The Endocrine System chemical messages (hormones) that are released into the blood Hormones control several major processes Reproduction - gametogenesis,
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1 The Endocrine Systemchemical messages (hormones) that are released into the bloodHormones control several major processesReproduction - gametogenesis, sexual desireGrowth and developmentMaintenance of homeostasis - salts, water, blood pressure, RBCsRegulation of metabolism - digestion, stress responsesMessenger system of the bodySlower communication system than nervous system. Effects also often longer lasting.Hormones are produced by specialized cellsCells secrete hormones into extracellular fluidsBlood transfers hormones to target sitesThese hormones regulate the activity of other cells
2 Endocrine System Characteristics Access to every cellEach hormone acts only on specific cells (target cells) that have matching receptorsEndocrine control slower than nervous systemEndocrine and nervous systems interactAccess to every cell - since every cell gets nutrients from blood. Exception is central nervous system, which is partly exempted by blood/brain barrier. contrast w/ nervous system, which requires hard wiring to reach a cell..Each hormone acts only on specific cells (target cells) - although signal is sent everywhere, only certain cells have correct receptor and can “hear” the signal. Allows precise sending of messages.Only specific cells have receptors for specific hormones - each cell can “hear” one or more hormones but will ignore all other signals.Endocrine control slower than nervous system - takes time to excrete hormone, travel via bloodstream and react with target cells. Minimum 20 sec. Effects can be longer-lasting. Slower control can be suited for homeostasis to avoid pushing pendulum too far in effort to correct condition.Endocrine and nervous systems interact - some hormones are released only in response to nervous signals. Development of sexual maturity involves both systems, signals btw them.Def of hormone - chemical secreted by cells into the extracellular fluids that regulate the metabolic activity of other cells.
3 Classification of Hormones: Steroid Steroid Hormones:Lipid soluble, derived from cholesterolEnter target cellsActivate specific genes to produce proteinsSlower acting: minutes to hoursDef of hormone - chemical secreted by cells into the extracellular fluids that regulate the metabolic activity of other cells.Steroids actually enter cells, go into nucleus and turns on certain genes, which then are used to produce proteins. Entire process has more steps than with non steroids, takes a bit longer.
4 Steroid Hormones: How does a steroid hormone cause changes in cells? Note solubility differences among classes of hormones. Linked to mechanism of action.
5 Hormones: Nonsteroid Amino acid-based hormones proteins, peptides, aminesWater solubleBind to receptors on target cell surfaceWork via second messengers to activate existing enzymesFaster action: seconds to minutesMechanism of action of hormones:Changes in plasma membrane permeability or electrical state. These hormones never enter the cell.Can stimulate Synthesis of proteins, such as enzymesOften causes Activation or inactivation of enzymesEx. Stimulation of mitosis
6 Non-Steroid Hormones: How does a non-steroid hormone cause changes in cells?
7 Control of Hormone Release Hormone levels are maintained by negative feedbackLow hormone levels or a stimulus triggers the release of more hormoneHormone release stops once an appropriate level in the blood is reachedAnalogy with furnace thermostat. Oven temperature.Slower mechanism of action of hormones (compared to nervous system) leads to smaller adjustments, less swing; closer to desired level of activity of cells, organs.Hormone release into blood stops as result of negative feedback, even before effects on other cells are achieved. So, negative feedback works before consequences of increased hormone are effective.Ex. Ca++ levels, K+ levels.Positive feedback is rare - contraction of uterus during childbirth is one example.NEXT: 3 ways that hormone release is triggered.
