Porth's Essentials of Pathophysiology, 4e

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Mechanisms of Endocrine Control

C h a p t e r 3 1

CNS input

CNS

Hypothalamus

Releasing hormone

Hypothalamus

Posterior pituitary (oxytocin and ADH)

Anterior pituitary

Anterior pituitary

Tropic hormone

Target gland

Growth hormone

Hormone

Target cell

TSH

Physiologic effect

ACTH

FSH LH

FIGURE 31-5. Hypothalamic-pituitary control of hormone levels.The dashed line represents feedback control. CNS, central nervous system.

DiagnosticTests Several techniques are available for assessing endocrine function and hormone levels. One technique measures the effect of a hormone on body function. Measurement of blood glucose, for example, is an indirect method of assessing insulin levels. However, insulin action (i.e., insu- lin activity) is also important in relation to glucose levels as hyperglycemia could occur if marked insulin resistance is present, despite the presence of a compensatory increase in insulin levels (i.e., hyperinsulinemia). This situation is com- mon in type 2 diabetes (see Chapter 33). Thus, the most common method is to measure hormone levels directly. BloodTests Hormones circulating in the plasma were first detected by bioassays using an intact animal or a portion of tissue from the animal. However, most bioassays lack the precision, sensitivity, and specificity to measure low concentrations of hormones in plasma, and they are inconvenient to perform. Blood tests provide information about hormone lev- els at a specific time. For example, blood insulin levels can be measured along with blood glucose after admin- istration of a challenge dose of glucose to measure the time course of change in blood insulin levels.

Thyroid (thyroid hormones)

Adrenal gland (glucocorticoids)

Ovaries (estrogen and progesterone)

Testes (testosterone)

FIGURE 31-6. Control of hormone production by the hypothalamic-pituitary–target cell feedback mechanism. Hormone levels from the target glands regulate the release of hormones from the anterior pituitary through a negative feedback system.The dashed line represents feedback control. ADH, antidiuretic hormone; ACTH, adrenocorticotropic hormone; CNS, central nervous system; FSH, follicle stimulating hormone; LH, luteinizing hormone;TSH, thyroid stimulating hormone.