The anterior pituitary gland, or adenohypophysis, is one of the endocrine glands in the body; others include the Hypothalamus, Thyroid Gland, Adrenal Glands, Sex Glands, and the Thymus. The pituitary gland is an extension of the hypothalamus and is composed of a pea-sized mass of glandular tissue that is located between the optic nerves at the bottom of the brain (University of Pittsburgh, 2013). The pituitary gland originates from an invagination of the oral ectoderm which forms the Rathke's pouch. The pituitary gland is activated from the hypothalamus through releasing hormones that travel via the hypothalamic-hypophyseal portal system. The hypothalamus also generates inhibiting hormones that inhibit the release of hormones from the anterior pituitary gland. The anterior pituitary gland is divided into three regions: the pars tuberalis, the pars intermedia, and the pars distalis. The pars tuberalis is the tubular region of the gland which forms a shealth around the stalk. The pars intermedia is located in the middle portion of the gland, but is usually extremely small in humans, making it difficult to differentiate if from the rest of the gland. The pars distalis is the distal portion of the gland and makes up the majority of the anterior pituitary; and is where most of the hormones are produced (Martin, 2011). The hormones that are produced travel through the endocrine system via the blood, which is a slow process that has longer lasting effects when compared to the neurological system. The anterior pituitary produces a number of different hormones including: adrenocorticotrophic hormone, thyroid-stimulating hormone, luteinizing hormone, follicle-stimulating hormone, prolactin, and growth hormone. These hormones function in the regulation of bodily functions such as growth, sexual development, skin pigmentation, thyroid function, and adrenocortical function (Tamarkin, 2011) and are regulated through negative feedback.
Growth Hormone (GH) is a protein-based peptide hormone that stimulates growth, cell reproduction and regeneration in humans and other animals. GH is synthesized, stored, and secreted by somatotroph cells within the lateral wings of the anterior pituitary gland (Mayo et al., 2000). GH is secreted throughout the day in a pulsatile manner in 3 to 5 hour intervals. The balance of GH released is affected by many physiological stimulators and inhibitors (e.g. free fatty acids). GH has an anabolic effect, meaning it builds up, in the tissues within the body (News Medical, 2013). GH deficiencies, as well as, excess GH can lead to various diseases among both children and adults (Bowen, 2006).
Pro-opiomelanocortin (POMC) is a precursor for ACTH production, among various other polypeptides. Adrenocorticotrophic hormone (ACTH) is a polypeptide hormone released from corticotrophs in the anterior pituitary gland that regulates the activity of the cortex (outer region) of the adrenal glands. The action of ACTH is limited to the areas of the adrenal cortex in which glucocorticoid hormones are formed and the secretion of ACTH is regulated by corticotropin-releasing hormone (CRH). In healthy individuals ACTH is secreted in a circadian rhythm and variations in the secretion of ACTH are caused by variations in the secretion of CRH by the hypothalamus. Increased secretion and deficiencies of ACTH can lead to disease (Encyclopaedia Britannica, 2013).
Luteinizing hormone, or LH, is a gonadotropin that acts on the gonads to stimulate the secretion of sex hormones from the gonads. In the ovary, LH stimulates ovulation, induces the corpus luteum to secrete progesterone, and the maturation of follicles. In the testes, LH stimulates the secretion of progesterone (Bowen, 2004). An acute rise in the Luteinizing hormone is known as an “LH surge”, this sudden spike evokes the ovary to release an egg from its tissue and ovulation occurs. This LH surge also develops the corpus luteum (Devoto et al., 2009). An insufficient amount of LH leads to the function of the gonads to decrease which results in hypogonadism (A.D.A.M. Medical Encyclopedia, 2012). The absence of the normal restricting feedback mechanism can cause LH activity to increase to a point which over-stimulates the system and may be a sign of premature menopause, castration, swyer syndrome, testicular failure, or Polycystic ovary syndrome (MedlinePlus, 2013).