Anatomy & Physiology

Anatomy & Physiology Study Guide • Four parathyroid glands are emplanted in the posterior surface of the thyroid gland. • Parathyroid chief cells produce parathyroid hormone (PTH) in response to lower-than- normal concentrations of Ca2+. • The parathyroid glands, aided by calcitriol, are the primary regulators of blood calcium levels in healthy adults. The suprarenal glands, consisting of a cortex and medulla, cap the superior borders of the kidneys and secrete several hormones: • One suprarenal (adrenal) gland lies along the superior border of each kidney. The gland is subdivided into the superficial suprarenal cortex and the inner suprarenal medulla. • The suprarenal cortex manufactures steroid hormones, called adrenocortical steroids (corticosteroids). The cortex can be subdivided into three sections: the zona glomerulosa, which releases mineralocorticoids, principally aldosterone; the zona fasciculata, which produces glucocorticoids, notably cortisol and corticosterone; and the zona reticularis, which produces androgens under ACTH stimulation. • The suprarenal medulla produces epinephrine (75–80 percent of medullary secretion) and norepinephrine (20–25 percent). The pineal gland, attached to the third ventricle, secretes melatonin: • The pineal gland contains pinealocytes, which synthesize melatonin. Suggested functions include inhibiting reproductive functions, protecting against damage by free radicals, and setting circadian rhythms. The pancreas, located within the abdominopelvic cavity, is both an exocrine organ and endocrine gland: • The pancreas consists of both exocrine and endocrine cells. Cells of the endocrine pancreas construct clusters called pancreatic islets (islets of Langerhans). These islets consist of alpha cells, which release the hormone glucagon; beta cells, which secrete insulin; delta cells, which release somatostatin (GH–IH); and F cells, which secrete pancreatic polypeptide. • Insulin decreases blood glucose by increasing the rate of glucose uptake and utilization; glucagon raises blood glucose by increasing the rates of glycogen breakdown and glucose production in the liver. Many organs have secondary endocrine functions: • The intestines produce hormones important to the coordination of digestive activities. • Endocrine cells in the kidneys produce the hormones calcitriol and erythropoietin and the enzyme rennin. • Calcitriol stimulates calcium and phosphate ion absorption along the digestive tract. • Erythropoietin (EPO) stimulates red blood cell creation by the bone marrow. • Renin converts angiotensinogen to angiotensin I. In the capillaries of the lungs, the latter compound is converted to angiotensin II, a hormone that stimulates the suprarenal production of aldosterone, stimulates the pituitary release of ADH, promotes thirst, and increases blood pressure. Achieve Page 219 of 368 ©2018