormones, which are arranged in spheres called the thyroid follicles.

PTH or Parathyroid Hormone is secreted from these four glands. It is released directly into the bloodstream and travels to its target cells which are often quite far away. It then binds to a structure called a receptor, that is found either inside or on the surface of the target cells.

Receptors bind a specific hormone and the result is a specific physiologic response, meaning a normal response of the body.

PTH finds its major target cells in bone, kidneys, and the gastrointestinal system.

Calcitonin, a hormone produced by the thyroid gland that also regulates ECF calcium levels and serves to counteract the calcium-producing effects of PTH.

The adult body contains as much as 1 kg of calcium. Most of this calcium is found in bone and teeth.

The four parathyroid glands secrete the parathyroid hormone (PTH). It opposes the effect of thyrocalcitonin. It does this by removing calcium from its storage sites in bones, releasing it into the bloodstream. It also signals the kidneys to reabsorb more of this mineral, transporting it into the blood. It also signals the small intestine to absorb more of this mineral, transporting it from the diet into the blood.

Calcium is important for steps of body metabolism. Blood cannot clot without sufficient calcium. Skeletal muscles require this mineral in order to contract. A deficiency of PTH can lead to tetany, muscle weakness due to lack of available calcium in the blood.

The parathyroid glands were long thought to be part of the thyroid or to be functionally associated with it. We now know that their close proximity to the thyroid is misleading: both developmentally and functionally, they are totally distinct from the thyroid.

The parathyroid hormone, called parathormone, regulates the calcium-phosphate balance between the blood and other tissues. Production of this hormone is directly controlled by the calcium concentration of the extracellular fluid bathing the cells of these glands. Parathormone exerts at least the following five effects: (1) it increases gastrointestinal absorption of calcium by stimulating the active transport system and moves calcium from the gut lumen into the blood; (2) it increases the movement of calcium and phosphate from bone into extracellular fluid. This is accomplished by stimulating osteoclasts to break down bone structure, thus liberating calcium phosphate into the blood. In this way, the store of calcium contained in bone is tapped; (3) it increases re-absorption of calcium by the renal tubules, thereby decreasing urinary calcium excretion; (4) it reduces the re-absorption of phosphate by the renal tubules (5)it stimulates the synthesis of 1,25-dihydrixycholecalciferol by the kidney.

The first three effects result in a higher extracellular calcium concentration. The adaptive value of the fourth is to prevent the formation of kidney stones.

If parathyroid glands are removed accidentally during surgery on the thyroid, there would be a rise in the phosphate concentration in the blood. There would also be a drop in the calcium concentration as more calcium is excreted by the kidneys and intestines, and more incorporated into the bone. This can produce serious disturbances, particularly in the muscles and nerves, which use calcium ions for normal functioning. Over activity of the parathyroid glands, which can result from a tumor on the glands, produces a weakening of the bones. This is a condition that makes them much more vulnerable to fracturing because of excessive withdrawal of calcium from the bones.

Adrenal glands
Adrenal glands are a pair of ductless glands located above the kidneys. Through hormonal secretions, the adrenal glands regulate many essential functions in the body, including biochemical balances that influence athletic training and general stress response. The glucocorticoids include corticosterone, cortisone, and hydrocortisone or cortisol. These hormones serve to stimulate the conversion of amino acids into carbohydrates which is a process known as gluconeogenesis, and the formation of glycogen by the liver. They also stimulate the formation of reserve glycogen in the tissues, such as in the muscles. The glucocorticoids also participate in lipid and protein metabolism. The cortex of the adrenal gland is known to produce over 20 hormones, but their study can be simplified by classifying them into three categories: glucocorticoids, mineralocorticoids, and sex hormones.

They are triangular-shaped glands located on top of the kidneys. They produce hormones such as estrogen, progesterone, steroids, cortisol, and cortisone, and chemicals such as adrenalin (epinephrine), norepinephrine, and dopamine. When the glands produce more or less hormones than required by the body, disease conditions may occur.

The adrenal cortex secretes at least two families of hormones, the glucocorticoids and mineral corticoids. The adrenal medulla secretes the hormones epinephrine (adrenalin) and norepinephrine (noradrenalin).

Adrenal Cortex: The hormones made by the Adrenal Cortex supply long-term responses to stress. The two major hormones produced are the Mineral Corticoids and the Glucocorticoids. The Mineral Corticoids regulate the salt and water balance, leading to the increase of blood volume and blood pressure. The Glucocorticoids are monitoring the ACTH, in turn regulating carbohydrates, proteins, and fat metabolism. This causes an increase in blood glucose. Glucocorticoids also reduce the body's inflammatory response.

Cortisol is one of the most active glucocorticoids. It usually reduces the effects of inflammation or swelling throughout the body. It also stimulates the production of glucose from fats and proteins, which is a process referred to as gluconeogenesis.

Aldosterone is one example of a mineralocorticoid. It signals the tubules in the kidney nephrons to reabsorb sodium while secreting or eliminating potassium. If sodium levels are low in the blood, the kidney secretes more renin, which is an enzyme that stimulates the formation of angiotensin from a molecule made from the liver. Angiotensin stimulates aldosterone secretion. As a result, more sodium is reabsorbed as it enters the blood.

Aldosterone, the major mineralocorticoid, stimulates the cells of the distal convoluted tubules of the kidneys to decrease re-absorption of potassium and increase re-absorption of sodium. This in turn leads to an increased re-absorption of chloride and water. These hormones, together with such hormones as insulin and glucagon, are important regulators of the ionic environment of the internal fluid.

The renin-angiotensin-aldosterone mechanism can raise blood pressure if it tends to drop. It does this in two ways. Angiotensin is a vasoconstrictor, decreasing the diameter of blood vessels. As vessels constrict, blood pressure increases. In addition, as sodium is reabsorbed, the blood passing through the kidney becomes more hypertonic. Water follows the sodium into the hypertonic blood by osmosis. This increases the amount of volume in the blood and also increases the blood pressure.

Adrenal Medulla The hypothalamus starts nerve impulses that travel the path from the bloodstream, spinal cord, and sympathetic nerve fibers to the Adrenal Medulla, which then releases hormones. The effects of these hormones provide a short-term response to stress.

Excessive secretion of the glucocorticoids causes Cushing's syndrome, characterized by muscle atrophy or degeneration and hypertension or high blood pressure. Under secretion of these substances produces Addison's disease, characterized by low blood pressure and stress.

