Organs of the Endocrine System and Their Products

1. Organs of the Endocrine System and Their Products • The following major glands will be covered one at a time with their products: 1. Pituitary gland / Hypothalamus 2. Thyroid gland 3. Parathyroid gland 4. Adrenal gland 5. Pancreas (also has exocrine function) 6. Gonadal hormones (ovaries and testes) 7. Thymus

2. 1. Pituitary Gland (Hypophysis) • located in sella turcica of sphenoid bone (in cranial cavity), inferior to hypothalamus • consists of two lobes: A. neurohypophysis (~ posterior pituitary) • attached to hypothalamus by infundibulum • contains axons and axon terminals of neurosecretory cells whose cell bodies are in hypothalamic nuclei B. adenohypophysis (~ anterior pituitary) • consists of glandular epithelium http://www.usc.edu/hsc/dental/ghisto/end/c_1.html

3. A. Neurohypophysis (Posterior Pituitary) • consists of nerve fibers (axons of neurosecretory cells with cell bodies in hypothalamus) and pituicytes (glial cells that support nerve fibers) • acts primarily as a storage and releasing area for hormones actually made in hypothalamic nuclei • hormones released in response to impulses from hypothalamus (neural control) • hormones are short amino acid chains (peptides) • oxytocin • antidiuretic hormone (ADH or “vasopressin”)

4. A. Neurohypophysis:Oxytocin (OT) • action, in pregnant or nursing women: • stimulates contraction of smooth muscle of uterine wall during labor and delivery • stimulates ejection of milk in lactating mothers • action, in men and non-pregnant women, may be involved in sexual arousal and orgasm

5. A. Neurohypophysis:Oxytocin (OT) • control: • during labor/delivery, positive feedback: stretching of uterus/cervix --> sensory impulses to hypothalamus --> increased secretion of OT --> increased contraction • suckling: sucking of infant on breast --> sensory to hypothalamus --> oxytocin release --> release of milk

6. A. Neurohypophysis: Antidiuretic Hormone (ADH) • action: antidiuretic hormone (ADH) directly affects blood pressure - acts as powerful vasoconstrictor --> increases blood pressure (hence name “vasopressin”) • action: affects water balance (indirect affect on blood pressure) - acts on tubules of kidney to increase reabsorption of water  less water lost in urine

7. A. Neurohypophysis: ADH • disorders: • hyposecretion due to damage of hypothalamic nucleus or neurohypophysis--> diabetes insipidus - excessive urine production (polyuria) and thirst • hypersecretion --> SIADH (syndrome of inappropriate ADH secretion) - water retention, headache, cerebral edema, weight gain, hypoosmolarity

8. Antidiuretic Hormone (ADH): Control • neural control: increased electrolyte (NaCl) concentration --> affects (supraoptic) nucleus in hypothalamus --> impulse to neurohypophysis --> release of ADH --> increased water reabsorption --> decrease in electrolyte concentration • other stimuli: pain, low BP, morphine, barbiturates, nicotine, aldosterone (hormone from adrenal cortex - hormonal control) • inhibition: alcohol (results in more urine production and, potentially, dehydration) • diuretic drugs - some act to supress ADH secretion; used to treat hypertension and congestive heart failure

9. B. Adenohypophysis (Anterior Pituitary) • linked to hypothalamus via hypophyseal portal system (capillary networks and small veins) • carries regulatory hormones from hypothalamus to pituitary • releasing hormones stimulate secretion of pituitary hormones • inhibitory hormones inhibit secretion • consists of epithelial cells • all hormones produced are proteins • tropic hormones - affect some endocrine glands or provide maintenance oversight for other organs

10. B. Adenohypophysis:Growth Hormone (GH) • highest levels during evening and sleep • action: stimulates increased rate of protein synthesis leading to cell growth and division • bones and skeletal muscle respond more than other body cells • action: stimulates use of fat as energy source and decreases rate of glucose uptake and glucose metabolism (diabetogenic effect – “spares” glucose) • control: • release stimulated by GHRH (growth hormone releasing hormone) from hypothalamus • inhibited by GHIH (from hypothalamus) and somatomedins (produced by liver under GH stimulation)

11. Growth Hormone (GH): Disorders Disorders: • hypersecretion • gigantism (in children) • up to 8’ tall, normal body proportions • acromegaly (after epiphyseal plates close) • enlargement of extremities and face, thickening of soft tissue • hyposecretion • pituitary dwarfism - in children, up to 4’ tall • progeria - premature aging, atrophy of body tissues

13. Growth Hormone Excess in childhood leads to GIGANTISM

14. Growth Hormone Excess in adulthood leads to ACROMEGALY

16. B. Adenohypophysis: Prolactin (PRL) • action: • stimulates milk production in mammary glands; • helps stimulate development of mammary glands (along with other hormones); • in males, may help regulate testosterone production • control: • stimulation: PRH (prolactin-releasing hormone from hypothalamus), high estrogens, breast-feeding • inhibition: PIH (hypothalamus), stimulated by rising PRL levels, low estrogen

17. B. Adenohypophysis:Prolactin (PRL) Disorders • hyperprolactinemia = hypersecretion due to adenohypophyseal tumors; results in galactorrhea, lack of menses and infertility in women, impotence in men

18. B. Adenohypophysis: Thyroid-Stimulating Hormone (TSH) • TSH = thyrotropin • action: • stimulates secretion of hormones from thyroid gland (T4 and T3); also stimulates development of thyroid in youth • control: • release stimulated by TRH (thyroid releasing hormone from hypothalamus) • inhibited by rising levels of thyroid hormones and by GHIH

19. B. Adenohypophysis: Adrenocorticotropic hormone (ACTH) • ACTH=corticotropin • action: stimulates release of hormones from adrenal cortex • control: • release stimulated by CRH (corticotropin-releasing hormone from hypothalamus) • release inhibited by rising levels of glucocorticoids from adrenal cortex

20. B. Adenohypophysis:Gonadotropins • regulate activity and secretion by gonads (testes in males; ovaries in females) • control: • stimulated by GnRH (gonadotropin-releasing hormone from hypothalamus) • release of GnRH is inhibited by rising levels of estrogens, progestins and androgens (testosterone) • two important hormones • FSH • LH

21. Gonadotropins:Follicle-Stimulating Hormone (FSH) • action: • females (ovaries) - stimulates development of ovarian follicles and estrogen production • males (testes) - stimulates sperm production and development • inhibited by inhibin and testosterone from testes (feedback to hypothalamus and anterior pituitary) and estrogen, progesterone and inhibin from ovaries (feedback to anterior pituitary)

22. Gonadotropins:Luteinizing Hormone (LH) • LH=lutropin • action: • females (ovaries) - induces ovulation; stimulates secretion of estrogens and progestins (e.g., progesterone) • males (testes) - stimulates production of androgens (e.g., testosterone ) • inhibited by estrogen, progesterone and inhibin form ovaries (feedback to anterior pituitary) and by inhibin and testosterone from testes (feedback to hypothalamus and anterior pituitary)