What is Breast Tissue?

The mammary gland is an accessory gland of the skin and is a multiple ductal vesicle. The male mammary glands gradually degenerate around one and a half years old. The glands have ducts but no acinar and no lobes. Women's mammary glands proliferate during puberty. After menstruation begins, breast development is nearly mature.

The mammary gland is an accessory gland of the skin and is a multiple ductal vesicle. The male mammary glands gradually degenerate around one and a half years old. The glands have ducts but no acinar and no lobes. Women's mammary glands proliferate during puberty. After menstruation begins, breast development is nearly mature.

Chinese name

Mammary gland

Foreign name

galactophore

Belongs to

Human tissue

Features

Lactation

Breast I. Physiological changes:

The mammary gland is affected by nerves and hormones, and has obvious age and function changes. The mammary gland has developed to its highest level around the age of 20, and has started to shrink around the age of 40, and has shrunk significantly after menopause. During the menstrual cycle, the size of the breast changes slightly. During pregnancy and lactation. There are significant changes in the structure and function of the breast. Breasts have no secretory activity when they are not pregnant. Hyperplasia of mammary glands during pregnancy, strong secretion during lactation, called active mammary glands.

(A) Breast during resting period:

The mammary gland has 15 to 25 leaves, and each leaf is an independent gland. It is opened by the lactiferous duct at the top of the nipple. Under the areola, the lactiferous duct expands into a sinus, called the lactiferous sinus. The large duct below the lactiferous sinus is branched into small ducts, the ends of which are connected to the acinus. The breast's leaves are separated by dense connective tissue and surrounded by adipose tissue. Connective tissue extends into the leaf and divides the leaf into many leaflets. The glandular tissues of the mammary glands during quiescence are scarce, and the leaves and leaflets are not distinguished clearly. Groups of tubules are scattered in a large amount of dense connective tissue. Fat cells are more abundant. The leaflets have few acinars and the acinar cavity is narrow.

(2) Breast during active period:

Under the action of estrogen and progesterone during pregnancy, the small ducts and acinars of the mammary glands rapidly proliferate, the acinars enlarge, the epithelium is a single layer of columnar or cubic cells, and the connective tissue and adipose tissue are reduced accordingly. In late pregnancy, under the influence of prolactin secreted by the pituitary gland, the acinus begins to secrete. The mammary gland is the apocrine secretion gland. The secretion contains lipid droplets, milk protein, lactoretin, etc., and is called colostrum. Colostrum also contains macrophages that eat fat, called colostrum bodies.

The structure of the breast during lactation is similar to that of the breast during pregnancy, but the glands develop better and the acinar cavity is enlarged. Acinars are in different secretion stages. Some acinars are in the early stage of secretion and the glandular cells are tall columnar. Some acinars are in the late stage of secretion. The cells are cubic or flat in shape. The glandular cavity is filled with milk. There are many secretory granules and lipid droplets in glandular cells such as reticulum and mitochondria.

After weaning, the level of prolactin decreases, the breast glands stop secreting, the glandular tissues gradually shrink, the connective tissue and adipose tissue increase, and the breasts turn into a stationary phase. After menopause, the levels of estrogen and progesterone in the body decrease, breast tissue shrinks and degenerates, and fat also decreases.

Breast Gland Function Regulation:

The function of the breast depends on complex neurological and endocrine factors. The growth and development of the mammary glands are the result of a synergistic effect of several hormones. Before puberty, breast development is slow. With the advent of puberty, the level of estrogen increases, the development of the breast accelerates, and the breast enlarges. Under estrogen stimulation, the ducts of the mammary glands proliferate. In adulthood, with the changes of ovarian endocrine during the menstrual cycle, there are slight periodic changes in the breast. During pregnancy, progesterone promotes acinar development. The hormones synthesized by the placenta can replace or enhance the effects of ovarian steroid hormones and pituitary prolactin, making the breast highly developed, and the acinars are significantly proliferated and in a state before secretion. After childbirth, prolactin stimulates milk production. The stimulation of sucking the nipple is transmitted to the paraventricular nucleus in the lower thalamus, which promotes the production of oxytocin by nerve secreting cells in the paraventricular nucleus, which is released into the bloodstream through the posterior pituitary. Oxytocin stimulates the myoepithelial cells of the breast to contract, causing milk to be ejected from the nipple. Due to the action of neurohormones, the milk in the acinar cavity is emptied. The pituitary gland can continuously secrete prolactin, so that the glandular cells continuously secrete milk. After weaning, the sucking stimulus disappears, oxytocin production stops, milk in the glandular cavity cannot be discharged, and lactation stops. The mammary glands gradually return to a resting state.