Epinephrine and norepinephrine produce the "fight or flight" response, similar to the effect from the sympathetic nervous system. Therefore, they increase heart rate, breathing rate, blood flow to most skeletal muscles, and the concentration of glucose in the blood. They decrease blood flow to the digestive organs and diminish most digestive processes.

The adrenal sex hormones consist mainly of male sex hormones (androgens) and lesser amounts of female sex hormones (estrogens and progesterone). Normally, the sex hormones released from the adrenal cortex are insignificant due to the low concentration of secretion. However, in cases of excess secretion, masculine or feminine effects appear. The most common syndrome of this sort is "virilism" of the female.

Should there be an insufficient supply of cortical hormones, a condition known as Addison's disease would result. This disease is characterized by an excessive excretion of sodium ions, and hence water, due to lack of mineralocorticoids. Accompanying this is a decreased blood glucose level due to a deficient supply of glucocorticoids. The effect of a decreased androgen supply cannot be observed immediately. Injections of adrenal cortical hormones promptly relieve these symptoms.

Hormonal production in the adrenal cortex is directly controlled by the anterior pituitary hormone called adrenocorticotropic hormone (ACTH).

The two adrenal glands lie very close to the kidneys. Each adrenal gland is actually a double gland, composed of an inner core like medulla and an outer cortex. Each of these is functionally unrelated.

The adrenal medulla secretes two hormones, adrenalin or epinephrine and noradrenalin or norepinephrine, whose functions are very similar but not identical. The adrenal medulla is derived embryologically from neural tissue. It has been likened to an overgrown sympathetic ganglion whose cell bodies do not send out nerve fibers, but release their active substances directly into the blood, thereby fulfilling the criteria for an endocrine gland. In controlling epinephrine secretion, the adrenal medulla behaves just like any sympathetic ganglion, and is dependent upon stimulation by sympathetic preganglionic fibers.

Epinephrine promotes several responses, all of which are helpful in coping with emergencies: the blood pressure rises, the heart rate increases, the glucose content of the blood rises because of glycogen breakdown, the spleen contracts and squeezes out a reserve supply of blood, the clotting time decreases, the pupils dilate, the blood flow to skeletal muscles increase, the blood supply to intestinal smooth muscle decreases and hairs become erect. These adrenal functions, which mobilize the resources of the body in emergencies, have been called the fight-or-flight response. Norepinephrine stimulates reactions similar to those produced by epinephrine, but is less effective in conversion of glycogen to glucose.

The significance of the adrenal medulla may seem questionable since the complete removal of the gland causes few noticeable changes; humans can still exhibit the flight-or-fight response. This occurs because the sympathetic nervous system complements the adrenal medulla in stimulating the fight-or-flight response, and the absence of the hormonal control will be compensated for by the nervous system.

Pancreas
The pancreas is very important organ in the digestion system and the circulatory system because it helps to maintain our blood sugar levels. The pancreas is considered to be part of the gastrointestinal system. It produces digestive enzymes to be released into the small intestine to aid in reducing food particles to basic elements that can be absorbed by the intestine and used by the body. It has another very different function in that it forms insulin, glucagon and other hormones to be sent into the bloodstream to regulate blood sugar levels and other activities throughout the body.

It has a pear-shape to it and is approximately 6 inches long. It is located in the middle and back portion of the abdomen. The pancreas is connected to the first part of the small intestine, the duodenum, and lies behind the stomach. The pancreas is made up of glandular tissue: any substance secreted by the cells of the pancreas will be secreted outside of the organ.

The digestive juices produced by the pancreas are secreted into the duodenum via a Y-shaped duct, at the point where the common bile duct from the liver and the pancreatic duct join just before entering the duodenum. The digestive enzymes carried into the duodenum are representative of the exocrine function of the pancreas, in which specific substances are made to be passed directly into another organ.

The pancreas is unusual among the body's glands in that it also has a very important endocrine function. Small groups of special cells called islet cells throughout the organ make the hormones of insulin and glucagon. These, of course, are hormones that are critical in regulating blood sugar levels. These hormones are secreted directly into the bloodstream to affect organs all over the body.

Insulin acts to lower blood sugar levels by allowing the sugar to flow into cells. Glucagon acts to raise blood sugar levels by causing glucose to be released into the circulation from its storage sites. Insulin and glucagon act in an opposite but balanced fashion to keep blood sugar levels stable.

A healthy working pancreas in the human body is important for maintaining good health by preventing malnutrition, and maintaining normal levels of blood sugar. The digestive tract needs the help of the enzymes produced by the pancreas to reduce food particles to their simplest elements, or the nutrients cannot be absorbed. Carbohydrates must be broken down into individual sugar molecules. Proteins must be reduced to simple amino acids. Fats must be broken down into fatty acids. The pancreatic enzymes are important in all these transformations. The basic particles can then easily be transported into the cells that line the intestine, and from there they can be further altered and transported to different tissues in the body as fuel sources and construction materials. Similarly, the body cannot maintain normal blood sugar levels without the balanced action of insulin and glucagon.

The pancreas contains exocrine and endocrine cells. Groups of endocrine cells, the islets of Langerhans, secrete two hormones. The beta cells secrete insulin; the alpha cells secrete glucagon. The level of sugar in the blood depends on the opposing action of these two hormones.

Insulin decreases the concentration of glucose in the blood. Most of the glucose enters the cells of the liver and skeletal muscles. In these cells, this monosaccharide is converted to the polysaccharide glycogen. Therefore, insulin promotes glycogenesis or glycogen synthesis, in which glucose molecules are added to chains of glycogen. Excess glucose is also stored as fat in adipose tissue cells in response to insulin.

Insulin deficiency leads to the development of diabetes mellitus, specifically type I, juvenile diabetes. As the pancreas does not produce sufficient insulin, it is treated by insulin injections. In type II or maturity onset diabetes, the pancreas does produce enough insulin, but the target cells do not respond to it.

As already stated, the pancreas is a mixed gland having both endocrine and exocrine functions. The exocrine portion secretes digestive enzymes into the duodenum via the pancreatic duct. The endocrine portion secretes two hormones, insulin and glucagon, into the blood.

Insulin is a hormone that acts directly or indirectly on most tissues of the body, with the exception of the brain. The most important action of insulin is the stimulation of the uptake of glucose by many tissues, particularly the liver, muscle and fat. The uptake of glucose by the cells decreases blood glucose and increases the availability of glucose for the cellular reactions in which glucose participates. Thus, glucose oxidation, fat synthesis, and glycogen synthesis are all accentuated by an uptake of glucose. It is important to note that insulin does not alter glucose uptake by the brain, nor does it influence the active transport of glucose across the renal tubules and gastrointestinal epithelium.

