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Transcript
Chapter 9 The Endocrine System Biology 112 Tri-County Technical College Pendleton, SC Hormones are flowing… Hormones are chemical substances secreted into extracellular fluid that regulate activity of other cells Hormones circulate to all organs but affect ONLY certain tissue cells/organs referred to as its TARGET CELLS/ORGANS Target MUST have specific protein receptors on its plasma membrane or interior to which hormone can attach Hormones, cont. Reproduction, growth & development, body’s defenses against stressors, electrolyte, water, & nutrient balance of blood, regulating metabolism & energy balance Typically one or more of following occur as result of hormone action: changes in PM permeability/electrical state synthesis of proteins or regulatory molecules activation/inactivation of enzymes stimulation of mitosis/meiosis Getting there Steroid hormones able to diffuse across PM Nonsteroid hormones require membrane receptors and utilize signal-transduction mechanism (second messengers) One of three mechanisms responsible for stimulating endocrine gland HORMONAL HUMORAL NEURAL Hormonal Action, Visual Stimulation, Visual Been there…done that Hormonal secretion triggered by some internal/external stimulus Rising hormone levels inhibit further hormone release even while promoting responses in target organs WOW!!! Negative feedback model again **End product controls the rate of the reaction or event Endocrine Glands Endocrine glands (ductless) release their secretions into blood or lymph Endocrine glands have a very rich blood supply Hypothalamus, pituitary, thyroid, parathyroid, adrenal, pineal, thymus, pancreas, and gonads (testes/ovaries) Location, Visual Pituitary Gland Pituitary gland about the size of a grape and hangs by a stalk from inferior surface of hypothalamus of the brain surrounded by “turk’s saddle” of sphenoid bone Has two functional lobes Anterior pituitary arises from glandular tissue Posterior pituitary arises from nervous tissue Anterior hormones: growth hormone (GH), prolactin (PRL), follicle-stimulating (FSH), luteinizing (LH), Thyroid stimulating (TSH) and Adrenocorticotropic (ACTH) Pituitary, cont. Growth hormone and prolactin exert their major effects on nonendocrine targets FSH, LH, TSH, and ACTH are all TROPHIC hormones Trophic hormone is hormone that regulates the activity of another ENDOCRINE gland All anterior pituitary hormones are proteins/peptides; act through 2nd messengers; are regulated by hormonal stimuli, and operate via negative feedback mechanism (in most cases) Anterior Pituitary, Visual Growth Hormone GH is protein-sparing & anabolic hormone causing amino acids to build into proteins Stimulates MOST target cells to grow in size and divide Causes fats to be broken down for energy Spares body’s supply of glucose thereby helping to maintain blood sugar homeostasis Pituitary Abnormalities Hyposecretion of GH during childhood leads to pituitary dwarfism body proportions fairly normal but person is living miniature (adult height ~ 4 feet) Hypersecretion during childhood leads to gigantism individual becomes extremely tall (8-9 feet) If hypersecretion occurs after long bone growth ended = acromegaly lower jaw and bony ridges under eyebrow enlarge as does hands and feet; thickening of soft tissue leads to coarse/malformed facial features Most hypersecretion of endocrine glands caused by tumors of affected gland Prolactin Abbreviated as PRL Protein hormone whose only known target in humans is the breast After childbirth, it stimulates and maintains milk production by mother’s breasts Its function is males is NOT known Same song, different verse… Adrenocorticotrophic hormone = ACTH Regulates activity of the cortex portion of the adrenal gland Thyroid-stimulating hormone = TSH TSH also known as thyrotropic hormone (TH) Influences growth and activity of the thyroid gland Follicle Stimulating Hormone Abbreviated as FSH Regulates activity of gonads (ovaries/testes) In females, FSH stimulates follicle development in ovaries As follicles mature, they produce estrogen and eggs are readied for ovulation In males, FSH stimulates sperm development by the testes Luteinizing Hormone Abbreviated LH In females, LH triggers ovulation of egg from ovary Also causes ruptured follicle to become corpus luteum LH then stimulates corpus luteum to produce progesterone and some estrogen In men, LH is referred to as interstitial cellstimulating hormone (ICSH) stimulates testosterone production by interstitial cells Pituitary and Sterility Hyposecretion of FSH or LH leads to sterility in both males and females Hypersecretion does NOT appear to cause any problem(s) Some drugs used to produce fertility stimulate release of FSH and LH Multiple births fairly common after their administration Anterior Pituitary/Hypothalamus Pituitary used to be called “master gland” Release of pituitary’s hormones controlled by releasing and inhibiting hormones produced by hypothalamus Hypothalamus