Page 23 Complete Your CE Test Online - Click Here placental hormones during pregnancy and stimulation of the nipples during lactation[3] . The posterior pituitary accounts for about 25% of the gland and is responsible for the secretion of antidiuretic hormone (ADH) and oxytocin[1,2,3] . ● ● Antidiuretic hormone (ADH): ADH controls water loss by the kidneys. It facilitates water reabsorption in the distal convoluted tubules and collecting ducts of the kidneys. Controlled by negative feedback, ADH release is stimulated by dehydration and increased plasma osmolarity[3] . ● ● Oxytocin: Oxytocin targets the uterus and mammary glands, causing uterine contractions during childbirth and milk production for lactation. Secretion of this hormone is controlled by positive feedback[2,3] . Anatomy and physiology alert! The hormones of the posterior pituitary are produced by the hypothalamus and transported via nerves to the pituitary gland, where they are stored [1,2] . Nursing consideration: The pituitary gland is generally considered to be the body’s “master gland.” Since it produces hormones that control many of the functions of other endocrine glands it is essential that nurses are able to differentiate among the hormones it produces and their effects. Assessment of the endocrine system, in many ways, begins with assessment of pituitary functioning. Thyroid gland The thyroid gland is located in the neck immediately below the larynx and partially in front of the trachea. The two lateral lobes of the thyroid are found on either side of the trachea and are joined by a narrow bridge of tissue called the isthmus. This “joining” gives the gland its characteristic butterfly shape[1,2,3] . The thyroid hormones regulate the metabolism of the body and help maintain normal blood pressure, heart rate, digestion, muscle tone, and reproductive functions. The thyroid gland also contributes to bone growth and nervous system development in children[1,2] . The two thyroid lobes function as one unit to produce triiodothyronine (T3), thyroxine (T4), and calcitonin[2] . TSH, which is produced by the pituitary gland, triggers secretion of T3 and T4, which are collectively known as thyroid hormone[1,3] . Thyroid hormone is the major metabolic hormone of the body. It regulates metabolism by increasing the speed of cellular respiration. T3 and T4, referred to collectively as thyroid hormone[3] : ● ● Increase metabolic rate. ● ● Increase consumption of oxygen. ● ● Increase glucose absorption. ● ● Increase body temperature. ● ● Affect growth and development. ● ● Improve the effects of the sympathetic nervous system. Calcitonin is responsible for maintaining the calcium level of the blood. It accomplishes this by slowing the release of calcium from bone. Calcitonin secretion is controlled by the concentration of calcium in the fluid surrounding thyroid cells[1] . Parathyroid glands The parathyroid glands are the smallest endocrine glands and are embedded in the posterior surface of the thyroid glands[1,3] . These glands work together as one entity and produce parathyroid hormone (PTH)[1] . The primary function of PTH is to regulate calcium balance in the blood by adjusting the rate at which calcium and magnesium ions are lost in the urine. PTH release is stimulated by decreased levels of calcium in the blood[3] . PTH increases plasma calcium levels by[3] : ● ● Stimulating the formation and action of osteoclasts. Osteoclasts cause the breakdown of bone tissue, which releases calcium from the bones into the blood. ● ● Triggering kidney tubules to increase calcium reabsorption. ● ● Facilitating increased calcium absorption from the gastrointestinal (GI) tract. Anatomy and physiology alert! PTH also increases the transport of phosphate ions from the blood to urine for excretion from the body [1] . Adrenal glands The two adrenal glands each lie embedded in adipose tissue on the top of each kidney[1, 3] . They are triangular in shape and consist of two distinct structures: the outer adrenal cortex and the inner adrenal medullar. These structures function as separate endocrine glands[1,3] . The majority of the adrenal glands is made up of the adrenal cortex, which has three zones[1] : ● ● Zona glomerulosa: This is the outermost zone of the adrenal cortex. It produces mineralocorticoids (aldosterone and deoxycorticosterone), which help maintain fluid balance by increasing the reabsorption of sodium[1,3] . ● ● Zona fasciculata: This middle zone is the largest of the three zones. It produces glucocorticoids including cortisol (hydrocortisone), cortisone, and corticosterone. These glucocorticoids help regulate metabolism and assist in the body’s efforts to resist stress. This zone also produces small amounts of androgen and estrogen[1,3] . ● ● Zona reticularis: This is the innermost zone. It produces some sex hormones[1] . The adrenal medulla is the inner layer of the adrenal gland and functions as part of the sympathetic nervous system. The adrenal medulla produces two catecholamines: epinephrine and norepinephrine [1, 3] . These hormones increase the release of ACTH and TSH[3] . The pancreas The pancreas is a triangular shaped organ located in the abdomen along the curve of the duodenum. It extends from behind the stomach to the spleen[1,3] . The pancreas performs both endocrine and exocrine functions. Its endocrine function is to secrete hormones. Its exocrine function is to secrete digestive enzymes. The pancreas is composed primarily of acinar cells, which regulate pancreatic exocrine function[1,2,3] . The islet cells or islets of Langerhans are the pancreatic endocrine cells. They occur in clusters of cells scattered among acinar cells. The islets contain alpha, beta, and delta cells that produce the following hormones[1,3] : ● ● Glucagon: Glucagon is produced by the alpha cells. Glucagon is a hormone that stimulates glycogenolysis, which raises the blood glucose level by causing the breakdown of glycogen to glucose. Glucagon helps maintain blood glucose levels during fasting or starvation[1,3] . ● ● Insulin: Insulin is secreted by beta cells that are innervated by adrenergic fibers. Insulin lowers the blood glucose level by stimulating movement of blood glucose across cells, converting glucose to glycogen[1,3] . ● ● Somatostatin: Somatostatin is secreted by delta cells and inhibits the release of GH, corticotrophin, and certain other hormones[1] . Nursing consideration: Nurses are aware that diabetes mellitus is a significant problem in the United States. Therefore, knowledge of the pancreas and how it functions is critical to the nurse’s ability to provide appropriate nursing care to those diagnosed with diabetes.