Mammary Glands

The mammary glands are modified sweat glands, paired structures (breasts) that contain glandular tissue & variable amounts of fat. Highly evolved & specialized organs develop on each side of the anterior chest wall. It is an exocrine gland in all female mammals & its primary function is to secrete milk through lactation. Mammary glands are present in both sexes but well developed in females but rudimentary in males.

1.0Mammary Gland Diagram

(A) Skin: It comprises the nipple & Areola.

• Nipple: The external pigmented projection in each breast, through which milk is expelled. It has a series of closely spaced openings of ducts called lactiferous ducts (15-20 ducts).
• Areola: Circular pigmented area of skin surrounding the nipple contains sebaceous glands, which help to protect & lubricate the nipple during breastfeeding.

(B) Lobules: These are glandular units that produce milk.

• Each lobule contains grapelike clusters of milk-secreting glands termed alveoli (alveoli ® small cavities).
• The alveoli open into mammary tubules.
• The alveoli are lined by epithelial cells & surrounded by myoepithelial cells, which contract to propel the milk towards the nipple.

(C) Mammary Ducts: The tubular structures transport milk from the Lobules to the nipple. 

• The tubules of each lobe join to form a duct.
• Several ducts join to form a wider mammary ampulla which is connected to a duct known as the lactiferous duct through which milk is sucked out. 
• Lactiferous ducts expand into lactiferous sinuses, where milk is stored before draining into a duct.

(D) Stroma: It is a connective tissue that surrounds & supports the lobules & ducts. It contains blood vessels, fat cells, lymphatic vessels and fibrous tissue.

2.0Mammary Gland Development

Embryonic Development

Milk lines or mammary ridge formation: During embryonic development, mammary ridges or milk lines form around the fourth to sixth week of gestation.

Primary bud formation: By the seventh week, primary mammary buds form & these buds will develop into the mammary glands.

Secondary bud formation: The Primary buds give rise to secondary buds, which will later develop into the ductal system of the mammary gland.

At Puberty

Ducts elongate & Branched: Under the influence of oestrogen, the mammary ducts elongate & branch.

Under the influence of estrogen & progesterone during menstrual cycles, further development of lobules & alveoli occurs, preparing the gland for lactation.

Adult 

• Pregnancy: During pregnancy, increased levels of progesterone, estrogen, prolactin and other hormones extensively proliferate the ducts, lobules and alveoli structure, preparing the gland for milk production.
• Lactation: After childbirth, prolactin & oxytocin levels rise, which promotes milk production & ejection.

3.0Histology of Mammary Gland

4.0Anatomy of the Female Breast

5.0Lactation