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I. Overview of the Endocrine Functions

I. Overview of the Endocrine Functions. Metabolism Control of food intake and digestion Tissue maturation Ion regulation Water balance Heart rate and blood pressure regulation Control of blood glucose and other nutrients Control of reproductive functions

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I. Overview of the Endocrine Functions

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  1. I. Overview of the Endocrine Functions • Metabolism • Control of food intake and digestion • Tissue maturation • Ion regulation • Water balance • Heart rate and blood pressure regulation • Control of blood glucose and other nutrients • Control of reproductive functions • Uterine contractions and milk release • Immune system regulation

  2. II. Special relationship of the Pituitary Gland and Hypothalamus • A. Where nervous and endocrine systems interact • B. Nervous system regulates homeostasis on a short term basis • C. Endocrine system regulates homeostasis on a longer time frame • D. But the two do interact • E. Hypothalamus regulates secretions of anterior pituitary • F. Posterior pituitary is an extension of the hypothalamus • H. Anterior pituitary produces nine major hormones that • Regulate body functions • Regulate the secretions of other endocrine glands

  3. I. Structure of the Pituitary Gland • 1. Posterior pituitary (neurohypophysis): • a. extension of the nervous system via the infundibulum • b. Secretes and stores neuropeptides like oxcytocin • 2. Anterior pituitary (adenohypophysis) • a. Connected to hypothalamus by portal vein running through the infundibulum • b. Hypothalamus controls the adenohypophysis by release of releasing hormone or inhibiting hormone • c. Example would be GHRH or GHIH (somatostatin)

  4. Hypothalamus, Anterior Pituitary, and Target Tissues

  5. J. Hypothalamic Releasing and Inhibiting Hormones

  6. Hypothalamus, Posterior Pituitary, and Target Tissues

  7. III. Hormones of Posterior Pituitary A. ADH • 1. Also called vasopressin. • 2. Osmoreceptors (specialized neurons of hypothalamus monitor changes in intercellular osmolality (relative concentrations of electrolytes and water). • 3. If the concentration of electrolytes increases or if the concentration of water decreases, then ADH secretion is stimulated. • 4. Baroreceptors (specialized neurons found in walls of atria of heart, large veins, carotid arteries, aortic arch) sense changes in blood pressure (BP). If BP decreases, then ADH secretion is stimulated. • 5. ADH works on the collecting ducts of the kidneys to produce a more concentrated urine as water is reabsorbed into the body

  8. B. Oxcytocin • 1. produced in the hypothalamus and stored in the posterior or neurohypophysis • 2. target tissues include myometrium and muscle cells around milk ducts of mammary glands • 3. stimuli bringing about release of oxcytocin stretching of the uterus, cervix, sexual intercourse, and stimulation of nipple during nursing • 4. functions: • a. Onset of delivery • b. Expulsion of uterine lining during menses • c. Sperm transport during intercourse • d. Milk letdown • 5. special cases • a. Nursing mothers and uterine shape • b. Neural input to oxcytocin release

  9. Control of ADH Secretion

  10. Control of Oxytocin Secretion

  11. III. Anterior Pituitary Hormones A. Summary list • 1. Growth hormone (GH) or somatotropin • 2. Thyroid-stimulating hormone (TSH) • 3. Adrenocorticotropic hormone (ACTH) • 4. Melanocyte-stimulating hormone (MSH) • 5. Beta endorphins • 6. Lipotropins • 7. Luteinizing hormone (LH) • 8. Follicle-stimulating hormone (FSH) • 9. Prolactin

  12. B. Generalized traits • 1. controlled by releasing and inhibiting hormones from the hypothalamus • 2. the hormones are proteins, glycoproteins, or polypeptides-generally too large to pass through the membrane • 3. bind to receptors on the target cell membrane • 4. short half life and generally quick acting • 5. many of the hormones are tropic hormones-stimulate other endocrine glands to produce hormones • 6. therefore sometimes called the master gland

  13. C. Specific Anterior Pituitary Hormones 1.Growth Hormone (GH or somatotropin) • a. Stimulates uptake of amino acids; protein synthesis • b. Stimulates breakdown of fats (lipolysis) to be used as an energy source but stimulates synthesis of glycogen (glycogenesis) • c. glucose sparing • d. Promotes bone, muscle and cartilage growth by bringing about the release of somatomedins (insulin-like growth factors) • e. Regulates blood levels of nutrients after a meal and during periods of fasting • f. Produced by biotech • g. Potentials for abuse-acromegaly

  14. Regulation of Growth Hormone Secretion

  15. 2. TSH (tropic hormone) and Thyroid Hormones • a. TRH from hypothalamus causes the release of TSH from anterior pituitary which causes secretion and storage of hormones T3 and T4 within the thyroid gland • b. T3 and T4 inhibit TRH and TSH secretion in a negative feedback pattern.

