Lactation

Question 1

What changes must the mammary gland undergo?

Answer 1

Gland maturation

Alveologenesis

Question 2

What causes the duct system to grow in early pregnancy?

Answer 2

GH
Estradiol
Progesterone

Question 3

What happens in mid-pregnancy?

Answer 3

Alveoli grow to form a lumen (estradiol, progesterone, hPL, GH)

Question 4

What inhibits milk production until birth?

Answer 4

Estrogen and proesterone

Question 5

Describe structure

Answer 5

12-20 galactopoietic (milk-producing) lobules which each empty into a common lactiferous duct which opens onto the nipple

Question 6

What does progesterone do?

Answer 6

Responsible for extensive side-branching

Promotes differentiation of alveoli (in combination with prolactin)

Question 7

Role of prolactin

Answer 7

Major regulator of lactational competence during pregnancy
Functions both indirectly (through regulation of ovarian progesterone production) and directly (via effects on mammary epithelial cells)
Produced by the pituitary, as well as other sites, such as the mammary epithelium

Question 8

What does the maintenance of lactation depend on?

Answer 8

Suckling stimulus

Question 9

Describe the suckling stimulus

Answer 9

The stimulation of nipple mechanoreceptors, which signal via afferents to oxytocin and dopamine neurones in the hypothalamus; this decreases dopamine secretion from hypothalamus, and increases oxytocin secretion from the posterior pituitary
The decrease in dopamine leads to increased release of maternal prolactin from the anterior pituitary, which stimulates synthesis and secretion of milk constituents; this dilates the alveoli
The oxytocin stimulates the ejection of milk by contraction of the myoepithelial cells which surround the alveoli (milk ejection reflex)

Question 10

What can be used to inhibit lacctation?

Answer 10

Prolactin release is controlled negatively by dopamine, and so dopamine agonists can be used to inhibit lactation (lactation also requires that progesterone and oestrogen levels fall)

Question 11

Milk composition

Answer 11

87.6% water, 3.8% lipid and 1.2% protein

Question 12

What are the secreted proteins?

Answer 12

Lactalbumin and casein are produced as classical regulated secretory proteins; immunoglobulins (IgA, IgM) are also secreted into the milk via transcytosis from the mother, and lactose and salts are also secreted in vesicles

Question 13

What is the first milk formed in the breast known as?

Answer 13

Colostrum

Question 14

Describe colostrum

Answer 14

This is a thin, yellowing, milk-like fluid secreted for the first few days
It is rich in protein, carbohydrate, but low in electrolytes and fat (the neonatal gut does not tolerate the high casein content of cow’s milk, well)
It also contains an abundance of IgA and IgM antibodies made by the mother, which readily pass across the neonatal gut epithelium – colostrum therefore protects the fetus against any local infections (passive immunity) while its own immune system develops
Colostrum production gradually gives way to that of milk

Question 15

What happens after weaning?

Answer 15

breast regresses

Question 16

Describe lactational amenorrhoea

Answer 16

During lactation, further pregnancy is inhibited (lactational amenorrhoea) – the daily suckling stimulus also alters the GnRH output from the hypothalamus, reducing its pulsatile release – in this way, lactation suppresses ovulation and so prevents a further pregnancy, which would create an excessive metabolic demand on the mother

Question 17

What other hormones are involved? What do they do?

Answer 17

In addition, parathyroid-related protein (PTH-rP) mobilises maternal calcium for the baby, and stimulates calcium uptake via 1,25-D3; calcitonin protects against excessive calcium loss