Physiology of lactation
This article ‘physiology of lactation’ highlights the stages of lactation in humans, the mechanism of lactation. After reading this article, you would understand the physiology of lactation and outline the process of lactation. Finally, this article shall soon be available in other file formats, such as physiology of lactation pdf; physiology of lactation ppt; and physiology of lactation slideshare.
Lactation is the secretion of milk from specialized glands (mammary glands) to provide nourishment to a newborn.
- Lactation is a hallmark feature in female mammals.
- Lactation is under endocrine control. The two main hormones involved are prolactin and oxytocin.
- Lactogenesis, the process of changes to the mammary glands (breasts) to start producing milk, begins during the late stages of pregnancy. The delivery of the placenta and the resulting dramatic reduction in progesterone, estrogen, and human placental lactogen concentrations stimulate milk production.
- Colostrum is the first milk a nursing mother produces. It contains higher amounts of leukocytes (white blood cells) and antibodies (immunoglobulins) than mature milk and is especially high in immunoglobulin A. This immunoglobulin coats the lining of the baby’s immature intestines, helping to prevent pathogens from invading the baby’s system. Pathogens are disease-causing organisms.
Definition of Terms
This is a form of milk produced by the mammary glands (breasts) in late stages pregnancy and the few days after delivery. Human colostrum is thick and yellowish has high concentrations of nutrients and antibodies. However, it is small in quantity.
2. Mammary gland
A mammary gland is an exocrine gland in mammals that produces milk to feed young offspring. Mammals get their name from the word “mammary“. Thus, it is a gland that produces milk for suckling an infant or offspring.
This refers to the secretion of milk from the mammary gland of a female mammal. In addition, it is the process of providing the milk to the young, such as breastfeeding. Finally, it can refer to the period that a mother lactates to feed her young; the lactation period.
Physiology of Lactation – Introduction
Lactation refers to the secretion of milk from the mammary glands and the period during which the mother lactates (produces milk) to feed her young. The process occurs in all female mammals, not only in humans.
In humans, the process of feeding milk is called breastfeeding or nursing.
What is the main function of lactation? The major function of lactation is to provide nutrition and immune protection to the young after birth. Proteins in colostrum and milk include maternal immunoglobulins, secreted into the ducts and absorbed intact by the infant’s intestinal epithelium. This process transfers some of the mother’s immunity to the infant during its first weeks of life.
In addition, in almost all mammals, lactation induces a period of infertility, which serves to provide the optimal birth spacing for survival of the offspring. A newborn has lost its source of maternal nourishment through the placenta and must rely on external source of food instead.
Specie-specific Variations in Lactation: 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 (endocrine disruption). This phenomenon may also be observed in newborn infants as well (for instance, witch’s milk).
What is galactopoiesis? Galactopoiesis is the maintenance of milk production. This stage requires two hormones: prolactin and oxytocin.
Preparation for Lactation
During puberty, the breasts start to develop under the influence of estrogen. The milk ducts grow and branch, and fat is deposited behind the glandular tissue.
During pregnancy, the glands develop further under the influence of estrogen, growth hormone and cortisol. The final development stage also requires progesterone, which converts the duct epithelium into secretory structure. This process is similar to progesterone effect on the uterus, in which progesterone makes the endometrium become a secretory tissue during the luteal phase.
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 the lactogenesis I stage. This is when the breasts make colostrum, a thick, sometimes yellowish fluid.
At this stage, high levels of progesterone inhibit most milk production. It is not a medical concern if a pregnant woman leaks any colostrum before her baby’s birth, nor is it an indication of future milk production.
The Role of Prolactin in Lactation (milk production)
Although estrogen and progesterone stimulate mammary gland development, they inhibit secretion of milk. Milk secretion is stimulated by prolactin from the anterior pituitary. Prolactin’s secretion is primarily controlled by prolactin-inhibiting hormone (PIH) from the hypothalamus. Mounting evidence suggest that PIH is actually dopamine.
During the later stages of pregnancy, PIH secretion falls, and prolactin reaches levels 10 or more times those found in non-pregnant women.
Production of Colostrum occurs prior to Delivery and shortly after delivery
Prior to delivery, when estrogen and progesterone are also high, the mammary glands produce only small quantities of a thin, low-fat secretion called colostrum.
After delivery, when estrogen and progesterone decrease, the glands produce greater quantities of calcium.
At birth, prolactin levels remain high, while the delivery of the placenta results in a sudden drop in progesterone, estrogen, and human placental lactogen levels. This abrupt withdrawal of progesterone in the presence of high prolactin levels stimulates the copious milk production of the lactogenesis II stage.
The Role of Suckling in Breastfeeding
Suckling, the mechanical stimulus of the infant nursing at the nipple, reinforces the inhibition of PIH, begun in the last weeks of pregnancy. In the absence of PIH, prolactin secretion increases, resulting in milk production.
Milk Let-down Reflex
The ejection of milk from the glands, known as the letdown reflex, requires the presence of oxytocin from the posterior pituitary. Oxytocin initiates smooth muscle contraction in the uterus and breasts. In the lactating breast, oxytocin causes contraction of myoepithelial cells surrounding the mammary glands. This contraction creates the pressure that sends the milk squirting into the infant’s mouth.
Although prolactin release requires mechanical stimulus of suckling, oxytocin release can be stimulated by various cerebral stimuli, including the thought of the child. For this reason, many nursing mothers experience inappropriate milk release triggered by hearing someone else child cry.
Pregnancy is not a requirement for Lactation
Note: Pregnancy is not a requirement for lactation, and some women who have adopted babies have been successful in breastfeeding.
When the breast is stimulated, prolactin levels in the blood rise and peak in about 45 minutes, then return to the pre-breastfeeding state about three hours later. The release of prolactin triggers the cells in the alveoli to make milk.
What is Colostrum?
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 pathogens 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.