As stated, insulin stimulates glycogen synthesis. It also increases the activity of the enzyme that catalyzes the rate-limiting step in glycogen synthesis. Insulin also increases triglyceride levels by inhibiting triglyceride breakdown, and by stimulating production of triglyceride through fatty acid and glycerophosphate synthesis. The net protein synthesis is also increased by insulin, which stimulates the active membrane transport of amino acids, particularly into muscle cells. Insulin also has effects on other liver enzymes, but the precise mechanisms by which insulin induces these changes are not well understood.

Insulin is secreted by beta cells, which are located in the part of the pancreas known as the islets of Langerhans. These groups of cells, which are located randomly throughout the pancreas, also consist of other secretory cells called alpha cells. It is these alpha cells that secrete glucagon. Glucagon is a hormone that has the following major effects: it increases hepatic synthesis of glucose from pyruvate, lactate, glycerol, and amino acids (a process called gluconeogenesis, which also raises the plasma glucose level); and it increases the breakdown of adipose tissue triglyceride, thereby raising the plasma levels of fatty acids and glycerol. The glucagon secreting alpha cells in the pancreas, like the beta cells, respond to changes in the concentration of glucose in the blood flowing through the pancreas; no other nerves or hormones are involved.

It should be noted that glucagon has the opposite effects of insulin. Glucagon elevates the plasma glucose, whereas insulin stimulates its uptake and thereby reduces plasma glucose levels; glucagon elevates fatty acid concentrations, whereas insulin converts fatty acids and glycerol into triglycerides, thereby inhibiting triglyceride breakdown.

The alpha and beta cells of the pancreas make up a push-pull system for regulating the plasma glucose level.

Sex organs
The Sex organs (Gonads) are the testes in the male, and the ovaries in the female. Both of these organs produce and secrete hormones that are balanced by the hypothalamus and pituitary glands.

The main hormones from the reproductive organs are:

Testosterone is more prominent in males. It belongs to the family of androgens, which are steroid hormones producing masculine effects. Testosterone stimulates the development and functioning of the primary sex organs. It also stimulates the development and maintenance of secondary male characteristics, such as hair growth on the face and the deep pitch of the voice.

Estrogen In females, this hormone stimulates the development of the uterus and vagina. It is also responsible for the development and maintenance of secondary female characteristics, such as fat distribution throughout the body and the width of the pelvis.

Male

The testes produce androgens (i.e., "testosterone"). Testosterone is classified as a steroid and is responsible for many of the physical characteristics in males like. Testosterone increases protein production. Hormones that build up protein are called anabolic steroids. Anabolic steroids are available commercially and are being used by athletes because they help improve their physical ability, however, they do have major side effects such as:
 * Broad shoulders
 * Muscular body
 * Hair
 * Liver and kidney disorders
 * Hypertension (high blood pressure)
 * Decreased sperm count and impotency
 * Aggressive behavior ("roid rage")
 * Balding
 * Acne

Female

The ovaries produce estrogen and progesterone. Estrogen increases at the time of puberty and causes the growth of the uterus and vagina. Without estrogen egg maturation would not occur. Estrogen is also responsible for secondary sex characteristics such as female body hair and fat distribution. Estrogen and Progesterone are responsible for the development of the breast and for the uterine cycle. Progesterone is a female hormone secreted by the corpus luteum after ovulation during the second half of the menstrual cycle. It prepares the lining of the uterus for implantation of a fertilized egg and allows for complete shedding of the endometrium at the time of menstruation. In the event of pregnancy, the progesterone level remains stable beginning a week or so after conception.

Pineal gland
The pineal gland (also called the pineal body or epiphysis) is a small endocrine gland in the brain. It is located near the center of the brain, between the two hemispheres, tucked in a groove where the two rounded thalamic bodies join. It consists of two types of cells 1. parenchymal cells 2. neuroglial cells.

The pineal gland is a reddish-gray body about the size of a pea (8 mm in humans) located just rostro-dorsal to the superior colliculus and behind and beneath the stria medullaris, between the laterally positioned thalamic bodies. It is part of the epithalamus.

The pineal gland is a midline structure, and is often seen in plain skull X-rays, as it is often calcified. The main hormone produced and secreted by the pineal gland is melatonin. Secretion is highest at night and between the ages of 0-5. Melatonin acts mainly on gonads.

Glossary
Adrenal Gland: endocrine gland that is located on top of each kidney

Amino Acid-derived: hormones that are modified amino acids

Antagonistic Hormones: hormones that act to return body conditions to within acceptable limits from opposite extremes

Calcitonin: hormone produced by the thyroid; contributes to the regulation of blood calcium levels

Eicosanoids: lipids that are synthesized from the fatty acid chains of phospholipids found in plasma membrane

Endocrine Glands: glands that have no duct and release their secretions directly into the intercellular fluid or into the blood

Endocrine System: a control system of ductless glands that secrete chemical messengers called hormones

Estrogen: hormone in females; stimulates the development of the uterus and vagina

Exocrine Glands: glands that release their cellular secretions through a duct which empties to the outside or into the lumen (empty internal space) of an organ

Hormone: a specific chemical substance produced by certain cells that control, or help to control, cellular processes elsewhere in an organism

Insulin: hormone that acts to lower blood sugar levels by allowing the sugar to flow into cells

Iodine: chemical in the body; Thyroid hormone can not be produced with out it

Lipid-soluble Hormones: diffuse through the cell membranes of target cells

Parathyroid: four masses of tissue, two embedded posterior in each lateral mass of the thyroid gland

Pancreas: organ involved with the digestion system and the circulatory system; helps to maintain blood sugar levels

Pineal Gland: small endocrine gland in the brain located near the center of the brain, between the two hemispheres, tucked in a groove where the two rounded thalamic bodies join

Pituitary Gland: endocrine gland that is attached to the hypothalamus of the lower forebrain

Polypeptide and Proteins: hormones that are chains of amino acids of less than or more than about 100 amino acids

Steroids: hormones that are lipids that are synthesized from cholesterol; characterized by four interlocking carbohydrate rings

Testosterone: hormone more prominent in males; belongs to the family of androgens, which are steroid hormones producing masculinizing effects

Thyroid Gland: endocrine gland that consists of two lateral masses that are attached to the trachea

