Human Physiology, 14th edition (2016)

Reproduction 747

Lobe

Lobule

Rib

Adipose

tissue

Intercostal

muscles

Pectoralis

major

Pectoralis

minor

Deep fascia

(a)

Secondary

tubules

(b)

Lactiferous

duct

Ampulla

Mammary

duct

Ampulla

Nipple

Areola

Mammary duct

Secondary

tubules

Figure 20.51 The structure of

the breast and mammary glands.

( a ) A sagittal section and ( b ) an anterior

view partially sectioned.

Figure 20.52 The hormonal control of mammary
gland development and lactation. Notice that milk
production is prevented during pregnancy by estrogen inhibition
of prolactin secretion. This inhibition is accomplished by the
stimulation of PIH (prolactin-inhibiting hormone) secretion from
the hypothalamus.

Placenta

Estrogen

Progesterone

PIH

Prolactin

Mammary

glands

Permissive

effects

Pancreas

Adrenal cortex

Thyroid

Insulin

Cortisol

Thyroxine

Milk

production

Growth and development

of glands and ducts

Anterior pituitary

Hypothalamus

Figure 20.53 Milk production and the milk-ejection

reflex. Lactation occurs in two stages: milk production

(stimulated by prolactin) and milk ejection (stimulated by

oxytocin). The stimulus of sucking triggers a neuroendocrine

reflex that results in increased secretion of oxytocin and

prolactin.

Hypothalamus

Posterior

pituitary

Anterior

pituitary

Oxytocin Prolactin

Milk ejection Milk production

Sensory

input

Suckling

Stimulus Responses