The Breast And Lactation

Question 1

Describe the changes that happen to the breast during pregnancy?

Answer 1

• increased vascularisation (8 weeks) -> tends to result in a marbled appearance of the skin du to the marked dilation of the superficial veins
• thickening of nipple skin
• tenderness of breasts, especially nipple areas due to engorgement of blood (4 weeks)
• full development of lobules (hypertrophy)
• dilation of alveoli and ducts
• pigmentation of nipple and areola (12 weeks)
• secondary areola may appear in darker skinned women
• montgomery’s tubules become prominent
• small quantity of clear colostrum may be expressed in latter half of pregnancy (16 weeks secretion)

Question 2

Describe the process of mammogenesis

Answer 2

• begins in the embryonic stage by 4th week of gestation
• primitive milk streaks from axilla to groin, this continues to thicken with inward growth to chest wall
• 12 to 13 weeks specialised cells differentiate further into smooth muscle areola and nipple
• epithelial cells develop into mammary buds, develop into a treelike pattern and proliferate to become alveoli
• placental sex hormones enter fetal circulation which stimulates formation of canals which continues until the fetus is 32 weeks
• from then lobular alveolar structures containing colostrum develop
  
  • > fetal mammary glands increase 4 times in mass
  • > nipple and areola develop further and pigment
• after birth neonates mammary tissue may secrete colostral milk

Question 3

Describe the structure of the breast

Answer 3

• extends from 2nd-6th rib tail of breast into axilla
• glandular cells
• ducts
• adipose tissue
• connective tissue
• divided into lobes (15-20) by fibrous septae run from behind nipple to pectoral muscle
  
  • > connections between lobes present
• attaching deep layer of subcutaneous tissue to skin are the suspensor ligaments or coopers ligament

Question 4

Describe the structure of the nipple

Answer 4

• the nipple is at the centre, ducts open into the nipple but approx 9 open onto surface
• areola surrounds nipple and both contain erectile tissue
• within areolar are montgomerys tubercles which consist of milk glands and sebaceous glands (together known as areolar glands)
• glandular tissue is arranged in a ductal alveolar system (4- 18 per breast)
• grouped in grapelike lobules around branching system of ducts which join to form main lactiferous duct leading to nipple
• lactiferous ducts dilate into the ampulla

Question 5

Describe the breast fatty tissue

Answer 5

• the external shape or size of the breast is not predictive of its lactation potential
• the ratio of glandular tissue to fat tissue rises to 2:1 in the lactating breast compared to a 1:1 ratio in non lactating women
• 65% of the glandular tissue is located within 30mm from the base of the nipple
• between 4 and 18 milk ducts are exiting the nipple
• the network of milk ducts is complex not homogenous, it is not always arranged symmetrically nor in a radial pattern
• the milk ducts near the nipple do not act as reservoirs for milk

Question 6

What are acini cells?

Answer 6

• alveoli contain acini cells which produce milk

- the acini cells are surrounded by myoepithelial cells which contract an propel milk along the ducts

Question 7

What happens when an infant breastfeeds?

Answer 7

• when an infant breastfeeds, the infant draws the nipple and areola into their mouth
• the mothers nipple elongates to about twice its normal length
• the nipple height is compressed between the tongue and the palate
• milk is ejected about 0.03 seconds per maximum nipple elongation
• suckling infants compress the areola with their gums which stimulates oxytocin release
  
  • -> the oxytocin release causes an increase in the diameter of the milk ducts and movement of milk in the ducts toward the nipple
• mothers may feel a sensation of pins and needles or pressure in he breast with milk ejection

Question 8

Describe the action of prolactin

Answer 8

• it is produced in the anterior pituitary gland and released into circulation
• regulation of prolactin levels in the plasma is controlled by the dopaminergic system
• prolactin acts on the human breast to produce milk
  
  • > occurs by binding to mammary epithelial cell receptors
  • > stimulates synthesis of mRNA of milk proteins
• takes several minutes of infant suckling to cause prolactin secretion
• prolactin is also important in inhibiting ovulation

Question 9

Describe the action of oxytocin

Answer 9

• it is produced by the posterior pituitary gland (neurohypophysis)
• suckling at the breast stimulates the posterior pituitary to produce and release oxytocin in an intermittent manner
• oxytocin acts on the breast to produce milk ejection or ‘milk let down’
• oxytocin also causes uterine contractions
• opiates and B endorphins released during stress can block the release of oxytocin

Question 10

What is FIL?

Answer 10

• it is feedback inhibitor of lactation
• recently described active whey protein which inhibits milk production in a full breast
• FIL seems to play an important role in regulation of milk supply
• FIL acts locally on each breast -> it is secreted into breast milk
• when the breast is not emptied FIL remains in contact with the alveolar cells
• FIL appears to act on an apical receptor on the alveolar cell
  
  • > this inhibits secretion of milk constituents

Question 11

Describe the process of lactogenesis for breast milk production

Answer 11

1. Mammogenesis -> breast growth increased
   - > proliferation of ducts and glands under influence of oestrogen and progesterone
2. Lactogenesis 1 -> initiation of milk synthesis mid pregnancy
   - > differentiation of alveolar cells from secretory cells
   - > prolactin stimulates secretory cells to produce milk
3. Lactogenesis 2 -> closure of tight junctions in alveolar cell - triggered by drop in progesterone levels
   - > onset of copious milk secretion
   - > switch from endocrine to autocrine control
   - > fullness and warmth in breasts
4. Galactopoiesis (day 9 beginning of involution)
   - > Maintenance of secretion
   - > control by autocrine system (supply and demand)
   - > breast size decreases between 6-9 months Postpartum
5. Involution (average 40 days after last breastfeed)
   - > decreased milk secretion from build up of inhibiting peptides
   - > high sodium levels

Question 12

What are the essential hormone changes for successful lactation?

Answer 12

• drop in progesterone
• release of prolactin from anterior pituitary
  
  • > stimulates Lactogenesis
  • > initiates milk secretion
• removal of breast milk by infant
• release of oxytocin from posterior pituitary

Question 13

Describe progesterones role in breastfeeding

Answer 13

• lactation in pregnancy is inhibited by high levels of progesterone
  
  • > it interferes with prolactin action at alveolar cell receptor level
• progesterone falls by about 10 times during the first 4 days

Question 14

Describe prolactins role during lactation

Answer 14

• it follows a circadian rhythm - levels are higher at night than during the day
• levels decline slowly over course of lactation but remains elevated as long as she breast feeds
• prolactin rises with suckling - the more feeding the higher the prolactin levels
• prolactin not related to milk yield especially after lactation is established
• delays return of ovulation by inhibiting ovarian response to FSH
• prolactin drops with cigarette smoking
• rises with anxiety and stress
• depressed mothers have lower serum prolactin

Question 15

Describe oxytocin’s role in breastfeeding

Answer 15

• in response to suckling the posterior pituitary releases oxytocin
  
  • -> it causes milk ejection reflex
  • -> it also causes contracting of myoepithelial cells surrounding the alveoli, which is necessary for the removal of milk from the breast
• it is released in pulsatile waves and carried through the bloodstream to the breast
  
  • -> here it interacts with receptors on myoepithelial cells causing contractions
  • -> this forces milk from alveoli into the ducts where it becomes available to the newborn
• oxytocin plays a role in continuance of breastfeeding
• levels rise within a minute of stimulation
• contracts uterus
• has peripheral effects increasing blood flow
• increased thirst
• breast massage increases levels