Lecture Outline - Chapter 20

20.1. How Hormones Work (p. 368)

1. Function along with the nervous system to coordinate and regulate body activities.
2. Compared to nervous system, endocrine system is slower due to diffusion of hormone in bloodstream to organs.
   • a. Hormones travel in blood throughout bloodstream; organ that responds to presence of hormone is target organ.
   • b. Target organ contains cells with specific receptors to hormone; receptors combine with hormone in lock- and-key manner.
3. Two Basic Categories of Hormones
   • a. Peptide Hormones
     • i. Produced by all except adrenal cortex, ovaries and testes.
     • ii. Activate existing enzymes in cells, therefore relatively rapid acting.
   • b. Steroid Hormones
     • i. Produced by adrenal cortex, ovaries or testes.
     • ii. Complex rings of carbon and hydrogen atoms.
     • iii. Trigger synthesis of new proteins, therefore slower acting but more sustained effect.
4. Steroid Hormones Activate DNA
   • a. Freely enter through plasma membrane and bind to receptors in cytoplasm and nucleus. (Fig. 20.1)
   • b. Inside nucleus, steroid hormones bind to receptors; examples include estrogen and progesterone.
   • c. Hormone-receptor complex on hormone binds to DNA; activates particular genes.
   • d. Transcription of DNA and translation of messenger RNA completes process by which steroid hormones cause protein synthesis.
5. Peptide Hormones Activate Enzymes (p. 369)
   • a. Peptide hormones bind to receptor on cell surface.
   • b. Results in the production of cyclic AMP (cAMP) or adenosine monophosphate, a compound made from ATP but with one phosphate group. (Fig. 20.2)
   • c. Peptide hormones termed "first messenger" since never enters cell; cAMP is "second messenger."
   • d. G proteins have ability to break down energy carrier GTP (guanine triphosphate) and are directly stimulated by hormone-receptor interaction. Activates enzyme within the cell, which sets an enzyme cascade in motion.
   • e. G proteins located in membrane also regulate action of many other membrane proteins.
   • f. cAMP activates one enzyme that activates another, etc., in enzyme cascade where one binding hormone molecule can result in 1,000-fold response.
   • g. Peptide hormones act quickly but for short period of time because cAMP is converted to inactive product and enzymes are inactivated.

1. Hypothalamus
   • a. Located beneath thalamus in third ventricle of brain.
   • b. Regulates heart rate, body temperature, water balance, glandular secretions of pituitary.
2. Posterior Pituitary Stores Two Hormones
   • a. Connected to hypothalamus by stalklike structure.
   • b. Neurons called neurosecretory cells in the hypothalamus secrete hormones transmitted to posterior pituitary by nerve axons; hormones then stored in posterior pituitary for secretion.
   • c. Hormones released from posterior pituitary include:
     • i. Antidiuretic hormone (ADH)
       - also called vasopressin.
       - promotes water reabsorption in collecting duct of kidneys.
       - osmoreceptors in hypothalamus determine blood is too concentrated, trigger release of ADH.
       - as blood becomes dilute, hormone is no longer released.
       - constitutes example of negative feedback control because effects of hormone eventually shuts down release of hormone.

       ii. Oxytocin

       - causes uterus to contract; used to artificially induce labor.

       - stimulates milk release from mammary glands for nursing.
3. Anterior Pituitary Is the Master Gland (p. 372)
   • a. Hypothalamus controls anterior pituitary by producing specific hypothalamic-releasing and release- inhibiting hormones.
   • b. Portal system connects capillary bed in anterior pituitary to capillary bed in hypothalamus. (Fig. 20.4)
   • c. Growth Hormones:
     • i. Growth hormone (GH) (also called somatotropin):
       - promotes cell division, protein synthesis, bone growth.

       ii. Abnormalities:

       - if too little produced as child, pituitary dwarf results.

