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| Has both exocrine and endocrine functions associated with feeding. In its exocrine function, the pancreas secretes digestive enzymes that are delivered into the lumen of the duodenum. In its endocrine function, the pancreas secretes at least three hormones. One is insulin, which promotes storage of glucose, fatty acids and amino acids. Another is glucagon, which has the opposite effects. A third hormone is somatostatin, which seems to be involved in regulating the release of glucagon and insulin when a meal is eaten. |
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the overies are the female gonads
the testes are the male gonads. |
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| plays a possible role in determining the daily (diurnal) rhythms in hormone secretion rate. |
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| The endocrine function of tissues in many organs that are not primarily endocrine glands. These organs include the liver, heart, digestive tract, skin, kidneys, adipose tissue. One hormone secreted by the kidneys and liver is erythropoietin, which stimulates red blood cells production. The abuse of this substance may have caused deaths of some athletes. |
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| Hormone-like chemical signaling agents: |
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| include the cytokines (a term that includes growth factors), which control cell proliferation, survival, and differentiation, and the eicosanoids (include prostaglandins), which produce a wide variety of biological effects, and the retinoids, which are important for developments. |
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| Exocrine function in Pancreas |
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Definition
| The pancreas consists mainly of exocrine acinar cells that secrete digestive enzymes. These enzymes pass into the duodenum through the system of pancreatic ducts |
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| Endocrine function in Pancreas |
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Definition
| The endocrine cells (only about 1-2% of all the cells in the pancreas) are scattered throughout the exocrine cells in little spherical clusters around blood vessels. These clusters (about one million of them) are called Islets of langerhans. The “Islet hormones” are secreted into the pancreatic vein and then pass to the hepatic portal vein. Since the hepatic portal vein delivers blood to the liver, this means that the liver is the first organ to be exposed to high concentrations of the Islet hormones. |
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| Hormornes secreted by Islet of Langerhans |
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Definition
| Each Islet of langerhans contains about 50-200 cells. The are four types. Each type secretes one hormone, which can be dected in histological sections using technique called immunostaining. The four hormones are glucagon, insulin, somatostatin, and pancreatic polypeptide. The first three are the most important. |
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| Four different cells Islets of Langerhans from the pancreas and what they secrete |
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Definition
a) alpha cells - account for about 25% of the cells in an Islet of Langerhans. They secrete glucagon
b) beta-cells - make up the core of the Islet of langer hans, and account for about 70% the cells in the Islet. They secrete insulin
c) delta-cells - 5-10% of Islet cells: secrete somatostatin
d) PP-cells - secrete pancreatic polypeptide |
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| this is a serous condition, and it represents 5% of all cancers. |
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| is the hormone of feeding. It is the most important hormone secreted during and after a meal |
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The major function of insulin is anabolic (builds large molecules from smaller ones.)
- Promotes synthesis of glycogen from glucose and inhibits breakdown
-Promotes synthesis of fats from fatty acids and inhibits their breakdown
-Promotes synthesis of proteins from amino acids. Therefore, insulin inhibits glucogeneosis by the liver because it deprives the liver of amino acids |
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| Regulation of insulin secretion |
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Definition
| the most important molecule that stimulates insulin secretion is glucose. When blood glucose increases, as happens after an average meal, so does the secretion of insulin. At low blood glucose levels no insulin is secreted - the hormone glucagon (secreted by the alpha-cells) stimulate insulin secretion -The hormone somatostatin (secreted by the delta cells) inhibits insulin secretion. |
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| Mechanism of insulin secretion |
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| Beta-cells have resting membrane potential, just like neurons or muscle cells. When glucose levels are high, the cells depolarize, opening calcium gates and triggering the fusion of insulin-containing vescicles with the plasma membrane and exocytosis of their contents. Note that this mechanism is virtually identical with the mechanism of neurotransmitter release at synapse |
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| Feedback control of insulin |
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Definition
| Insulin operates in a feedback control system with glucose. An increase in the amount of glucose circulating in the blood stimulates secretion of insulin, which promotes utilization of glucose by stimulating its uptake, storage and metabolism. This lowers blood glucose back to the “set” level, and reduces insulin secretion. |
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| Reason for controlling blood glucose |
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a) high blood glucose (hyperglycemia) can increase the osmotic pressure in the extracellular fluid, leading to cell dehydration, including brain neurons.
