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Lactogenesis - The Onset of Milk Secretion or Lactation

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Lactogenesis is the formation of milk from a woman’s mammary gland. This article delivers the knowledge one must possess about lactogenesis.

Medically reviewed by

Dr. Sonal Prasad

Published At June 14, 2022
Reviewed AtMay 14, 2024


Lactation is a process of milk formation that begins in the mid-stage of pregnancy, even before the initial latch of the newborn takes place. A woman's breast tends to undergo various changes in composition, size, and shape during puberty, pregnancy, and lactation. All these stages are governed by a cascade of physiologic changes essential to successful breastfeeding in a woman’s body.

In the postpartum period, some women may experience breastfeeding difficulty if they have inadequate milk production, poor milk extraction, or insufficient caloric intake to meet their body demands. Therefore, all lactating mothers are recommended to have an extra 300-500 calories per day to meet lactation needs. Besides, all women are suggested to frequently empty their breasts, usually every two hours to three hours, to maintain proper milk supply.

What Is Lactogenesis?

Lactogenesis is the onset of milk secretion from the mammary gland. It includes all the changes occurring in the mammary epithelium from undifferentiated mammary gland to fully developed lactation in a woman.

The release of prolactin hormones from the anterior pituitary gland and oxytocin from the posterior pituitary gland regulates milk secretion from the mammary gland. It is maintained by frequent removal of milk. Stimulation of the nipple by the suckling ability of the infant triggers the release of these hormones. The mammary gland must receive hormonal signals to maintain milk secretion. Although these hormones act independently, their collective action is essential for successful breastfeeding.

There is a change in concentration and milk volume from colostrum to transitional milk and mature milk. Therefore, it varies according to the growing needs of the infants. That is why breast milk is considered the best source of nutrition for an infant's growth and development. All breastfeeding mothers are suggested to breastfeed their newborn as often as possible to maintain a proper flow of milk supply in the mammary ducts.

What Is the Physiology of Lactation?

Women's breasts are composed of two major structures called ducts and lobules. Approximately ten major ducts open onto the skin surface of the nipple. Large ducts lead to the terminal duct lobular unit, and these terminal ducts branch into grape-like clusters of small acini to form a lobule. There are mainly three types of lobules. These lobules are formed at different stages of a woman's development. These lobules increase progressively in number and size by the end of pregnancy. The breast is composed entirely of lobules separated by small amounts of the stroma at this stage.

During puberty, the formation of lobule type 1 occurs. The level of estrogen and progesterone during each menstrual cycle stimulates lobule 1 to produce new alveolar buds. This leads to the formation of type-2 and type-3 lobules in the breasts. After puberty, no further change occurs in the female breast until pregnancy.

What Are the Stages of Lactogenesis?

Lactogenesis is the process of developing the ability to secrete breast milk. The method of lactation involves the maturation of alveolar cells. There are two main stages: secretory initiation and secretory activation.

  • Stage I Lactogenesis: It is secretory initiation during the mid-stage of pregnancy. During that period, the placenta supplies more progesterone, which inhibits further differentiation. As a result, some women may notice small amounts of milk secretion by week 16th of gestation, and some may express colostrum by late pregnancy.

  • Stage II Lactogenesis: It is secretory activation that begins with copious milk formation after delivery. It is stimulated by removing the placenta at delivery, the rapid drop in progesterone levels, and elevated prolactin, cortisol, and insulin levels. It is commonly reported that most women experience swelling of the breast and copious milk production on the second or third day of postpartum. Some reports claim lower milk volume in women who had cesarean births than those who delivered vaginally. Women with placental remnants, diabetes, and stressful vaginal deliveries show a late onset of milk production. The retained placental fragments could inhibit lactogenesis stage II by continued secretion of progesterone that remains the same until the remaining placental fragments are removed.

The secretion of prolactin hormone increases rapidly with the suckling of the nipple by the infant, as it stimulates the nerve endings located around the nipples. Oxytocin is responsible for milk ejection or the letdown reflex. It leads to the contraction of cells, hence forcing milk into the mammary ducts that come out through the nipple. Additionally, oxytocin has a psychological effect, and it can induce a calm state to reduce stress. Ultimately, it helps to enhance the feelings of affection between the mother and the child, which is essential for their bonding.

After establishing lactation, production is regulated by the interaction of physical and biochemical factors. For example, when breast milk is not removed, an elevation in the intramammary pressure causes the accumulation of a feedback inhibitor of lactation to reduce milk production and initiate mammary involution.

However, if breast milk is adequately removed from the breast, the inhibitor is also removed, and the secretion of breast milk will continue normally. The feedback inhibitor of lactation regulates the milk volume, which is primarily determined by how much milk the baby takes.

When Does a Person Lactate During Pregnancy?

Lactation starts in the initial two weeks during the second trimester of the pregnancy. During this time, estrogen and progesterone increase, and the body prepares for lactation by improving the number of milk ducts in the breast. These milk ducts will transport milk to the nipple from the alveoli. During the middle of pregnancy, the body produces colostrum, which is the first milk for the baby.


Lactogenesis stage I starts when the woman is six months pregnant. Some may experience milk secretion from their breast by the end of pregnancy. Lactogenesis stage II is the onset of the secretion of copious breast milk called colostrum. It occurs during the first four days of postpartum. Colostrum has various health benefits for infants. It provides a protective shield for newborns and prevents many systemic diseases in the later stages of life. Sometimes, delayed lactogenesis can occur with stressful deliveries or in the case of an underlying systemic disease like diabetes. One may seek the help of a lactation specialist if the milk formation is delayed for an extended period.

