The development and formation of the breast, especially the female breast, is unique and influenced by many factors: the process of embryonic development, endocrine balance, fat metabolism, distribution, skin quality, and the effect of gravity over time.
The whole process of formation and development of the female breast can be divided into the following stages: embryonic, early childhood, adolescence, menstruation, pregnancy, lactation, adulthood and old age.
In these artificially divided stages, the shape of the breast has different changes, but these changes are continuous and regular, mainly influenced by the regulation of endocrine hormones within the organism.
1.Embryonic stage
Embryonic development is the first step in the formation of the breast, which is a derivative of the ectoderm. In the sixth week of embryonic development, the mammary line appears on the ectoderm, referred to as the mammary line. The mammary line is located on both sides of the anterior wall of the embryonic trunk and consists of multiple ectodermal cells that thicken locally to form the crestal breast primordium, which is composed of 4-5 layers of migrating epithelial cells, with the deeper layer being the mesodermal cells that are rich in glandular ducts. During the ninth week of embryonic life, the upper and lower third of the mammary line begins to degenerate, leaving only the breast primordia in the thorax to continue to develop.
The ectodermal cell layer sinks into the deeper mesodermal cells to form a concave structure, and the basal cells of the epidermis also descend as they proliferate to form the breast buds. The breast buds are involved in the development of both breasts. During the third month of embryonic life, the adjacent part of the bud forms the lobular bud, which is the primitive structure of the mammary alveoli, and the distal part of the bud develops into the milk duct and its distal end into the nipple. This structure is maintained until after birth and remains largely unchanged until puberty. If during the embryonic period
not completely degenerated, additional nipples and even breasts may appear along the upper and lower part of the mammary line mammary glands, called parametrium, which can have one or more. If the mammary line is completely degenerated during the embryonic period or if it is completely degenerated on one side, it presents as a congenital absence of the breast or a unilateral
If all or one side of the mammary gland degenerates during the embryonic period, the congenital absence of the breast or the absence of one side of the breast will appear.
2. Early Childhood
The fetus is influenced by the maternal gonads and the sex hormones produced by the placenta in the womb, and there is a certain degree of breast development and physiological activity. Therefore, at birth, regardless of gender, the baby’s breasts can be slightly elevated and 1-2 cm large can be palpated
The lump can be palpable and milk-like secretions can be squeezed out from the nipple, which is called witch’s milk. It usually appears within 2-3 days after birth and gradually disappears after 1-3 weeks, after which the mammary gland enters a quiescent state in early childhood. In girls around 10 years old, the subthalamic
The secretion of hormones from the hypothalamus and pituitary gland gradually increases, stimulating the further development of follicles and secreting a small amount of sex hormones, preparing for the development of puberty.
3. Puberty
Puberty is the most important period of breast development in a person’s life, and there is a clear difference between male and female breast development during this period.
In women, the secretion of gonadotropins from the hypothalamus and pituitary gland increases and their effects are enhanced, the ovaries enlarge, the sensitivity of follicle cells to gonadotropins increases, follicles develop further and estrogen is produced. Under the effect of estrogen, the internal and external genital organs
Other female signs appear, axillary and pubic hairs appear, fat is distributed on the shoulders, chest and buttocks to form a female body with enlarged breasts and enlarged nipples and areolas, and the color begins to deepen. About one year after entering puberty, the whole breast is disc-shaped, generally about 3-5 years of puberty, at the end of puberty, that is, when menstruation begins, the development of the breast only tends to perfect, the shape should be mostly hemispherical. At this time, the subcutaneous fibers and fatty tissues of the breast increase in large quantities; the fibers around the milk ducts increase and the blood vessels increase; the milk ducts increase in size.
The breast ducts are lengthened, expanded and branched, but the glandular lobules have not yet been formed. In males, puberty begins later than in females, and the degree of development is less regular and the duration of puberty is shorter. In most men, the breasts are slightly more prominent than before, and in some cases, coin-sized fibrous tissue can be palpated under the nipples, with a hard texture, light tenderness, or sensory allergy when touched.
