The production of breast milk initiates in larger amounts between 2 and 4 days after the birth of the baby and the breastmilk is said to have 'come in'. It is the sole best source of nutrition for an infant, providing an adequate amount of nutrients, growth factors, and antibodies required for the nourishment of the baby. Breast milk should be exclusively used for nutrition until 6 months of age after which breastmilk should be used in addition to complementary foods for at least 12 months of age. [1

Alhawaj, AF

Sabir, S

Shah, R

English

UCL Discovery

10/5/2019 Physiology, Breast Milk - StatPearls - NCBI Bookshelfhttps://www.ncbi.nlm.nih.gov/books/NBK539790/ 1/5NCBI Bookshelf. A service of the National Library of Medicine, National Institutes of Health.StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2019 Jan-.Physiology, Breast MilkRutvi Shah; Ali F. Alhawaj.AuthorsRutvi Shah ; Ali F. Alhawaj .Affiliations Pramukhswami Medical College Imam Abdulrahman Bin Faisal University, Dammam, Saudi ArabiaLast Update: March 20, 2019.IntroductionBreast milk is one of the major sources of nutrition for a newborn. It provides fats,carbohydrates, proteins, vitamins, and minerals needed exclusively for the first 6 months of life.Furthermore, it provides the neonate with resources to develop immunity to infections and aids indigestion and absorption of other substances. Issues of ConcernIn many societies, formula feeding is becoming more prominent, and breast milk has become theleast preferred choice.[1] Further evidence demonstrates how formula and bottle feeding leads toan increased risk of oral disease and alterations in oxygenation, thermoregulation, and gutbacteria of the newborn.[1] Formula feeding is necessary for some situations. However, the mostappropriate recommendation to a newborn is exclusive breastfeeding for at least six monthsbefore adding complementary feeding.[2][3]CellularBreast milk is composed of fats (3 to 5%), carbohydrates (6.9 to 7.2%), proteins (0.8 to 0.9%),vitamins, minerals, and bioactive substances.[4][5][6] Breast milk yields around 60 to 75kcal/100 ml. The colostrum (breast milk in the early days) has more proteins, and maturemilk contains more carbohydrates.[4]FatsThe content of fat in breast milk ranges from 3.5 to 4.5%. Triglycerides account for the majorityof the lipids. Saturated fatty acids account for nearly half of the fatty acids with palmitic acidbeing around 23%. Breast milk contains two essential fatty acids: linoleic acid and alpha-linoleicacid. These get converted to arachidonic acid (AA) and eicosapentaenoic acid (EPA). EPAconverts to docosahexaenoic acid (DHA).[6] The fatty acid composition varies somewhat uponthe diet of the mother.[4]Carbohydrates Breast milk mainly contains lactose. There are 30 or more oligosaccharides with the terminalGal-(beta1,4)-Glc as well. They range from 3 to 14 saccharide units per molecule.[4]ProteinsAuthor Information1 21210/5/2019 Physiology, Breast Milk - StatPearls - NCBI Bookshelfhttps://www.ncbi.nlm.nih.gov/books/NBK539790/ 2/5Breast milk primarily consists of casein and whey proteins. Whey consists of alpha-lactalbumin,lactoferrin, and immunoglobulin A.[6] Casein is more difficult to digest than is whey. Breastmilk initially contains more whey than casein. Eventually, however, both casein andwhey become equal. Other proteins include lysozyme, folate-binding protein, bifidus factor,lipase, amylase, alpha1-antitrypsin, antichymotrypsin, and haptocorrin.[6]Vitamins and MineralsBreast milk contains most vitamins except vitamin K and D. Hence, and vitamin K is given atbirth. Mothers are advised to expose their infants to the sun or supplement them with vitamin D.Breast milk contains sodium, potassium, calcium, magnesium, phosphorus, and chlorine. Iron,copper, and zinc are also present in breast milk but vary in quantity. The infant's iron needsdepend upon the mother's intake.[4]Bioactive SubstancesBreast milk contains white blood cells, IgA, IgG, IgM, cytokines, chemokines, growth factors,hormones, and anti-microbial substances.[5]DevelopmentThe mammary tissue consists of alveoli and ducts. The breast milk production is into the alveoliwhere it gets stored and then pumped through the ducts during lactation.During pregnancy, the mother undergoes stage II mammogenesis due to high levels ofprogesterone; this increases secretory tissue in the breast. The high levels of chorionicgonadotropin form type three lobules in the breast alveoli. These lobules consist of epithelialcells and acini of increased size and number. During the latter part of pregnancy, the aciniatrophy and give leeway for colostrum storage in the lumen.