Porth's Essentials of Pathophysiology, 4e

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Endocrine System

U N I T 9

Treatment of hypopituitarism includes treating any identified underlying cause. Hormone deficiencies require replacement therapy with appropriate hormones. Cortisol replacement is started when ACTH deficiency is present, thyroid replacement when TSH deficiency is detected, and sex hormone replacement when LH and FSH are deficient. Growth hormone replacement is indi- cated for pediatric GH deficiency and is being increas- ingly used to treat GH deficiency in adults. 2,7,8

excessive levels inhibit growth, apparently because of their antagonistic effect on GH secretion.

Growth Hormone Growth hormone, also called somatotropin , is a 191-amino-acid polypeptide hormone synthesized and secreted by special cells in the anterior pituitary called somatotropes. 2 For many years, it was thought that GH was produced primarily during periods of growth. However, this has proved to be incorrect because the rate of GH production in adults is almost as great as in children. Growth hormone is necessary for growth and contrib- utes to the regulation of metabolic functions (Fig. 32-1). All aspects of cartilage growth are stimulated by GH; one of the most striking effects of GH is on linear bone growth, resulting from its action on the epiphyseal growth plates of long bones. The width of bone also increases because of enhanced periosteal growth. Visceral and endocrine organs, skeletal and cardiac muscle, skin, and connec- tive tissue all undergo increased growth in response to GH. In many instances, the increased growth of visceral and endocrine organs is accompanied by enhanced func- tional capacity. For example, increased growth of cardiac muscle is accompanied by an increase in cardiac output.

Growth and Growth Hormone Disorders

Several hormones are essential for normal body growth and maturation, including growth hormone, insulin, thyroid hormone, and androgens. 9 Insulin, for example, plays an essential role in growth processes, in addi- tion to its actions on carbohydrate and fat metabolism. Children with diabetes, particularly those with poor control, often fail to grow normally even though GH levels are normal. When levels of thyroid hormone are lower than normal, bone growth and epiphyseal closure are delayed. Androgens such as testosterone and dihy- drotestosterone exert anabolic growth effects through their actions on protein synthesis. Glucocorticoids at

Hypothalamus

Anterior pituitary

Growth-promoting actions

Anti-insulin effects

Growth hormone

Liver

IGF-1

Adipose tissue

Carbohydrate metabolism

Increased protein synthesis

Body organs

Bone and cartilage

Decreased glucose use

Increased lipolysis Increased FFA use

Muscle

Increased size and function

Increased linear growth

Increased lean muscle mass

Increased blood glucose

Decrease in adiposity

FIGURE 32-1. Growth-promoting and anti-insulin effects of growth hormone. FFA, free fatty acids; IGF-1, insulin-like growth factor-1.