  16. 3. Adrenocorticotrophic Hormone (ACTH) • a. CRH (corticotropin releasing hormone) from hypothalamus causes release of ACTH from anterior pituitary • b. ACTH causes cortisol secretion from the adrenal cortex (a glucocorticoid from the zona fasciculata) • c. Causes aldosterone secretion from the adrenal cortex (a mineralocorticoid from the zona glomerulosa) • d. If adrenal cortex is diseased and malfunctional, ACTH levels rise and • e. Binds directly to melanocytes of the skin; causes increase in production of melanin. • f. ACTH, lipotropins, B endorphins and MSH are manufactured from the same precursor

  17. 4. Melanocyte Stimulating Hormone, Endorphins, and Lipotropins • a. ACTH, MSH, endorphins and lipotropins all derived from the same large precursor molecule when stimulated by CRH • b. MSH causes melanocytes to produce more melanin • -plays a role in appetite • -sexual behavior?? • c. Endorphins act as an analgesic; produced during times of stress. • d. Lipotropins cause adipose cells to catabolize fat, lipolysis

  18. 5. LH, FSH, Prolactin • a. Gonadotropins: glycoprotein hormones that promote growth and function of the gonads • b. LH and FSH • Both hormones regulate production of gametes and reproductive hormones • Testosterone in males • Estrogen and progesterone in females • c. GnRH from hypothalamus stimulates LH and FSH secretion • d. Prolactin: role in milk production • Regulation of secretion: prolactin-releasing hormone (PRH) and prolactin-inhibiting hormones (PIH)

  19. IV. Thyroid Gland • A. One of largest endocrine glands; • 1. Highly vascular. • 2. appears dark red • 3. Iodine enters follicular cells by active transport. • 4. low levels of iodine thryroid hypertrophies called goiter • B. Composed of follicles: • 1. follicular cells surrounding thyroglobulin/thyroid hormone • 2. Parafollicular cells: between follicles secrete calcitonin • 3. calcitonin reduces blood calcium levels by stimulating activity of osteoblasts in bone

  20. C. Thyroid hormones • 1. two major iodine based hormones produced- triodothyronine (T3) and thyroxine (T4) • 2. more thyroxine is produced than the T3 which is physiologically more active • 3. these hormones are carried in the blood connected to globulin molecules which protects them from breakdown-gives them a very long half life • 4. a lot of these hormones are stored in the thyroid gland which also helps to maintain very stable levels of these two hormones in the blood • 5. when thyroid function is being measured by blood work, it is the TSH which is measured • 6. it is a more direct barometer of thyroid activity • 7. these two hormones elevate metabolic rate • 8. Increase rate of glucose, fat, protein metabolism in many tissues thus increasing body temperature • 9. Normal growth of many tissues dependent on presence of thyroid hormones • 10. hypothyroidism vs. hyperthyroidism

  21. D. Regulation of Calcitonin Secretion • 1. Produced by parafollicular cells • 2. Secretion triggered by high Ca2+ concentration in blood; acts to decrease Ca2+ concentration • 3. Primary target tissue: bone. Decreases osteoclast activity, lengthens life span of osteoblasts. • 4. calcitonin concentrations decrease with age more in females than males • 5. postmenopausal women and calcitonin nasal sprays

  22. V. Parathyroid Glands • 1. Embedded in thyroid • 2. Historical surgery story • 3. Two glands on each side • 4. Secrete PTH: target tissues are bone, kidneys and intestines. • Increases blood calcium and phosphate levels • Stimulates osteoclasts • Promotes calcium reabsorption by kidneys and PO4 excretion because rise of both causes bone deposition in wrong amounts • Increases synthesis of vitamin D which, in turn, increases absorption of Ca and PO4 by intestines. Net loss of PO4 under influence of PTH. • 5. Regulation depends on calcium levels. • 6. inactive parathormone-hypocalcemia-open voltage-gated sodium ion channels

  23. VI. Adrenal Glands A. Anatomy • 1. Near superior poles of kidneys; retroperitoneal • 2. Inner medulla; outer cortex • 3. Medulla: formed from neural crest; sympathetic. Secretes epinephrine and norepinephrine • 4. Cortex: three zones from superficial to deep • Zona glomerulosa • Zona fasciculata • Zona reticularis