b) Low blood glucose (hypoglycemia) imapirs the function of the brain, which must have glucose to able to operate ( the retina and certain cells in the gonads also require glucose - this does not apply to most other tissues, which can use fatty acids as an energy source). low blood sugar leads to symptms of hypoglycemic shock |
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| Inulin effects on Carbohydrates, Lipids, Proteins |
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Definition
Carbohydrates:
-transport of glucose into cells, notably the liver
-glycogen synthesis
-reduces the amounts of amino acids for glucogenesis
Lipids:
-promotes synthesis and storage of fat in adipose tissue
-inhibits breakdown of fats, therefore reducing the release of free fatty acids.
Proteins:
-increases transport of amino acids into tissues, notably skeletal muscles
-these amino acids are then used in the synthesis of proteins: insulin also inhibits the breakdown of protein, therefore reducing the release of amino acids and reducing the availability of amino acids for gluconeogenisis.
-by stimulating protein synthesis, insulinpromotes growth. |
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| Tissues acted on by insulin have insulin receptors (they are tyrosine kinases). The major sites of action of insulin are liver, muscle and adipose tissue. Liver, muscle and adipse tissues have insulin receptors, which are plasma membrane proteins. Like most receptors, the insulin receptor can be “downregulated” - that is if the plasma levels of insulin are for some reason maintained in an elevated condition, then the number of insulin receptors in the cell membranes decreases. |
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| Insulin has little effect on the brain, which never theless depends almost exclusively on glucose as a source of energy for its neurons. The glucose passes through the the blood-brain barrier and into brain neurons by a process of facilitated diffusion, using special glucose-transpoter proteins (GLUT). |
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| What happens to blood insulin levels during a meal? |
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| Increased blood glucose during a meal stimulates insulin secretion, and insulin levels in the blood may increase by as much as eight times. Insulin stops plasma glucose from skyrocketing. |
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| Insuin overdose and insulin-secreting tumor (insulinoma) |
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Definition
| If a person were injected with an insulin overdose (as could happen with a diabetic), the excess insulin would lower blood glucose and cause hypoglycemic shock. Hypoglycemic shock can also occur in a patient with an insulin-secreting tumor (inulinoma) of the pacnreas. Symptoms: -confusion and syncope, low blood sugar, high insulin |
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| Diabetes Mellitus: TYPE 1 (insulin-dependent diabetes mellitus or IDDM) |
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Definition
| Is caused by insulin defienzy due to loss of Beta-cells. It is less common than type II, and tends to develop in children and adolescents. Individuals suffering from type I diabetes mellitus require insulin injections to remain alive. Type I is autoimmune disease that affects .3% of the world’s population. It is caused by destruction of Beta-cells by a T-cell-mediated autoimmune disorder in genetically-predisposed people. |
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| the lack of insulin in type I diabetes mellitus increases glucose production and depresses glucose use. Therefore plasma glucose levels are high and glucose is excreted through the kidney in very large volumes of urine. As a result, patients are always thristy. Breakdown of protein is increased to provide amino acids for gluconeogenesis. Accelerated breakdown of fats increases free fatty acids in the blood. Blood pH can drop less than 6.8 because the accumulation in the blood of acids (“ketoacids”) that result from the almost exclusive use of farry aids as an energy source. These ketoacids can be used by the brain for energy when glucose is in short supply. |
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| Diabetes Mellitus: Type II (non-insulin-dependant diabetes mellitus, or NIDDM: also known as insulin-resistant diabetes mellitus) |
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| The most common type of diabetes. It usually does not appear untile 40 years of age, and is often associated with obesity. The disease may be triggered by insulin resistance at the target cells, perhaps caused by lipid overload and elevated levels of fatty acids in the blood. Secondarily, the Beta-cells gradually become unresponsive to high blood glucose and become desensitized. This leads to a deficiency of insulin Treatment many not require insulin administration. More importantly, weight reduction (including regulation of the number of calories eaten) is used to improve tissue responsiveness to insulin and Beta-cell responsiveness to glucose. Certain drugs may also be used to supplement the effects of weight reduction. |