8 1. Hormonal Stimulus Endocrine glands are activated by other hormones Most common signal- coordinates response of several glandsMost common signal for hormone release.Hormone levels tend to be rhythmic, rising and falling repeatedly.Reason for this type of stimulation:1. Amplification of signal; impt b/c2.target groups of glands needed for overall response.3. Coordinated response to maintain homeostasis.Figure 9.2a
9 2. Humoral StimulusChanging blood levels of certain ions stimulate hormone releasePTH - to raise Ca++Calcitonin - to decrease Ca++Insulin - to decrease glucoseHUMORAL refers to factors in blood that are NOT hormonal.Ex. Ca++ in blood. As per diagram.Other examples: calcitonin released by thyroid, insulin, produced by pancreas.Figure 9.2b
10 3. Neural Stimulus Nerve impulses stimulate hormone release Usually by sympathetic nervous systemRelease of epinephrine and norepinephrine released during periods of stress.Some exceptions to these 3 means of stimulating hormone release. Most done by one of these 3 methods.Figure 9.2c
11 Location of Major Endocrine Organs Total mass is only about 4 ounces.Hypothalamus - part of nervous system, but also a gland b/c it produces hormonesSome glands are only endocrine (ductless): anterior pituitary, thyroid, adrenalsSome are both endocrine and exocrine: pancreas, gonads.Difference: ductless, well vascularized (product released into the blood)Ducts, products released externally (surface) or into cavity open to the surface (digestive system).Figure 9.3
12 Pituitary - Hypothalamus Relationship Release of anterior pituitary hormones is controlled by hormones from hypothalamusHypothalamus produces two hormones that are stored in the posterior pituitaryposterior pituitary releases hormones when neurally stimulated by hypothalamusRelease of hormones is controlled by releasing and inhibiting hormones produced by the hypothalamus. So, endocrine stimulation.Hypothalamus produces two hormones that are transported to neurosecretory cells of the posterior pituitary. So, neural stimulation of posterior pit’y.Portal circulation - veins from hypothalamus dump into vessels which drain into capillaries of pituitary.The posterior pituitary is not strictly an endocrine gland, but does release hormones when stimulated neurally by hypothalamus.
13 Hormones of the Posterior Pituitary OxytocinStimulates contractions of the uterus during laborCauses milk ejectionAntidiuretic hormone (ADH)Can inhibit urine productionIn large amounts, causes vasoconstrictionOxytocin - positive feedback. So, as labor begins, oxytocin released, causing stronger contractions of uterus, leads to more oxytocin released. Positive, rather than negative feedback.Oxytocin (Pitocin) most often used to induce uterine contractions and speed up delivery of baby. Also to induce faster contraction and shrinkage of uterus AFTER delivery, to limit blood loss of mother.ADH - In large amounts, causes vasoconstriction leading to increased blood pressure (vasopressin)Alcohol depresses ADH (anti diuretic hormone) secretion, which allows more urine to be made. Result is dehydration. So, cure for hangover usually involves fluid replacement.Diuretics cause more urine to be flushed from body. Help to avoid edema, fluid retention.
14 Hormones of the Anterior Pituitary Six anterior pituitary hormones; common characteristics:Proteins (or peptides)Act through second-messenger systemsRegulated by hormonal stimuli, mostly negative feedbackSix anterior pituitary hormonesTwo affect non-endocrine targetsFour stimulate other endocrine glands (tropic hormones)Characteristics of all anterior pituitary hormonesProteins (or peptides)Act through second-messenger systemsRegulated by hormonal stimuli, mostly negative feedback
15 Growth Hormone (GH) General metabolic hormone Major effects are directed to growth of skeletal muscles and long bonesCauses amino acids to be built into proteinsCauses fats to be broken down for a source of energyFats broken down for energy, rather than glucose. Helps to maintain blood sugar level.Reputation as being the fountain of youth. Does help to reverse decline in elderly patients, AIDS patients with wasting away. Builds muscle mass, reduces fat tissues.Lots of WEB scams on this drug. Oral version is not effective, must be injected.
16 Functions of Other Anterior Pituitary Hormones Prolactin (PRL)Stimulates milk production following childbirthFunction in males is unknownAdrenocorticotropic hormone (ACTH)Regulates the adrenal cortex (affects salt, glucose levels)Thyroid-stimulating hormone (TSH)Influences thyroid glandACTH - effects alter glucose, salt concentrations of blood.
17 Functions of Other Anterior Pituitary Hormones Gonadotropic hormones - appear at pubertyFollicle-stimulating hormone (FSH)Stimulates follicle development (ovaries) and sperm development (testes)Luteinizing hormone (LH)Triggers ovulationStimulates testosterone production in malesInteraction of FSH, LH on lining of uterus results in monthly menses. Interaction w/ estrogen, progesterone to maintain lining, maintain pregnancy.Testosterone produced mostly by testes.Estrogen, progesterone produced mainly by ovaries, uness pregnancy.