       - if too much is produced as a child, person may become a giant. (Fig. 20.5)

       - if too much produced as an adult, causes acromegaly. (Fig. 20.6)

       iii. GH causes liver to release somatomedins which affect cartilage and bone growth by promoting cell division, protein synthesis in these tissues.
   • d. Prolactin (PRL) (p. 373)
     • i. Produced after childbirth.
     • ii. Causes the mammary glands to develop and produce milk.
     • iii. Role in carbohydrate and fat metabolism.
   • e. Melanocyte-stimulating hormone (MSH)
     • i. Concentrations low in humans; function in humans is obscure.
     • ii. Causes skin changes and color variation in fish, amphibians, reptiles.
   • f. Thyroid-stimulating hormone (TSH) stimulates thyroid to produce thyroxin.
   • g. Adrenocorticotropic hormone (ACTH) stimulates adrenal cortex of adrenal gland to produce cortisol.
   • h. Gonadotropic hormones (FSH and LH) stimulate gonads (testis in male, ovary in female) to produce sex hormones.
   • i. Above hormones illustrate the three-tiered relationship: hypothalamus to pituitary to thyroid, gonads, or adrenal cortex.

1. Thyroid is large gland located in neck; parathyroids are imbedded in posterior surface of thyroid.
2. Thyroid Gland
   • a. Composed of many follicles.
   • b. Filled with stored thyroid hormone.
3. Thyroxin
   • a. Hormone produced by thyroid gland.
   • b. Thyroxine
     • i. Usually secreted as T₄ (tetraiodothyronine) with four iodine atoms.
     • ii. Eventually T₄ is converted to T₃ (triiodothyrone) which is active form.
   • c. Requires iodine for synthesis.
   • d. If iodine is lacking in diet, thyroid gland enlarges to form simple goiter; iodized salt prevents shortage in diet. (Fig. 20.7)
   • e. TSH from anterior pituitary gland stimulates thyroid to secrete thyroxin.
   • f. Increased level of thryroxin feeds back to anterior pituitary, ceases TSH production.
   • g. Low level of thyroxin in blood (hypothyroidism) keeps pituitary secreting TSH and stimulating thyroid; goiter results because there is no inhibition of TSH because no thyroxin is produced.
   • h. Thyroxin increases metabolic rate of most cells; does not have one target organ.
   • i. Cretinism
     • i. Exhibit short, stocky frame.
     • ii. Due to hypothyroidism since infancy.
     • iii. Causes mental retardation if thyroxin treatment not begun within first two months.
   • j. Myxedema
     • i. Due to hypothyroidism in adults
     • ii. Characterized by lethargy; weight gain; bagginess under eyes; lowered temperature; slower pulse rate; and thick, puffy skin.
   • k. Graves' Disease (hyperthyroidism)
     • i. When thyroid is enlarged and overactive.
     • ii. Caused by too much thyroxin.
     • iii. Causes goiter to form (called exophthalmic goiter). (Fig. 20.8)
     • iv. Eyes protrude due to edema in eye socket.
     • v. Person may be hyperactive, nervous, suffer from insomnia.
     • vi. May be helped by surgery removing portion of thyroid.
4. Calcitonin
   • a. Also produced by thyroid gland.
   • b. Regulates calcium levels in blood.
   • c. Opposes action of parathyroid hormone.
5. Parathyroid Glands (p. 376)
   • a. Four small glands on posterior thyroid surface produce parathyroid hormone.
   • b. Parathyroid hormone (PTH)
     • i. Causes calcium (Ca⁺⁺) level in blood to increase; phosphate (HPO₄) level to decrease.
     • ii. Promotes:
       - breakdown of bone.
       - retention of calcium in kidneys.
       - activation of vitamin D which in turn stimulates absorption of calcium from intestine.
       - excretion of phosphate in urine by kidneys.

       iii. Inhibiting osteoblasts and promoting osteoclasts causes demineralization of bone and raises calcium level in blood. (Fig. 20.10)

       iv. Calcitonin has opposite effect; therefore homeostatic balance achieved.

       v. When insufficient PTH produced, blood calcium drops resulting in tetany in which body shakes from continuous muscle contraction. (Fig. 20.9)

       vi. When calcium level is lowered, PTH secretion is stimulated; when calcium level rises, PTH secretion is inhibited.

