Breast development, also known as mammogenesis, is a complex biological process in primates that takes place throughout a females life. It occurs across several phases, including prenatal development, puberty, and pregnancy. At menopause, breast development ceases and the breasts atrophy. Breast development results in prominent and developed structures on the chest known as breasts in primates, which serve primarily as mammary glands. The process is mediated by an assortment of hormones (and growth factors), the most important of which include estrogen, progesterone, prolactin, and growth hormone. Biochemistry
Hormones
The master regulators of breast development are the steroid hormones, estrogen and progesterone, growth hormone (GH), mostly via its secretory product, insulin-like growth factor 1 (IGF-1), and prolactin. These regulators induce the expression of growth factors, such as amphiregulin, epidermal growth factor (EGF), IGF-1, and fibroblast growth factor (FGF), which in turn have specific roles in breast growth and maturation.At puberty, gonadotropin-releasing hormone (GnRH) is secreted in a pulsatile manner from the hypothalamus. GnRH induces the secretion of the gonadotropins, follicle-stimulating hormone (FSH) and luteinizing hormone (LH), from the pituitary gland. The secreted gonadotropins travel through the bloodstream to the ovaries and trigger the secretion of estrogen and progesterone in fluctuating amounts during each menstrual cycle. Growth hormone (GH), which is secreted from the pituitary gland, and insulin-like growth factor 1 (IGF-1), which is produced in the body in response to GH, are growth-mediating hormones.
Birth control pills come in a variety of formulations. The main division is between combined oral contraceptive pills, containing both estrogens and synthetic progestogens (progestins), and progestogen only pills. Combined oral contraceptive pills also come in varying types, including varying doses of estrogen, and whether the dose of estrogen or progestogen changes from week to week. Mechanism of action
Combination pills usually work by preventing the ovaries from releasing eggs (ovulation). They also thicken the cervical mucus, which keeps sperm from penetrating into the uterus and joining with an egg. The hormones in combination and progestogen-only pills also thin the lining of the uterus. This could prevent pregnancy by interfering with implantation of a blastocyst. Main action in typical use is prevention of ovulation. Combined oral contraceptive pills
All contain an estrogen, ethinylestradiol or mestranol, in varying amounts, and one of a number of different progestogens. (Regarding the estrogen, the inactive 3-methyl ether of ethinylestradiol, which must be metabolized by the liver into the active ethinylestradiol; 50 μg of mestranol is equivalent to only 35 μg of ethinylestradiol and should not be used when high-dose [50 μg ethinylestradiol] estrogen pills are needed; mestranol was the estrogen used in the first oral contraceptive, Enovid). They are usually taken for 21 days with then a seven-day gap during which a withdrawal bleed (often, but incorrectly, referred to as a menstrual period) occurs.