Hyperparathyroidism, an excess of parathyroid hormone in the blood, causes calcium levels in the blood to become elevated by the withdrawal of calcium from the bones, leaving the skeleton demineralized and subject to spontaneous fractures. The excess calcium may be deposited as stones in the kidneys.

ADRENAL GLANDS
The adrenal glands are located on the superior surface of each kidney, fitting like a cap (fig. 1-47). They consist of an outer portion, the cortex, and an inner portion, the medulla.

Adrenal Cortex
Specialized cells in the outer layer of the adrenal cortex produce three types of steroid hormones that are of vital importance.

MINERALOCORTICOIDS.-Mineralocor- ticoids are regulators of fluid and electrolyte balance. They are sometimes called salt and water hormones because they regulate the excretion and absorption of sodium, chlorine, potassium, and water.

GLUCOCORTICOIDS.-Glucocorticoids are essential to metabolism. They increase certain liver functions and have an anti-inflammatory effect. Clinically, they are used to suppress inflammatory reactions, to promote healing, and to treat rheumatoid arthritis.

ANDROGENS AND ESTROGENS.-The adrenal cortex also produces sex hormones, some with male characteristics (androgens), others with female characteristics (estrogens). These hormones appear in different concentrations in both men and women.

Adrenal Medulla
The adrenal medulla secretes epinephrine (adrenalin) in the presence of emotional crises, hypoglycemia (low blood sugar), or low blood pressure. Epinephrine causes powerful contractions of many arterioles (especially in the skin, mucous membranes, and kidneys), but it dilates other arterioles (such as those of the coronary system, skeletal muscles, and lungs). Heart rate, respiration rate and depth, blood pressure, blood sugar levels, and metabolism are all increased by epinephrine. It also stimulates the production of other adrenal cortical hormones.

Norepinephrine is also produced in the adrenal medulla. It is a chemical precursor to epinephrine. Its effects are similar to those of epinephrine, but its action differs. Despite these marked influences, the medullary tissue of the adrenal gland is not essential to life, because its various functions can be assumed by other regulatory mechanisms.

PANCREAS
The pancreas contains two types of secretory tissues. The first secretory tissue secretes digestive juice through a duct to the small intestine, while the other tissue releases hormones into body fluids. The endocrine portion of the pancreas consists of cells arranged in groups, called "islands (islets) of Langerhans." The islands (islets) of Langerhans contain three types of endocrine cells: alpha, beta, and delta. The alpha cells secrete the hormone glucagon. Glucagon causes a temporary rise in blood sugar levels. The beta cells secrete insulin, which is essential for carbohydrate metabolism. Insulin lowers blood sugar levels by increasing tissue utilization of glucose and stimulating the formation and storage of glycogen in the liver. Together, glucagon and insulin act to regulate sugar metabolism in the body. Delta cells produce the hormone somatostatin. Somatostatin helps regulate carbohydrates by inhibiting the secretion of glucagon.

When the islet cells are destroyed or stop functioning, the sugar absorbed from the intestine remains in the blood and excess sugar is excreted by the kidneys into the urine. This condition is called diabetes mellitus, or sugar diabetes. Insulin, a synthetic hormone, is given to patients having this disease as part of their ongoing treatment.