[7]In the initial week after pregnancy, the mother secretes colostrum, which is a thick and yellowliquid. From days 7 to 14, the mother secretes transitional milk. This type is a combination ofcolostrum and mature milk. After two weeks, the mature milk is formed and secreted.[5]Two hormones are involved in the development of breast milk: prolactin and oxytocin. Prolactinincreases during pregnancy to prepare the mammary tissue to start forming the milk. However,due to high levels of progesterone and estrogen, prolactin is inhibited from forming any milk.After placental delivery, progesterone and estrogen levels fall, allowing prolactin to exert itseffect and secrete the milk. Oxytocin acts on the cells to expel the stored milk.[7][8]Organ Systems InvolvedThe organs and structures involved in breast milk formation are the mammary glands, theanterior pituitary gland, and the posterior pituitary gland. The individual roles of those organs arediscussed below. FunctionBreast milk is the primary source of nutrients for the newborn. The composition of breast milkserves many functions. The general makeup of breast milk is water, fat, protein, and lactose. Because of the constantgrowth of a newborn, the breast milk adapts itself to accommodate the child's needs. When eachnursing session begins, the foremilk satisfies the baby's thirst due to the high content of lactose.10/5/2019 Physiology, Breast Milk - StatPearls - NCBI Bookshelfhttps://www.ncbi.nlm.nih.gov/books/NBK539790/ 3/5The hindmilk is more abundant in fat to provide the nutrition a baby requires. Breast milk candiffer depending on maternal health, environmental exposure, and the age of the infant.[6]The fats in the milk are necessary for growth regulation, inflammatory responses, immunefunction, vision, cognitive development, and motor systems in newborns.[6]The lactose in the milk aids in the absorption of minerals and calcium.[6] Furthermore,carbohydrates are also able to produce certain strains of lactobacilli. These strains, in turn, helpsto control the intestinal flora in the gut.[4]Compared to formulas, human breast milk contains higher levels of whey protein, makingdigestion easier for the newborns. Furthermore, various whey proteins provide differentfunctions necessary for the newborn. For example, immunoglobulin A antibody protects the gutsurface and destroys bacteria. Also, both lactoferrin and lysozymes stop pathogenic bacteria.[6]Vitamins and minerals play a critical role in the development of the newborn. They are necessaryfor enzymatic functions and constitute the building blocks of many molecular substances.However, vitamin D and K are not present in breast milk and require external supplementation.Iron requirement is also essential to a newborn to prevent anemia. The newborn can have directiron supplementation, or the mother's diet can be fortified with iron-rich foods and the ironpassed on in the breast milk.[8]MechanismEarly on in the pregnancy, prolactin secretion increases. Prolactin stimulates epithelialproliferation of breast tissue to start secreting milk. High levels of both progesterone andestrogen in pregnancy lead to prolactin inhibition. After delivery, progesterone and estrogenlevels decrease rapidly, allowing mammary epithelial cells to synthesize milk in response toprolactin.[9][10]The baby suckling the nipple also stimulates prolactin secretion. It reaches its peak levels in theblood about 30 minutes after the feeding. Hence, prolactin is necessary to provide milk for thenext feed. Furthermore, prolactin secretion is at its maximum height at night. Thus, breastfeedingat night is considered significant.[9] Prolactin is beneficial to the mother as well. It causes a feeling of happiness and relaxation.Prolactin secretion also affects the release of gonadotropin-releasing hormone (GnRH).Inhibition of GnRH in its turn decreases the release of follicle-stimulating hormone andluteinizing hormone, which leads to a natural birth control mechanisms in the mother calledlactational amenorrhea.[9]Oxytocin is known as the "let-down" hormone. It acts on the myoepithelial cells around thealveoli, contracting them to help release the milk, allowing ejection of the already-made milkfrom the breast.[9][10]Oxytocin secretion occurs when the mother starts seeing, smelling, or even thinking about herchild, and also when the baby sucks the nipple, constituting the sucking reflex. This reflexexplains why a mother and child should be roomed together as often as possible. If the mother isemotionally unbalanced, this reflex can be affected; hence keeping the mother emotionally stableis essential.[11]Oxytocin also promotes bonding and affection between the mother and child.