Histology of the Breast Flashcards
What is the breast?
A subcutaneous exocrine gland
Basic structure of the non-lactating breast?
Secretory tissue consists of 15-25 lobes, each consisting of a compound tubulo-acinar gland that drains via a series of DUCTS leading to the nipple
Adjacent to the secretory lobules is dense FIBROUS tissue, which is, in turn, surrounded by ADIPOSE tissue, i.e: lobules are set in fibrocollagenous tissue and adipose tissue separates them
Larger condensations (SUSPENSORY LIGAMENTS)) extend from the skin dermis to the deep fascia, overlying the muscle of the anterior chest wall
Function of suspensory ligaments?
Support breast tissue (mainly present in the upper breast)
What is the Terminal Duct Lobular Unit (TDLU)?
Basic functional secretory unit of the breast
Pathway of the TDLU in the non-lactating breast?
Terminal ductules lead into an intralobular collecting duct, which leads into the lactiferous duct for that lobule
Lactiferous duct leads to the nipple, passing via an expanded duct region near the nipple (AKA the lactiferous sinus)
NOTE - each lactiferous duct serves a single lobule
Structure of a lobule?
Possess both extra and introlobular ducts
Rudimentary secretory acini, at the duct endings; within the lobule, the acini are surrounded by looser CT, allowing rapid expansion during pregnancy
The lobule is surrounded by dense fibrocollagenous tissue and have adipose tissue in between
Cells lining the acini within the lobule?
Secretory epithelial cells, which vary from cuboidal to columnar
Secretory cells of the acinus are surrounded by myoepithelial cells (MEp), which are contractile epithelial cells; these are, in turn, surrounded by the basal lamina ADD
NOTE - in the image, the MEp cells are pink
Structure of the ducts?
Larger ducts, e.g: lactiferous duct, are lined by an epithelium that varies from thin stratified squamous to stratified cuboidal epithelium from superficial to deep
i.e: as the duct approaches the surface, it is lined with SSE but, deeper, it is lined with SCE
NOTE - in the image, the red staining in the duct is coagulated proteinaceous material
Origin of the mammary gland?
Although not universally accepted, many believe the mammary glands are modified sweat glands
Structure of the nipple?
Has a wrinkled surface and is covered by a thin, highly keratinised stratified squamous epithelium
Core of dense, irregular CT mixed with bundles of smooth muscles
What changes occur in the mammary gland during the menstrual cycle?
During the menstrual cycle, breast changes occur even in the absence of pregnancy
During the luteal phase:
- Epithelial cells increase in height
- Lumina of the ducts becomes enlarged
- Small amounts of secretions appear in the ducts
What changes occur in the mammary gland during pregnancy?
Dramatic changes occurs In the 1st trimester:
- Elongation and branching of smaller ducts
- Proliferation of epithelial cells of the glands and MEp cells
In the 2nd trimester:
- Glandular tissue continues to develop with differentiation of alveoli
- Plasma cells and lymphocytes infiltrate the nearby CT
In the 3rd trimester:
- Secretory alveoli continue to mature
- Development of extensive rough ER These changes are accompanied by a reduction in the amount of CT and adipose tissue present
Hormonal stimulation of breast changes of the lactating mammary gland?
During pregnancy, oestrogen and progesterone stimulate proliferation of secretory tissue and fibro-fatty tissue becomes sparse
Composition of human milk?
Approximately:
- 88% water
- 1.5% protein, mainly lactalbumin and casein
- 7% carbohydrate, mainly lactose
- 3.5% lipid
There are also small quantities of ions, vitamins and IgA antibodies
Types of secretion involved with breast milk?
Different components of milk are secreted via different mechanisms
Lipid droplets are secreted surrounded by membrane and they carry a small amount of cytoplasm within; this is called APOCRINE SECRETION
Proteins in milk are made in the rER, packaged in the Golgi and secreted via vesicles, which merge with the apical membrane to release only their contents into the duct system; this is called MEROCRINE SECRETION (AKA exocytosis)
