Mammary gland histology

Now, let's get a closer look. The mammary glands of each breast consist of about 15 to 25 sections called lobes with each lobe containing many smaller structures called lobules.Each lobule consists of a large number of alveolar glands, which are the small sac-like structures that produce milk.The milk produced by the alveolar glands drain into the terminal ducts that join together to form the intralobular ducts.These ducts converge further and form the lactiferous ducts, which drain the lobes and eventually lead to the nipple.All of the lobules and ducts are also surrounded by fibro-fatty tissue that provide a supportive and protective function.Before pregnancy, the mammary glands are considered to be in an inactive state, and they’re structurally different from mammary glands that are in the active state.The active state occurs during pregnancy and during lactation after childbirth.During pregnancy, the alveolar glands and the duct system will grow in preparation to produce milk for a newborn baby.This low power image is an example of lactating mammary glands in the active state.A portion of a lobe can be seen surrounded by a thick layer of connective tissue that contains a small number of fat cells or adipocytes within the connective tissue as well.Within the lobe, thinner layers of connective tissue separate the lobe into lobules.In a neighboring lobe, we can also see a couple of large lactiferous ducts.These ducts are lined with a double layer of columnar or cuboidal cells with a surrounding layer of connective tissue.If we take a closer look at one of the lobules, we can see some of the smaller intralobular ducts that are typically lined with 1 to 2 layers of cuboidal cells that also have a thin layer of connective tissue that surround the ducts.

In this image of a different lobule, we can see a good example of a few alveoli and a longitudinal cross-section of the terminal duct that’s responsible for draining the milk produced by these alveoli.Both the terminal ducts as well as the alveoli are lined with either cuboidal or columnar secretory cells.The supportive tissue between the ducts and alveoli is called the intralobular stroma.It consists mostly of loose connective tissue, but it also contains small blood vessels, fibroblasts, plasma cells, a few adipocytes, and myoepithelial cells.Although the wavy connective tissue can be easily seen in this image, some of the other structures can’t be identified as easily since the intralobular stroma is typically very thin and sparse in mammary glands that are in the active state.Now, if we compare mammary glands in the active state to an image of an inactive or resting mammary gland, the most significant difference seen histologically is the nearly complete absence of the milk producing alveoli, which we can see even in these lower power images.As a result, the majority of the resting mammary glands consist of connective tissue and adipose tissue.The lactiferous ducts will still be present, but they’ll typically be smaller and will often appear flattened or collapsed.But the lining of these ducts are still the same, with a double layer of columnar or cuboidal cells.The general structure of the terminal ductules are also still the same in resting mammary glands, with a simple cuboidal epithelium and a surrounding intralobular space that consists of connective tissue, fibroblasts, myoepithelial cells, and in this image we can also see a small blood vessel present in the upper right.Myoepithelial cells surround the terminal ducts, but they also surround the lactiferous ducts and alveoli.During breast-feeding, increased oxytocin will stimulate these smooth muscles to contract and lead to milk ejection from the nipple.The myoepithelial cells are typically located between the secretory cells and the basement membrane, so they are also an important histological marker for the presence and progression of primary breast carcinomas.As a breast tumor progresses, the reduction or disappearance of myoepithelial cells may suggest a transition to an infiltrating or invasive status.Alright, as a quick recap… The mammary glands consist of alveolar glands that are organized into lobules along with the terminal and intralobular ducts that drain the alveoli.The active state starts during pregnancy, when the lobules increase in both size and total number, and the alveolar glands become the most prominent structures in the breast.The inactive or resting state is when an adult female is not pregnant or breast-feeding.

In this state, the ducts are smaller and the secretory alveoli are undeveloped.In both states, the alveoli and terminal ducts are lined with cuboidal or columnar secretory cells, the intralobular ducts will have 1 to 2 layers of cuboidal cells, and the lactiferous ducts will have 2 layers of columnar or cuboidal cells.

an active or resting state is when an adult female is not pregnant or breastfeeding. And this date, the Ducks are smaller in the secretory, alveoli are undeveloped.

Is both dates. The alveoli and terminal docks are lined with cuboidal or columnar secretory cells.

The intralobular ducts will have one to two layers of cuboidal cells in the like tippers. We'll have two layers of columnar or cuboidal cells.