This document discusses the physiology of the breast. It describes how estrogen and progesterone affect breast growth and development. During pregnancy, the breasts enlarge significantly as the ducts and lobules grow and branch in preparation for lactation. By the second trimester, the breasts begin to produce colostrum. After birth, prolactin levels rise dramatically to promote milk secretion from the acini. Oxytocin released during suckling causes the myoepithelial cells to contract and expel milk from the alveoli into the ducts. During menopause, the lobules recede leaving mostly ducts, adipose, and fibrous tissue behind.

1. Physiology
of the breast

2. Tanner Staging

3. Effect of estrogen and progesterone on
breast
Estrogen
Progesteron
1. Growth of mammary
glands
2. Deposition of fat in the
breast
1. Additional growth of
lobules
2. Budding of alveoli
3. Secretory changes just like
in the endometrium

4. Cyclical changes of breasts during
menstrual cycle

5. Changes during pregnancy
• Ducts grow and branch;
• breasts enlarge to twice their normal weight
• increase in mammary blood flow leads to
vascular engorgement
• The areola of the nipples pigmentation and
diameter increases.
• The Montgomery's glands enlarge and tend to
protrude.
• By the 16th week (2nd trimester) the breasts
begin to produce colostrum

6. Changes during lactation

7. Prolactin
• The hormone prolactin promote milk
secretion
• During pregnancy the hormone concentration
in blood rises steadily from the 5th week of
pregnancy until birth of the baby
• At full term prolactin level rises to 10 to 20
times the normal non pregnant level.
• Acini become dilated and engorged with
colostrum and then milk.

8. Prolactin
After birth:

9. Oxytocin
• Sensory impulses via somatic nerves from the nipples
to hypothalamus and posterior pituitary- release of
oxytocin and prolactin
• The oxytocin causes myoepithelial cells to contract
• milk is expressed from the alveoli into the ducts at a
pressure of +10 to 20 mm Hg.
 Suckling on one breast causes milk flow not only in
that breast but also in the opposite breast.
 Fondling of the baby by the mother or hearing the
baby crying often gives enough of an emotional signal
to the hypothalamus to cause milk ejection.

10. Menopause
• Lobules begin to recede
• Mostly ducts adipose tissue and fibrous tissue
• Histologically postmenopausal and prepubertal
breasts are very similar.
• Hormone therapy may delay postmenopausal
changes in the breast and mimic a more active
physiologic or premenopausal state (ie cyclic
tenderness due to increased nodularity etc).