Thyroxine: serves to stimulate oxidative metabolism in cells; increases the oxygen consumption and heat production of most body tissues

Water-soluble Hormones: bind to a receptor protein on the plasma membrane of the cell

Chapter Review Questions

 * Answers for these questions can be found here

1. My child just fell and was hurt, the anxious feeling that I feel is caused by:
 * A) glucagon
 * B) insulin
 * C) epinephrine
 * D) adrenocorticotropic
 * E) None of these

2. All of Bob’s life he has had to take insulin shots, this is caused because
 * A) his beta cells don’t function correctly
 * B) his alpha cells don’t function correctly
 * C) his DA hormone isn’t functioning correctly
 * D) his GHRH hormone isn’t functioning correctly

3. The reason iodine is in salt is
 * A) to prevent diabetes
 * B) to prevent simple goiters
 * C) to prevent Addison’s disease
 * D) to prevent Cushing's syndrome

4. All hormones react to a negative feedback except
 * A) progesterone
 * B) estrogen
 * C) prolactin
 * D) oxytocin
 * E) none of these

5. If I have a high blood calcium level it may be due to
 * A) calcitonin
 * B) parathyroid
 * C) glucocorticoids
 * D) glucagon

6. Hormones that are lipids that are synthesized from cholesterol
 * A) protein
 * B) amino acid-derived
 * C) polypeptide
 * D) steroids
 * E) eicosanoids

7. This type of hormone must bind to a receptor protein on the plasma membrane of the cell
 * A) water soluble
 * B) lipid soluble
 * C) steroid
 * D) polypeptide
 * E) a and d
 * F) b and c

8. Endocrine glands release hormones in response to
 * A) Hormones from other endocrine glands
 * B) Chemical characteristics of the blood
 * C) Neural stimulation
 * D) All of the above

9. The anterior pituitary secretes
 * A) oxytocin
 * B) endorphins
 * C) ADH
 * D) TRH

10. Chief cells produce
 * A) epinephrine
 * B) glucagon
 * C) insulin
 * D) mineralocorticoids
 * E) parathyroid hormone

11. Name the eight major endocrine glands.

12. Name the four major groups hormones can be chemically classified into.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

title: Human Physiology/The endocrine system


text: Category:Book:SNFO Flight Planning

title: Category:Book:SNFO Flight Planning


text:
Jeep Liberty/Lockers/Aussie Locker

The Aussie Locker XD-13027 is an automatic locker for Dana 30 27 spline axles with open carriers. A "lunchbox" type device, it replaces the internal parts of the stock carrier. It needs to be installed in an open differential. If the axle already has an LSD, it will need to be converted to an open differential prior to the Aussie Locker installation. No ring and pinion gear set up is required and installation shouldn't take more than a few hours.

title: Jeep Liberty/Lockers/Aussie Locker


text: Category:Book:Sanskrit

title: Category:Book:Sanskrit


text: Category:Book:Saxophone

title: Category:Book:Saxophone


text:
Mac OS X Tiger/Utilities/Activity Monitor

Activity Monitor is a utility integrated into OS X that allows you to see what is happening within your computer - specifically in regard to your processor, hard disk, memory, and network. Activity Monitor lets you identify and administer the applications and processes running on your computer. It also allows you to observe CPU activity, as well as your use of your memory, disks, and network. The activity can be viewed in the program itself or an icon representation in the dock.

Windows
Windows Task Manager (only on Windows operating systems that are based on the NT architecture, such as Windows NT, Windows 2000, Windows XP, Windows Server 2003, Windows Vista)


text: Category:Book:Scienceshow

title: Category:Book:Scienceshow


text: Category:Book:Scouting

title: Category:Book:Scouting


text:
Nature

Prologue

 * /Preface/
 * /Introduction/
 * Basic statements of the scientific worldview

The basics

 * What is nature?
 * Matter, energy and information
 * Atoms, molecules, elementary particles, photons
 * The four forces
 * Space and time

The history of nature

 * The history of inanimate nature, astronomy
 * What is life?
 * The evolution of life
 * The evolution of man

The human mind and its performance

 * How do we see the world?
 * Spirit, soul, consciousness, free will
 * Good and evil in nature, conscience
 * Basics of a natural ethic
 * Achievements of man, transcendence of nature

The natural sciences

 * What are the natural sciences and how do they work?
 * What are laws of nature?
 * Boundaries of the scientific worldview and the limits of nature
 * The big errors of science
 * The open questions in science
 * Natural criticism of other worldviews
 * Criticism of science and its worldview

Epilogue

 * What does the future look like?

Natur

title: Nature


text: Category:Book:Screen Printing

title: Category:Book:Screen Printing


text: Category:Book:Sedimentation

title: Category:Book:Sedimentation


text:
Talk:Human Physiology/The Nervous System

How to insert an image
In respone to a question from Brittine on inserting an image, I will tell you EXACTLY how to do it. For any sort of editing tricks, the easiest thing is to go to a chapter where you see something you like, click on "edit" and copy their code. Then paste that code into your chapter and modify it to suit your purposes. For the specific question of how to insert photos, you must first find a photo (or drawing) that is free of any copyrights. On the beginning page of our book I have a "Note to authors" section with a link to Wikimedia Commons. You should either find your images there or, if you have a different image you should first upload it to the Commons. In other words, all image files are stored at the Commons, not in the individual articles or books. You simply link to a file at the Commons from within your chapter.

Here is a concrete example of how to do this: I followed the link from the Note to Authors, then went to the Neurosciences section. I found a picture I liked of an Action Potential. Here is the link to that image: http://commons.wikimedia.org/wiki/Image:422px-Action_potential_vert.png

Note that the end of the link is: Image:422px-Action_potential_vert.png

Next I went to a chapter that had an image (I went to Ch 18 on Development, since I know Brent and Anthony have figured out how to edit Wikibooks better than me). On a paragraph with an image I clicked "edit" and saw the following code:. I copied this and then went back to the Nervous System chapter. Under the heading Structure and Function of Neurons someone had written "Generation & propagation of an action potential." I turned that into a separate heading and decided it was a good place for the image I had found. So now I just paste the code I had copied and replaced one image name with the other so it looked like this:

==Generation & propagation of an action potential==

I then hit "Show preview" and saw that with the image at the left all the text afterwards was put to the side of it. Since I did not have anything written about action potentials I deleted the "|left" of the code and hit "Show preview" again.

That looked pretty good to me, so I wrote in the summary "added action potential image" (the summary is a nice way to let people know what changes were made), then I hit "Save page."

