Physiology of Lactation

LACTATION

Adequate nutrition for the mother during lactation is also of vital importance as the infant is dependant on mothers milk for its nutrition for the first few months of life. As the mother has to nourish the fully developed and rapidly growing infant, she needs extra nutrients to meet the baby's increasing needs in addition to her own requirements. A satisfactory diet during pregnancy will ensure a good store of nutrients for satisfactory breast feeding. Inadequate nutrition during lactation is reflected on both the quality and quantity of milk secreted.

PHYSIOLOGY OF LACTATION

Hormonal changes markedly increase breast areola and nipple size. During pregnancy estrogen secreted by the placenta bring about rapid development of glands in the breasts. Large quantities of progesterone change the glandular cells to actual secreting cells.

By the time the baby is born breasts reach a degree of development capable of producing milk. Yet, oestrogen and progesterone, despite their developmental effects on breast inhibit the actual formation of milk until after the baby is born. Thus during pregnancy the placental hormones inhibit the secretion of lactating hormones by the pituitary gland.

With the sudden expulsion of placenta during delivery the source of placental hormones is removed and secretion of lactogenic hormones is increased which bring about production and secretion of milk.

The process of milk production and secretion occurs in two distinct stages.

i. Prolactin reflex

When the baby sucks the breast, nerve impulses are passed up the spinal cord to the hypothalamus which stimulates anterior pituitary leading to the secretion of prolactin. Prolactin is carried via the blood stream to the alveoli in the breasts where it stimulates milk production.

ii. Let down reflex

When the baby sucks, nerve impulses are passed to the posterior pituitary producing another hormone, oxytocin. Oxytocin contracts the muscle cells around the alveoli, squeezing out milk and propelling it down to the nipples.

The let down reflex is highly sensitive to emotional and psychological disturbances as well as physical contact. The mother's emotions, the baby's cry or even the baby's thought might initiate this reflex. On the other hand, anxiety, fear and tension may inhibit this reflex. Hence the mother should be comfortable and relaxed while feeding the baby.

These two reflexes operate simultaneously and release milk. Fig.  represents the process of stimulation of milk production.

As long as pituitary produces these lactogenic hormones, it cannot produce sufficient Follicle Stimulating Hormone (FSH) and Leutenizing Hormone (LH) which bring about ovulation. Thus lactation brings about natural contraception.

Composition of breast milk

Soon after delivery small quantities of thick, yellowish, viscous liquid called colostrum is secreted which is rich in antibodies and Vitamin A. This should be given to the baby and not discarded.

After a few days of lactation the mother secretes larger amounts of less viscous and whitish milk known as 'mature milk' which is more or less a complete food nutritionally. A healthy mother secretes 850ml of milk daily for which her nutritional needs are increased enormously.

gives the composition of mother's milk.

Composition of mother's milk

Nutrient     Quantity / 100 ml

Energy        65 k.cal

Protein        1.1g

Carbohydrate       7.4g

Fat    3.4g

Calcium      28mg

Iron   Negligible

Vitamin A (Retinol)       137 I.U.

Thiamine    0.02 µg

Riboflavin   0.02 µg

Vitamin C   3mg

Source : Gopalan C., Ramasastri B.V. and Balasubramanian S.C., (2000). Nutritive value of Indian Foods, NIN, ICMR, Hyderabad, India.