Estrogens

These are the hormones responsible for female gender characteristics and fertility.

Estrogens are messenger molecules that travel in the blood, and act on different organs.

In the liver, for example, estrogens increase the blood levels of good cholesterol (HDL), while reducing the harmful type (LDL). In the breast they promote cellular division.

Every month, in accord with their blood concentration, estrogens stimulate the production of hundred of cells in the mammary glands and uterus walls, preparing the woman for a possible pregnancy. Traveling in the blood stream, they cross the cell membrane to enter the nucleus. There, estrogens bind specific receptors in the DNA, activating genes with instructions for cellular multiplication and division.

This ability to stimulate cell multiplication contributes to the aggressiveness of breast tumors with estrogen receptors (RE+).

Usually estrogen is produced by the ovaries, but can be made in other organs such as the adrenal glands, though in much smaller quantities.