Review of Medical Physiology - William F. Ganong 2002

Endocrine System, Metabolism, and Reproduction
Pituitary Gland
Introduction

The anterior, intermediate, and posterior lobes of the Pituitary Gland can be viewed as a collection of distinct endocrine Organs that, in some animal species, produce 14 or more hormonally active substances. In humans, the intermediate lobe is vestigial. Six Hormones secreted by the anterior pituitary have been identified: thyroid-stimulating hormone (TSH, thyrotropin), adrenocorticotropic hormone (ACTH), luteinizing hormone (LH), follicle-stimulating hormone (FSH), prolactin, and Growth Hormone (Table 22-1). ACTH, prolactin, and growth hormone are simple Polypeptides or Proteins, whereas TSH, LH, and FSH are Glycoproteins. Prolactin acts on the mammary gland. These five hormones are tropic to a certain degree, meaning they stimulate the release of hormonally active substances by other Endocrine glands or, as in the case of growth factor, by the Liver or other Tissues (see below). In addition, the anterior pituitary secretes ß-lipotropin (ß-LPH). This single-chain polypeptide consists of 91 amino acid residues and, although its precise physiological role remains unknown, it contains Amino acid sequences found within endorphins and enkephalins—Peptides that bind to opiate receptors (see Chapter 4). The anterior and intermediate lobes also contain other hormonally active derivatives of proopiomelanocortin (see below). Hormones tropic to specific endocrine glands are discussed in other chapters: TSH in Chapter 18; ACTH in Chapter 20; the gonadotropins FSH and LH, along with prolactin, in Chapter 23. The hormones released by the posterior pituitary in mammals (oxytocin and vasopressin), as well as the neural regulation of anterior and posterior pituitary secretion, are described in Chapter 14. Growth hormone, ß-lipotropin, and the melanotropic hormones (MSH) of the intermediate lobe—a-MSH and ß-MSH—are the focus of this chapter, along with a General Overview of the pituitary gland.

Class="center">Table 22-1. Mammalian Pituitary Hormones1

Name and Source

Principal Action

Anterior Lobe

Thyroid-stimulating hormone (TSH, thyrotropin)

Stimulates thyroid hormone secretion and Thyroid Gland growth

Adrenocorticotropic hormone (ACTH, corticotropin)

Stimulates the secretion and growth of the zona fasciculata and zona reticularis of the adrenal cortex

Growth hormone (GH, somatotropin)

Accelerates body growth; stimulates the release of Insulin-like growth factor 1 (IGF-1)

Follicle-stimulating hormone (FSH)

Stimulates ovarian follicle growth in females and Spermatogenesis in males

Luteinizing hormone (LH)

Stimulates ovulation and luteinization of ovarian follicles in females and testosterone secretion in males

Prolactin (PRL)

Stimulates milk secretion and maternal behavior

ß-Lipotropin (ß-LPH)

?

y-Melanocyte-stimulating hormone (y-MSH)

See Intermediate Lobe

Intermediate Lobe

a-, ß-, y-Melanocyte-stimulating hormones (a-, ß-, y-MSH; collectively known as melanotropin or intermedin)

Proliferation of melanophores in fish, amphibians, and reptiles; stimulates melanin synthesis by melanocytes in humans

y-Lipotropin (y-LPH), corticotropin-like intermediate lobe peptide (CLIP), other proopiomelanocortin fragments

?

Posterior Lobe

Vasopressin (antidiuretic hormone, ADH)

Promotes Water retention

Oxytocin

Triggers milk ejection and contraction of the pregnant Uterus

1 In addition, various gastrointestinal and other polypeptides have been detected in one or more lobes of the pituitary gland: cholecystokinin (CCK), gastrin, renin, angiotensin II, and Calcitonin Gene-related peptide (CGRP).



Last update: 10/08/2026

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