releases these regulatory hormones into portal circulation which connects blood supply of hypothalamus with that of anterior pituitary Posterior Pituitary Posterior pituitary (neural tissue) STORES two hormones produced by hypothalamus Oxytocin and antidiuretic hormone (ADH) Both are peptide hormones Produced in hypothalamus Transported along axons of hypothalamic neurosecretory cells to posterior pituitary for storage Released into blood in response to nerve impulses from the hypothalamus Posterior Pituitary, Visual OH!!! for Oxytocin Released in significant amounts only during childbirth and in nursing women Stimulates powerful contractions of the uterine muscles during labor, sexual relations, and when female is nursing Also causes milk ejection (letdown reflex) in nursing women Natural/synthetic oxytocic drugs (pitocin) used to induce/hasten labor, stop postpartum bleeding, and stimulate milk ejection reflex Antidiuretic Hormone Diuresis is urine production Antidiuretic is chemical that inhibits and/or prevents urine production ADH causes kidneys to reabsorb more water from forming urine Results in urine volume DECREASE and blood volume INCREASE In large amounts, ADH increases blood pressure by causing constriction of arterioles (small arteries) ADH sometimes called VASOPRESSIN Diabetes Insipidus Hyposecretion of ADH leads to condition of excessive urine output called diabetes insipidus Individuals with this problem are continually thirsty and drink large amounts of water Thyroid Gland Thyroid located at base of throat, inferior to Adam’s apple where easily palpated Large gland of two lobes joined by central mass called isthmus Internally, composed of hollow structures called follicles which store sticky colloidal material Thyroid iodine-containing hormone derived from colloid Produces 2 active hormones: T3 and T4 Also produces calcitonin (thyrocalcitonin) Thyroid, Visual T3 and T4 Thyroid hormone (body’s major metabolic hormone) actually two iodinecontaining hormones Tetraiodothyronine (thyroxine or T4) Triiodothyronine (T3) Thyroxine (T4) is major hormone secreted by thyroid follicles Most T3 formed at target tissues by conversion of T4 to T3 The T’s, cont. Both are very similar—two tyrosine amino acids linked by either 3 or 4 iodine atoms Controls rate at which glucose is converted to chemical energy and heat EVERY cell in body is target for thyroid hormone Also important for normal tissue growth and development especially in reproductive and nervous systems Remember it well… GOITER is enlargement of thyroid gland caused by diet deficient in iodine TSH keeps calling for thyroxine and thyroid gland continues to enlarge to make more… Only peptide part of molecule is made but without iodine it is NONFUNCTIONAL fails to provide negative feedback to inhibit TSH release Uncommon in US today because of iodized salt Cretinism, Myxedema, and more Cretinism results in dwarfism where adult body proportions remain childlike Caused by hyposecretion of throxine in early childhood Untreated leads to mental retardation, scanty hair, and very dry skin Discovered early, HR can prevent signs and symptoms of deficiency C, M, and more…cont. Myxedema caused by hyposecretion of thryoxine during adulthood Mental and physical sluggishness, puffiness of face, fatigue, poor muscle tone, low body temperature, obesity, and dry skin Oral thyroxine is prescribed HYPERTHYROIDISM usually results from tumor of thyroid gland = extreme overproduction of thyroxine C, M, and more…cont. High metabolic rate, intolerance of heat, rapid heart beat, weight loss, nervous and agitated behavior, & inability to relax Grave’s disease is one form of hyperthyroidism May also cause thyroid to enlarge & eyes to bulge or protrude anteriorly in condition called exophthalmos Calcitonin Calcitonin (thyrocalcitonin) is second major hormone of the thyroid gland Decreases blood calcium levels by causing calcium to be deposited in bone Antagonistic to parathyroid hormone Made by “C cells” found in connective tissue between follicles Released into blood in response to >ing levels of blood calcium Believed calcitonin production is meager or absent in elderly Calcitonin is hypocalcemic hormone; < calcium in blood Calcium Homeostasis, Visual Parathyroid Glands Are tiny masses of glandular tissue found on posterior surface of thyroid gland Typically 2 on each lobe (8 reported) Secrete parathyroid hormone (PTH) or parathormone **Most important regulator of calcium ion (Ca2+) in blood Calcium levels drop below certain level, parathyroids release PTH which stimulates bone destruction cells (osteoclasts) Parathyroids, cont. Osteoclasts break down bone matrix and increase blood levels of calcium **PTH is hypercalcemic hormone because it acts to > blood levels of calcium Another example of negative feedback PTH also stimulates kidneys and intestine to absorb MORE calcium from forming urine and foodstuff Hypo versus Hypercalcemia Hypocalcemia can be caused by hypoparathyroidism (poor diet, lack of vitamin