Lactation Flashcards
Describe the basic anatomy of the breast
- Alveoli surrounded by fat
- Ducts branch right to the end of the nipple
- Glandular tissue lies very close to the nipple
- Subcutaneous fat is minimal at the base of the nipple
What are the 4 stages of breast growth and development?
- Mammogenesis - the period of development from conception, through puberty and into pregnancy
- Lactogenesis I & II - transition from pregnancy to lactation - neuroendocrine response
- Galactopoiesis - maintenance of established milk production - autocrine response
- Involution - process that removes the milk producing cells on weaning
Describe the development of breasts during embryogenesis
- Development begins at 4 weeks gestation for males and females
- Week 12-16 = development of nipples and areola
- Lactiferous ducts open into mammary pit which elevates to become the nipple and areola
- No further development until puberty
Describe the development of breasts during puberty
- Increasing levels of oestrogen and progesterone lead to growth of lactiferous ducts, alveoli, the nipple and areola
- Increase in breast size caused by deposition of adipose tissue
- Oestrogen and pituitary factor influence breast growth with proliferation of milk ducts
- Progesterone stimulates alveolar development
Describe the development of breasts in week 3-4 of pregnancy
- Prickling, tingling sensation, particularly around the nipple
- Caused by increased blood supply
Describe the development of breasts in week 6-8 of pregnancy
- Oestrogen promotes growth of lactiferous ducts
- Progesterone, prolactin and hPL levels lead to proliferation and enlargement of alveoli
- Veins become visible
- Increase in size and become painful, tense and nodular due to hypertrophy of alveoli
Describe the development of breasts in week 8-12 of pregnancy
- Montogmery’s tubercles become more prominent on areola
- Pigmented area around nipple (primary areola) darkens, may enlarge and become more erectile
- Caused by hypertrophic sebaceous glands secreting sebum which keeps nipple soft and by increased melanin activity
Describe the development of breasts in week 16 of pregnancy
- Colostrum produced (lactogenesis I) due to prolactin and hPL
- Complete milk production suppressed by oestrogen and progesterone
- Secondary areola develops with further extension of pigmented area, causing a mottled appearance
Describe the development of breasts in week 24 of pregnancy
- Colostrum may leak
- Nipples become more prominent and mobile due to progesterone
What is an epulis?
A specific angiogranuloma which can be caused by advanced gingivitis
What is leptin?
A peptide hormone secreted by placental and adipose tissue that plays a key role in regulation of body fat and energy expenditure
What is the first indication that a woman is pregnant?
Breast changes
Which hormones are involved in breast changes during pregnancy?
- Progesterone
- hPL
- Prolactin
- Oestrogen
Outline the major changes that occur to the breasts in pregnancy
- Skin appears more thin/ translucent
- Veins become more prominent
- Areola diameter increases and nipple/areola become darker
- Nipples become more erect
- Ductal system proliferates (oestrogen)
- Lobes, lobules and alveoli increase in size (progesterone)
Describe what happens to the Montgomery’s tubercles during pregnancy
- Enlarge
- Combination of sebaceous glands and mammary milk glands
- Secretions provide maternal protection from mechanical stress of sucking and pathogenic invasion
How is the milk brought into the ducts?
- Stimulation of nipples initiates milk ejection via initiation of nerve impulses to the hypothalamus
- This stimulates posterior pituitary gland to release oxytocin into blood
- This causes myoepithlial cells surrounding alveoli to contract, forcing milk into ducts
Outline what occurs in lactogenesis I
- Occurs during 2nd part of pregnancy and lasts until 2 days postpartum
- Initiation of milk synthesis
- Prolactin stimulates milk (colostrum) production as we all increasing breast mass
Outline what occurs in lactogenesis II
- Occurs day 3-8 postpartum
- Triggered by delivery of placenta which causes rapid drop in progesterone levels, oestrogen, hPL and PIF
- Onset of copious milk secretion
- Retained placenta can inhibit milk production because hormone levels don’t drop
What does PIL stand for?