That was a long-winded way to answer your question, so I hope it made good sense. I did not tell you how to add images to the Commons area if you find a non-copyrighted image that you want to use from some other location. If you need to upload to the Commons, then let me know. Also, if you see an image in Wikipedia and you want to use it, then you should only need to look at the code, get the name of the image, and insert it into the code for linking to images.

Work hard and do great things! ~Kevin Provophys 07:04, 28 July 2006 (UTC)

Thanks This is so helpful. Cindy the helper (discuss • contribs) 13:27, 2 September 2021 (UTC)

are we covering the limbic system?
It was my understanding when we asked kevin about it that we were not going to have more than a basic over view of the limbic system. Am I incorect? --Clareceglanville 22:32, 7 August 2006 (UTC)

Goals for this chapter.

 * 1 Create a key terms section
 * 2 provide pictrues for the synapsis and firing of a neuron
 * 3 bold all key terms within the chapter
 * 4 create a sub heading to give the somatic nervous system it's own section

Please feel free to add more--Clareceglanville 00:33, 10 August 2006 (UTC)

Jody's Review
This chapter has a lot of great information in it. I was impressed with the flow and ease of the chapter in understandig the information. One suggestion I have is at the very beginning it lists overview of the entire nervous system and then lists (CNS, PNS, Efferent, Afferent, Somatic, Visceral, etc. ...) I thought it might be helpful to actually right out the "central nervous system" where "cns" is and periphreal nervous system w/ "pns" I just thought it might be easier for someone to understand that is not to familiar with the terms (someone who has not just taken anatomy)  Just a thought. Great Job. --Jtervortn 13:45, 23 August 2006 (UTC)

WhiteKnight...Oh, WhiteKnight
Wherefore art thou, Whiteknight!!?? We added a case study right after the sub-heading that talked about the Myelin Sheath. We were wondering if there was anything fun we could add to that case study, perhaps a border? Or just something that may make it stand out a bit from the rest of the chapter. Please let us know if you have any ideas. Thanks!!Pwoodson 19:20, 23 August 2006 (UTC)

RiRi's Review
Sorry guys I'm with Jamie on the whole busy thing! I too was busy with my own chapter to give in put,BUT here I am!...anyways!...I honestly think this was the hardest chapter to put together as far as anyone else's and you guys that have been working on it did a great job! I added some pictures towards the end of the chapter if you guys want to edit them I wont care by all means! Also since everyone is changing chapters this next week, who ever is going to take over this chapter i totally recomend the web site |"How stuff works.com".you guys can link the animation videos to this chapter. They show easy understandable short videos on how the nervous system works.It's really cool!. If you go to Integumentry system and look and the link i put in for breast tissue and look at the edit page it will show you how I put it in if you dont know. Anyways I can't waite to do the homework for this chapter!{RiRi82 02:54, 3 September 2006 (UTC)}

Sodium-potassium pump
I found an image that may be useful for this chapter: but for some reason it is not showing up! Provophys 23:26, 8 March 2007 (UTC) I have used this one File:Scheme sodium-potassium pump-en.svg 167.30.56.22 (discuss) 04:13, 23 March 2012 (UTC)

Neuron image
It would be nice to have an imange of a neuron and the structure of.!

Club drugs
Just reading through and found that the term, "club drugs," used in the drugs section seems to be just a generalisation, perhaps it would be better to remove this and just leave the specific examples? (unsigned)

On the subject of drugs, I think the page contains more than enough content on recreational drugs and needs an edit to return to physiology scope for this chapter. I disagree with this paragraph ''Some say that abuse begins when the user begins shirking responsibility in order to afford drugs or to have enough time to use them. Some say it begins when a person uses "excessive" amounts, while others draw the line at the point of legality, and others believe it amounts to chronic use despite degenerating mental and physical health in the user. Some think that any intoxicant consumption is an inappropriate activity.''

My suggestion for replacement - ''The nervous system is able to accomodate or adjust for various stimuli. The body develops tolerance to psycho-active substances and the drug user must repeat the dose in order to feel 'normal'. The combination of some individuals and substances develop tolerance to a stage where the user increases the dose to acheive the euphoric "high" effect and access to continued supply becomes a compulsive and sometimes problematic theme. The immediate physical effects of the drug may be insignificant compared with the psychosocial dislocation with comes alongside abuse, such as dishonest or risk-taking behaviour. The effects of drug abuse are sufficient to have become a universal public health and law enforcement concern'' Tradimus (discuss • contribs) 05:13, 23 March 2012 (UTC)

Marijuana
I don't see this as a safety record I think a more accurate representation would be 'marijuana has a low lethality in overdose' Tradimus (discuss • contribs) 07:57, 20 March 2012 (UTC)
 * Dependence
 * Anxiety and depression
 * Sleep problems
 * Lowered sex drive
 * Learning difficulties and poorer educational outcomes
 * Memory problems
 * Respiratory illnesses such as chronic cough and bronchitis
 * Increased risk of cancer of the lung, mouth, throat and tongue
 * Paranoia and other psychotic symptoms such as hallucinations with increased risk of developing schizophrenia


text:
Talk:Human Physiology/Genetics and inheritance

I added an inheritance table; I found it from a Merlot site. I moved your definitions down before your review questions, Kevin had a format he recomended. Dorothy

Subject: Genetics & Ineritance
Message no. 43 Author: Dorothy Duncan Date: Monday, July 31, 2006 9:40am Angie, Melissa, & Tori I have put a few images on your chapter, just an idea, maybe you have some others that you would prefer, I can help with that. Also, you should put your References down, possibly as your last subject; you can look at at my ch. Pregnancy & Birth to get some ideas.

Kevin, I went to the discussion page, I can't figure out how to leave this goup a message there.

