|
Mammary glands are milk-secreting adaptations of sweat glands.
The basic components of the mammary gland are the alveoli lined with
milk-secreting epithelial
cells and surrounded by myoepithelial cells and a rich capillary network. These
alveoli join up to form lactiferous ducts that drain into openings in the areola.
In human females there are usually two mammary glands, one in each breast, although
polythelia (accessory nipples) and polymastia (accessory glands) can occur
anywhere from the knee to the neck.
Development of mammary glands
The development of mammary glands is controlled by hormones. Estrogen (also
spelt oestrogen) promotes formation, while testosterone inhibits it.
Prolactin, which is stimulated by estrogen, acts on the mammary glands to produce
milk (lactation).
At birth, there are lactiferous ducts but no alveoli. Little branching
occurs before puberty when ovarian estrogens stimulate
branching differentiation of the ducts into spherical masses of cells that will become alveoli. True secretory alveoli only develop
in pregnancy, where rising levels of estrogen and progesterone cause further branching and differentiation of the duct cells, together with an increase in
adipose tissue and a richer blood flow.
Colostrum is secreted in late pregnancy and for the first few days after
giving birth. True milk secretion begins a few days later due to a reduction in circulating oestrogens and progesterone.
|