Week 2: breast and lactation

Question 1

Anatomical structure of breast

Answer 1

• 15-25 lobes.
• lobes separated by CT, including Cooper’s ligaments that connect with dermis
• Each lobe empties through a lactiferous duct –> lactiferous sinus –> opens independently on surface of nipple
• nipple: no sweat glands or hair. has duct openings and sebaceous glands
• areola: area around nipple. Has sweat, sebaceous and montgomery glands
• mammary gland: each lobe is one gland.
• alveoli: secretory units of mammary gland. lined by simple epithelium. Surrounded by myoepithelial cells.

Question 2

Mammary gland development

Answer 2

• fetus: beings to develop breast under maternal estrogen, progesterone, prolactin. Regresses after birth
• prepubertal: lactiferous ducts and sinuses. CT and small amount of fat.
• puberty: estrogens stimulate breast development. Accumulate adipose and CT. Ducts lengthen, branch, enlarge.
• resting adult: with regular menses, lobules develop but few alveoli present. most are blind ended interlobular ducts (terminal duct lobular units). like a tree in winter
• pregnancy: breasts grow, ducts expand, lobulo-aveolar growth.

Question 3

Hormones involved in preparation for lactation

Answer 3

• high levels of estrogen during pregnancy stimulate ductal growth. Estrogen stimulates pituitary to secrete more prolactin, and increases blood flow to breast. Estrogen also inhibits milk production.
• progesterone: promotes growth of alveoli in combo with estrogen
• prolactin: stimulated by estradiol. increases estrogen receptors in mammary glands

Question 4

Initiation of lactation

Answer 4

• colostrum: when estrogen and progesterone falls after birth, lactation begins. First milk is called colostrum-higher protein
• milk: 2-3 days after delivery. Milk produced by epithelium lining alveoli, accumulates in alveoli. With suckling, myoepithelial cells contract to move milk to nipple.

Question 5

Milk secretion

Answer 5

• 1. proteins: casein, transferrin, lactaalbumin. Lots of RER in cells. Released by merocrine secretion.
     
     2. Fat: released by apocrine secretion, surrounded by layer of membrane. prevents fat from aggregating.

Question 6

Hormones for lactation

Answer 6

• prolactin stimulates milk secretion. Under tonic inhibition by dopamine.increased suckling stimulates greater prolactin synthesis.
• oxytocin induces milk ejection. Stimulated by suckling. causes contraction of myoepithelial cells. oxytocin also stimulated by conditioned stimuli such as baby’s cry.
• Lactation governed by supply and demand.

Question 7

Lactational amenorrhea

Answer 7

• high levels of prolactin inhibit FSH and LH
• duration depends on frequency of nursing, amount of supplemental feeding, nutritional status of mother
• good health with good nutrition resumes cycles earlier