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HomeHealth articleslactationWhat Is the Physiology of Lactation?

Physiology of Lactation - Anatomical Features, Phases, and Role of Colostrum

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Breastfeeding is a natural process induced by various hormones. Read more to learn about the science behind breast milk production.

Medically reviewed by

Dr. Richa Agarwal

Published At December 26, 2022
Reviewed AtJune 28, 2023

Introduction:

The male and female human bodies contain mammary glands. These glands do not further develop in males, but females undergo breast development during puberty and pregnancy. A female has a pair of mammary glands that start developing from puberty under the stimulus of various hormones. During conception, the body starts producing various hormones for the ejaculation of milk out of these mammary glands.

What Are the Anatomical Features Seen Around a Lactating Breast?

The breast tissue comprises the following cells:

  • Muscles: Both pectoralis major and minor muscles cover the roof and bottom of the breast tissues on the left and right sides.
  • Myoepithelial Cells: These cells are responsible for the ejection of milk outside the mammary gland. They are seen in a network fashion. It is made up of muscle cells and performs contraction to eject milk.

  • Lactiferous Ducts: The milk is ejected through these narrow ducts.

  • Areolae: They are present in a circular shape and are dark in color. The vision of the child is not developed during infancy. Hence, this marks an identification spot for the child to suck breast milk. The areolae also produce a lipid fluid to moisturize the mammary gland from cracks due to repeated sucking of breast milk. Lipoid fluid is secreted from these areolae, which have an aroma. The baby can smell this and initiates the feeding mechanism.

  • Fatty Tissue: The fat cells present give the breasts their mass structure, supporting other tissues. It also acts as a shock absorbent suspensory cell, Cooper’s ligaments, protecting breasts. It is made up of collagen and elastin cells.

  • Blood and Nerve Vessels: Various receptors in the nerve cell give signals to the brain to produce hormones responsible for milk production. The blood vessels supply oxygenated blood and help heal any injury present.

  • Alveolus: These are modified sweat glands that produce milk.

What Are the Different Phases Involved in Lactation?

Different stages combined help in milk secretion. There are mainly four stages involved in the lactation process. They are

  • Mammogenesis: The breast is prepared for milk secretion.

  • Lactogenesis: The synthesis and production of milk occur.

  • Galactokinesis: The milk is ejected from mammary ducts.

  • Galactopoiesis: The process of ongoing lactation is maintained.

What Is the Physiology Behind Breast Milk Production?

During pregnancy, the body starts producing various hormones for the growth and development of the baby and preparing the breasts for milk production. Following are some of the physiological processes which take place during pregnancy.

  • Ductal Growth: The ducts present in the mammary gland start dividing and making more branches. This process occurs due to estrogen hormone stimulation. Estrogen also helps in the deposition of fat.

  • Lobulo-alveolar Growth: The alveolus at the tip of ducts starts developing due to the branching of ducts. This occurs due to the stimulation of the progesterone hormone.

  • Prolactin: The prolactin hormone is elevated in the body from conception. This hormone is responsible for the secretion of milk but does not produce milk until the baby is delivered. This inhibition is caused due to estrogen and progesterone hormones.

  • Placenta: The placenta produces human placental lactogen (HPL) and progesterone.

  • Anterior Pituitary Gland: It produces prolactin hormone. The production of HPL, progesterone, and prolactin together prepare the alveolar cells to make milk.

  • Post-delivery: Once the baby is delivered, the estrogen and progesterone hormone levels start reducing. Along with the expulsion of the placenta, estrogen and progesterone hormones are also expelled from the body. This gives rise to the process of lactogenesis or milk secretion with the help of the prolactin hormone.

What Is a Witch’s Milk?

After the delivery, when the estrogen and progesterone hormones get expelled from the body, it starts the process of milk secretion. Sometimes, there is a high rise in prolactin hormone in the maternal blood. This high prolactin level gets transferred to the baby’s body. This initiates minor milk secretion in the newborn. This is known as ‘witch’s milk.’

Which All Hormones Are Produced During Pregnancy?

Hormones that play a crucial role during pregnancy are as follows:

  • Estrogen: It helps the pregnancy journey. Estrogen promotes the growth and development of infants.

