Physiology Of The Anterior Pituitary Gland

There are six anterior pituitary hormones whose physiologic importance is clearly established. They include the hormones that govern the function of the thyroid and adrenal glands, the gonads, the mammary glands, and bodily growth. They have been called trophic or tropic from the Greek trophos, meaning "to nourish,'' or tropic, meaning "to turn toward.'' Both terms are generally accepted. We thus have, for example, thyro-trophin, or thyrotropin, which is also more accurately called thyroid-stimulating hormone (TSH). Because its effects are exerted throughout the body or soma in Greek, growth hormone (GH) has also been called the somato-tropic hormone (STH), or somatotropin. Table 1 lists the anterior pituitary hormones and their various synonyms. The various anterior pituitary cells are named for the hormones they contain. Thus we have thyrotropes, corticotropes, somatotropes, and lactotropes. Because a substantial number of growth hormone-producing cells also secrete prolactin, they are called somatomammo-tropes. Some evidence suggests that somatomammo-tropes are an intermediate stage in the interconversion of somatotropes and lactotropes. The two gonadotropins are found in a single cell type, called the gonadotrope.

All of the anterior pituitary hormones are proteins or glycoproteins. They are synthesized on ribosomes and translocated through various cellular compartments where they undergo post-translational processing. They are packaged in membrane-bound secretory granules and secreted by exocytosis. The pituitary gland stores relatively large amounts of hormone, sufficient to meet physiologic demands for many days. Over the course of many decades, these hormones were extracted, purified, and characterized. Now their three-dimensional configurations and the structure of their genes are known, and we can group the anterior pituitary hormones by families.

Glycoprotein Hormones

The glycoprotein hormone family includes TSH, whose only known physiologic role is to stimulate secretion of thyroid hormone, and the two gonadotro-pins, follicle-stimulating hormone (FSH) and luteinizing hormone (LH). Although named for their function in women, both gonadotropic hormones are crucial for the

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