L14: Phys of Lactation

what are the five main pathways for milk production by alveolar epithelial cells?

1- secretory pathway 2- transcellular endocytosis and exocytosis 3- lipid pathway 4- transcellular salt and water transport 5- paracellular pathway

what happens during the transcellular salt and water transport of milk production?

at apical and basolateral membranes, small electrolytes move from interstitial fluids into alveolar lumen water follows osmotic gradient generated by lactose

describe sexual maturity of breast development

at birth, mammary glands is mostly lactiferous ducts with few alveoli estrogen causes ducts to sprout and branch forming alveoli as menstrual cycle is established, mammary tissues is exposed to estrogen and progesterone so increases in size

what hormones affect breast development?

at puberty: estrogen and progesterone during pregnancy: PRL, hPL, estrogen, progesterone

what is the job of oxytocin in lactation?

enhances milk ejection by stimulating contraction of myoepithelial cells surrounding the alveoli and ducts

what inhibits lactogenesis?

estrogen and progesterone

what happens in the lipid pathway of milk production?

fats predominant in milk come from diet or fat stores in surrounding adipose tissue fatty acids form lipid droplets that move to apical membrane as apical membrane surrounds the droplet and pinch off, milk lipids are secreted to lumen in membrane-bound vesicle

what happens in the secretory pathway of milk production?

lactalbumin and casein made in ER Ca2+ and phosphate added to lumen of golgi lactose synthetase in lumen of golgi catalyzes lactose synthesis water enters secretory vesicles by osmosis

describe the organization of the mammary gland.

made up of lobes each lobe is made of lobules of alveoli, blood vessels, and lactiferous ducts lobules drain into ductules lactiferous duct carries secretions to outside

what are the classes of hormones that affect the breast?

mammogenic= promotes proliferation of alveolar and ductal cells lactogenic= promotes initiation of milk production by alveolar cells *prolactin* galactokinetic= promotes contraction of myoepithelial cells leading to milk ejection *oxytocin* galactopoietic= maintains milk production after established *prolactin*

what happens during the transcellular endocytosis and exocytosis of milk production?

maternal immunoglobulins (IgA) are taken up by endocytosis through basolateral membrane immunoglobulins are transported to the apical membrane and secreted by exocytosis baby's GI tract picks up immunoglobulins for immunity

what is the job of the cells of alveolar epithelium?

milk synthesis and secretion

what is the job of the myoepithelial cells?

move milk from alveoli into ducts - contractile

what inhibits oxytocin release?

negative maternal emotions= frustration, anger, anxiety suppresses milk ejection reflex

what is colostrum?

produces late in pregnancy thin, yellowish milk secreted the first few days after parturition with a high concentration of immunoglobulins

what happens in the paracellular pathway of milk production?

salt and water can also move into the lumen of the alveolus through tight junctions cells (leuks) squeeze b/w cells and enter milk

describe the HP-boob axis for oxytocin release.

suckling causes more oxytocin to be synthesized and released

describe the HP-boob axis for prolactin release.

suckling feeds back to hypothalamus: --> decrease dopamine release --> prolactin secretion --> decrease in GnRH= decrease in LH and FSH BUT high levels of prolactin= lactational amenorrhea

what are the effects of suckling on hormone release?

suckling stimuli activates afferent neural pathway from boob to spinal cord to hypothalamus dopamine release inhibited resulting in release of prolactin spinal cord neurons oxytocin released from posterior pituitary resulting in let-down of milk spinal cord neurons inhibit arcuate and preoptic area of hypothalamus causing decrease in GnRH production= less FSH and LH= inhibit ovarian cycle

why is suckling important?

w/o suckling, milk secretion will last 3-4 weeks suckling stimulates prolactin secretion by neuroendocrine reflex * primary neural stimulus*

what causes cessation of lactation?

when suckling stimulus is discontinued, milk accumulates - atrophy of epithelial structures - rupture of alveolar walls lobular-acinar structures become smaller ductal system predominates can take 3m to involute