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Chapter 6

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NUTR 2050
Simone Holligan

Chapter 6 Nutrition During LactationLactation of the Mammary Gland Functional Units of the Mammary GlandMammary gland the source of milk for offspring also commonly called the breast o The presence of mammary glands is a characteristic of mammalsAlveoli a rounded or oblongshape cavity present in the breastSecretory cells cells in the acinus milk gland that are responsible for secreting milk components into the ductsMyoepithial cells specialized cells that line the alveoli and that can contract to cause milk to be secreted into the ductsOxytocin a hormone produced during letdown that causes milk to be ejected into the ductsMammary Gland DevelopmentThe cyclic release of estrogen and progesterone governs pubertal breast developmentThe mammary gland develops its lobular structure under the cyclic production of progesterone and is usually complete within 12 to 18 months after menarcheAs the ductal system matures cells that can secrete milk develop the nipple grows and its pigmentation changesFibrous and fatty tissues increase around the ductsIn pregnancy the luteal and placental hormones allow further preparation for breastfeedingEstrogen stimulates development of the glands that will make milkProgesterone allows the tubules to elongate and the cells that line the tubules to duplicate LactogenesisBreast milk production lactogenesis occurs in three stages o Lactogenesis I Milk begins to form and the lactose and protein content of milk increaseExtends through the first few days of postpartum o Lactogensis II Begins 25 days postpartum and is marked by increased blood flow to the mammary glandConsidered the onset of copious milk secretion when milk comes inSignificant changes in both the milk composition and the quantity of milk that can be produced occur over the first 10 days of the babys life o Lactogensis III Begins about 10 days after birth and is the stages in which the milk composition becomes stable Hormonal Control of LactationProlactin and oxytocin are necessary for establishing and maintaining a milk supplyProlactin hormone that stimulates milk productionSuckling is a major stimulator of prolactin secretion levels doubleStress sleep and sexual intercourse also stimulate prolactin levelsTo prevent milk production in the last 3 months of pregnancy prolactin activity is suppressed by a prolactininhibiting factor that is released by the hypothalamus o Allows the mothers body to prepare for milk production during pregnancyOxytocin release is also stimulated by suckling or nipple stimulationMain role is in letdown or the ejection of milk from the milk gland acinus into the milk ductsWomen may experience tingling or sometimes sharp shooting pain and corresponds with contractions in the milk ducts o Oxytocin also acts on the uterus causing it to contract seal blood vessels and shrink in size Secretion of MilkSecretory cell in the breast uses five pathways for milk secretionSome components like lactose are made in the secretory cells and secreted into ductsWater sodium potassium and chloride are able to pass through alveolar cells membranes in either direction passive diffusionMilk fat comes from triglycerides from the mothers blood and from new fatty acids produced in the breastFats are made soluble in ilk by addition of a proteins carrier to form milkfat globulesMilkfat globules are then secreted into ductsImmunoiglobulin A and other plasma proteins are captured from the mothers blood and taken into the alveolar cellsThese proteins are then secreted into the milk ducts Letdown ReflexStimulates milk release from the breastStimuli from the infant suckling are passed through nerves to the hypothalamus which respond by promoting oxytocin release from the posterior pituitary glandOxytocin causes contraction of the myoepithelial cells surrounding the secretory cellsMilk is released through the ducts making it available to the infantOther stimuli such as hearing a baby cry sexual arousal and thinking about nursing can also cause letdown and milk will leak from the breasts Human Milk CompositionFor approximately 6 moths yhe composition of milk is designed not only to nurture but also to protect infants from injectious and certain chronic diseases Colostrum
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