Hormones

The pituitary has long been called the master gland because of the vast extent of its activity. It lies deep in the brain just behind the nose. The pituitary is divided into anterior and posterior regions with the anterior portion comprising about 75% of the total gland. The posterior region secretes the peptide hormones vasopressin, also called anti-diuretic hormone (ADH), and oxytocin. Both are synthesized in the hypothalamus and moved to the posterior pituitary prior to secretion. ADH targets the collecting tubules of the kidneys, increasing their permeability to water. ADH causes the kidneys to retain water. Lack of ADH leads to a condition called diabetes insipidus characterized by excessive urination. Oxytocin targets the uterus and the mammary glands in the breasts. Oxytocin begins labor prior to birth and also functions in the ejection of milk. The drug, pitocin, is a synthetic form of oxytocin and is used medically to induce labor.

The anterior pituitary (AP) secretes a number of hormones. The cells of the AP are classified into five types based on what they secrete. These cells are somatotrophs, corticotrophins, thyrotrophs, lactotrophs, and gonadotrophs. Respectively, they secrete growth hormone (GH), ACTH, TSH, prolactin, and LH and FSH. Each of these hormones is either a polypeptide or a glycoprotein. GH controls cellular growth, protein synthesis, and elevation of blood glucose concentration. ACTH controls secretion of some hormones by the adrenal cortex (mainly cortisol). TSH controls thyroid hormone secretion in the thyroid. In males, prolactin enhances testosterone production; in females, it initiates and maintains LH to promote milk secretion from the mammary glands. In females, FSH initiates ova development and induces ovarian estrogen secretion. In males, FSH stimulates sperm production in the testes. LH stimulates ovulation and formation of the corpus luteum which produces progesterone. In males, LH stimulates interstitial cells to produce testosterone. Each AP hormone is secreted in response to a hypothalamic releasing hormone.