Prolactin Inhibiting Factor
What does hPL stand for?
Human Placental Lactogen
How are the alveoli adapted for lactation?
- Contain acini cells which produce milk
- Surrounded by myoepithlial cells which contract and propel the milk out
What is the purpose of the lactiferous ducts?
- Carry milk to alveoli
- Several large ducts = Lactiferous tubules (emerge on nipple surface)
- Myoepithlial cells lie longitudinally along ducts and, under influence of oxytocin, these smooth muscle cells contract and tubule becomes shorter and wider - called the let down reflex
- Tubule distend during active milk flow while myoepithelial cells maintain state of contracting
- Fuller breast = greater ductal distension
What does distend mean?
Swell or cause to swell by pressure from inside
What happens as lactation progresses?
- Prolactin response to suckling diminishes and milk removal becomes driving force behind milk production
- Due to whey proteins in milk able to inhibit synthesis of milk constituents
- Protein accumulates in breast as milk accumulates and exerts negative feedback control on continued milk production
- Removal of this autocrine inhibitory factor by removing milk allows milk production to increase again; this is the Feedback Inhibitor of Lactation
What is the role of progesterone?
- Most is secreted from placenta
- Maintains pregnancy
- Inhibits lactation
- Lactogenesis II is triggered by decrease in progesterone levels
Where is prolactin released from?
Anterior pituitary gland
What are the main functions of prolactin?
- Acts on alveoli
- Essential for initiating and maintaining milk production
- Production influenced by nipple sensation
- Involved in suppression of ovulation, so BF mothers less likely to get pregnant
What is Circadian rhythm?
Prolactin levels are higher at night
What causes the prolactin levels to rise and fall?
- Frequency, intensity and duration of feed
- Always a baseline level present
- Increases with anxiety/ psychological stress and beer drinking
- Decreases with smoking
What happens if too many feeds occur in 1 day (8 feeds)?
Prevents decrease in prolactin concentration between feeds
How long do prolactin levels stay high for if BF is delayed?
1 week
Describe the relationship between feeding frequency and milk output
Frequent feeding in early lactation stimulates faster increase in milk output due to development of more prolactin receptors in response to suckling
Describe the Prolactin Receptor Theory
- Receptor sites need to be activated
- Number of receptors per cell increases in early lactation, then remains constant
- People with small number of prolactin receptor sites may not produce enough milk
- Number of receptor sites switched on depends on prolactin levels
What are milk-secreting cells called?
Lactocytes
Describe the bell curve distribution of prolactin receptor sites
- Small population have few prolactin receptor sites
- Small population have loads of prolactin receptor sites
- Majority have an average number of prolactin receptor sites
Where is oxytocin produced?
Posterior pituitary gland
What is the milk ejection reflex?
Oxytocin acting on myoepithelial cells, causing them to contract
Describe the effects of oxytocin
- Role in the continuance of BF
- During suckling, released in discrete impulses
- Levels rise with a minute of stimulation, returning to baseline level within 6 minutes after feed finishes
What effect does oxytocin have on the mother’s emotions?
- Has calming effect
- Perceived that stress levels are lower in mothers who BF
- Nipple sensation appears to have no influence to oxytocin levels
- Associated with ‘love, labour and lactation’
What positive effects does skin to skin contact have?
- BF incidence at 1-3 months
- BF duration
- Maintenance of infant temp
- Infant blood glucose
- Infant crying
Explain the endocrine vs. autocrine action in breastfeeding
- The shift in lactation from hormonal control to being driven by milk removal
- BF not major factor in initiating lactation but is essential for continuation of lactation
Describe the Feedback Inhibitor of Lactation
- Autocrine feedback mechanism
- Locally controls milk synthesis
- Presence of FIL in milk inhibits milk synthesis - slows milk production when breast is full
- Protein accumulation exerts negative feedback control on continued milk production
- Demand and supply
