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Histology of the breast
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Seen under the microscope, the breast is arranged like a tree. The large ducts branch again and again until they lead into what is called the terminal duct lobular unit, where they open into clusters of acini, which are small sacs shaped like grapes on a stem. Those acini together with their duct make up the lobule.
What lines the inside of those tubes and sacs is not one layer but two, and that double layer is the signature of normal breast tissue. On the inside, facing the space the milk passes through, sit the luminal cuboidal cells.
On the outside, wrapped around them, sit the myoepithelial cells: long and spindle-shaped, carrying the properties of smooth muscle, meaning they can contract. They work like a mesh that squeezes from the outside and helps push the milk out during lactation.
In brief
Under the microscope, the large ducts of the breast lead to the terminal duct lobular unit, where terminal ducts branch into grape-like clusters of small acini that form a lobule.
The epithelium lining those ducts and acini is not one layer but two; luminal cuboidal cells form the inner portion.
The outer portion is made of myoepithelial cells, which are spindle-shaped, have smooth muscle properties, and take part in milk ejection during lactation.
Sources (2)
- National Center for Biotechnology InformationPhysiology, Lactation. StatPearls
- National Center for Biotechnology InformationHistology, Mammary Glands. StatPearls
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