breast physiology

Question 1

define galactorrhea, macromastia, hypomastia, and mastitis

Answer 1

Galactorrhea – production of milk at times other than lactation. Due to elevated prolactin levels. Macromastia – excessive breast enlargment. Hypomastia – complete absence of breast tissue and nipples or absent or delayed sexual maturation. Mastitis – infection of milk ducts often linked to duct blockage. Associaed with painful lumps in the breast. Mastitis is distinguished from blocked ducts by the presence of chills, fever and malaise.

Question 2

Breast anatomy

Answer 2

Lobes – Glandular units of the breast. Composed of 4-14 lobules (aka lobuloalveolar units or terminal ductal lobular units) containing alveoli (milk producing units) that are connected by a ductal network that empties into single milk duct. Milk ducts from multiple lobes feed into the nipple

Question 3

structure of breast alveoli

Answer 3

single layer of specialized secretory epithelial cells surrounding a lumen. The secretory epithelial cells are surrounded by a mesh-like network of myoepithelial cells.

Question 4

production of milk

Answer 4

requires the coordinated actions of both the secretory epithelial and myoepithelial cells. The secretory cells produce and secrete milk, the myoepithelial cells contract to push milk through the ductal system to the nipple. Coordination of these processes is hormonally mediated

Question 5

Breast Glandular Expansion and Maturation

Answer 5

lactating: 62% glandular, 7% intraglandular fat, 24% subcut fat, 7% retro fat. Non-lactating: 20% glandular, 49% intraglandular fat, 24% subcutaneous fat, 7% retro fat

Question 6

embryonic development of breasts

Answer 6

Mammary glands are derived embryologically from ectodermal invaginations into mesenchyme. The sites of these invaginations ultimately become nipples. Epidermal cells become epithelial cells, and dermal mesenchymal cells become mammary mesenchymal cells.

Question 7

Hormonal Control of Nipple Morphogenesis

Answer 7

PTHrP secreted by epithelial cells induces differentiation of dermal mesenchyme to mammary mesenchyme. Mammary mesenchyme maintains mammary fate of epithelial cells, triggers morphogenesis of mammary gland and stimulates nipple formation.

Question 8

Cause of amastitia

Answer 8

Blomstrands chondroplasia (amastia)
aka mammary gland doesn’t form.  In the absence of PTHrP signaling dermal mesenchyme fails to differentiate to mammary mesenchyme and epithelial cells revert to epidermal fate Blomstrands chondroplasia (amastia)
aka mammary gland doesn’t form.  In the absence of PTHrP signaling dermal mesenchyme fails to differentiate to mammary mesenchyme and epithelial cells revert to epidermal fate

Question 9

Neonatal Breast Morphology

Answer 9

Maternal hormones can influence. 1. Elevated prolactin and decreased progesterone at parturition can induce temporary milk secretion in both male and female neonates (witches milk). 2. Simple ductal network ending with TEB structures.. 3. Temporary, GnRH driven, spike in progesteron during infancy stimulates branching and lobule formation.

Question 10

macroscopic breast development at puberty

Answer 10

driven by estrogen. growth and branching of the ductal network in the breast. The increase in breast size however is due to increased fat accumulation in breast adipose cells.

Question 11

Breast Glandular Expansion and Maturation

Answer 11

Occurs during puberty. Increased estrogen levels during puberty in combination with GH induce elongation and branching of the ductal network by increasing IGF-1 production by the stroma. The secretion of progesterone during the luteal phase of the menstrual cycle brings about side branching and lobulo-alveolar (tdlu) development. TDLU regress at the end of luteal phase unless pregnancy occurs.

Question 12

Types of lactogenesis

Answer 12

Lactogenesis-I: Initiation of milk protein expression and development of secretory capacity. Lactogenesis-II: Copious milk production

Question 13

Breast changes during pregnancy

Answer 13

Increased lobules, differentiation of alveolar cells (progesterone and prolactin dependent), inhibition of milk secretion. Influenced by estrogen, progesterone, placental lactogen, prolactin

Question 14

Milk protein expression during pregnancy

Answer 14

Milk protein expression is initiated during pregnancy by prolactin or placental lactogen but milk secretion is held in check by high progesterone levels

Question 15

What causes initiation/ maintenance of lactation

Answer 15

Milk secretion is initiated by the fall in progesterone at parturition – removal of the placenta. Elevated prolactin levels maintain synthesis and secretion of milk

Question 16

Milk secretion vs ejection

Answer 16

Secretion: prolactin, milk removal. Ejection: oxytocin, suckling

Question 17

suckling and lactation

Answer 17

Dopamine released by neurons from the arcuate nucleus tonically inhibits prolactin release from anterior pituitary. Suckling inhibits dopamine release > prolactin released from anterior pituitary > milk secretion. PRL is released in pulses and the pulse size/frequency is regulated by suckling

Question 18

How does oxytocin stimulate milk ejection

Answer 18

Stimulates contraction of myoepithelial cells. Oxytocin release from posterior pituitary is stimulated by suckling

Question 19

Factors affecting lactation

Answer 19

anxiety/stress, delayed lactation initiation, pituitary disorders or damage, excessive weight

Question 20

sequence of events in lactogenesis

Answer 20

milk volume increases > tight junctions close > transcytosis of sIgA > coordinated increase in secretory activity (increased minerals, nutrients, etc)

Question 21

How is glandular integrity/ lactation maintained

Answer 21

removal of milk