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| Glucagon is a small protein hormone with a molecular weight of 3500. It is synthesized, soted and released by alpha-cells of the Islets of Langerhans. Glucagon’s principal function is to stimulate glucose output by the liver and maintain plasma glucose levels. It is secreted in response to glucose deficiency, and increase criculating glucose. It is therefore an anti-insulin hormone |
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| Regulation of glucagon secretion and feedback control |
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Definition
| Regulation is the opposite of insulin. glucagon secretion is inhibited by high glucos and stimulated by low glucose. High glucose not only inhibits glucagon secretion directly, it also stimulates secretion of insulin, and this hormone inhibits glucagon secretion. Therefore, the effect of high glucose on glucagon secretion is reinforced by the simultaneous release of insulin, which acts in a paracrine mode with the Islet. Glucagon secretion is also inhibited by free farry acids. However, glucagon secretion is stimulated by amino acids in the same way as insulin. Exersice, which releases catecholamines into the circulation, also stimulates glucagon secretion. |
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- It promotes mobilization of glucose and free farry acids, and stimulates their release.
-Glycogen breakdown is stimulated, and glycogen synthesis from glucose is inhibited.
-Glucagon stimulates glucogenesis
-Glucagon actions on adipose tissue and muscle are not significant uless insulin is absent. Unlike insulin, glucagon does not affect peripheral glucose utilization. |
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| What happens after a meal? |
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| A protein meal and amino acids in the bloodstream stimulate glucagon secretion, but if carbohydrate is present, then the resulting high glucose and insulin secretion precent any large increase in plamsa glucagon. in contrast, after a meal there is always large increase in plasma insulin. |
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-Increases trantport of glucose into tissues (particularly skeletal muscle and adipose tissue)
-Stimulates glycogen synthesis from glucose
-Inhibits breakdown of glycogen
-Inhibits gluconeogenesis
-Promotes syntheseis and storage of fat
-Inhibits breakdown of fats, reduces release of free fatty accids -Incerases transport of amino acids into tissues
-Promotes synthesis of proteins and inhibits their breakdown, therefore reducing the release of amino acids
-Promotes growth by stimulating protein synthesis |
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| Somatostatin is a peptide hormone containing 14 amino acids. It was originally discovered in the hypothalamus, where it is an inhibitor of growth hormone secretion. Somatostatin is synthesized by delta-cells of the pancreas, where it is also an inhibitor of hormone secretion. Somatostatin is paracrine inhibitor of insulin and glucagon secretion. Somatostatin is also present throughout the intestinal tract, where it acts as an inhibitor of many gastrointestinal functions. |
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| The secretion of somatostatin |
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Definition
| is stimulated by a variety of factors, including glucose, free fatty acids, and amino acids. Its function may be to limit the release of glucagon and insulin when a meal is eaten. |
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| The ovaries and the testes are referred to as the gonads. The ovaries are the female gonads (they produce ova) and testes are the male gonads (they produce spermatozoa or sperm cells). |
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| the testes manufacture three hormones: the steroid androgens (the “male” hormones - mainly testosterone), the protein inhibin, and (surprisingly) certain cells in the testes also manufacture the steroid “female” hormones known as estrogens. The estrogens are important for sperm develoopment in the testes, and very high levels are present in seminal fluid. It is mainly the androgens and inhibin that are secreted into the blood stream, although low levels of estrogen occur in the blood of males. |
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| The ovaries manufacture four hormones - the steroid estrogens and progesterone, the protein hormone inhibin, and (surprisingly) some cells in the ovaries also manufacuture estrogens. Because the steroid hormones are not soluble in water, they are transported in the bloodstream bound to serum albumin (mainly) as well as specific estrogen- and progesterone-binging proteins. |
