S4: Breastfeeding Flashcards
Describe anatomy of the breast
- The breast is composed of about 20 radially (radiating around areola) arranged lobes with a duct system draining that drains down to the nipple. The lobes are further divided into lobules that produce the milk, they have an alveoli like structure.
- More recent evidence suggests that only about 9/10 lobes are functional while the rest are now vestigial (no longer serve a purpose).
- The non-lactating breast also has more fat (is 50% fat) than the lactating breast (around 30%) as the lactating breast has hyperplasia of glandular tissue that takes up the space.
- Each lobe can be considered a separate functional unit.
- About 9 ducts emerge at the nipple where milk is secreted and the ducts are tortuous and branch near the nipple.
- Also about 70% of the glandular tissue is located within 8cm of the nipple.
Describe mammary gland structure
- The mammary gland is composed of basic secretory units that have an alveoli structure that is sitting within connective tissue.
- The alveoli structure is lined by mammary epithelial cells (cuboidal or low columnar) and myoepithelial cells surround the alveoli.
- These myoepithelial cells are contractile and responsible for milk ejection.
What are the two stages in breast milk production?
- Phase 1 is lactogenesis I.
2. Phase 2 is lactogenesis II post partum.
Describe phase 1 of breast milk production
- Once pregnant there is an increase in the hormones human placental lactogen and prolactin that promote development of the breast, these cause hyperplasia of the glandular tissue within the breast.
- At the same time the high progesterone and oestrogen released from the placenta inhibit the actual milk production, but the breast is being prepared which is why they increase in size.
Describe phase 2 of breast milk production
- After birth, there is a fall in progesterone and oestrogen levels that this releases the inhibition to milk production. This is lactogenesis post partum (lactogenesis II).
- Suckling of the infant on the breast will stimulate prolactin release from anterior pituitary which enter the blood and act on cuboidal cells of the milk producing alveoli to increase milk synthesis. It also causes release of oxytocin that drives milk ejection in a positive feedback manner.
These two are very important!! So more suckiing = more milk produced. - There is some autocrine inhibition by duct cells, this describes how duct cells will inhibit further milk production if there is lots around already. If milk isn’t removed from the breast the woman will not produce more milk. This is a feedback loop.
Describe the ‘Let down’ reflex
Suckling stimulates nerve pathways that signal to the hypothalamus, this causes release of oxytocin from the posterior pituitary gland.
The oxytocin causes the myoepithelial cells to contract and secrete milk down the milk duct and out of the nipple. Because the process is controlled by higher centres, let-down reflex can also be caused by other stimuli like thinking about your baby or hearing other babies cry.
Describe some drugs that augement lactation (encourage it to occur)
- By increasing prolactin secretion with dopamine antagonists such as domperidone and metoclopramide. These are galactogogues.
- This is useful when a mother gives birth to a preterm infant that is then taken away to an incubator. The mother lacks the normal stimuli that allow her to produce breast milk e.g. suckling/skin to skin contact. Thus medication can help here.
Describe some drugs that suppressing lactation
- Isn’t really done in neonatal setting, but can be done.
- This would be done by decreasing prolactin secretion by giving dopamine agonists e.g. bromocriptine and cabergoline.
Describe the 5 secretory pathways that get components of milk into the lumen of the milk producing alveoli
- Exocytosis: The major components of milk such as the milk proteins, lactose, calcium and phosphate are packaged into secretory vesicles are secreted by exocytosis. The milk proteins are synthesised by the RER, these then travel to the golgi body where calcium and phosphate are added. Within the Golgi vesicle lactose is synthesised and as it cannot move out, water gets drawn in osmotically. The vesicle fuses with the apical membrane and the contents transferred to the alveolar lumen.
- MFG (milk fat globule): Lipids are produced on the smooth endoplasmic reticulum, packaged into milk fat globules and these fat globules then get surrounded by a thin basement membrane. These are then found in the milk.
- Osmosis: Secretion of certain ions, water, Na+ and K+ can freely move out of the cell into the lumen
- Immunogloblin secretion: Secretory IgA binds to a receptor on the basolateral cellular membrane. The receptor and IgA are transported in an endocytotic vesicle and emptied to the Golgi body or apical membrane.