D, and/or renal failure) Blood calcium levels drop too low, neurons become extremely irritable/overactive Neurons deliver impulses to muscles at such rapid rate that muscles go into uncontrollable spasms (tetany) Convulsions, intestinal cramps, weak heartbeat, cardiac arrhythmias, osteoporosis (what a lesson) Hypo/Hyper, cont. Hypercalcemia results when calcium blood levels become too high Can be caused by hyperparathyroidism (cancer, vitamin D toxicity, calcium supplement overdose) Confusion, muscle pain, cardiac arrhythmias, kidney stones, fatigue, and calcification of soft tissue Is it catching…???? Adrenal Glands Adrenal glands curve over top of kidneys Each is structurally/functionally two endocrine glands Like pituitary, the adrenal has glandular (cortex) and neural (medulla) parts Central medulla enclosed by adrenal cortex which contains three separate layers of cells Adrenal cortex produces 3 major groups of STEROID hormones called corticosteroids Adrenal Glands, cont. Mineralocorticoids, Glucocorticoids, and sex hormones Mineralocorticoids, mainly aldosterone, produced by outermost adrenal cortex layer Important in regulating mineral (salt) content of blood—especially [ ] of sodium and potassium ions Their target is kidney tubules that selectively reabsorb minerals or allow them to be flushed out in urine Adrenal glands, cont. Blood levels of aldosterone >, kidney tubule cells reclaim >ing amounts of sodium ions Allows more potassium ions to be excreted in urine When sodium reabsorbed, water follows Results in >ed blood volume and blood pressure Mineralocorticoids help regulate both water and electrolyte balance in body fluids Aldosterone Release, Visual Adrenals and Glucocorticoids Cortisone & Cortisol are 2 glucocorticoids produced by MIDDLE cortex layer Promote normal cell matabolism and help body resist long-term stressors primarily by >ing blood glucose levels High levels of glucocorticoids in blood prompt body cells to convert fats and proteins to glucose Glucocorticoids are hyperglycemic hormones Glucocorticoids cont. Help control inflammation by <ing edema Reduce pain by inhibiting pain-causing molecules called prostaglandins Often prescribed for patients with rheumatoid arthritis to suppress inflammation **Glucocorticoids released from adrenal cortex in response to rising blood levels of ACTH Adrenals and Sex hormones Regardless of gender, adrenal cortex produces small amounts of both male and female sex hormones throughout life Innermost layer of adrenal cortex produces the bulk of the adrenalproduced sex hormones Androgens (male hormones) and some estrogen also produced Addison’s Disease Addison’s disease caused by hyposecretion of adrenal cortex hormones Major sign is peculiar bronze skin tone Aldosterone levels <; sodium & water lost from body = problems with electrolytes and water balance causes muscles to become weak/shock possible Low levels of glucocorticoids results in hypoglycemia = lessened ability to cope with stress (burnout) and suppression of immune system & increased susceptibility to infection Complete lack of glucocorticoids=auf wiedersehen Cushing’s Syndrome Hypersecretion usually result of tumor If tumor in middle cortex region, Cushing’s syndrome occurs Excessive output of glucocorticoids results in “moon face” and appearance of “buffalo hump” of fat on upper back Also high BP, hyperglycemia, and possible diabetes, weakening of bones, and severe depression of the immune system Trying things on… Tumor in zona reticularis of cortex layer can cause excessive production of either androgens or estrogen If androgen >s dramatically, produces symptoms of adrenogenital syndrome In women=gradual development of male secondary sexual characteristics (body and facial hair, adipose tissue distribution, and muscular development) In estrogen >s, leads to gynecomastia Male develops female secondary sexual characteristics ANS and Adrenal Medulla Adrenal medulla (like posterior pituitary) develops from neural tissue When stimulated sympathetic NS neurons, its cells release 2 similar hormones Hormones called catecholamines Epinephrine (adrenaline) & norepinephrine (noradrenaline) Sympathetic division called “fight or flight response” division of ANS > heart rate, blood pressure, blood glucose levels and dilation of small passageways of lungs Body better able to deal with short-term stressor The Pancreas Pancreas located close to stomach in abdominal cavity and is MIXED gland (both endocrine & exocrine) Tiny masses of hormone-producing cells scattered among enzyme-producing cells pancreatic islets (islets of Langerhans) Islet cells produce insulin & glucagon Both help regulate sugar (glucose) in blood but in opposite ways Beta cells produce insulin and Alpha cells produce glucagon Pancreas, Visual Release and Function of Insulin High blood levels of glucose stimulate beta cells to produce insulin Insulin acts on ALL body cells and >s their ability to transport glucose across their PMs Once inside, glucose used for energy or