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2. Breastfeeding

3. Hormonal Control of Lactation


Lactation describes the secretion of milk from the mammary glands and the period of time that a mother lactates to feed her young.

The process occurs in all female mammals. In humans the process of feeding milk is called breastfeeding or nursing.

The male may produce milk as the result of a hormone imbalance.

Galactopoiesis is the maintenance of milk production. This stage requires prolactin and oxytocin.

The chief function of lactation is to provide nutrition and immune protection to the young after birth.

Lactation induces a period of infertility, which serves to provide the optimal birth spacing for survival of the offspring.

When the baby sucks its mother’s breast, oxytocin compels the milk to flow from the alveoli, through the ducts into the sacs behind the areola and then into the baby’s mouth.

Initiation of lactation

Expulsion of placenta leads to a decline in estrogens and progesterone level

Drop in estrogen initiates lactation

Prolactin and estrogen synergize in producing breast growth

Estrogen antagonizes milk producing effect of prolactin on the breast


Estrogens are used to stop lactation in mothers who do not wish to nurse baby or have lost baby at delivery

Suckling evokes reflex oxytocin release and milk ejection

Suckling maintains and augments milk secretion because of the stimulation of prolactin secretion produced by suckling

Milk contains an inhibitory peptide. If the breasts are not fully emptied, the peptide accumulates and inhibits milk production.

This autocrine action thus matches supply with demand.

Breast development


1.Estrogen-duct proliferation 2.Progesterone-lobule development 3.Human chorionic somatomammotropin 4.Prolactin’s role during puberty in humans?

Steady increase of prolactin, and elevated levels of estrogen and progesterone during pregnancy up to term

Breast development

Growth of the ductal system are 3 other hormones:

1.growth hormone,

2. the adrenal glucocorticoids, and 3.insulin.

Each play at least some role in protein metabolism, which presumably explains their function in the development of the breasts.

Hormonal Control of Lactation

From the 24th week of pregnancy, 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, high levels of progesterone inhibit lactation before birth. Progesterone levels drop after birth, this triggers the onset of copious milk production.

Oestrogenstimulates the milk duct system to grow and differentiate. Like progesterone high levels of oestrogen also inhibit lactation. Oestrogen levels also drop at delivery and remain low for the first several months of breastfeeding.

It is recommended that breastfeeding mothers avoid oestrogen-based birth control methods, as a spike in estrogen levels may reduce a mother’s milk supply.

Prolactincontributes to the increased growth and differentiation of the alveoli, also influences differentiation of ductal structures. High levels of prolactin during pregnancy and breastfeeding also increase insulin resistance, increase IGF-1 and modify lipid metabolism in preparation for breastfeeding.

During lactation PL is the main factor maintaining tight junctions of ductal epithelium and regulating milk production through osmotic balance.

Hormonal Control of Lactation

GH is structurally very similar to prolactin and contributes to its galactopoietic function.

ATCH and glucocorticoids have an important lactation inducing function in several animal species. ACTH is thought to contribute as it is structurally similar to prolactin. Glucocorticoids play a complex regulating role in the maintenance of tight junctions.

TSH is a very important galactopoietic hormone, its levels are naturally increased during pregnancy.

Oxytocincontracts the smooth muscle of the uterus during and after birth, and during orgasm(s).

After birth, oxytocin contracts the smooth muscle layer of band-like cells surrounding the alveoli to squeeze the newly-produced milk into the duct system. Oxytocin is necessary for the milk ejection reflex, or let-down to occur.

Human placental lactogen (HPL)—From the second month of pregnancy, the placenta releases large amounts of HPL. This hormone appears to be instrumental in breast, nipple, and areola growth before birth.

By the fifth or sixth month of pregnancy, the breasts are ready to produce milk.


During the latter part of pregnancy, the woman’s breasts enter into Lactogenesis . The breasts make colostrum, a thick, sometimes yellowish fluid.

At this stage, high levels of progesterone inhibit most milk production.

At birth, prolactin levels remain high, while the delivery of the placenta results in a sudden drop in progesterone, estrogen, and HPL levels.

This abrupt withdrawal of progesterone in the presence of high prolactin levels stimulates the copious milk production.

When the breast is stimulated, prolactin levels in the blood rise, peak in about 45 min, and return to the pre-breastfeeding state about 3hrs later. The release of prolactin triggers the cells in the alveoli to make milk.

Prolactin also transfers to the breast milk. Some research indicates that prolactin in milk is greater at times of higher milk production, and lower when breasts are fuller, and that the highest levels tend to occur between 2 a.m. and 6 a.m.

