This liquid is rich in antibodies and nutrients to sustain an infant during the first few days of life. After childbirth, progesterone levels decrease and the levels of prolactin remain raised. This signals the mammary glands to begin lactating.
Each time a baby is breastfed the milk is emptied from the breast. Immediately afterward, the mammary glands are signaled to continue producing milk. As a woman approaches menopause, the time when menstruation stops, the tissues of the ductile system become fibrous and degenerate. This causes involution, or shrinkage, of the mammary gland, and thereafter the gland loses the ability to produce milk. In mammals, a mammary duct is present in order to produce milk.
The mammary duct is an organ known as an exocrine gland, which is a type of gland that…. The major muscle in the chest is the pectoralis major.
This large fan-shaped muscle stretches from the armpit up to the collarbone and down across the…. The jejunum is one of three sections that make up the small intestine. The cytoplasm is full of intermediate filaments tonofilaments , some of which are attached to the desmosomal plaque.
Under it, you can see connective tissue, which we will study next time. Note how thin the epithelium is. Shown is the epithelial lining cell of a proximal tubule in the kidney. VIew VIrtual EM Slide You can appreciate that this epithelium skin is stratified has multiple layers of cells and that the layers near the surface at the top of the micrograph have keratinized lost their nuclei and become a layer of keratin.
The spiny appearance of cells deeper in the epithelium can also often be seen in the light microscope. They are points of cell-cell attachment, made more obvious by shrinkage during preparation. What junctions are found here? This is the lining of the esophagus, where it is no longer necessary to have an outer keratinized layer to protect against desiccation, as it was for skin. Thus, the outermost layer is still cellular and contains a nucleus.
Note again the spiny appearance of the cells, due to the desmosomal attachments. Note that most of them are filled with secretory product mucus and that they do not have cilia. The line indicates the plane of section on EM Note the tops of the goblet cells protruding between the cilia.
What are the differences among cilia, microvilli, stereocilia and kinocilia which you will come across later? This micrograph displays the transitional epithelial lining of the bladder. The wall of the urinary bladder contains 3 layers of somewhat irregularly arranged smooth muscle. The junctions found in the spinous layer are called desmosomes. The spinous layer of stratified squamous epithelium got its name because the desmosomes linking adjacent cells gives them a "spiny" appearance.
Identify the type of epithelium in this image. Correct answer 4. The urinary tract - epithelium shown is transitional epithelium note the DOME-shaped cells , which lines the urinary tract. Correct answer 1.
They contain a core of keratin intermediate filaments. A type of intercellular junction as viewed by routine transmission electron microscopy in panel A and in a freeze-fracture preparation in panel B.
Which statement about this type of junction is correct? Correct answer 3. It allows for the passage of ions and other small molecules from one cell to another.
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 slide View Image 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 slide View Image 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. 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 inactive gland note the dense irrengular interlobular connective tissue found between quiescent glandular lobulesthat 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 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 slide View Image 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 duc t slide View Image 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 slide intralobular connective tissue and note the abundance of plasma cells View Image. These plasma cells are the source of secretory IgA. Lipid granules are released covered with a small amount of mammary gland cell cytoplasm, as well as the cell membrane.
On the other hand, the protein components are released by the usual mechanism of exocytosis. Intralobular connective tissue the connective tissue around the ducts of each lobule is a looser, more vascular and cellular connective tissue.
The cellularity comes not only from fibroblasts, but also from an abundant number of plasma cells that produce the IgA that is secreted into the milk. Interlobular between lobules connective tissue, on the other hand, is dense and collagenous and contains fewer cells.
Some bands of connective tissue, called suspensory Cooper's ligaments, extend through the breast from the skin to the underlying muscles. The amount and distribution of the adipose tissue determines the size and shape of the breast. Each lobe consists of lobules that contain the glandular units. A lactiferous duct collects the milk from the lobules within each lobe and carries it to the nipple.
Just before the nipple, the lactiferous duct enlarges to form a lactiferous sinus ampulla , which serves as a reservoir for milk. After the sinus, the duct again narrows and each duct opens independently on the surface of the nipple.
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