  24. B. Hormones of the Adrenal Medulla • 1. Secretory products are neuropeptides: epinephrine and norepinephrine • 2. Combine with adrenergic membrane-bound receptors • 3. Secretion of hormones prepares body for physical activity • 4. Effects are short-lived; hormones rapidly metabolized; half-life is minutes • 5. Epinephrine • Increases blood levels of glucose via glycogenolysis • Increases fat breakdown in adipose tissue • Causes dilation of blood vessels in skeletal muscles and cardiac muscles. • 6. Epinephrine and norepinephrine increase heart rate and force of contraction; cause blood vessels to constrict in skin, kidneys, gastrointestinal tract, and other viscera

  25. C. Hormones of Adrenal Cortex • 1. Mineralocorticoids: Zona glomerulosa • Aldosterone produced in greatest amounts. Increases rate of sodium reabsorption by kidneys increasing sodium blood levels • Stimulus for production is low blood pressure • Increases water reabsorption and therefore blood volume • 2. Glucocorticoids: Zona fasciculata • Cortisol is major hormone. Increases fat and protein breakdown, increases glucose synthesis(gluconeogenesis), promotes the increased use of fats and proteins by muscles, decreases inflammatory response • 3. Androgens: Zona reticularis • Weak androgens secreted then converted to testosterone by peripheral tissues. Stimulate pubic and axillary hair growth and sexual drive in females

  26. VII. Pancreas • A. Located along small intestine and stomach; retroperitoneal • B. Exocrine gland • Produces pancreatic digestive juices • C. Endocrine gland • Consists of pancreatic islets • Composed of • Alpha cells; secrete glucagon • Beta cells; secrete insulin • Delta cells; secrete somatostatin

  27. D. Histology of the Pancreatic Islets

  28. E. Effects of insulin • 1. direct effect is to reduce blood glucose • 2. acts on a number of different target tissues • 3. muscle-causes uptake of glucose to promote glycogenesis • 4. adipose tissue-lipogenesis • 5. liver-glycogenesis and increased use of glucose to drive ATP production • 6. also acts to increase uptake of amino acids and stimulates protein synthesis • 7. insulin is a protein hormone-therefore binds to a membrane receptor • 8. increases the number of glucose carrier molecules • 9. low levels of insulin lead to a very rapid increase of blood glucose

  29. G. Effects of glucagon • 1. Affects of glucagon are antagonistic to insulin • 2. acts to increase blood glucose levels • 3. secreted from pancreas alpha cells and enters hepatic portal circulation • 4. travels directly to liver where it stimulates the liver to break down glycogen stores-glycogenolysis • 5. also stimulates glucose sparing and encourages the use of alternate fuels for energy source • 6. important to maintain adequate glucose levels as the nervous system is an obligate consumer of glucose • 7. promotes gluconeogenesis in liver from amino acids • 8. glucagon does not affect many other target tissues as the liver breaks down glucagon before it can pass on to other organs

  30. H. Diabetes mellitus • 1. normal range fasting blood sugar is 70-100 mg./deciliter • 2. low insulin activity raises this level drastically-diabetes usually confirmed with reading of 200mg/deciliter • 3. two types of diabetes • a. Type I • -individuals don’t produce sufficient insulin • -usually children • - approximately 10% of diabetic population • -insulin dependent • b. Type II • -individuals don’t respond to insulin normally produced • -faulty receptors or enzymes produced after insulin combines • -majority • -adult onset • -meds taken to increase insulin production • -exercise

  31. 4. Symptoms of diabetes type I • a. Frequent urination –due to high osmotic pressures of glucose in urine • b. Unusual thirst –replacing fluid loss in the high urine production • c. Extreme hunger-satiety center in hypothalamus insulin dependent • d. Unusual weight loss- low fuel source availability • e. Extreme fatigue and irritability

  32. Insulin and Glucagon

  33. 18.7 Hormonal Regulation of Nutrient Utilization

  34. 18.7 Hormonal Regulation of Nutrient Utilization

  35. Regulation of Blood Nutrient Levels During Exercise

  36. VIII. Hormones of the Reproductive System Previously Discussed

  37. IX. Hormones of the Pineal Gland • Main hormone is melatonin • Melatonin inhibits GnRH and therefore inhibits reproductive function • Also may help sleep cycles by stimulating sleep • Some animals pineal regulates breeding cycles 1. light inhibits pineal secretion of melatonin 2. dark stimulates pineal’s secretion of melatonin 3. animals that breed in spring experience increased day length and decreased melatonin secretion-reproductive structures hypertrophy 4. repurcussion- -use as a sleep aid -earlier onset of puberty

  38. X. Thymus gland • A. Location-superior mediastinum • B. Produces hormone thymosin • C. Activity-maturation and development of the immune system • D. Culinary-sweet breads

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