[11]Pathophysiology10/5/2019 Physiology, Breast Milk - StatPearls - NCBI Bookshelfhttps://www.ncbi.nlm.nih.gov/books/NBK539790/ 4/51.2.3.4.5.6.7.8.9.One of the main maternal concerns is not having enough breastmilk. Since breast milk isindispensable to a newborn, physicians should be able to discern milk supply difficulties. Signsinclude low weight gain, dry mucous membranes of the baby, weak cry, infrequent hard stools,and frequent strong smelling urine.[12] Many factors can affect breast milk supply such as poormaternal health (e.g., anemia), abnormalities in the breast tissue, retained fetal products in-utero,urinary tract infections in the mother, and poor feeding habits.[12] Effective feeding habitsand optimizing the mother's health status helps to achieve optimum feeding.[12]Clinical SignificanceBreast milk is vital for the newborn's development. However, due to the increased norm ofworking mothers, pumping and storage of breast milk has become a widespread practice. Themaintenance of this practice is crucial to prevent the spread of pathogens through expressed milk.Preserving the integrity of the breast milk is essential, hence using proper hygiene is advised.Furthermore, short-term storage of the milk can be achieved by the refrigerator to preventcontamination.[13]Breastfeeding correlates with decreased risk for cardiovascular diseases, atopic diseases, andseveral infectious diseases. Additionally, breastfeeding has links to a reduction in the risk ofbehavioral and developmental disorders.[1]QuestionsTo access free multiple choice questions on this topic, click here.ReferencesBrahm P, Valdés V. [The benefits of breastfeeding and associated risks of replacement withbaby formulas]. Rev Chil Pediatr. 2017 Feb;88(1):7-14. [PubMed: 28288222]Jenness R. The composition of human milk. Semin. Perinatol. 1979 Jul;3(3):225-39.[PubMed: 392766]Ballard O, Morrow AL. Human milk composition: nutrients and bioactive factors. Pediatr.Clin. North Am. 2013 Feb;60(1):49-74. [PMC free article: PMC3586783] [PubMed:23178060]Martin CR, Ling PR, Blackburn GL. Review of Infant Feeding: Key Features of Breast Milkand Infant Formula. Nutrients. 2016 May 11;8(5) [PMC free article: PMC4882692][PubMed: 27187450]Pillay J, Davis TJ. StatPearls [Internet]. StatPearls Publishing; Treasure Island (FL): Oct 27,2018. Physiology, Lactation. [PubMed: 29763156]Kramer MS, Kakuma R. The optimal duration of exclusive breastfeeding: a systematicreview. Adv. Exp. Med. Biol. 2004;554:63-77. [PubMed: 15384567]Kramer MS, Kakuma R. Optimal duration of exclusive breastfeeding. Cochrane DatabaseSyst Rev. 2012 Aug 15;(8):CD003517. [PubMed: 22895934]Lee S, Kelleher SL. Biological underpinnings of breastfeeding challenges: the role ofgenetics, diet, and environment on lactation physiology. Am. J. Physiol. Endocrinol. Metab.2016 Aug 01;311(2):E405-22. [PMC free article: PMC5005964] [PubMed: 27354238]Neville MC, Anderson SM, McManaman JL, Badger TM, Bunik M, Contractor N, Crume T,Dabelea D, Donovan SM, Forman N, Frank DN, Friedman JE, German JB, Goldman A,Hadsell D, Hambidge M, Hinde K, Horseman ND, Hovey RC, Janoff E, Krebs NF, LebrillaCB, Lemay DG, MacLean PS, Meier P, Morrow AL, Neu J, Nommsen-Rivers LA, RaitenDJ, Rijnkels M, Seewaldt V, Shur BD, VanHouten J, Williamson P. Lactation and neonatal10/5/2019 Physiology, Breast Milk - StatPearls - NCBI Bookshelfhttps://www.ncbi.nlm.nih.gov/books/NBK539790/ 5/510.11.12.13.nutrition: defining and refining the critical questions. J Mammary Gland Biol Neoplasia.2012 Jun;17(2):167-88. [PMC free article: PMC3428522] [PubMed: 22752723]Aono T. [Hormonal control of lactation]. Nippon Sanka Fujinka Gakkai Zasshi. 1990Aug;42(8):867-72. [PubMed: 2230414]Sue Carter C. Oxytocin and Human Evolution. Curr Top Behav Neurosci. 2018;35:291-319.[PubMed: 28812268]Amir LH. Breastfeeding--managing 'supply' difficulties. Aust Fam Physician. 2006Sep;35(9):686-9. [PubMed: 16969436]Peters MD, McArthur A, Munn Z. Safe management of expressed breast milk: A systematicreview. Women Birth. 2016 Dec;29(6):473-481. [PubMed: 27318564]Copyright © 2019, StatPearls Publishing LLC.This book is distributed under the terms of the Creative Commons Attribution 4.0 International License(http://creativecommons.org/licenses/by/4.0/), which permits use, duplication, adaptation, distribution, and reproduction inany medium or format, as long as you give appropriate credit to the original author(s) and the source, a link is provided to theCreative Commons license, and any changes made are indicated.Bookshelf ID: NBK539790 PMID: 30969612

Physiology, Breast Milk

https://discovery.ucl.ac.uk/10126740/1/Physiology%2C%20Breast%20Milk%20-%20StatPearls.pdf

Physiology, Breast Milk

Abstract

Similar works

Full text

Available Versions

UCL Discovery