Thanks, Dorothy

I thought this was good info. You have talked alot about the two types of hemophilia but you never say what factor is missing. Give some examples of whether a women carries this gene or the man will pass the gene to his off spring. Also when I took this class before kevin talked about queen victoia having hemophilia. I think it is always easier to learn when you can relate the concepts to an actual situation. Andrea Keller "Patients with hemophilia A lack the blood clotting protein, factor VIII, and those with hemophilia B lack factor IX. There are about 20,000 hemophilia patients in the United States. Each year, about 400 babies are born with this disorder. Approximately 85% have hemophilia A and the remainder has hemophilia B." http://www.medceu.com/tests/hemophilia.htm

It is generally considered unsightly to write a page in all capital letters. I recommend that somebody fix this to use proper capitalization. --Whiteknight (talk) (projects) 17:57, 21 July 2006 (UTC)

Definitions list
In response to Whiteknight I changed your page to non-capitals. I also formatted your definitions with a definition list format (you will see how to do it when you edit your page). If you decide to do a list of definitions you mights want to search google with "define: genetics" and define: inheritance and so forth. That way you can look at several definitions while deciding upon your own. Thanks for jumping right in--I look forward to seeing additional content soon! Provophys 19:39, 21 July 2006 (UTC)

Thanks for fixing the chapter. my keyboard was having issues number lock and caps were permanently stuck on at random times. I finally broke down and spent the 10 dollars to get a new keyboard. If I would have known how cheap they were I would have bought one awhile ago. Melissasmith 02:13, 28 July 2006 (UTC)

 * That's a funny story!

Big subject!
I lectured on genetics to my microbiology class yesterday and was reminded what a big, complex topic genetics is. I like your approach so far. Just keep in mind who your audience is--introductory physiology students with an interest in medicine--and I think you will be able to wade through everything and glean what is most applicable. Do you think you should talk about replication? Transcription and translation? Mitosis vs meiosis (probably not)? Mendelian genetics? Mutations? I think using genetic diseases to highlight and explain principles might be useful. Treatment for inherited diseases varies quite a bit--for some inherited diseases nothing can be done, for others (such as hemophilia) a functioning protein can be given by injection to compensate for the mutated gene, while for others (cystic fibrosis) gene therapy offers great promises.

I'll be watching with interest! ~Kevin Provophys 20:30, 27 July 2006 (UTC)

Thanks for the advice. I have been looking up information on genetic diseases and there is A LOT! I am going to go through it all and try to find the best info to put into the chapter. If you have any really good web sites you could tell me about I would appreciate it. Thanks again.Melissasmith 02:12, 28 July 2006 (UTC)

Images
I've found some images that might be of use in this chapter. Feel free to add them if you think they are appropriate:

 * [[Image:Autorecessive-3.png]]
 * [[Image:DNA animation.gif]]
 * [[Image:Autorecesiva.png]] (in spanish)
 * [[Image:Ccl7 code.GIF]]
 * [[Image:Chromatin chromosom.png]]
 * [[Image:Copiadna.JPG]]
 * [[Image:Dna-split.png]]

And there are many others to be found at: commons:Category:Genetics. Let me know if you need any help. --Whiteknight (talk) (projects) 14:28, 7 August 2006 (UTC)

Review
This is a very intense area of study and heavy chapter but it looks very good. I like the table of contents, I think that it is arranged very well and covers the most needed information.I thought mabey there couold be more of an introduction to the chapter that could really grab the reader or give more of an overview to what is going to be discussed in the chapter and is there any more information to add to the gene section?I love the timeline of notable discoveries and find the inheritance section and information to be interesting. The last thing that I would suggest is that mabey the smaller sections like polygenic traits, be subsectioned or added somewhere else. There are a few that seem too small to have their own section unless you find more information to add. That way you can condense a little or add to fill those little sections. Good work and good luck, thanks!--JamBam 00:54, 18 August 2006 (UTC)

Thoughts on what to include or exclude
In thinking about what is of greatest value to a beginning physiology student, there are several things that come to my mind (of course, this list would be different for others). I think an introduction of genetics should include the basic structure of DNA, a brief history of the study of inheritance, and explanations of chromosomes and genes. Maybe some treatment of the nature vs nurture debate, and some examples showing effects of both. I think it helpful to explain the processes of replication, transcription, and translation so people understand the basics of what DNA is used for. An explanation of inheritance, focusing on simple dominant/recessive traits first, is good, then you can discuss variations to that model with polygenic traits, sex-linked traits, etc. A discussion of mutations followed by a discussion of several genetic disorders (such as cystic fibrosis, hemophilia, etc). Discussion of current and possible future treatments for genetic diseases, and maybe ethical issues that branch off of that. Maybe discussing implications of completing the map of the human genome. I would perhaps exclude, or at least move to a less-prominent position, the section entitled "Areas of Genetics."

I relegated several headings to subheadings under "Exceptions to Simple Inheritance." I'm not sure about that section. All those exceptions are interesting, but perhaps we should focus on the norm and not get too caught up in the exceptions. Also, I would move multifactorial inheritance directly after unifactorial inheritance, and expand upon sex-linked inheritance. I would recommend checking a few beginning biology books or a few anatomy/phys books to see what they include.

For your introductory story, you mentioned a narrative of Mendel. That would be interesting, but I think it may flow better with the other chapters if you give a medical situation of someone with an inherited disorder. Discuss it as a group and make the decision.

Finally, if you could tie in homeostasis. . . turning genes on and off is the body's ultimate regulatory switch over several processes (e.g. embryonic development, puberty, aging, etc).

Those are my thoughts for today. I'll be anxious to see what you come up with. Keep up the good work! Provophys 22:09, 21 August 2006 (UTC)

Review
This is a large complex subject. I like how you have aranged it and what you have focused on. There is one part that I was confused on....The mutant gene section is confusing. It said that “a mutant gene can be indifferent because the mutation is no different than the original.” If it isn’t different than the original how is it mutate. Good luck. --Clareceglanville 22:24, 21 August 2006 (UTC)

cell cycles
the uniqueness of the events of cell cycle in human Adna hassan (discuss • contribs) 18:13, 14 January 2019 (UTC)


text: Category:Book:Serial Programming

title: Category:Book:Serial Programming


text:
Talk:Human Physiology/Blood physiology

Images
I found some more images for you to use in your chapter.

