HUMAN BIOLOGY

the hypothalamus and pituitary gland

n The hypothalamus and pituitary gland interact as a major

brain center that controls activities of other organs. Many

of these organs also have endocrine functions.

n    Links to Management of water balance by the kidneys 12.4,

Hypothalamus 13.7

Recall from Chapter 13 that the hypothalamus in the

forebrain monitors internal organs and states related to their

functioning, such as eating. It has secretory neurons that

extend down into the slender stalk to its base, then into the

lobed, pea-sized pituitary gland. These neurons deliver sev-

eral hormones to the pituitary. Two of them are later secreted

from the pituitary’s posterior lobe. Others have targets in the

anterior lobe of the pituitary, which makes and secretes its

own hormones. Most of these govern the activity of other

endocrine glands (Table 15.3).

the posterior pituitary lobe stores

and releases hormones made in

the hypothalamus

Axons of certain neurons in the hypothalamus extend

downward into the posterior lobe, ending next to a capil-

lary bed. The neurons make ADH (antidiuretic hormone)

and oxytocin, which are stored in the axon endings.

When one of these hormones is released, it diffuses

through tissue fluid and into capillaries, then travels the

bloodstream to its targets (Figure 15.3).

D The

hormone

molecules

move into

the general

circulation.

kidney

nephrons

mammary

glands

muscles in

uterus wall

ADH oxytocin

B The ADH or

oxytocin moves

downward inside

the axons of the

secretory neurons

and accumulates in

the axon endings.

A Secretory

neurons in the

hypothalamus

synthesize ADH

or oxytocin.

C Action potentials

trigger the release

of these hormones,

which enter blood

capillaries in the

posterior lobe of

the pituitary.

Figure 15.3 The posterior pituitary lobe stores and releases

hormones from the hypothalamus. The diagram also shows

main targets of the posterior lobe’s hormones. (© Cengage Learning)

15.3

Table 15.3 Primary Actions of Hormones Released from the Pituitary Gland

Pituitary Lobe Secretions abbreviation Main Targets Primary actions

Posterior Antidiuretic hormone ADH Kidneys Causes water conservation as required to maintain

Nervous tissue

(extension of

hypothalamus)

(vasopressin) extracellular fluid volume and solute concentrations

Oxytocin OT Mammary glands Causes milk to move into secretory ducts

Uterus Causes uterine contractions during childbirth

Anterior

Glandular

tissue, mostly

Adrenocorticotropic

hormone (corticotropin)

ACTH Adrenal glands Stimulates release of cortisol, an adrenal steroid hormone

Thyroid-stimulating

hormone (thyrotropin)

TSH Thyroid gland Stimulates release of thyroid hormones

Follicle-stimulating

hormone

FSH Ovaries, testes In females, stimulates estrogen secretion, egg maturation; in

males, helps stimulate sperm formation

Luteinizing hormone LH Ovaries, testes In females, stimulates progesterone secretion, ovulation, corpus

luteum formation; in males, stimulates testosterone secretion,

sperm release

Prolactin PRL Mammary glands Stimulates and sustains milk production

Growth hormone

(somatotropin)

GH Most cells Promotes growth in young; causes protein synthesis, cell

division; roles in glucose, protein metabolism in adults

290 Chapter 15

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