Biology of Disease

THE PITUITARY GLAND

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Figure 7.10 Mechanism of action of a hormone

that binds to an intracellular receptor. See text for

details.

Transcription

Target cell

Nucleus

DNA

CRP-H

CRP-H

CRP

CRP

H

H

CP

CP-H

mRNA

mRNA

New protein synthesis

Hormone response

CP carrier protein

H hormone

CRP cytoplasmic receptor protein

H

7.5 The Pituitary Gland

The pituitary gland is often referred to as ‘the master gland’ given that its
secretions regulate the activities of many of the other hormone-producing
glands. Despite its crucial role, it weighs only about 0.5 g. The pituitary is found
in a bony cavity at the base of the skull and is connected to the hypothalamus
by a pituitary stalk composed of blood vessels and nerve fibers. It is composed
of two lobes, an anterior pituitary or adenohypophysis and a posterior pituitary
or neurohypophysis (Figure 7.12).

The anterior pituitary secretes a number of hormones (Figure 7.13) that are
regulated by the release of peptides from the hypothalamus with stimulatory or
inhibitory effects on the anterior pituitary. The principal peptides released by
the hypothalamus reach the anterior pituitary by a portal blood circulation.
These peptides include thyrotrophin releasing hormone (TRH), growth
hormone releasing hormone (GHRH), gonadotrophin releasing hormone
(GnRH), corticotrophin releasing hormone (CRH) and dopamine. With
the exception of dopamine, all are stimulatory, controlling the release
of thyroid stimulating hormone (TSH), growth hormone (GH), follicle
stimulating hormone (FSH) together with luteinizing hormone (LH) and
adrenocorticotrophic hormone (ACTH) respectively. Thyroid stimulating
hormone targets the thyroid gland causing it to release thyroid hormones.