Menstruation: The menstrual breast, also known as the sexually mature breast, refers to adult infertile women. Due to the normal physiological activities of the pituitary gland, adrenal glands and ovaries, breast development under the action of estrogen and progesterone, like the endometrium, shows cyclical changes and is therefore divided into premenstrual hyperplasia and postmenstrual recovery period. Premenstrual hyperplasia: This is the period from a few days after menopause to the next menstrual period. During this period, the milk ducts of the breast are dilated, the epithelial cells are enlarged and increased, especially at the end of the milk ducts, and there is lymphocytic infiltration around the milk ducts, newly synthesized fibers are increased, and the stroma is edematous. The changes of the whole breast are an increase in volume, especially in the premenstrual period, hardening and swelling of the breast, and in some cases, small nodules in the breast can be palpated, with pain and pressure, which are the manifestations of more severe breast hyperplasia. After menstruation, the symptoms disappear or decrease, and gradually return to the recovery period.
4.Post-menstrual recovery period
This is the period from the beginning of menstruation to the days after menstruation. During this period, the end of the milk ducts and the lobules of the mammary glands are recovered and reduced most significantly. The milk ducts shrink, the epithelial cells atrophy, the fibers around the ducts decrease and the lymphocytes disappear. Regardless of the degree of breast hyperplasia, the breast symptoms that appear during the premenstrual hyperplasia period generally disappear during this period Breast tissue is enlarged or reduced with the changes in the menstrual cycle, which is the most characteristic of the breast during this period.
5.Pregnancy period
After 5-6 weeks of pregnancy, the breasts begin to gradually increase in size, engorgement is obvious, pregnant women feel swelling or tingling in the breasts, and superficial veins on the surface of the breasts are clearly visible. The breast enlargement is most obvious in the first half of pregnancy. The lobules at the end of the milk ducts fuse into large lobes, the lumen expands into vesicles, the epithelial cells are rectangular, and fat droplets appear in the cells; later the lobes expand, the vesicles gradually enlarge, and the secretions inside them increase, most of the fibers around the milk ducts disappear due to pressure and are replaced by more capillaries, and the milk ducts are also filled with secretions. The enlarged follicles result in tougher breasts. The nipples are enlarged and colored and easily erected. The areola is colored and the sebaceous glands on the areola are hypertrophied forming small scattered elevations called Montserrat’s nodes. If the ends of the milk ducts in the mammary glands do not fully develop into lobules during pregnancy, there will be a lack of milk during lactation.
6.Lactation period
At this time, the lobes of the mammary glands are highly hyperplastic and hypertrophied, the epithelium of the glandular vesicles is arranged in a single row and filled with milk, the fibrous tissue around the milk ducts almost disappears and is replaced by capillaries.
The lobe of the breast is highly hyperplastic and hypertrophied. The development of glandular lobules varies from person to person and from one part of the breast to another, which means that the amount of milk production varies from person to person and from one period to another. Late in the breastfeeding period, mammary gland changes vary with weaning. If you do not breastfeed after giving birth, the pressure in the milk ducts becomes progressively higher, the milk ducts expand and compress the duct walls and mammary lobules, and the above-mentioned mammary structures undergo rapid degenerative changes after a few days, which are so rapid and extensive that the volume of the breast is smaller than the pre-pregnancy level after recovery. If you are breastfeeding after delivery, you will continue to secrete milk, and the length of the secretion period varies. Generally, milk secretion begins to decrease gradually around 8 months after delivery, and the mammary glands begin to degenerate. The reason for this is that the fibrous tissue in the mammary stroma does not regenerate in time to replenish its consumption. Generally speaking, the shape of the breast can be fully restored a few months after weaning.
7.Adulthood
After women’s breasts enter adulthood, the fat in their glands gradually increases, while the glandular structures such as lobules and ducts gradually decrease or atrophy, and the fibrous tissue around the ducts also increases and is denser, the degree of this change is related to the number of births, the number of births or those who have not given birth is light and changes occur late. Due to the deposition of fat and the sagging of the skin on the surface of the breasts, the breasts gradually sag, and this phenomenon becomes more and more obvious with the increase of age.
Ageing: After menopause, due to the endocrine changes in the body, the structure of the breast also changes accordingly, the fibers around the milk ducts increase, some also appear calcification, small milk ducts and blood vessels gradually sclerosis and occlusion, the breast is only filled with fibers and fatty tissue. Obese people are mostly fatty, thin people are mostly fibrous, and the breasts are thin and dried out.