  • Progesterone: It helps the attachment of embryos to the uterus lining. Progesterone prepares the breasts for lactation.

  • Oxytocin: These are hormones of uterine contraction during child labor. It also aids in milk production.

  • Cortisol: It maintains the blood sugar level and is produced by adrenal glands above the kidneys.

  • Thyroid Hormone: The thyrotropin-releasing hormone (TRH) helps increase prolactin hormone production. At the same time, the thyroid hormone decreases the production of prolactin hormone.

  • Growth Hormone: This helps in the growth and development of the fetus, like the maturation of organs and bone formation.

  • Relaxin: It helps in blood regulation and prevents premature delivery. It composes the cervix at the time of birth.

  • Prolactin: These are hormones that are primarily responsible for milk production and the development of breasts.

  • Human Chorionic Somatomammotropin (HCS): It is also known as human placental lactogen (HPL). This hormone has a similar function to that of growth hormone. It helps in the development of the fetus and the production of milk. It also produces insulin-like growth factors (IGF) one and two. Both IGF one and two promote the growth of cells.

What Is a Letdown Reflex of Lactation?

During pregnancy, the action of various hormones helps produce milk, but the hypersecretion of progesterone hormone can prevent milk letdown, and the breasts stop producing milk. This leads to the enlargement of breast tissue. When the child develops breast latching and starts sucking breast milk, the mechanoreceptor cells get stimulated and send signals to the hypothalamus. The hypothalamus then starts the production of prolactin and oxytocin hormones. The prolactin hormone stimulates alveolar cell milk production, and oxytocin stimulates the myoepithelial cells to contract to eject the milk. This process is known as milk letdown, oxytocin, prolactin, or suckling reflex. The sound of the baby crying can also initiate the letdown reflex.

What Is the Role of Colostrum in an Infant’s Life?

The very first milk pumped out of a mother's breast is thick and yellowish in color, known as the colostrum. This milk is immediately used to feed the child. The colostrum is rich in immune cells and antibodies that protect the child from infections. The white blood cells in colostrum are rich in neutrophils and macrophages that protect the baby from infections. It is low in fat content. Colostrum coats the lining of the gastrointestinal tract of babies and helps the baby to pass the first stools or meconium. Gradually, the breasts start producing milk which is higher in fat content. Human milk consists of the following composition:

  • Water: 88.5%.

  • Fat: 3.3%.

  • Lactose: 6.8%.

  • Casein: 0.9%.

  • Lactalbumin and Other Proteins: 0.4%.

  • Ash or Trace Elements or Electrolytes: 0.2%.

In human milk, there is a high amount of lactose, whereas in cow’s milk, there is only 4.8% of lactose. Lactose adds sugar to milk and helps the baby fight infections like diarrhea.

What Is Known by Lactational Amenorrhea?

Post delivery, the level of prolactin hormone is high and helps in milk secretion. The elevated prolactin level lowers the production of gonadotropin-releasing hormone (GnRH). This, in turn, causes decreased secretion of luteinizing hormone (LH) and follicular stimulating hormone (FSH). The absence of these hormones causes the inactivation of the ovaries. The whole process of ovulation stops and leads to amenorrhea, meaning a lack of menstruation. This is known as lactational amenorrhea, caused due to increased prolactin surge in the human body.

What is Chiari-Frommel Syndrome?

This is an abnormal condition with persistent milk production and persistent inhibition of menstruation. This is caused due to persistent secretion of the prolactin hormone. It is a rare pathological condition seen commonly in women who do not breastfeed their children.

Conclusion:

An average human body produces one point five liters of milk daily. This depends on the supply and demand of the child, as seen differently in the case of twins and multiples. The process of lactation begins within one hour of delivery. The primary source of milk secretion depends on the letdown reflex. The suckling reflex of the baby stimulates this reflex. The baby's sight, sound, and thoughts can initiate milk secretion. Therefore, physical stimulation also has a crucial role in milk synthesis apart from hormonal stimulation.

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Dr. Richa Agarwal
Dr. Richa Agarwal

Obstetrics and Gynecology

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