18 Thyroid Gland Found at the base of the throat Produces two hormones Thyroid hormone - controls metabolismCalcitonin - affects Ca++ levels in bloodThyroid hormone - Major metabolic hormoneComposed of two active iodine-containing hormonesThyroxine (T4) – secreted by thyroid folliclesTriiodothyronine (T3) – conversion of T4 at target tissuesBoth hormone components contain iodine, as indicated by T4 and T3. Target tissue cells convert T4 to T3.If there is insufficient iodine in one’s diet, then low levels of thyroid hormone in blood, and more TSH released by pituitary. This constant stimulation by high levels of TSH results in enlargement of the thyroid gland = goiter. This is the reason that salt is iodized. Can also get iodine from seafood, which usually has high levels.Thyroid hormone controls metabolic rate of cells, ALL cells.Hence, hypothyroidism can cause symptoms of obesity, tiredness, mental sluggishness in adults.Thyroid hormone also needed for normal growth and development of reproductive and nervous systems.In children, hypothyroidism can lead to cretinism, with altered proportions of body such that legs are shorter than is usual, and mental retardation. Preventable with early diagnosis and replacement therapy.Hyperthyroidism has opposite effects: high metabolic rate of cells, weight loss, hyper behavior - not relaxed.Knock out the thyroid gland with radioactive iodine - iodine absorbed by thyroid, radiation kills cells that take it up.
19 CalcitoninDecreases blood calcium levels by causing calcium deposition in bone (in children)Antagonistic to PTH, parathyroid hormoneSecond hormone secreted by thyroid gland, by a different group of cells than those that secrete thyroxine.Good example of how 2 glands function together to maintain homeostasis within the body. Opposite effect of two hormones = antagonistic. Helps to maintain Ca++ levels within narrow range.Calcitonin is released as a direct response to high levels of Ca++ in the blood.Causes Ca++ to be deposited in bone, only in children. Mech. rarely used in adults.Parathyroid gland = 4 tiny masses on the posterior of the thyroidSecrete parathyroid hormone - PTH in response to lowered blood calcium levels, nonsteroidalStimulate osteoclasts to remove calcium from boneStimulate the kidneys: (retention of calcium and excretion of phosphate) and intestine to absorb more calcium. Via PTH role in final activation of Vit D in kidneys.Overall effect: Raise calcium levels in the bloodWhy? Recall that Ca++ is needed in large quantities for muscle contraction. If Ca++ levels get too low, neurons misfire, continually stimulate muscles, which contract in spasms. Lethal.Figure 9.9
20 Adrenal Glands Two glands Cortex – outer glandular region in three layersMedulla – inner neural tissue regionSits on top of the kidneysFunctionally and structurally, the adrenals are two glands. Similar to pituitary gland.Adrenal cortex makes 3 groups of hormones, all called corticosteroids.Adrenal Medulla is neural tissue (as is posterior pituitary).
21 Hormones of the Adrenal Cortex Mineralocorticoids (mainly aldosterone)Regulate mineral content in blood, water, and electrolyte balance via kidney actionGlucocorticoids (cortisone, cortisol)Promote normal cell metabolismHelp resist long-term stressorsdepress inflammatory responseAndrogen, estrogenMineralocorticoids (mainly aldosterone)Mineralocorticoids, because they regulate level of minerals in bloodProduced in outer adrenal cortexRegulate mineral content in blood, water, and electrolyte balance; esp Na+ and K+ ions.Target organ is the kidney. Aldosterone causes more Na to be reabsorbed, more K+ secreted. Water retained AND balance of ions is changed. Affects BP and blood volume.Glucocorticoids - 95% of these are cortisol. Released in response to increased blood levels of ACTH A. Promotes normal cell metabolism by increasing use of fats, proteins to maintain glucose levels in blood. B. resist long term stressors by raising blood glucose levels. C. causes depression of immune system, long term. D. also reduce pain of inflammation, inhibit pain-causing prostaglandins.Levels of glucocorticoids that are too low are fatal. Too much gives variety of symptoms, including moon face, hump of fat on upper back, high BPAlso releases Sex hormones - produced on low amounts by inner layer of the adrenal cortexAndrogens (male) and some estrogen (female). Both hormones produced in both sexes. If over production, leads to masculine features, such as body and facial hair of male pattern.