Colostrum is the first milk a breastfed baby receives. It contains higher amounts of WBCs and Ab than mature milk, and is especially high in IgA, which coats the lining of the baby’s immature intestines, and helps to prevent pathogens from invading the baby’s system.

Secretory IgA also helps prevent food allergies. Over the first two weeks after birth, colostrum production slowly gives way to mature breast milk.


The hormonal endocrine control system drives milk production during pregnancy and the first few days after the birth.

When the milk supply is more firmly established, autocrine control system begins.

During this stage, the more that milk is removed from the breasts, the more the breast will produce 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 deficitspoor latching techniquehypoplastic breast tissue

a metabolic or digestive inability in the infantinadequate calorie intake or malnutrition of the mother

Let down reflex Oxytocin simultaneously stimulates the

contraction of the:

1.myometrium in the uterus and

2.myoepithelial cells lining the duct walls of the breast to squeeze out the milk.

Milk ejected through the nipple

Composition of milk

Human breast milk is the healthiest form of milk for babies. There are few exceptions, such as when the mother is taking certain drugs or is infected with human T-lymphotropic virus, HIV, or has active untreated tuberculosis.

Breastfeeding promotes health and helps to prevent disease. Artificial feeding is associated with more deaths from diarrhea in infants in both developing and developed countries.

The WHO emphasize the value of breastfeeding for mothers as well as children. Both recommend exclusive breastfeeding for the first six months of life and then supplemented breastfeeding for at least one year and up to two years or more.

Not all the properties of breast milk are understood, but

its nutrient content is relatively stable. Breast milk is made from nutrients in the mother’s bloodstream and bodily stores.

Breast milk has just the right amount of fat, sugar, water, and protein that is needed for a baby’s growth and development. Because breastfeeding uses an average of 500 calories a day it helps the mother lose weight after giving birth.

The composition of breast milk changes depending on how long the baby nurses at each session, as well as on the age of the child.

Composition of milk

ConstituentHuman Milk (%)Cow’s Milk (%)
Lactalbumin and other proteins0.40.7


Scientific research has found many benefits to breastfeeding for the infant. These include:

Greater immune health

During breastfeeding, antibodies pass to the baby. This is one of the most important features of colostrum. Breast milk contains several anti-infective factors such as

bile salt stimulated lipase (protecting against amoebic infections),

lactoferrin (which binds to iron and inhibits the growth of intestinal bacteria)

and IgA protecting against microorganisms.

2. Fewer infections

Among the studies showing that breastfed infants have a lower risk of infection than non-breastfed infants are:

In a 1993 University of Texas Medical Branch study, a longer period of breastfeeding was associated with a shorter duration of some middle ear infections (otitis media with effusion) in the first two years of life.

A 1995 study of 87 infants found that breastfed babies had half the incidence of diarrheal illness, 19% fewer cases of any otitis media infection, and 80% fewer prolonged cases of otitis media than formula fed babies in the first twelve months of life.

Breastfeeding appeared to reduce symptoms of upper respiratory tract infections in premature infants up to seven months after release from hospital in a 2002 study of 39 infants.

A 2004 case-control study found that breastfeeding reduced the risk of acquiring urinary tract infections in infants up to seven months of age, with the protection strongest immediately after birth.

3. Protection from SIDS

Breastfed babies have better arousal from sleep at 2–3 months. This coincides with the peak incidence of sudden infant death syndrome.

A study conducted at the University of Münster found that breastfeeding halved the risk of sudden infant death syndrome in children up to the age of 1.

4. Higher intelligence

Studies have examined whether breastfeeding in infants is associated with higher intelligence later in life. Many have found a connection:

In “the largest randomized trial ever conducted in the area of human lactation,” between 1996 and 1997 maternity hospitals

and polyclinics in Belarus were randomized to receive or not receive breastfeeding promotion modeled on the Baby Friendly Hospital Initiative.

Of 13,889 infants born at these hospitals and polyclinics and followed up in 2002-2005, those who had been born in hospitals and polyclinics receiving breastfeeding promotion had IQs that were 2.9-7.5 points higher (which was significantly higher).

Since (among other reasons) a randomized trial should control for maternal IQ, the authors concluded in a 2008 paper that the data “provide strong evidence that prolonged and exclusive breastfeeding improves children’s cognitive development.”