1. Two adrenal glands; one lies atop each kidney.
2. Adrenals
   • a. Consists of outer layer called cortex; inner core called medulla.
   • b. No physiological connections between medulla and cortex.
   • c. Both sections controlled by hypothalamus; stress and recovery from stress triggers adrenals via control of pituitary's production of ACTH.
3. Adrenal Medulla
   • a. Produces epinephrine (adrenalin) and norepinephrine (noradrenalin) under stress conditions. (Fig. 20.11)
   • b. Postganglionic fibers of sympathetic nervous system also secrete norepinephrine; control adrenal medulla.
   • c. "Fight-or-flight" reactions:
     • i. increased heart and breathing rate.
     • ii. blood vessels to muscles dilate, to digestive tract constrict.
     • iii. increased blood glucose level and metabolic rate.
4. Adrenal Cortex
   • a. Outer portion of adrenals produce glucocorticoids and mineralocorticoids; also produce both male and female sex hormones in both sexes.
   • b. Glucocorticoids
     • i. Major glucocorticoid is cortisol.
       - Promotes hydrolysis of muscle proteins into amino acids that enter blood.
       - Increase in amino acid causes higher glucose blood levels when liver breaks down amino acids, in opposition to insulin.
       - Favors metabolism of fatty acids over carbohydrates.
       - Counteracts inflammatory response; cortisol decreases pain and swelling of joints in arthritis and bursitis.
   • c. Mineralocorticoids
     • i. Aldosterone is most significant mineralocorticoid.
       - Promotes renal sodium absorption and potassium renal excretion.
       - Part of renin-angiotensin-aldosterone system. (Fig. 20.12)
       - If blood sodium concentration is low, renin is released from kidneys; converts angiotensinogen to angiotensin I which becomes angiotensin II in lungs.
       - Angiotensin II causes the release of aldosterone which causes more sodium to be reabsorbed, maintaining water and blood volume, and arterial constriction which increases pressure.
   • ii. ADH is previously discussed hormone for increasing blood volume.
   • iii. Atrial natriuretic hormone (ANH) from cardiac cells inhibits secretion of renin by kidneys and secretion of aldosterone from adrenal cortex; causes natruiuresis or excretion of sodium, which lowers blood volume and pressure.
5. d. Disorders of Adrenal Cortex (p. 379)
   • i. Addison Disease (Fig. 20.13)
     - Due to lack of cortisol, patient has low blood glucose.
     - Due to lack of aldosterone, patient has low blood sodium, low blood pressure, and possible severe dehydration.

     ii. Cushing Syndrome (Fig. 20.14)

     - Due to high cortisol level.

     - Patient may increase subcutaneous fat and decrease muscular protein, leading to an oversized trunk.

     - High blood sodium causes, edema of face, high blood pH, and hypertension.

     - Increased adrenal male sex hormones may masculinize women.

1. Pancreas is long organ located between kidneys and near duodenum. (Fig. 20.15)
2. Exocrine portion produces and secretes digestive juices by ducts into small intestine.
3. Endocrine tissue is called pancreatic islets (of Langerhans) and secretes two hormones:
   • a. Insulin
     • i. Secreted when there is high blood glucose level (i.e., after a meal).
     • ii. Stimulates liver, muscle, and fat cells to take up and metabolize glucose.
     • iii. Stimulates liver and muscles to store glucose as glycogen.
     • iv. Promotes buildup of fats and proteins; inhibits their use as energy.
     • v. Overall, helps lower blood glucose level.
   • b. Glucagon
     • i. Secreted from pancreas between eating.
     • ii. Causes breakdown of glycogen and other stored nutrients, thereby increasing blood glucose level.
     • iii. Effect is opposite that of insulin.
4. Diabetes Mellitus (p. 380)
   • a. Symptoms:
     • i. Sugar in urine.
     • ii. Frequent and copious urination.
     • iii. Abnormal thirst.
     • iv. Rapid weight loss.
     • v. General weakness.
     • vi. Drowsiness and fatigue.
     • vii. Itching of genitals and skin.
     • viii. Visual disturbances including blurring.
     • ix. Skin disorders, boils, carbuncles, infection.
   • b. Cause
     • i. Due to lack of insulin, sugar is not metabolized by cells
     • ii. Liver fails to store glucose as glycogen.
     • iii. Blood glucose level rises very high after eating; excess blood glucose is excreted in urine, and individual becomes very thirsty.
     • iv. Body uses fats and proteins for energy, which leads to ketone buildup, acidosis, and possibly coma and death. (Table 20.2)
     • v. Time usually available to reverse symptoms.
5. Types of Diabetes (p. 380)
   • a. Type I (insulin-dependent) Diabetes
     • i. Pancreas is not producing insulin.
     • ii. Suspected due to exposure to an environmental agent, perhaps a virus, that causes cytotoxic T cells to destroy pancreatic islets.
     • iii. Requires daily insulin injections.
     • iv. Overdose of insulin or lack of regular eating may bring on insulin shock; "cured" by ingesting sugar (sugar cube, fruit juice, etc.). (Table 20.2)
     • v. Transplant of islet cells may be recommended.
   • b. Type II (insulin-independent) Diabetes
     • i. Ten out of 12 million U.S. diabetics have this type of diabetes.
     • ii. Insulin is produced but cells do not respond due to lack of receptors.
     • iii. Occurs in obese and inactive people of any age.
     • iv. Controlled by low-fat diet and exercise; some oral drugs.