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| In the dark, the pineal produces melatonin, a hormone that affects daily rhythms and is sometimes described as the chemical expression of darkness |
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| Peaks at about the time of getting up in the morning, and is lowest the beginning of sleep in people maintained on a normal day-night schedule. THe peak in the morning may be connected with the need to deal with the stresses of the day. If lighting condition are reversed, the cortisol rhythm follows, and is also reversed in about 3 weeks of the new conditions. |
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| Unlike cortisol, blood levels of growth rise sharply after the onset of sleep, whether this is an afternoon nap or normal nightly slumber. If the sleep-wake cycle is changed, the GH rhythm follow it. |
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| Evolution of the pineal gland |
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| -used to have phororeceptors, “third eye” -However once we get to mammals the pineal cells (pinealocytes) no longer photoreceptors properties. -neuroendocrine secrete melatonin, which is synthesized from serotonin -The chemical expression of darkness |
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| What is the function of melatonin? |
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| The light-dark cycle regulates its concentration in the blood - levels are low during the day and high at night. Therefore, it could signal to various systemes in the body (including the glands that produce cortisol and growth hormone) whn it is daytime and when it is night. Melatonin may affect the activity of neurons in the circadian clock region of the suprachiasmatic nucleus. Melatonin agonists used in treating certain sleep disorders. |
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| Organs containing Endocrine Tissue |
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Definition
-Liver
-heart
-skin
-placenta
-digestive tract
-kidneys
-adipose |
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| The liver is the major site of synthesis and secretion of somatomedin, also someties called insulin-like growth factor or IGF. There are actually three closely-related somatomedins. Somatomedin secretion by the liver is stimulated by growth hormone (somatotropin). Somatomedin stimulates growth, notably of bone and cartilage. In fact, most of the growth-stimulating action of GH are actually due to the somatomedin released from the liver. The liver secretes a small amount of erythropoietin, but most of this hormone comes from the kidney. |
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| The atria secrete a small peptide called atrial natriuretic factor or atrial natriuretic peptide. The stimulaus for secretion is stretching of the atrial walls. Secretion of atrial natriuretic peptide is therefore sensitive to the volume of blood filling the atria. The hormone was mentioned las semester. It stimulates the kidney to secrete sodium and water, and therefore acts homeostatically to reduce volume of fluid in the body, reduce atrial stretching, and therefore to relieve the load on the heart. |
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| The skin is involved in vitamin D production. Vitamin D is a steroid hormone. Vitamin D_3 (cholecalciferol) is generated by ultraviolet irradiation of 7-dehydrocholesterol in the skin. In this respect, the skin can be reagarded as having a kind of endocrine function. Vitamin D_3 is really a “prohormone,” and must be carried by blood to the liver and kidneys, where it is further processed into the physiologically active form. |
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| In addition to its other functions, the placenta is a complex endocrine organ that produces steroid hormones and peptide hormones. There is an intricate interaction between the placenta, fetus and mother during pregnancy. |
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| Steroid hormones produced by the Placenta |
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| Estrogens. The major one is estriol (E_3), which the placenta synthesizes from other steroids originating in the adrenal glands of the mother and the fetus Progesterone. In contrast, progesterone (which is also secreted by the corpus luteum of the ovary at the begining of pregnancy) is secreted in enormous quantities by the placenta, and is essential for the normal progression of pregnancy. |
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| Peptides and protein produced by Placenta |
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Definition
| They include human chorionic gonadotropin, relaxin and human chorionic somatomamotropin (or human placental lactogen). The most importat is Human chorionic gonadotropin, which belongs to a family of glycoprotein hormones that includes LH, FSH and TSH. All of these hormones have certain features of their chemical structures in common. |
