Objectives

1. Identify the histological structures in matured breast tissue.
2. Identify active and inactive breast tissue and post-menopausal breast tissue.

Overview

Mammary glands, or breasts, develop along mammary ridges. Mammary glands are similar in both males and females until puberty. In males, testosterone inhibits further growth while in females, estrogen and progesterone stimulate growth. In females, growth continues through puberty and also undergoes cyclic changes in response to hormone released during the menstrual cycle and pregnancy.

Structure:

• Modified tubuloalveolar apocrine sweat glands in the subcutaneous tissue
• 15-20 irregular lobes (inactive tissue)
• Terminal duct lobular units (TDLUs)- clusters of secretory alveoli (active) or terminal ductules (inactive) that drain to intralobular collecting ducts > lactiferous ducts. Alveoli are surrounded by intralobular stroma (loose CT)
• Lactiferous ducts (stratified squamous) become dilated as lactiferous sinuses (2 layers of cuboidal cells to simple columnar or cuboidal) that open at the nipple
• Suspensory (Cooper) ligaments extend from the dermis to divide the tissue
• Nipple and areola have highly pigmented stratified squamous, keratinized epithelium. Pigmentation can change, especially during pregnancy. There are some smooth muscle fibers deep to the skin of the areola that surround the lactiferous ducts.
• Cell Types:
  • Glandular epithelial cells– line the duct system.
  • Myoepithelial cells– lie between epithelial cells and basal lamina, more apparent in the alveoli; contract for milk ejection during lactation.
  • Alveolar cells– produce milk through merocrine (protein) and apocrine (fatty component) secretion.
  • Stromal cells (surrounding glands and ducts)- fibroblasts, plasma cells, lymphocytes, eosinophils.

Stages of Breast Tissue

Generally, the mammary gland is in an inactive state with few glands, not fully developed. You can observe subtle changes in cell height, increase in lumen size and little product secretion that coincides with progression through the mensural cycle. When pregnancy occurs, hormones induce proliferation and gland development in the breast tissue in preparation of producing breast milk after parturition (birth) resulting in active breast tissue. Involution of tissue occurs after menopause. Major structural changes:

• First trimester structure changes: elongation and branching of terminal ductules, proliferation of epithelial and myoepithelial cells
• Second trimester structure changes: alveoli differentiate from the distal ends of the terminal ductules. Glandular tissue is highly variable between lobules. Infiltration of white blood cells into the stroma occurs.
• Third trimester structure changes: maturation of alveoli, epithelial gland cells become cuboidal. Enlargement is due to hypertrophy of secretory cells and accumulation of secretory product. There is an overall decrease in connective and adipose tissues.
• Post-menopausal tissue structure changes: glands atrophy, TDLUs disappear, connective tissue degenerates through a decrease in fibroblasts, loss of collagen and loss of elastic fibers.