We have already seen how the nervous system

regulates body functions by means of nerve impulses
and integration of information by the spinal cord and
brain. The other regulating system of the body is
the endocrine system, which consists of endocrine

glands that secrete chemicals called hormones. These

glands, and the names of the hormones they secrete,

are shown in Fig. 10–1.

Endocrine glandsare ductless; that is, they do not

have ducts to take their secretions to specific sites.

224 The Endocrine System

Anterior: GH, TSH, ACTH

FSH, LH, Prolactin

Posterior: ADH, Oxytocin

Melatonin

PTH

Releasing hormones

for anterior pituitary

Thyroxine and T 3

Calcitonin

THYMUS GLAND

Immune hormones

Insulin

Glucagon

Cortex: Aldosterone

Cortisol

Sex hormones

Medulla: Epinephrine

Norepinephrine

Testosterone

Inhibin

THYROID GLAND

HYPOTHALAMUS

PITUITARY (HYPOPHYSIS) GLAND

PINEAL GLAND

PARATHYROID GLANDS

ADRENAL (SUPRARENAL) GLANDS

PANCREAS

OVARIES

Estrogen

Progesterone

Inhibin

TESTES

Figure 10–1. The endocrine system. Locations of many endocrine glands. Both male

and female gonads (testes and ovaries) are shown.

QUESTION:Why is the location of the thyroid gland not really important for its function?