converted to glycogen or fat for storage Insulin sweeps glucose from blood=hypoglycemic Blood glucose levels fallinsulin release ends (classic negative feedback) Insulin, cont. Insulin is ONLY hormone that <s blood glucose levels It is absolutely necessary for use of glucose by body cells Glucagon, glucocorticoids, and epinephrine increase blood glucose levels and are hyperglycemic Blood Glucose Regulation Diabetes Millitus Condition in which blood glucose levels rise to 600 mg/100 ml compared to normal of 80100 mg/100 ml because of lack of insulin Kidney tubules cannot absorb glucose fast enough so spills into urine As glucose flushes from body, water follows leading to dehydration Cells cannot use glucose so fats/proteins broken down for energy=decline in body weight Loss of body proteins=decreased ability to fight infections Diabetes Millitus, cont. Use of large amts. of fat for energy results in ketones in blood=acidosis as blood becomes more acidic Unless corrected=death 3 cardinal signs of diabetes milliuts Polyuria (excessive urination) Polydipsia (excessive thrist) Polyphagia (hunger) Mild cases (Type II/adult onset) treated with special diets/oral meds to stimulate islets Type I (juvenile/brittle) requires insulin injections Glucagon Function/Release Glucagon released by alpha cells of islets Release stimulated by LOW blood levels of glucose Action is basically hyperglycemic Primary target organ is liver where stimulates breakdown of glycogen to glucose and its release into the blood Pineal Gland/Body Small, cone-like gland found in roof of 3rd ventricle of brain Secretes melatonin; >s at night; <s during day Plays role in body’s day and night cycle May be related to mating behavior and coordination of hormones of fertility Inhibits sexual maturation occurrence during childhood Thymus Gland Located upper thorax, posterior to sternum Large in infants, decreases in size during adulthood—by old age just fibrous connective tissue and fat Produces thymosin which programs T cells In childhood, is “incubator” for maturation of T lymphocytes (WBCs important in immunity) Ovaries Paired, almond shaped organs located in pelvic cavity Produce estrogens and progesterone Estrogens (estrone & estradiol) produced by Graafian follicles of ovary & stimulate development of secondary sexual characteristics Work with progesterone to prepare uterus to receive fertilized egg results in cyclic changes = menstrual cycle Ovaries, cont. Estrogens help maintain pregnancy and prepare breasts for lactation placenta source at this time and not ovaries Progesterone (with estrogen) bring about menstrual cycles During pregnancy, quiets muscles of uterus to prevent abortion Also assists in preparing breasts for lactation Ovaries, cont. Progesterone also secreted by corpus luteum CL produces estrogen/progesterone in >ing amounts Ovaries stimulated to release estrogen and progesterone in cyclic way by anterior pituitary gonadotropic hormones of FSH and LH Testes Testes produce male sex hormones (androgens) of which testosterone is most important Testosterone produced by interstitial cells of testes and causes development of adult male sex characteristics Promotes growth/maturation of reproductive system Promotes development of SSC’s such as growth of beard, development of heavy bones/muscles, lowering of voice Stimulates male sex drive Testes, cont. Testosterone necessary for continuous sperm production during adulthood Production is stimulated by LH from anterior pituitary gland It’s the testosterone that killing us, guys, but what a Catch 22!!! Placenta Formed temporarily in uterus of pregnant woman Has role in respiratory, excretory, and nutrition delivery system for fetus Also produces hormones that help maintain pregnancy Human chorionic gonadotropin (hCG) produced by conceptus and then by fetal part of placenta Found only in urine of pregnant women/is basic for EPTs (monoclonal antibody technology) Placenta, cont. hCG stimulates corpus luteum to continue producing estrogen/progesterone so uterine lining NOT sloughed off In 3rd month, placenta assumes job of production and ovaries become inactive Human placental lactogen (hPL) works with estrogen/progesterone to prepare breasts for lactation Relaxin causes mother’s pelvic ligaments & pubic symphysis to relax and become more flexible Eases birth passage Old dogs/children/WM wine Endocrine system seems to work smoothly until old age Late middle age = menopause for women Estrogen deficiency can lead to arteriosclerois, osteoporosis, decreased skin elasticity, changes in operation of sympathetic nervous system, fatigue, nervousness, and mood changes For most part, men produce testosterone throughout life Watermelon wine, cont. Efficiency of endocrine system gradually declines in old age Target organs become less productive GH declines = muscle atrophy Most older people = hypothyroid Pineal gland calcifies and immune system becomes compromised Decline in insulin production occurs and adult-onset diabetes common in elderly