Lactation MCB 135E Lecture 22. Nutrition of the Infant Survival & growth depends on : the mother’s...
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Transcript of Lactation MCB 135E Lecture 22. Nutrition of the Infant Survival & growth depends on : the mother’s...
Nutrition of the Infant
Survival & growth depends on:
• the mother’s ability to breastfeed
• the baby’s ability to suck
• good development/function of the gastrointestinal system
• good development/function of the central nervous system
(which regulates & coordinates GI functions)
Background• Breastfeeding was once a
universal requirement for infant survival and still is for many world areas
• 1920s until after WWII: breastfeeding rates declined in industrialized countries
• 1970s: <25% of all infants breastfed at birth; 5% at 6 months
Background• Since 1970 there has been a reversal in this
downward trend• Currently breastfeeding rates vary widely with
the ethnicity & education level – 60% Caucasian women breastfeed v. 30% African-
American women– 70% of women with over
13 years of education breastfeed v. 30% of those who did not complete high school
Growth of Mammary GlandsEmbryology
• 6th week of gestation: Mammary glands begin to develop as solid growths of epidermis called mammary ridges
• Under the influence of estrogen (E) from placenta, mammary ridges canalize to form ducts
• At birth, mammary glands of males and females are identical, composed of ~15-20 rudimentary lactiferous ducts
Development of Breasts:Puberty
Female breasts develop further after puberty
(under influence of E from developing follicle & corpus luteum each month)
• Enlargement occurs due to deposition of fat & connective tissue
• Nipple becomes enlarged and pigmented
• Further growth & branching of lactiferous ducts
Development of Breasts: Pregnancy• More intense growth and branching of lactiferous
ducts (under high levels of E from corpus luteum & placenta)
• GH, glucocorticoids, prolactin (PRL), insulin all influence growth
• Final development of mammary glands occurs under the influence of progesterone (P), which (in concert with hormones mentioned above) cause alveoli to bud from the ends of the lactiferous ducts
• Each alveolus is lined by milk secreting cells
Milk Production(during pregnancy)
• PRL, secreted by anterior pituitary gland, stimulates milk production
• During pregnancy, PRL levels increase 20 fold but action of PRL inhibited by high E & P levels
• Human chorionic somatomammotropin ( i.e. placental lactogen) plays role in lactogenesis
• Towards end of pregnancy, breasts are fully developed but milk production is suppressed except for small amount of colostrum (same concentration of proteins and lactose as regular milk but hardly any fat)
Milk Production(after birth)
• After birth, E and P levels drop and milk is produced in 1-7 days
• Milk production requires: secretion of hormones involved in protein, glucose & calcium regulation (GH, cortisol, insulin, PTH)
• PRL levels return to normal within a few weeks. Each time an infant feeds, neurohumoral reflex leads to burst of PRL secretion
Milk Ejection• Alveolar milk accumulate in
the lactiferous sinuses (enlargements of ducts near opening of nipple)
• Suckling hypothalamus release of oxytocin from post. pituitary. Oxytocin contraction of myoepithelial cells around the ducts.
• Negative maternal emotions (frustration, anger, anxiety) can inhibit oxytocin secretion & suppress milk ejection reflex
Cessation of Lactation
• After mother stops breastfeeding & PRL levels decline, alveoli degenerate and reabsorb. Duct structure remains until menopause
• PRL inhibits pulsatile secretion of GnRH by the hypothalamus, resulting in amenorrhea during lactation
• This is an unreliable method of contraception used by many women
Benefits of Breastfeeding Compared to Formula-fed Babies
Incidence and severity of infections
Growth until one year of age
Incidence of obesity in adulthood
Improves mentaldevelopment
Benefits of Breastfeeding: Mother
Metabolic demands
Weight loss afterdeliver
Psychological benefitsfor mother, child
& father
Amenorrhea during lactationmay act as contraceptive
and, possibly, decreased risk of breast cancer
Complications of Breastfeeding• In the past, health professionals recommended
breastfeeding only under ideal circumstances. They recommended formula feeding with maternal illness, stress, or inadequate milk production.
• Today, mothers receive much greater encouragement to start and continue breastfeeding at least through the first six months, even in the face of complications.
Complications of BreastfeedingHIV:
Risk of transmission of infection at birth
breastfeeding.
Hep B + mothers:Infant must receive
globulin
Drugs secreted in the milk may impair growth
And development
Nutritional supplementsrequired for premature
infants
Immunology• Infant immune system is immature at birth.
• In utero, transfer of antibodies across placenta.
• This protection tapers off quickly after birth.
• Breast milk contains a number of different agents to protect the infant:– Secretory IgA– WBCs: neutrophils and macrophages– Growth factors: EGF, NFG, IFG