- Paracellular route: These are normally closed, but can be open in pregnancy as well as in conditions like mastitis and involuting breasts. In these instances there will be higher NaCl and lower concentrations of lactose and K in breast milk.
Thus a woman who has a very preterm baby her breast milk will be different initially.
Describe the components of breastmilk
- Nutrients: Macronutrients (major component, protein, carb, fat) and trace elements (low solute load, good for neonate kidneys).
- Immunoglobulin: Secretory IgA.
- Cells: Macrophages and lymphocytes.
- Non specific immune components.
- Growth factors.
Describe macronutrients in breast milk and formula milk
- Human milk is better than formula milk, having about 70kcal of energy per 100ml in mature milk, 7.3g of lactose, 0.9g protein and 4.2g fat which is all higher than formula milk.
- More protein in formula milk than mature milk as there are extra proteins added specially but this is not necessarily a good thing.
- Formula milk is made from cows milk with things added. However cows milk is different in composition to human milk.
Describe the volume and composition of breast milk changes over time post partum
- At start of feed composition changes from the end. Composition also changes over time.
Volume of milk produced increases days postpartum in response to demand. - Initially on days 1-2, very little milk is produced. However by day 3 milk production increases a lot and continues to increase to meet the infants demand. You can fully breastfeed in this way up to 6 months of age.
- Composition of breast milk changes over time, initially the milk has lower levels of lactose that then increase over time. The salt level of the milk is initially relatively high and then decreases over time.
- There are also changes in composition of breast milk within a single feed. · As time goes on during the course of a feed the amount of fat increases in the milk, this is called the hindmilk and is fat rich. So fat concentration increases as baby feeds.It used to be that women were advised to feed on each breast for 5min but this meant missing the hindmilk so is no longer advised. So now mothers are encouraged to let babies empty breast milk in one breast before moving onto the other in order to get fat rich hind milk.
Describe nutrition benefits for the baby from breast milk
Protein:
- Human breastmilk is species specific biological fluid.
- Human milk contains a higher whey fraction (70%) to casein fraction (30%). Whey is more soluble in acid media so is more soluble in the stomach and promotes gastric emptying.
- Cows milk contains less whey (18%) and much higher casein (82%) and the latter is less soluble and less digestible.
- It is the lactoferrin, lysozyme and secretory IgA that are the whey proteins that are important in the baby’s defence.
Lipids:
- In terms of lipid components human milk contains LCPUFA (long chain polyunsaturated fatty acids) that are important for brain and retinal development.
- Cows milk only contains the carbon 18 LCPUFA which is linoleic and linolenic precursors which is not enough on its own for the baby.
- The LCPUFA are essential for the baby!!
- The breastmilk also contains lipase that is activated when it comes into contact with bile salts in the babies stomach, these are bile salt activated lipase. This helps digest the fat component.
Describe gastrointestinal benefits for the baby from breast milk
- Human milk improves gastric emptying.
- Human milk is also important in preventing necrotizing enterocolitis (NEC), which is a transmural necrosis of the bowl wall. Just giving formula milk puts a baby at higher risk of NEC.
- When a mother has a preterm baby she is strongly encouraged to produce breast milk for the baby.
Describe immunity benefits for baby from breast milk
- If a mother delivers at term, the IgG is transferred to the baby across the placenta in the third trimester so the baby will have inbuilt (passive) immunity. If the mother delivers preterm, then the baby has missed out on the IgG, therefore the immunity from the mothers breast milk becomes really important.
- sIgA: Most important one. Specific immune response, binds bacterial adherence sites.
- Complement: C1 to C9 present in low concentrations in human milk, with higher amounts of C3 (able to opsonise bacteria in conjunction with IgA).
- Lactoferrin: Inhibits bacterial growth by binding iron.
- Lysozyme: Cleaves peptidoglycans of bacterial walls.
- Cytokines: anti-inflammatory cytokines predominate in human milk, allows human milk to protect but not injure the gastrointestinal tract(not pro-inflammatory cytokines).
- PAF acetylhydrolase: Inhibits platelet activating factor.
- Oligosaccharides: Inhibit binding of enteric/respiratory pathogens epithelial cells.
- Epidermal growth factors: Enhance development of gastrointestinal epithelium.
- Cellular elements: Neutrophils and macrophages help destroy bacteria.
