lactation

1 the period following birth during which milk is secreted; "lactation normally continues until weaning"

2 the production and secretion of milk by the mammary glands

3 feeding an infant by giving suck at the breast [syn: suckling]

English

Pronunciation

• Rhymes: -eɪʃǝn

Noun

1. The secretion of milk from the mammary gland of a female mammal.
2. The process of providing the milk to the young; breastfeeding.
3. The period of time that a mother lactates to feed her young.

Derived terms

• lactational
• lactation period

Related terms

• lactate
• lactic
• lactose

Translations

Lactation describes the secretion of milk from the mammary glands, the process of providing that milk to the young, and the period of time that a mother lactates to feed her young. The process occurs in all female mammals, and in humans it is commonly referred to as breastfeeding or nursing. In most species milk comes out of the mother's nipples; however, the platypus (a non-placental mammal) releases milk through ducts in its abdomen. In only one species of mammal, the Dayak fruit bat, is milk production a normal male function. In some other mammals, the male may produce milk as the result of a hormone imbalance. This phenomenon may also be observed in newborn infants as well (for instance witch's milk).

Purpose

The chief function of lactation is to provide nutrition to the young after birth. In almost all mammals lactation, or more correctly the suckling stimulus, induces a period of infertility, usually by the suppression of ovulation, which serves to provide the optimal birth spacing for survival of the offspring.

Human lactation

Hormonal influences

From the fourth month of pregnancy (the second and third trimesters), a woman's body produces hormones that stimulate the growth of the milk duct system in the breasts:

• Progesterone — influences the growth in size of alveoli and lobes. Progesterone levels drop after birth. This triggers the onset of copious milk production.
• oestrogen — stimulates the milk duct system to grow and become specific. Oestrogen levels also drop at delivery and remain low for the first several months of breastfeeding.

Other hormones—notably insulin, thyroxine, and cortisol—are also involved, but their roles are not yet well understood. Although biochemical markers indicate that Lactogenesis II begins about 30–40 hours after birth, mothers do not typically begin feeling increased breast fullness (the sensation of milk "coming in") until 50–73 hours (2–3 days) after birth.

Colostrum is the first milk a breastfed baby receives. It contains higher amounts of white blood cells and antibodies than mature milk, and is especially high in immunoglobulin A (IgA), which coats the lining of the baby's immature intestines, and helps to prevent germs from invading the baby's system. Secretory IgA also helps prevent food allergies. Over the first two weeks after the birth, colostrum production slowly gives way to mature breast milk. Research also suggests that draining the breasts more fully also increases the rate of milk production. Thus the milk supply is strongly influenced by how often the baby feeds and how well it is able to transfer milk from the breast. Low supply can often be traced to:

• not feeding or pumping often enough
• inability of the infant to transfer milk effectively caused by, among other things:
  • jaw or mouth structure deficits
  • poor latching technique
• rare maternal endocrine disorders
• hypoplastic breast tissue
• a metabolic or digestive inability in the infant, making it unable to digest the milk it receives
• inadequate calorie intake or malnutrition of the mother

Milk ejection reflex

The release of the hormone oxytocin leads to the milk ejection or let-down reflex. Oxytocin stimulates the muscles surrounding the breast to squeeze out the milk. Breastfeeding mothers describe the sensation differently. Some feel a slight tingling, others feel immense amounts of pressure or slight pain/discomfort, and still others do not feel anything different.

The let-down reflex is not always consistent, especially at first. The thought of breastfeeding or the sound of any baby can stimulate this reflex, causing unwanted leakage, or both breasts may give out milk when an infant is feeding from one breast. However, this and other problems often settle after two weeks of feeding. Stress or anxiety can cause difficulties with breastfeeding.

A poor milk ejection reflex can be due to sore or cracked nipples, separation from the infant, a history of breast surgery, or tissue damage from prior breast trauma. If a mother has trouble breastfeeding, different methods of assisting the milk ejection reflex may help. These include feeding in a familiar and comfortable location, massage of the breast or back, or warming the breast with a cloth or shower.

Afterpains

The surge of oxytocin that triggers the milk ejection reflex also causes the uterus to contract. During breastfeeding, mothers may feel these contractions as afterpains. These may range from period-like cramps to strong labour-like contractions and can be more severe with second and subsequent babies.

Lactation without pregnancy

Women who have never been pregnant are sometimes able to induce enough lactation to breastfeed. This is called "induced lactation". A woman who has breastfed before and re-starts is said to "relactate". If the nipples are consistently stimulated by a breast pump or actual suckling, the breasts will eventually begin to produce enough milk to begin feeding a baby. Once established, lactation adjusts to demand. This is how some adoptive mothers, usually beginning with a supplemental nursing system or some other form of supplementation, can breastfeed. There is thought to be little or no difference in milk composition whether lactation is induced or a result of pregnancy. Rare accounts of male lactation (as distinct from galactorrhea) exist in medical literature.

Some drugs, primarily atypical antipsychotics such as Risperdal, may cause lactation in both women and men. Also, some couples may use lactation for sexual purposes.

References

See also

• Galactogogue
• Milk line
• Udder

External links

• How mammals lost their egg yolks - Did mammals develop nutritional milk before or after they abandoned yolky eggs? (New Scientist, 18 March 2008)

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