- The mammary glands are specialized exocrine glands found in mammals, responsible for the production and secretion of milk to nourish offspring.
- In humans, mammary glands are most developed in females, where they are contained within the breasts, while in males they remain rudimentary. These glands undergo complex development, especially during puberty, pregnancy, and lactation, and are regulated by an intricate network of hormonal signals.
- Anatomically, each mammary gland is made up of 15 to 20 lobes, arranged radially around the nipple. Each lobe contains numerous lobules, which are clusters of alveoli—the milk-producing units. Alveoli are lined with secretory epithelial cells that synthesize milk, and are surrounded by myoepithelial cells, which contract to push milk into a network of ducts. These ducts converge at the lactiferous ducts, which open at the nipple, allowing milk to exit the breast. The surrounding adipose tissue and connective tissue stroma give the breast its shape and support.
- The development and function of the mammary gland are hormonally regulated. During puberty, rising levels of estrogen and progesterone stimulate the growth of the ductal system and lobular structures. Prolactin, secreted by the anterior pituitary gland, is the primary hormone responsible for milk synthesis, while oxytocin, released by the posterior pituitary in response to infant suckling, triggers milk ejection by contracting myoepithelial cells. Additional hormones such as insulin, cortisol, and thyroid hormones also contribute to the metabolic support required for milk production.
- During pregnancy, elevated levels of estrogen, progesterone, human placental lactogen, and prolactin further stimulate the proliferation and differentiation of mammary tissue. However, high levels of estrogen and progesterone inhibit lactation until after delivery, when their levels drop. This hormonal shift, along with the suckling stimulus from the newborn, initiates lactogenesis, the process of milk secretion.
- The milk produced by mammary glands provides complete nutrition for the newborn, including proteins (casein, whey), lipids, carbohydrates (lactose), vitamins, minerals, immunoglobulins (especially IgA), and various bioactive molecules that support immune function and gut development. Breast milk adapts over time to meet the changing needs of the growing infant.
- Mammary glands can be affected by various physiological and pathological conditions. Mastitis, an inflammation of breast tissue, often occurs during breastfeeding and is typically caused by bacterial infection. Fibrocystic changes are benign and common, characterized by lumpiness or tenderness. The mammary glands are also the site of breast cancer, one of the most prevalent cancers among women worldwide. Breast cancer arises from epithelial cells of the ducts or lobules and is influenced by genetic, hormonal, and environmental factors.