And there are more images for use in the following category:

 * commons:Category:Blood cells

Let me know if you need anything else. --Whiteknight (talk) (projects) 23:57, 7 August 2006 (UTC) Thank you so much for the pictures! We really need them, your a great help! Thank you!--Jacquel 02:08, 9 August 2006 (UTC)

Thoughts on what to include or exclude
Just glancing through the chapter, the one thing that first stood out as missing is a description of blood clotting (platelet plug; clotting cascade). The section on disorders is pretty long--especially (I thought) the section on sickle cell disease. It is easy to get a lot of information on disorders, but we need to stick to the physiology of what is causing the disorders. Also, it is worth considering what disorders to include. There could be more ties made between the blood and other systems. Blood volume, for example, is largely regulated by the kidneys. Actually, the kidneys are heavily involved in potassium ion levels and other ions in the blood as well as regulating pH. I think in class I will talk quite a bit on the mechanism of blood clotting, as well as bring up bleeding disorders (well, hemophilia at least) and anticoagulants and their clinical use. Other thoughts for possible things to include: a discussion of hypertension, flow of blood in the capillaries and how exchange takes place with interstitial fluids, and hypovolemic shock (maybe some of these topics are in the chapter on cardiovascular system). Provophys 23:20, 12 March 2007 (UTC)

ideas
Thanks for the ideas on what could be changed this helped me alot to know where to get started. Do we need to have all of those references and external links or can they be removed also?

help
I dont know what happened when I saved the pg it was really horizontal. Please fix I dont know how. Please feel free to add to my brief discussion on blood clotting I have only just begun.

a duplication
7-5-2011 In the description of RBCs it first says there are 250 million hemoglobin (molecules)- then later it says there are around 200 million. It only needs to say one or the other.

Blood Clotting Edit
I took the liberty to cut this portion out of the section on blood clotting. If anyone is feeling attached to it, I don't mind if you put it back in. I tried to make this section more clear. Hope it is. I still haven't figured out how to talk about the "extrinsic pathway". Any ideas?

"Coagulation is initiated within 20 seconds after the injury. Platelets immediately form a hemostatic plug at the site of injury. This is called primary hemostasis. Platelets are activated by thrombin and aggregate at the site of injury, forming a temporary plug. The protein fibrinogen is primarily responsible for stimulating platelet clumping. Platelets clump by binding to collagen that becomes exposed following the injury. Upon instigation, platelets release nucleotide, ADP and the eicosanoid, TXA2 (both of which activate additional platelets), serotonin, phospholipids, lipoproteins, and other proteins that are important for coagulation. Platelets then change their shape to the formation of the plug. To make sure the clot is strong enough to ensure no more blood loss, fibrinogen is converted into fibrin. This makes a strong barrier over the blood platelets. This forms a permanent blood clot until vessels and tissue have completed the repair.

Secondary hemostasis then follows; Blood plasma components called coagulation factors respond (in a complex cascade) to form fibrin strands which strengthen the platelet plug."

Well, that's all for now! never2late 05:45, 15 March 2007 (UTC)

Confusing statements
Excellent article that I find helpful in which to refer my high school and college students. I have found two statements that are confusing or in error. The first is the last sentence in the Plasma makeup section. Carbon dioxide has 3 forms in the blood: 10% dissolved, 70% in the form of bicarbonate, and 20% bound to hemoglobin. Oxygen has 2 forms: 3% dissolved and 97% bound to hemoglobin. I don't understand where you get that 97% of CO2 is carried by the plasma. By my thinking I would exclude that bound to hgb as you did with O2 and also exclude what is in the form of bicarb to end up with 10% rather than 97%. Also, in the Platelets section, you wrote, "are about 1/10th to 1/20th as abundant as white blood cells." A normal WBC count is 4,500 to 10,000 cells/mcL whereas a normal platelet count is 150,000 to 450,000 cells/mcL. So I think you meant the reverse, that platelets are 10 to 20 times more abundant than white blood cells.

Thanks! --Kris (discuss • contribs) 18:38, 28 December 2011 (UTC)

Or perhaps you meant that platelets are 1/10 to 120th as abundant as RED blood cells. --Kris (discuss • contribs) 00:01, 30 December 2011 (UTC)

title: Talk:Human Physiology/Blood physiology


text:
Nature/Preface

As a child, I owned a little booklet by, called The History of Nature, which is still available. It left a great impression on me, because this book described the basic natural sciences of the world in clear, concise words. Despite some factual errors, it is still readable and inspired this Wikibook.

Unfortunately, I have not found a critical examination of religion by C.F. Weizsäcker. It would have been interesting to read his opinion on a delimitation of what is acceptable to the Christian faith and other religions and what is to be rejected from a scientific point of view.

Meanwhile, I have also discovered the following book by CFvW, which I'm going read. Perhaps it will bring me some new insights about his relationship to religion:

Some of the material used in creating this Wikibook has come from http://www.madeasy.de, and is in the public domain.

In August 2005. User:Rho (at German Wikibooks)

In the evening twilight, a man came to the village and said he was the prophet. But the peasants did not believe him. "Prove it!" they demanded. The man pointed to a [nearby] fortress wall and asked: "If this wall [started] talking, would you believe me?" "By God, we [would] believe you," they cried. The man turned to the wall, reached out, and commanded, "Speak, O wall!" The wall began to speak, "This man is not a prophet, he is deceived, he is a liar."

title: Nature/Preface


text:
Talk:Human Physiology/The respiratory system

Chapter Objectives
You may add to this list, and even subtract from it if you feel it is appropriate to do so. Here are some objectives for the respiratory chapter:

 * Understand the basic anatomy of the respiratory system
 * Understand the mechanics of breathing
 * Know which muscles are involved in inspiration and expiration
 * Compare ventilation, external respiration (at the alveoli), internal respiration (at the tissues), and cellular respiration (in the mitochondria)
 * Understand changes in intrapulmonary and intrapleural pressures during ventilation
 * Understand the role of surfactant
 * Understand the regulation of the breathing response
 * Understand the role of chemoreceptors, such as in the medulla oblongata
 * Understand how oxygen and carbon dioxide are carried into the blood
 * Understand various lung volumes as measured in spirometry (e.g. tidal volume, expiratory reserve volume, etc)
 * Understand the role of the respiratory system in regulating blood pH levels
 * Understand various pulmonary disorders (asthma, emphysema, and other causes of COPD, cystic fibrosis, shallow water blackout, puncture wound, etc)

Let's see what we can do to explain these concepts within the chapter. Remember, you can post any thoughts or questions about the chapter on this page too. Or, if you make a big change you may want to post a summary of it here so people know why you did something.

I appreciate your good work! Provophys 22:37, 27 March 2007 (UTC)

I felt that the first part of the chapter was a little too wordy and too much about less essential functions. So I am going to narrow it to the ones we discussed in class. I will put down here anything cut out in case someone feels it needs to go back into the chapter. OK I have a question.. I like the picture of the snow covered mountain... but why is it in this chapter? Can we take it off and see the table of contents right off? What do you think?never2late 01:54, 28 March 2007 (UTC)

I agree about the mountain- I was wondering the same thing as to why it's there. I plan on taking it out if no one else does. Stephanie greenwood 15:09, 28 March 2007 (UTC)

I think that the great picture of the mountain should be left. All that we need is a small comment concerning the percentage of oxygen in the air at sea level versus the lack of vital oxygen as you get higher and higher up that mountain.ShakahTodd

I agree about the picture.. can we bring it back with a comment about sea level air?