Frequently Asked Questions


What Hormone Is Responsible for Lactogenesis?

Lactation is the process of producing milk. Prolactin is the hormone produced by the small gland in the base of the brain called the pituitary gland. The prolactin hormones are high in pregnant women. Prolactin is the hormone responsible for breast tissue development and milk production. This hormone is also known as lactotropin hormone and is found in elevated levels in breastfeeding and pregnant women.


What Are Lactogenesis and Galactopoiesis?

 - Lactogenesis- It is the process of secreting milk that involves the maturation of alveolar cells of the breast tissue. Stage 1 lactogenesis takes place during the second half of pregnancy. A small amount of milk is generated by the 16th week of gestation. In stage 2 lactogenesis there is copious production of milk after delivery of the baby.
 - Galactopoiesis- Prolactin is the hormone responsible for galactopoiesis. Galactopoiesis is the maintenance of milk production. Regular and frequent removal of milk from the mammary gland stimulates further milk secretion.


How Lactogenesis Is Stimulated?

When the baby sucks the nipples the nerves are stimulated that induces the body to produce more oxytocin and prolactin. The prolactin hormone controls the production of milk. Prolactin makes the alveoli produce more milk and the breast muscles are contracted by oxytocin which causes muscle contractions and pushes the milk through the alveoli ducts.


What Is Lactation Milk Called?

Lactation is the process of secreting milk from the breast. Colostrum is the first milk of the breasts that is created during lactation and it is thick and yellow. Hence it is called liquid gold. Colostrum is rich in minerals, proteins, vitamins, and antibodies. This stage of first milk production begins during pregnancy and is loaded with immunity-boosting compounds and nutrients.


What Is Milk Secretion Called?

Milk secretion is called lactation. Lactation is the process of producing milk from the mammary glands of the breast. The hormones signal the mammary glands to produce milk. Lactation ends when the body stops producing milk. The primary reason for lactation is to feed a baby. It is a biological response that occurs after pregnancy to feed the baby. A series of hormones trigger the lactogenesis process.


What Are Examples of Lactogenic Hormones?

- Examples of lactogenic hormones are prolactin and human placental lactogen (hPL). Placental lactogen is a peptide hormone that is secreted by an animal and human endocrine cells. The hormone is released by the placenta during pregnancy. During pregnancy, these hormone levels rise and they drop after pregnancy. It is involved in metabolic functions and insulin resistance.
- Prolactin is the hormone responsible for breast tissue development and milk production. This hormone is also known as lactotropin hormone and is found in elevated levels in breastfeeding and pregnant women.


What Are the Two Hormones That Stimulate Milk Secretion?

Prolactin and oxytocin are the two hormones that secrete milk. Prolactin stimulates the mammary gland to produce milk. The milk produced in the initial lactation days is called colostrum. It prepares the mammary gland for milk secretion. The prolactin concentration is increased during pregnancy. Oxytocin is called the "milk ejection reflex” because it makes milk ready for flow to the baby so that the baby gets milk easily.


What Is the Average Timing of Lactogenesis?

Stage 1 of lactogenesis occurs during the second half of pregnancy. A small amount of milk is secreted during the 16th week of gestation. Lactogenesis is the onset of copious production of milk that occurs between 48 hours and 72 hours postpartum.


What Controls the Milk Secretion?

The prolactin hormone controls milk secretion in the body. Prolactin is produced in the early stage of pregnancy. Prolactin induces the alveoli of the breast to make more milk. Prolactin promotes the synthesis of milk within the alveolar cells of the breast. Prolactin helps make milk. It is involved in the development of mammary glands within the breast and milk production. Prolactin hormone is synthesized from the lactotrophs of the anterior pituitary gland (a small gland in the brain). Human prolactin is also produced in the brain, breasts, prostate, skin, and adipose tissues.


What Hormones Affect Lactation?

The two hormones prolactin and oxytocin affect lactation. 
 - Oxytocin- The oxytocin reflex is called the ‘milk ejection reflex’. It contracts the muscles of the breast to eject the milk. It makes the milk flow out for feeding and helps the baby get milk easily.
 - Prolactin- Prolactin promotes the growth of the alveoli of the mammary gland. Prolactin promotes the synthesis of milk within the alveolar cells of the breast. Prolactin helps make milk.


What Is the Role of Prolactin in Lactation?

Prolactin promotes the mammary gland alveoli which are the components of the mammary gland of the breast. The actual production of milk happens in the alveoli of the mammary gland. Prolactin promotes the growth of the alveoli of the mammary gland. Prolactin promotes the synthesis of milk within the alveolar cells of the breast. Prolactin helps make milk.


What Is Lactogenesis vs Galactogenesis?

 - Galactogenesis- It is the process of production of milk by the mammary glands. Galacterogenesis is termed milk production whereas lactogenesis is milk formation. 
 - Lactogenesis- It is the process of development of the ability to produce milk that involves the maturation of alveolar cells in the breast tissue. Stage 1 lactogenesis takes place during the second half of pregnancy. It is the process where the female achieves the ability to produce milk that involves the development of alveolar cells.


Which Enzyme Is Responsible for Milk Secretion?

Several enzymes are taking part in milk secretion within the mammary gland that includes trypsin, and elastase. Research studies say that several enzymes are taking part rapidly in the digestion of human milk proteins including trypsin, chymotrypsin, elastase, and glutamyl endopeptidases like enzymes,s, and proline endopeptidase.
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Dr. Sonal Prasad
Dr. Sonal Prasad

Obstetrics and Gynecology


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