Mammary Gland Overview and Structure

Mammary Gland Overview

• The mammary gland is an exocrine, compound tubuloalveolar gland.
• The structure of the mammary gland is the same in both males and females.
• In females, puberty triggers breast development, influenced by hormones. Estrogen leads to increased adipose tissue (fat) and duct branching.
• Full development of the female mammary gland occurs around age 20.
• Major cyclical changes occur through pregnancy and lactation.
• Mammary glands reach their full morphological and functional status during pregnancy and lactation.
• Atrophy happens after age 40 and throughout menopause.
• Male breasts have a rudimentary duct system and some connective tissue. Enlargement can occur during puberty, but it's usually minimal, self-limiting, and reversible.

Mammary Gland Structure

• The mammary gland has two main components: stroma and parenchyma.
• Stroma: The supportive connective tissue (C.T septa).
  • Inter-lobar septa: Dense irregular C.T originating from the dermis and reaching pectoral fascia, divide the breast into lobes (15-20). -Inter-lobular septa: Incomplete irregular extensions stemming from inter-lobar septa, dividing lobes into lobules
  • Intralobular C.T.: Loose connective tissue surrounds lobules for internal support, origins from the dermis
• Parenchyma: The functional part of the gland.
  • Alveoli: Secretory units of the gland. During lactation become distended with secretion
  • Ducts: Tubular structures that conduct milk from the alveoli to the nipple. -Intra-lobular ducts: smaller ducts lined with simple columnar epithelium. -Lactiferous duct/sinus: Larger ducts/sinuses near the nipple lined with stratified squamous epithelium

Mammary Gland Alveoli (Secretory Units)

• Mammary glands are activated under hormonal influence (estrogen, progesterone, human chorionic somatomammotropin) during pregnancy to become lactating.
• The terminal portions of the ducts, and the alveoli develop and mature during pregnancy.
• Alveoli, are the main secretory structures.
• Lipids and proteins are produced in the alveoli.

Alveolar Cell Secretions

• Alveolar cells secrete two main types of substances: lipids and proteins.

• Lipids: Stored as droplets within the cytoplasm. The droplets coalesce and move to the periphery of the cell, surrounded by a portion of the cell membrane (cytoplasmic bleb). The droplets are released by apocrine exocytosis.

• Proteins: Produced in rough endoplasmic reticulum, processed in the Golgi apparatus, and released by merocrine exocytosis.

Colostrum and Milk

• Colostrum: The initial secretion after childbirth. It has less lipids and more proteins, primarily antibodies (mostly IgA). It provides passive immunity to newborns.
• Milk: A fluid containing proteins, lipids, lactose, lymphocytes, monocytes, antibodies, minerals, and fat-soluble vitamins.

Nipple and Areola

• The nipple is a conical, raised area covered with stratified squamous epithelium. It has 12-20 small openings (lactiferous ducts). The nipple contains connective tissue, elastic fibers, and smooth muscle cells.
• The areola is pigmented skin surrounding the nipple. It includes Montgomery glands, modified sebaceous glands, that produce lubricating and protective secretions.

Lactating vs. Resting Mammary Glands

• Lactating(Active):

  • Stroma: Thin fibrous septa, little to no fat, reduced intralobular C.T.
  • Parenchyma: Well-developed duct system, well-developed alveoli with secretion, showing signs of secretory activity (e.g., well-developed cell organelles). These are distended with secretion.

• Resting (Inactive):

  • Stroma: Thick interlobar and interlobular dense C.T. septa, substantial amount of fat cells in the subcutaneous, interlobar and interlobular septa.
  • Parenchyma: Duct system only, no developed alveoli. Lobules are filled with loose cellular intralobular C.T.

Hormonal Control

• Estrogen: Responsible for breast enlargement at puberty by stimulating adipose tissue accumulation and duct branching.
• Estrogen, Progesterone, and Human chorionic somatomammotropin (hCS): Development of alveoli and breast size increase during pregnancy.
• Prolactin: Initiates Milk secretion from alveoli during lactation.
• Oxytocin: Induces contraction of myoepithelial cells that surround the alveoli and ducts, pushing milk into the ducts.

Post-Lactational Changes

• After weaning, alveoli undergo degeneration and dead cells are removed by macrophages.
• Breast returns to a resting state.

Breast Cancer

• Breast cancer is a leading cancer type in females in many countries.
• Early detection (self-exam, mammography) and early treatment improve outcomes and reduce mortality.

Explore the fascinating anatomy and physiology of the mammary gland. This quiz covers its development, cyclical changes during pregnancy and lactation, and structural components such as stroma and parenchyma. Test your knowledge on how these glands function differently in males and females.