Introduction to the Hypothalamo- Pituitary-adrenal (hpa) Axis

OBJECTIVES: • Identify appropriate hypothalamic factors that control the secretion of each of the anterior pituitary hormones, and describe their route of transport from the hypothalamus to the anterior pituitary. • Contrast the anterior and posterior pituitary lobes with respect to cell types, vascular supply, development, and innervation (hypothalamic). • Diagram the short-loop and long-loop negative feedback control of anterior pituitary hormone secretion. Predict the changes in secretory rates of hypothalamic, anterior pituitary, and target gland hormones caused by over-secretion or under-secretion of any of these hormones or receptor deficit for any of these hormones. • Describe the biosynthesis, structure, and actions of ACTH. • Explain the importance of pulsatile and diurnal secretion. • Identify the functional zones in the adrenal gland (one medullary and three cortical zones) and the principal hormones secreted from each zone. • Describe the biosynthesis of the adrenal steroid hormones (glucocorticoids, mineralocorticoids, and androgens) and the key structural features that distinguish each class. • Predict the effects of inherited defects in 17α-, 21ß-, and 11ß-hydroxylase on glucocorticoid and mineralocorticoid production and activity. • Understand the cellular mechanism of action of adrenal cortical hormones. • Identify the major actions of glucocorticoids on metabolism and the target organs on which they are produced. • Describe the actions of glucocorticoid hormones in injury and stress. • Describe the components of the neuroendocrine axis that control glucocorticoid secretion and describe how factors in the internal and external environment influence the neuroendocrine axis. • Identify the chemical nature of catecholamines, their biosynthesis, half-life in blood and how they are degraded and removed from the body. Identify how the structure of norepinephrine differs from epinephrine. • Describe the biological consequences of activation of the adrenal medulla and identify the target organs or tissues for catecholamines along with the receptor subtype that mediates the response. Understand the mechanism by which epinephrine and norepinephrine can produce different effects in the same tissues. • Name the key stimuli causing catecholamine secretion. List the factors that can modulate a) the secretory response and b) the responses of target tissues. • Describe the interactions of adrenal medullary and cortical hormones in response to stress. KEY WORDS: adrenocorticotropin (ACTH) adrenal gland adrenocortical hormone aldosterone anterior pituitary cortisol corticotropin releasing hormone (CRH) follicle stimulating hormone (FH) glucocorticoid gonadotropin releasing hormone (GnRH) growth hormone (GH) growth hormone releasing hormone (GHRH) hypothalamo-pituitary axis hypothalamo-pituitary-adrenal axis luteinizing hormone (LH) mineralocorticoid pituitary …