Overview of the Endocrine System
The pituitary gland is divided into two main parts, the anterior and posterior lobes. The anterior pituitary consists of endocrine cells that synthesize and secrete hormones directly into the blood. The posterior pituitary is an extension of the hypothalamus. It stores and secretes two hormones that are made by a set of neurosecretory cells in the hypothalamus.
The posterior pituitary releases the hormones oxytocin—which acts on muscles of the uterus—and antidiuretic hormone (ADH), which acts on the kidneys. Oxytocin induces contraction of the uterine muscles during childbirth and causes mammary glands to eject milk during nursing. ADH acts on the kidneys, increasing water retention and thus decreasing urine volume.
The anterior pituitary produces six different hormones. Growth hormone affects a wide variety of tissues. The correct level of growth hormone production is essential, as too little or too much can have serious detrimental effects. Prolactin stimulates mammary gland growth and milk synthesis. Follicle stimulating hormone (FSH) stimulates production of ova and sperm, and luteinizing hormone (LH) stimulates the ovaries and testes. LH is needed for ovulation and the formation of a corpus luteum in the female menstrual cycle. LH also stimulates the testes to produce testosterone. FSH and LH are referred to as gonadotropins because they stimulate the activities of the gonads. Thyroid-stimulating hormone, stimulates the thyroid gland to produce thyroxine. Adenocorticotropic hormone influences the adrenal cortex to produce and secrete steroid hormones.
- Campbell, N.A., and Reece, J.B. (2002). Biology, 6th Edition. San Francisco, CA: Pearson Benjamin Cummings.
- Clark, Joe O.E. (1999). A Visual Guide to the Human Body. London: Barnes and Noble, Inc.
- SEER Training Modules: Pituitary and Pineal Glands. Illustration courtesy of the National Cancer Institute, NIH.
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