Essentials of Anatomy and Physiology

MAMMARY GLANDS

The mammary glandsare structurally related to the
skin but functionally related to the reproductive sys-
tem because they produce milk for the nourishment of
offspring. Enclosed within the breasts, the mammary
glands are anterior to the pectoralis major muscles;
their structure is shown in Fig. 20–8.
The glandular tissue is surrounded by adipose tis-
sue. The alveolar glandsproduce milk after preg-
nancy; the milk enters lactiferous ducts that converge
at the nipple. The skin around the nipple is a pig-
mented area called the areola.
The formation of milk is under hormonal control.
During pregnancy, high levels of estrogen and proges-
terone prepare the glands for milk production.
Prolactinfrom the anterior pituitary gland causes the

actual synthesis of milk after pregnancy. The sucking

of the infant on the nipple stimulates the hypothala-

mus to send nerve impulses to the posterior pituitary

gland, which secretes oxytocinto cause the release of

milk. The effects of these hormones on the mammary

glands are summarized in Table 20–2 (see also Box

20–6: Mammography).

THE MENSTRUAL CYCLE

The menstrual cycleincludes the activity of the hor-

mones of the ovaries and anterior pituitary gland and

the resultant changes in the ovaries (ovarian cycle) and

uterus (uterine cycle). These are all incorporated into

Fig. 20–9, which may look complicated at first, but

refer to it as you read the following.

Notice first the four hormones involved: FSHand

The Reproductive Systems 467

Mons pubis

Labium major

Labium minor

Vaginal opening Anus

Hymen

Urethral

opening

Clitoris

Figure 20–7. Female external genitals (vulva)
shown in inferior view of the perineum.
QUESTION:What is the function of the labia majora
and minora?

Skin

Adipose tissue

Areola

Nipple

Lactiferous duct

Lactiferous glands

Intercostal muscles

Pectoralis major muscle

Ribs

Figure 20–8. Mammary gland shown in a mid-
sagittal section.
QUESTION:Name the hormones that stimulate the
production of milk and release of milk.