Breastfeeding
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Describe the anatomy of the breast
• 20 lobes with duct system draining down to nipple • -> ~9 lobes are functional, rest vestigal • Each lobe = separate functional unit • Non-lactating breast about 50% fat, lactating about 30% fat
The ducts are tortuous and branch near nipple. How many ducts emerge at the nipple?
~ 9
How much of the glandular tissue is wihtin 8cm of the nipple?
70%
Describe the structure of the mammary gland mid-trimester
• Basic secretory unit is alveoli, set within connective tissue • Lined by mammary epithelial cells (cuboidal or low columnar) • Myoepithelial cells surround alveoli -> these are contractile + responsible for milk ejection
What hormone is released at around 10 weeks of gestation?
Prolactin
What happens in lactogenesis I?
• Occurs in pregnancy • Placental lactogen and prolactin promote development of breast tissue • Progesterone + oestrogen inhibit milk secretion
What happens in lactogenesis II?
• Post partum • Fall in progesterone + oestrogen reduces inhibition to milk prod • Suckling stimulus releases prolactin –> more milk synthesis • Suckling (+ higher cntrs) release oxytocin –> milk ejection • Some autocrine inhibition from duct cells (negative feedback mechanism - need to take away milk before more can be made)
What controls milk synthesis?
• Sucking -> nerve pathway -> anterior pituitary -> prolactin in blood -> milk producing alveolus • Prolactin released by anterior pituitary, in response to sucking. • Milk synthesis is led by infant demand overall
Describe the mechanism of the “let down” reflex by oxytocin
• Oxytocin release causes milk ejection • Suckling -> afferents to CNS (hypothalamus) -> posterior pituitary -> oxytocin in blood -> mammary gland -> acts on myoepithelial cells to cause milk ejection • This higher reflex can be inhibited by anxiety or stress eg. delivering prematurely can inhibit oxytocin release + milk ejection • Reflex may also become conditioned - hearing another baby cry might result in your own milk ejection
Which drug(s) will increase prolactin and hence augment lactation?
Dopamine antagonists eg. Maxolon, Domperidone, metoclopramide
Which drug(s) will decrease prolactin and hence suppress lactation?
Dopamine agonists eg. bromocriptine, cabergoline
There are 5 main secretory pathways in production of milk. What is the first major secretory pathway?
• Pathway 1 - transcellular • Proteins made in RER, packaged into golgi vesicles • Calcium + phosphate added • Within golgi vesicle, lactose synthesised • Golgi impermeable to lactose so water drawn into vesicle • Vesicle moves to apex of cell -> exocytosis • Released into alveolar lumen
What is the second secretory pathway?
• Pathway 2 - transcellular • Milk fat secretion • Triglycerides synthesised in cytoplasm + SER, become larger droplet • Droplets enveloped in apical membrane + separate from cell • Form milk fat globule
What is the third secretory pathway?
• Pathway 3 - transcellular • Osmosis • Secretion of ions (Na, K, Cl) + water permeate apical cell membrane
What is the fourth secretory pathway?
• Pathway 4 - transcellular • Immunoglobulin secretion • IgA + specific receptor combine on basolateral cellular wall • Both transported in an endocytotic vesicle • Emptied into either golgi or apical membrane
What is the fifth secretory pathway?
• Pathway 5 - paracellular • Normally closed but open in pregnancy + mastitic breasts • Causes high conc of Na + Cl as well as plasma protein • Causes low conc of lactose + K
Is it better for pre-term infants to be breastfed or formula fed?
Breastfed
What are the components of breastmilk?
• Nutrients - macronutrients + trace elements • Immunoglobulin (IgA) • Cells (macrophages + lymphocytes) • Non-specific immune components • Growth factors
What happens to the volume and composition of breast milk over days postpartum?
• Volume increases • Na+ and Cl- decrease • Lactose increases • Potassium increases slightly then decreases
What happens to the fat concentration as the baby feeds?
• Fat conc goes up over duration of baby feeding • Thinner more protein-rich milk at the beginning, fatty at the end
Describe the whey and casein content of human milk and why it’s better than cow milk
• Human milk: whey 70%, casein 30% • Cow milk: whey 18%, casein 82% Whey is good as it remains in solution in the acidic media (stomach), so more easily digested and promotes gastric emptying. Casein has a low solubility in acid media, so less favourable.
Which whey proteins specifically are present in human milk and what is their function?
• Lactoferrin, lysozyme and sIgA • Important in host defence
What is the lipid content of breast milk and how is it of benefit?
• Contains LCPUFA important for brain/retinal development • Substantial amount of lipase (activated by bile-salt), which is inactive in cow milk
What is the benefit of breastmilk to the gastrointestinal system of the newborn?
• Human milk improves gastric emptying • Human milk important in preventing necrotizing enterocolitis in preterm infant