Hypothalamic Control of Posterior Pituitary

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1 Hypothalamic Control of Posterior Pituitary Hypothalamus neuron cell bodies produce ADH: supraoptic nuclei Oxytocin: paraventricular nuclei Transported along the hypothalamohypophyseal tract Stored in posterior pituitary Release controlled by neuroendocrine reflexes

2 Hypothalamic Control of Anterior Pituitary Hormonal control rather than neural Hypothalamus neurons synthesize releasing and inhibiting hormones Hormones are transported to axon endings of median eminence Hormones secreted into the hypothalamo-hypophyseal portal system regulate the secretions of the anterior pituitary

3 Feedback Control of Anterior Pituitary Anterior pituitary and hypothalamic secretions are controlled by the target organs they regulate Secretions are controlled by negative feedback inhibition by target gland hormones Negative feedback at 2 levels The target gland hormone can act on the hypothalamus and inhibit secretion of releasing hormones The target gland hormone can act on the anterior pituitary and inhibit response to the releasing hormone

4 Short feedback loop: Retrograde transport of blood from anterior pituitary to the hypothalamus Hormone released by anterior pituitary inhibits secretion of releasing hormone Positive feedback effect: During the menstrual cycle, estrogen stimulates LH surge

5 Higher Brain Function and Pituitary Secretion Axis: Relationship between anterior pituitary and a particular target gland. Pituitary-gonad axis Hypothalamus receives input from higher brain centers Psychological stress affects: Circadian rhythms, menstrual cycle

6 Adrenal Glands Paired organs that cap the kidneys Each gland consists of an outer cortex and inner medulla Adrenal medulla: Derived from embryonic neural crest ectoderm (same tissue that produces the sympathetic ganglia) Synthesizes and secretes catecholamines (mainly Epi but some NE)

7 Adrenal cortex does not receive neural innervation Must be stimulated hormonally (ACTH) Consists of 3 zones Zona glomerulosa Zona fasciculata Zona reticularis Secretes corticosteroids

8 Functions of Adrenal Cortex Zona glomerulosa: Mineralcorticoids (aldosterone) Stimulate kidneys to reabsorb Na + and secrete K + Zona fasciculata: Glucocorticoids (cortisol) Inhibit glucose utilization and stimulate gluconeogenesis Zona reticularis: Sex steroids(dhea) Supplement sex steroids

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10 Functions of Adrenal Medulla Innervated by preganglionic sympathetic axons Increase respiratory rate Increase HR and cardiac output Vasoconstrict blood vessels, thus increasing venous return Stimulate glycogenolysis Stimulate lipolysis

11 Stress and Adrenal Gland Non-specific response to stress produces the general adaptation syndrome (GAS) Alarm phase: Adrenal glands activated Stage of resistance: Stage of readjustment Stage of exhaustion: Sickness and/or death if readjustment is not complete

12 Thyroid Hormones Thyroid gland is located just below the larynx Thyroid is the largest of the pure endocrine glands Follicular cells secrete thyroxine Parafollicular cells secrete calcitonin

13 Production of Thyroid Hormones Iodide (I - ) actively transported into the follicle and secreted into the colloid. Oxidized to iodine (I o ) Iodine attached to tyrosine within thyroglobulin chain Attachment of 1 iodine produces monoiodotyrosine (MIT) Attachment of 2 iodines produces diiodotyrosine (DIT) MIT and DIT or 2 DIT molecules coupled together. T 3 and T 4 produced TSH stimulates pinocytosis into the follicular cell hydrolyze T 3 and T 4 from thyroglobulin secrete the free hormones into the blood

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15 Actions of T 3 Stimulates protein synthesis Promotes maturation of nervous system Stimulates rate of cellular respiration by Production of uncoupling proteins Increase active transport by Na + /K + pumps Lower cellular [ATP] Increases metabolic heat and metabolic rate Stimulates consumption of glucose, fatty acids and other molecules

16 Diseases of Thyroid Iodine-deficiency goiter Abnormal growth of the thyroid gland In the absence of sufficient iodine, cannot produce adequate amounts of T 4 and T 3 Lack of negative feedback inhibition Stimulates TSH, which causes abnormal growth Adult myxedema: Accumulation of mucoproteins and fluid in subcutaneous tissue Symptoms: Decreased metabolic rate, weight gain, decreased ability to adapt to cold, lethargy

17 Grave s disease: Hyperthyroidism, Autoimmune disorder Exerts TSH-like effects on thyroid Not affected by negative feedback Cretinism: Hypothyroid from end of 1 st trimester to 6 months postnatally Severe mental retardation

18 Parathyroid Glands Embedded in the lateral lobes of the thyroid gland Parathyroid hormone (PTH): Only hormone secreted by the parathyroid glands Single most important hormone in the control of blood [Ca 2+ ] Stimulated by decreased blood [Ca 2+ ] Promotes rise in blood [Ca 2+ ] by acting on bones, kidney and intestines

19 Pancreatic Islets (Islets of Langerhans) Alpha cells secrete glucagon Glucagon secretion is stimulated by a fall in the plasma glucose concentration and insulin secretion that occurs when a person is fasting Stimulates glycogenolysis and lipolysis Stimulates conversion of fatty acids to ketones Beta cells secrete insulin Stimulus is an increase in blood [glucose] Promotes entry of glucose into cells Converts glucose to glycogen and fat Aids entry of amino acids into cells

20 Pineal Gland Secretes melatonin Production stimulated by the suprachiasmatic nucleus in hypothalamus SCN is primary center for circadian rhythms Light/dark changes required to synchronize Melatonin secretion increases with darkness and peaks in middle of night May inhibit GnRH May function in the onset of puberty (controversial)

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22 Gonads and Placenta Gonads (testes and ovaries) secrete sex hormones Testosterone Estradiol 17-β After menopause, produces estrone Progesterone Placenta secretes large amounts of estriol, progesterone, hcg, hcs

23 Autocrine and Paracrine Regulation Autocrine: Produced and act within the same tissue of an organ All autocrine regulators control gene expression in target cells Paracrine: Produced within one tissue and regulate a different tissue of the same organ Cytokines (lymphokines) regulate different cells (interleukins) Growth factors promote growth and cell division in any organ Neutrophins guide regenerating peripheral neurons

24 Prostaglandins Most diverse group of autocrine regulators Produced in almost every organ Wide variety of functions Different prostaglandins may exert antagonistic effects in some tissues Immune system: Promote inflammatory process Reproductive system: Play role in ovulation Digestive system: Inhibit gastric secretion Respiratory system: May bronchoconstrict or bronchodilate Circulatory system: Vasoconstrictors or vasodilators Urinary system: Vasodilation

25 Inhibitors of prostaglandin synthesis Non-steroidal anti-inflammatory drugs (NSAIDS) Aspirin, indomethacin, ibuprofen: inhibit COX1 Celecoxib and rofecoxib: inhibit COX2