I just cut out a small part about the bicarbonate buffer... if anyone wants to put it back.. please do. Here it is: "So, if you are going in respiratory acidosis the 1st equation will occur. 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 2nd equation will occur.  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.  Whereever there is a leak the body will "fill the hole"."never2late 07:43, 29 March 2007 (UTC)

I have no problem adding the mountain back in as long as it has a reason and isn't just a pretty pic- tell me where you want it and I'll put it back inStephanie greenwood 02:38, 30 March 2007 (UTC)

I feel this chapter is good but does it seem to short? I tried to paste a picture, but I am not sure how can anyone give the details on how to do so? Thank you, Danseyffert 05:17, 30 March 2007 (UTC)

I noticed that the heading CENTRAL CONTROL is blank. Probably it was meant to be filled in but accidentally overlooked. I imaging details about the medulla influenced by the pons as well as the Hering-Breuer reflex would go here (or somewhere in this book)? Thanks. Kris (discuss • contribs)


text:
User talk:Just.blaze

Hi, I've just added some lessons in Tagalog Simple Sentences, but it's not yet finished. -- Perryv 18:57, 21 July 2006 (UTC)

title: User talk:Just.blaze


text: Category:Book:Singing

title: Category:Book:Singing


text:
Nature/Introduction

The scientific point of view is successful
There are many ways to look at the world that can be taken as a foundation of one's thinking. The scientific point of view may be an exception. No other way was so successful until now. No other view is so widely spread in schools, the media and in our brains. The voice of science and nature is not loud, but you cannot ignore it. Many other views have their basis in science, or must change in part to fit its demands.

Some more characteristics of this view
We must widen the word scientific and add other characteristics, which grant its success.

Mathematical
Science is mathematical.

Mathematics is in a strict sense not a science. But its language has proofed as universal. In this language the laws of science can be written down very comprehensively.

Critical
Science is critical.

No other conception of the world submits its own basis of a so fundamental criticism. In addition, the criticism turns outward too. All other conceptions of the world are subjected to this criticism and the scientific search for truth.

Rational
Science is rational.

Reason, that means clear, logical thinking, is the basis of science, even if this may not appear at the first glance. The rational basis results already from the characterisation of the scientific view as mathematical, because logic is part of mathematics.

However the rational basis still goes beyond this: It rejects all unverifiable, supernatural arguments: In the scientific view of the world everything happens with good reasons. Unresolved questions of nature are answered better with a natural and not with a supernatural explanation.

Open - not closed in its self
The scientific view is open.

May be the scientific view of the world looks as a stable and finished system. That is not the case. There are still many open questions in this conception of the world and also fundamental things are not clear yet. Openness becomes thus a virtue of this conception of the world. Every once in a while something in science changes and obvious contradictions are a stimulus for advancement.

For open questions there is a separate chapter in this Wikibook: See Open questions in science

Emotional
The marriage of the soul with nature will make your mind fertile and will produce phantasy. Henry David Thoreau

The next part of the text should show, that the scientific point of view can be emotional as well. Nature is the essential basis of human life. When nature is so important for us, why don't we choose it for the basis of our thinking ?

Looking up to the sky, we see the stars, the moon, the sun and the planets. On their way through space they follow simple rules, which developed and are followed without any human influence. These rules show the constance and determanism in some parts of nature.

Links

 * Philosophy of science
 * Weltanschauung

title: Nature/Introduction


text:
Nature/Basic statements

The 3 main categories of science

10 basic scientific statements
1. The world is made of matter, energy and information. The first two can show many different forms and structures, described as information.

2. The world is ruled by four physical forces: The weak and strong force in atoms, the electromagnetic force and gravitation. These forces can act on objects, although there must not be a direct physical contact between them.

3. Atoms are the smallest parts of mater, which still have distinct chemical properties. Atoms can be further divided into elementary particles. There are more than 90 different sorts of atoms (elements), which can join together to a variety of different molecules. The smallest parts of radiation are so called photons. They also have a wave character.

4. The world has gone through a long history, which lasted more than 10 billion years. This development followed strict scientific laws. Sun and earth are also very old. The sun produces lots of energy by nuclear fusion and delivers part of that energy in a billion years old stream of sunlight to the earth.

5. The start of life on earth is a rather seldom cosmic incident in an surrounding that is not favourable for life in a huge and quite empty universe. The existence of extraterrestrial life is possible, but there is no proof for it yet.

6. The development of life has been a natural process without an aim. The first forms of life wher preceded by a chemical evolution of self organizing and copying molecules. Out of them multiplying units emerged. These units joined to bigger cellcolonies and more complicated organisms. Mankind is also a product of this development. But, there is no true scientific way to explain the complexity of the beginning of life.

7. The plan for each form of life is found in its genes. The biological evolution partly follows the laws of randomness ( mutation, variation, recombination), partly it follows not random rules (selection). Biological evolution shows a trend to develop more sophisticated structures and organisms. But biological evolution did not follow a plan or did have no aim.

8. The human brain and the human mind are instruments of survival for us. They allow it, to drive the right conclusions about our environment and ourselves. But the human senses can fail. Man can make mistakes. 9. Everything in the world happens in a natural way. Science was very successful to look at any supernatural explanation very critical. In doubt the supernatural explanation is rejected and a natural solution is searched for.

10. Every human being must die. The active mind and the active soul of every man and woman are mortal. They die latest when their body dies. The whole life on erath is mortal and will die latest when the sun will burn out.

These basic statements cannot be proofed more or less well. Mostly they are still in scientific discussion. -

title: Nature/Basic statements


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Talk:Human Physiology/The gastrointestinal system

colon cleansing
Who thinks this section is unneccesary and should be removed or shortened drastically? Me Danseyffert 05:28, 30 March 2007 (UTC)

I think we should rip it out! May I have the honor? never2late 22:18, 30 March 2007 (UTC)

So I took it apon my self to delete a big chunk of the begining of this section. It didn't make any sence at all!!!!

pharynx! the glossary?

Pylorus or "atrium"?
The pyloric antrum is the area leading from the stomach body to the pylorus but I am unfamiliar with the pylorus being known also as the atrium. Kris (discuss • contribs) 01:11, 22 September 2014 (UTC)