Mammary Glands (Breast)


The breast or mammary gland is a highly efficient organ mainly used to produce milk and is a mass of glandular, fatty, fibrous tissues. Mammary glands are exocrine glands that are enlarged and developmentally are modified sweat glands that are actually part of the skin. They are also classified as tubualveolar glands and are located in the breast lying on the top of the pectoralis major muscles. These glands are present in males and females; however, they normally function in the latter gender only.


The biological role of the mammary glands is to produce milk to nourish a newborn baby and to pass antibodies needed for baby’s protection against infections (passive immunity) while the immature immune is initiating its function.

Breast Anatomy
The breast is internally composed of the following parts:
  • Lobes and Lobules
    • Internally, the mammary gland is composed of 15-25 lobes that radiates around the nipple. Each lobe consists of about 20-40 lobules, a smaller milk duct that contains 10-100 supporting alveoli.

  • Glandular tissue
    • Glandular tissues are responsible for milk production and transportation which is composed of:
      • Alveoli – epithelial grape-like cluster of cells where milk is produced.
      • Ductules – branch-like tubules extending from the clusters of alveoli and empties to larger ducts called lactiferous ducts.
      • Lactiferous ducts – widen underneath the areola and nipple to become lactiferous sinuses.
      • Lactiferous sinuses – collect milk from lactiferous ducts and narrows to an opening in the nipple (nipple pore).
  • Connective tissue
    • Connective tissue supports the breast. Cooper’s ligaments are fibrous bands that attach the breast to the chest wall and keep the breast from sagging.
  • Blood
    • nourishes breast tissue and supplies the nutrients to the breast needed for milk production.
  • Nerves
    • make the breast sensitive to touch, hence allowing the baby’s suck to stimulate the release of hormones that trigger the let-down or milk ejection reflex (oxytocin) and the production of milk (prolactin).

  • Lymph nodes
    • removes waste products
  • Adipose tissue (fat)
    • protects the breast from injury.
The breast is externally composed of the following parts:
  • Areola
    • pigmented area at the center of each breast.
  • Nipple
    • protruding area at the center of each breast.

The function of producing milk is regulated by hormones. Stimulation of the female sex hormone, estrogen, causes the development of glandular tissue in the female breast during puberty. Increase estrogen levels during pregnancy causes the breast size to increase in size through the accumulation of adipose tissues.

Presence of progesterone stimulates the growth and maturation of the duct system. During pregnancy levels of estrogen and progesterone rises (levels are needed to sustain pregnancy) that further enhances the development of the mammary glands. This is the main reason why pregnant women has larger and more enhanced breast.

Another hormone important for the implementation of mammary gland function is the presence of prolactin and oxytocin. Without these hormones, milk will not be produced and ejected out of the breast. Prolactin from the anterior pituitary gland stimulates the production of milk in the glandular tissues while oxytocin causes the ejection of milk from the glands.

Physiology of Breast Milk Production

Regardless of the mother’s physical condition, method of delivery (Cesarean section or vaginal delivery) or breast size, milk will be produced. Increase levels of estrogen and progesterone during pregnancy suppresses lactation as increase in the level of these hormones inhibits prolactin production. However, increase levels of these hormones early in pregnancy stimulate the growth of milk glands in preparation for lactation. This is the main reason why pregnant women’s breasts tend to increase in size due to larger glands that result to more fluid accumulation and formation of some extra adipose tissue.

Estrogen and progesterone levels drop after delivery that stimulates the production of prolactin. Prolactin is responsible for breast milk production. If the mother wants to suppress lactation, lactation suppressing agents should be given immediately after placental delivery to be effective. The milk ducts become distended when breast milk begins to form. The woman’s breasts become fuller, larger and firmer. For some this is accompanied by a throbbing pain or feeling of heat in the breasts. The feeling of tension in the breast that most likely occurs by the third or fourth pospartal day is called engorgement. Relief is achieved when the neonate starts to effectively suck the breasts or for those who have no plans of breastfeeding using a breast pump would be provide immediate alleviation.

The infant has to effectively suck the milk for relief to occur. Effective sucking means the infant is actually receiving milk. A baby can suck the breast without actually swallowing milk but rather swallowing air. Onecriteria of knowing that effective sucking is done by the baby is when the mother hears a soft “ka” or “ah” sound during feeding. This indicates that the infant is swallowing the colostrum or milk.

Let-down reflex is the one responsible for pushing the milk outside the breast. This reflex is stimulated by the release of oxytocin. Oxytocin on the other hand, is released when an infant sucks the breast or the mother uses a breast pump.

The following sequential pattern occurs during breast milk production:
  1. Levels of estrogen and progesterone drops after the delivery of the baby.
  2. Decreasing amounts of these hormones stimulates the anterior pituitary glands (APG) to produce prolactin.
  3. Prolactin stimulates the foremilk production in the glandular tissues of the breasts.
  4. Foremilk is stored in the collecting tubules of the breasts, ready for infant feeding.
  5. When the infant sucks the breast or a breast pump is used by a woman, the posterior pituitary gland (PPG) is stimulated to produce oxytocin.
  6. Oxytocin causes contraction of the smooth muscles or the collecting tubules. (this is the reason why afterpains are felt by women who breast feed their babies)
  7. 7. Contraction causes the ejection of the milk forward and outside the breasts – Let-down or Milk Ejection Reflex.
  8. Hindmilk is produced.