1. Testes (controlled by gonadotropic hormones of anterior pituitary)
   • a. In scrotum of male.
   • b. Produce androgens (testosterone) male sex hormones.
   • c. Testosterone Functions:
     • i. Increase muscle strength.
     • ii. Normal development of sex organs.
     • iii. Maturation of sperm.
     • iv. Hair growth.
     • v. Vocal cords enlargement.
     • vi. Sweat gland development.
     • vii. Baldness develops if combined with genes for baldness.
     • viii. Sex drive and probably aggressiveness.
2. Ovaries (controlled by gonadotropic hormones of anterior pituitary)
   • a. In abdominal cavity of female.
   • b. Produce female sex hormones estrogen and progesterone.
   • c. Estrogen Functions:
     • i. Increase fat beneath skin.
     • ii. Normal development of uterus and vagina.
     • iii. Maturation of eggs.
     • iv. Hair growth pattern.
     • v. Pelvic girdle enlarges for potential childbearing.
     • vi. Breast development.
     • vii. Regulation of uterine cycle.
   • d. Progesterone Functions:
     • i. Breast development.
     • ii. Regulation of uterine cycle.
3. Thymus: Most Active in Children
   • a. Located in upper thoracic cavity.
   • b. Most active in childhood; shrinks and becomes fatty with age.
   • c. Lymphocytes pass through thymus; are transformed into T cells.
   • d. Thymus hormones (thymosins) stimulate T cell differentiation.
4. Pineal Gland: Hormone at Night
   • a. Located near surface in fish and amphibians; functions as "third eye."
   • b. In mammals, secretes melatonin chiefly at night and establishes a daily (circadian) rhythm.
   • c. Exposure to light improves depression of people affected by Seasonal Affective Disorder (SAD) in winter; melatonin makes symptoms worse.
   • d. May be related to sexual development cycles.
5. Nontraditional Sources (p. 383)
   • a. Heart produces atrial natriuretic hormone (ANH) that promotes renal excretion of sodium and water, inhibits renin release and aldosterone and ADH.
   • b. Peptide growth factors stimulate cell division and mitosis.
   • c. Other Growth Factors
     • i. Blood contains lymphokines and blood cell growth factor.
     • ii. Platelet-derived growth factor helps in healing.
     • iii. Epidermal growth factor.
     • iv. Nerve growth factor.
     • v. Tumor angiogenesis factor stimulates capillary networks.
     • vi. Prostaglandins (PG):
       - derived from fatty acids stored in cell membranes.
       - many different types produced by many different tissues.
       - cause uterine pain and discomfort.
       - some used to treat ulcers, hypertension, prevent thrombosis.

1. Three categories of environmental signals. (Fig. 20.16)
2. Pheromones are chemical messengers that work at a distance between individual organisms.
   • a. Female silkworm moths release a sex attractant that can be received by male silk moths several miles away.
   • b. Ants lay down a pheromone trail to direct other ants to food.
   • c. Dogs leave urine markers establishing their territories.
3. Hormones and neurosecretory cell secretions act at a distance between body parts of the same organism; secretions of hypothalamus, and endorphins and norepinephrine (both a hormone and neurotransmitter) represent overlap between nervous and endocrine systems as body signaling systems.
4. Signals are passed locally between adjacent cells; this includes neurotransmitters, histamine from mast cells when skin is cut, etc.