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The kidneys synthesize two proteins
-Erythropoietin
-Renin |
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| Erythropoietin is a glycoprotein hormone that increases the production of red blood cells from precursor cells in the red bone marrow Eighty to ninety percent of the erythropoietin in normal person is secreted by the kidneys. The remainder is produced mainly in the liver. Diseases of the kidney can cause a deficiency of erythropoietin, leading to anemia. Synthesis of erythropoietin - is stimulated by tissue caused by: high altitudes, hemorrhage, impaired oxygenation of the blood due to respiratory or cardiac diseases |
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| an important regulator of the renin-angiotensin-aldosterone system Renin is proteolytic enzyme that is released by the juxtaglomerular cells of the kidney in response to a variety of related conditions that activate the sympathetic nervous system. THese include a decrease in blood volume (hemorrhage) and a decrease in blood pressure. In the blood, renin splits angiotenstinogen (secreted by the liver) into a small peptide called angiotensin I, which is converted into a smaller peptide called angiotensin II by andiotensin-converting enzyme (mainly in the lung) |
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| The endocrine system of the digestive track plays an important role in controlling and coordinating its funcitons. The digestive tract hormones are secreted into the blood by individual cells that are not organized into glands. These cells are scattered throughout the epithelium of the digestive tract mucosa, and have an outer surface that borders the lumen. Therefore, they can respond to changes in the chemical composition of the fluid within the lumen. In the blood, the hormones travel to target smooth muscle cells or to secretory cells in the exocrine glands of the digestive tract. |
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| mainly a stomach hormone. Stimulates secretion and movement |
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| A small interstinal hormone. Stimulates secretion of bicarbonate by the exocrine cells of the pancreas and by the epithelial cells lining the bile duct |
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| A small intestinal hormone. It stimulates the pancreas to secrete pancreatic juice. The hormone also inhibits acid secretion in the stomach and stomach emptying. Cholecystokinin causes contractions of the gall bladder and relaxation of the sphinter of Oddi, allowing ejection of bile into the small intestine. |
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| Gastric inhibitory peptide Somatostatin |
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Definition
| Also a small intestinal hormone. It inhibits (via somatostatin) gastin release and there acid secretion and stomach empyting somatostatin mediates action of GIP |
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| Adiposcytes (the cells that store triglycerides in adipose tissue) secrete the hormone leptin, which signals to the hypothalamus the state of the body’s fat (=energy) reserves. People with genetic defects in the hormone itself or its receptors in the hypothalamus suffer from morbid obesity and fail to become sexually mature during puberty. |
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| are signalling molecules that are secreted by many cells in the body. These peptides or proteins include the interleukins, colony-stimulating factors, growth factors,. Cytokines are often paracrine, and reach their target cells by local diffusion. The cytokines are very important in immune reactions. |
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| Eicosanoids - The Prostaglandins and Leuktrienes |
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Definition
| prostaglandins and leukotrienes are important signalling molecules that belong to a family compounds known as the eicosanoids. They derived from arachidonic acid, a fatty acid found in membrane phospholipids. eicasonoids produce a wide variety of biological effects, which include smoth muscle contraction and relaxation, platelet aggregation, and inflammation. Prostaglandins are important in uterine contraction, and we discussed their vasoactive properties last semester. Drugs such as aspirin work by inhibiting prostaglandin synthesis |
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| - substanes derived from Vitamin A (retinol) The most important retinoid is retinoic acid (vitamin A acid), which is known to play an important role in embryonic development. Tetinoids are similar to thyroid hormone and other lipid-soluble hormones such as viramin D in that they bind to intracellular receptor proteins that activate or silence variety of genes. |
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