22 Hormones of the Adrenal Medulla Produces two similar hormones (catecholamines)EpinephrineNorepinephrineprepare the body to deal with short-term stress= adrenaline. Causes increased blood flow to heart, brain, muscles. Raises glucose level in blood.Responds to stimulus of nervous system. Fast response.Ask students: what type of hormones are these likely to be? (non-steroid)Compare that with role of adrenal cortex. Diag on next slide
23 Roles of the Hypothalamus and Adrenal Glands in the Stress Response Hypothalamus controls trigger for both levels of response.Neural stimulus in adrenal medulla leads to rapid response of epinephrine, norepinephrine.Hormonal stimulus of hypothalamus on anterior pit’y on adrenal cortex. Longer term response.Figure 9.12
24 Pancreatic Islets pancreas is a mixed gland islet cells produce hormones:Insulin – allows glucose to cross plasma membranes into cellsGlucagon – allows glucose to enter the bloodSomatostatinMIXED = both endocrine and exocrine gland. Exocrine secretions are digestive enzymes. Later.Endocrine portion is the pancreatic islets, groups of cells within the pancreas.Islets spread throughout pancreas, interspersed among exocrine cellsIslets consist of 3 cell types ; alpha and beta, delta, all interspersed within islet. Well supplied with capillaries.3 important hormones,:insulin, glucagon, somatostatin. First two are antagonists that maintain blood sugar homeostasisInsulin produced by beta cells when blood sugar levels are high. Essential compound for uptake of glucose and utilization of it by ALL cells of the body. Th4, called the hypoglycemic hormone. the only hormone that causes drop in blood sugar. Q. which hormones cause INCREASE in blood glucose?Lack of insulin = diabetes mellitus. Glucose levels are very high in blood, excess gets excreted in urine “sweet siphon”. Body must use fats, proteins for energy. Wasting, weak immune system. Ketones build up, causing acidosis of blood. Result is coma and death. TYPE I, juvenile.Mild diabetes mellitus (type II, adult onset) produce insulin but are resistant to its effects. Careful diet, drugs to increase sensitivity to insulin needed.GLUCAGON secreted by alpha cells. Stimulates liver to break apart glycogen, release glucose into blood.Triggered by low glucose levels in blood.Somatostatin - from delta cells. Complete function not clear. Seems to inhibit secretion of both insulin and glucagon. Not unique to pancreas, also made by hypothalamus (inhibits GH secretion) and digestive system (controls digestive secretions). Effect depends on target cells.Homeostasis. Antagonistic effect of hormones. Shows importance of glucose level. Brain uses ONLY glucose as energy source.Other hormones that affect glucose level:Glucocorticoids, epinephrineFigure 9.13
25 Diabetes Diabetes mellitus - “sweet siphon” Type I - lack of insulin juvenileType II - resistant to effects of insulinAdult onsetLack of insulin = diabetes mellitus. Glucose levels are very high in blood, excess gets excreted in urine “sweet siphon”. Body must use fats, proteins for energy. Wasting, weak immune system. Ketones build up, causing acidosis of blood. Result is coma and death. TYPE I, juvenile.Mild diabetes mellitus (type II, adult onset) produce insulin but are resistant to its effects. Careful diet, drugs to increase sensitivity to insulin needed.GLUCAGON secreted by alpha cells. Stimulates liver to break apart glycogen, release glucose into blood.Triggered by low glucose levels in blood.Somatostatin - from delta cells. Complete function not clear. Seems to inhibit secretion of both insulin and glucagon. Not unique to pancreas, also made by hypothalamus (inhibits GH secretion) and digestive system (controls digestive secretions). Effect depends on target cells.Homeostasis. Antagonistic effect of hormones. Shows importance of glucose level. Others that affect glucose level: Glucocorticoids, epinephrine
26 Other Hormone SourcesThymus: thymosin and thymopoietin, assist maturation of T lymphocytesPineal gland: melatoninHeart: atrial natriuretic hormone (ANH)Digestive system: gastrin, secretin, cholecystokininKidney: erythropoietin, reninOther tissues in body use hormone signals.Melatonin - regulates sleep cycle. Reset clock when traveling across time zones.ANH from heart - helps to lower blood pressure by causing kidney to excrete more Na+, dilate blood vesselsGastrin,secretin, cholecystokinin - stimulate action of stomach, pancreas, gallbladder.Leptin - produced by fat tissue when fats are eaten; depresses appetite.Ghrelin - counteracts leptin, increases appetite.Erythropoietin stimulate production of RBCRenin - stim adrenal cortex to produce aldosterone, constricts blood vessels.