chapter  18
chapter eighteen
Pages 14

Glands of the endocrine system secrete various hormones that play a key role in maintaining normal homeostasis as well allowing the body to deal with periods of physiologic stress. Abnormalities of endocrine glands generally fall into one of the several categories:

1. Hypersecretion • Excess activity of a specific hormone or hormones • May be due to overproduction of a hormone due to abnormal

glandular function, glandular hypertrophy/hyperplasia or the presence of tumors that secrete hormone

2. Hyposecretion • Reduced activity of a specific hormone or hormones • May be due to atrophy of glandular tissue or damage from auto-

immune attack, infection or neoplasia 3. Altered responsiveness of a tissue to a specific hormone

• Tissue no longer responds to a specific hormone • May involve downregulation of receptors or altered receptor/sec-

ondary messenger function • Circulating levels of hormone may be normal or even elevated

(example: type II diabetes)

The

hypothalamus

is often referred to as the “master gland” of the body by virtue of its regulatory role over other glands. The hypothalamus lies at the base of the brain and receives neural input from a number of higher brain regions. These neural connections allow the hypothalamus to integrate many of the interactions between the autonomic nervous system and endocrine system. The hypothalamus is connected to the

pituitary

gland through a stalk called the

infundibulum

. Hypothalamic releasing hormones are carried by a blood vessel portal system found within the infundibulum to the anterior pituitary where they in turn stimulate the release of specific hormones from the anterior pituitary. Two hormones of the posterior pituitary (oxytocin and vasopressin) are actually synthesized in neuron clusters within the hypothalamus and transported down axons to the posterior pituitary where they are released. A summary of the hypothalamic and pituitary hormones is given in Tables 18.1 and 18.2.