5. Less diabetes

Infants exclusively breastfed have less chance of developing diabetes mellitus type 1 than peers with a shorter duration of breastfeeding and an earlier exposure to cow milk and solid foods. Breastfeeding also appears to protect

against diabetes mellitus type 2, at least in part due to its effects on the child’s weight.

6. Less childhood obesity

Breastfeeding appears to reduce the risk of extreme obesity in children aged 39 to 42 months. The protective effect of breastfeeding against obesity is consistent, though small, across many studies, and appears to increase with the duration of breastfeeding.

7. Less tendency to develop allergic diseases (atopy)

In children who are at risk for developing allergic diseases, atopic syndrome can be prevented or delayed through exclusive breastfeeding for four months, though these benefits may not be present after four months of age. However, the key factor may be the age at which non-breastmilk is introduced rather than duration of breastfeeding. Atopic dermatitis, the most common form of eczema, can be reduced through exclusive breastfeeding beyond 12 weeks in individuals with a family history of atopy, but when breastfeeding beyond 12 weeks is combined with other foods incidents of eczema rise irrespective of family history.

Longterm benefits

Breastfeeding may decrease the risk of cardiovascular disease in later life, as indicated by lower cholesterol and C-reactive protein levels in adult women who had been breastfed as infants.

The 2007 review for the WHO concluded that breastfed infants “experienced lower mean BP” later in life. A 2006 study found that breastfed babies are better able to cope with stress later in life.

Less overweight

Doctors have long known that breast-fed infants are less likely to become overweight. A study in Today’s Pediatrics associates solid food given too early to Formula-fed babies before 4 months old will make them 6 times as likely to become obese by age 3. It does not happen if the babies were given solid foods with breast feeding.

Benefits for mothers

1. Breastfeeding is a cost effective way of feeding an infant, providing nourishment for a child at a small cost to the mother. Frequent and exclusive breastfeeding can delay the return of fertility through lactational amenorrhea, though breastfeeding is an imperfect means of birth control. It is possible for women to ovulate within two months after birth while fully breastfeeding and get pregnant again.

2. Bonding

Hormones released during breastfeeding help to strengthen the maternal bond. Teaching partners how to manage common difficulties is associated with higher breastfeeding rates. Support for a mother while breastfeeding can assist in familial bonds and help build a paternal bond between father and child.

3. Hormone release

Breastfeeding releases oxytocin and prolactin, hormones that relax the mother and make her feel more nurturing toward her baby. Breastfeeding soon after giving birth increases the mother’s oxytocin levels, making her uterus contract more quickly and reducing bleeding.

4. Weight loss

As the fat accumulated during pregnancy is used to produce milk, extended breastfeeding— at least 6 months—can help mothers lose weight. However, weight loss is highly variable among lactating women; monitoring the diet and increasing the amount/intensity of exercise are more reliable ways of losing weight.

Effect of lactation on menstrual cycle

Menses return after 6 weeks if mother does not breastfeed child

Regular breastfeeding promotes amenorrhea in most women for 25 to 30 weeks postpartum

Nursing stimulates prolactin secretion


Inhibits GnRH secretion

Inhibits actions of GnRH on the pituitary

Antagonizes action of gonadotropins on the ovaries

Ovulation is inhibited and ovaries are inactive

Estrogen and progesterone production falls below the threshold

Lactation amenorrhea

Only 5-10 % of women become pregnant again while breastfeeding

Nursing is an old but partially effective method of birth control

Almost 50% of cycles in the first six months after resumption of menses are anovulatory

Chiari-Frommel Syndrome-rare condition where amenorrhea and galactorrhea persists in mothers who choose not to nurse their babies


Gynecomastia is the abnormal development of large mammary glands in males

The condition can occur physiologically in neonates due to female hormones from the mother, in adolescence, and in the elderly.

Both in adolescence and elderly it is an abnormal condition associated with disease or metabolic disorders. In adolescent boys the condition is often a source of distress, but for the large majority of boys whose pubescent gynecomastia is not due to obesity, the breast development shrinks or disappears within a couple of years.

Gynecomastia is generally attributed to an imbalance of sex hormones or the tissue responsiveness to them.

Approximately 4 to 10% cases of gynecomastia are due to drugs.

Breast prominence can result from hypertrophy of breast tissue, chest adipose tissue (fat) and skin, and is typically a combination. Breast prominence due solely to excessive adipose is often termed pseudogynecomastia or lipomastia.

Gynecomastia should be distinguished from muscle hypertrophy of the pectoralis muscles caused by exercise (e.g., swimming, bench

press, etc.)