Lactation (colostrum)

Lactation

Colostrum . 

( 1 ) Colostrum is the first milk which is sticky and yellowish secreted by the mammary glands soon after the parturition .

 ( 2 ) Being high protein in its content , it nourishes the newly born child . 

( 3 ) The antibodies present in it helps in developing resistance for the newborn baby at a time when its own immune response is not fully developed .

Lactation (lak-TAˉ-shun) is the production and ejection of milk

from the mammary glands. A principal hormone in promoting milk production is prolactin (PRL), which is secreted from the anterior pituitary gland. Even though prolactin levels increase as the pregnancy progresses, no milk production occurs because

progesterone inhibits the effects of prolactin. After delivery, the

levels of estrogens and progesterone in the mother’s blood decrease, and the inhibition is removed. The principal stimulus in maintaining prolactin secretion during lactation is the sucking action of the infant. Suckling initiates nerve impulses from stretch

receptors in the nipples to the hypothalamus; the impulses decrease hypothalamic release of prolactin-inhibiting hormone

(PIH) and increase release of prolactin-releasing hormone (PRH),

so more prolactin is released by the anterior pituitary.

 Oxytocin causes release of milk into the mammary ducts via

the milk ejection reflex . Milk formed by the glandular cells of the breasts is stored until the baby begins active

suckling. Stimulation of touch receptors in the nipple initiates

sensory nerve impulses that are relayed to the hypothalamus. In

response, secretion of oxytocin from the posterior pituitary increases. Carried by the bloodstream to the mammary glands, oxytocin stimulates contraction of myoepithelial (smooth musclelike) cells surrounding the glandular cells and ducts. 

The resulting compression moves the milk from the alveoli of the mammary

glands into the mammary ducts, where it can be suckled. This process is termed milk ejection (let-down). Even though the actual ejection of milk does not occur until 30–60 seconds after nursing begins (the latent period), some milk stored in lactiferous

sinuses near the nipple is available during the latent period. Stimuli other than suckling, such as hearing a baby’s cry or touching

the mother’s genitals, also can trigger oxytocin release and milk ejection. The suckling stimulation that produces the release of oxytocin also inhibits the release of PIH; this results in increased

secretion of prolactin, which maintains lactation. During late pregnancy and the first few days after birth, the

mammary glands secrete a cloudy fluid called colostrum. Although it is not as nutritious as milk—it contains less lactose and

virtually no fat—colostrum serves adequately until the appearance of true milk on about the fourth day. Colostrum and maternal

milk contain important antibodies that protect the infant during the first few months of life.

 Following birth of the infant, the prolactin level starts to return

to the nonpregnant level. However, each time the mother nurses

the infant, nerve impulses from the nipples to the hypothalamus

increase the release of PRH (and decrease the release of PIH),

resulting in a tenfold increase in prolactin secretion by the anterior pituitary that lasts about an hour. Prolactin acts on the mammary glands to provide milk for the next nursing period. If this

surge of prolactin is blocked by injury or disease, or if nursing is

discontinued, the mammary glands lose their ability to produce

milk in only a few days. Even though milk production normally

decreases considerably within 7–9 months after birth, it can continue for several years if nursing or breastfeeding continues.

 Lactation often blocks ovarian cycles for the first few months

following delivery, if the frequency of sucking is about 8–10 times

a day. This effect is inconsistent, however, and ovulation com-

monly precedes the first menstrual period after delivery of a baby.

As a result, the mother can never be certain she is not fertile.

Breast-feeding is therefore an unreliable birth control measure.

The suppression of ovulation during lactation is believed to occur

as follows: During breast-feeding, neural input from the nipple

reaches the hypothalamus and causes it to produce neurotransmit-

ters that suppress the release of gonadotropin-releasing hormone

(GnRH). As a result, production of LH and FSH decreases, and ovulation is inhibited

• Beneficial cells. Several types of white blood cells are present in

breast milk. Neutrophils and macrophages serve as phagocytes,

ingesting microbes in the baby’s gastrointestinal tract. Macro-

phages also produce lysozyme and other immune system com-

ponents. Plasma cells, which develop from B lymphocytes, pro-

duce antibodies against specific microbes, and T lymphocytes

kill microbes directly or help mobilize other defenses.

• Beneficial molecules. Breast milk also contains an abundance

of beneficial molecules. Maternal IgA antibodies in breast

milk bind to microbes in the baby’s gastrointestinal tract and

prevent their migration into other body tissues. Because a

mother produces antibodies to whatever disease-causing microbes are present in her environment, her breast milk affords

protection against the specific infectious agents to which her

baby is also exposed. Additionally, two milk proteins bind

to nutrients that many bacteria need to grow and survive:

B12-binding protein ties up vitamin B12, and lactoferrin ties up

iron. Some fatty acids can kill certain viruses by disrupting

their membranes, and lysozyme kills bacteria by disrupting

their cell walls. Finally, interferons enhance the antimicrobial

activity of immune cells.

• Decreased incidence of diseases later in life. Breast-feeding

provides children with a slight reduction in risk of lymphoma,

heart disease, allergies, respiratory and gastrointestinal infec-

tions, ear infections, diarrhea, diabetes mellitus, and meningitis.

• Miscellaneous benefits. Breast-feeding supports optimal in-

fant growth, enhances intellectual and neurological develop-

ment, and fosters mother–infant relations by establishing early

and prolonged contact between them. Compared to cow’s milk,

the fats and iron in breast milk are more easily absorbed, the

proteins in breast milk are more readily metabolized, and the

lower sodium content of breast milk is more suited to an in-

fant’s needs. Premature infants benefit even more from breast-

feeding because the milk produced by mothers of premature

infants seems to be specially adapted to the infant’s needs; it has

a higher protein content than the milk of mothers of full-term

infants. Finally, a baby is less likely to have an allergic reaction

to its mother’s milk than to milk from another source.

 Years before oxytocin was discovered, it was common practice

in midwifery to let a first-born twin nurse at the mother’s breast to

speed the birth of the second child. Now we know why this prac-

tice is helpful—it stimulates the release of oxytocin. Even after a

single birth, nursing promotes expulsion of the placenta (after-

birth) and helps the uterus return to its normal size. Synthetic

oxytocin (Pitocin) is often given to induce labor or to increase

uterine tone and control hemorrhage just after parturition.