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Through the Looking Glass - From Stem Cells to Tissues and Organs

Learning Resources The University of Michigan Medical School

Nipple, Areola, and Mammary Gland

Atlas Wheater's, pgs. 386-390, Breasts
Text Ross and Pawlina, Chapters 23 pages 863-870
Ross and Pawlina, Plates, p.892-895
Lab Resources

A. Nipple and Areola

265 Nipple, areola H&E Webscope Imagescope

The 16-20 lactiferous ducts #105-1  Webscope ImageScope, one from each lobe, open at the summit of the nipple.  These ducts are lined by stratified squamous epithelium near the opening and the lumens are frequently filled with desquamated cells.  Deeper in the connective tissue, the ducts acquire a stratified columnar appearance that is really a cuboidal duct cell sitting on a myoepithelial cell as in the sweat gland. 

Sebaceous glands #105-1  Webscope ImageScope are present to a variable extent, especially in the areola.  Note that the dense irregular connective tissue of the dermis is interrupted by numerous fascicles of smooth muscle #105-1  Webscope ImageScope that insert into the dermal connective tissue (much like arrector pili muscles).  These muscle bundles are responsible for erection of the nipples.  Occasional nerves are also present in the dermis.

B. Mammary Gland

259 Mammary gland inactive nulliparous H&E Webscope Imagescope
258 mammary gland active H&E pregnant Webscope Imagescope

Like the other tissues in the female reproductive system, alterations in circulating hormone levels result in histologically demonstrable changes in the mammary gland. Compare the examples of an inactive and active glands, noting the differences in the amount of glandular tissues. In slide #259 (inactive gland) note the dense irrengular interlobular connective tissue found between quiescent glandular lobules that consist of only a few clusters of small ducts surrounded by a mass of less dense intralobular connective tissue. Many ducts appear to be composed of 2 layers of cuboidal epithelium. The inner layer are the actual ductal epithelial cells whereas the outer layer of cells is, in fact, a layer of myoepithelial cells

In slide #258 (active gland), you can see that the amount of the glandular tissues has increased, while that of the connective tissue has decreased.  This increase involves the numbers of both the epithelial cells and myoepithelial cells.   The proliferation of these cells lead to the formation of secretory alveoli. Note also the increased cellularity (especially, the plasma cells) of the intralobular connective tissue. This tissue was probably taken from an individual before the last trimester. When compared with the inactive mammary gland, you can see that the intralobular ducts have proliferated to form additional secretory regions. Both the epithelial cells and myoepithelial cells increase in number. Alveoli #261 Alveoli Webscope ImageScope have formed, their epithelial cells have large, clear areas of apical cytoplasm, a region occupied by glycogen and lipid. Note the increased cellularity of the intralobular connective tissue. Note also that not all lobules within the gland have proliferated to the same degree. In many sections, portions of a large excretory, lactiferous duct #261 lactiferous duct Webscope ImageScope are present. The epithelial lining is again two layered, the bottom layer being principally myoepithelium. Compare the morphology of the inactive and active gland. Observe the intralobular connective tissue and note the abundance of plasma cells #261 intralobular connective tissue and note the abundance of plasma cells Webscope ImageScope. These plasma cells are the source of secretory IgA.