Breast Development and Hormones

Breast Development

• Progesterone, estrogen, growth hormone, prolactin, adrenal glucocorticoids, and insulin develop the mature breast lobules, with budding of alveoli and progress of secretory characteristics in the cells of the alveoli.
• Progesterone is required for full development of the lobule-alveolar system.

Hormonal Regulation of Lactation

• Prolactin promotes lactation, inducing milk secretion and causing the breasts to secrete milk.
• Estrogen and progesterone during pregnancy inhibit milk secretion, allowing only a few milliliters of fluid to be secreted until after the baby is born.
• After birth, estrogen and progesterone levels drop, and prolactin induces milk secretion in 1-7 days.
• Prolactin concentration in the mother's blood rises steadily from the 5th week of pregnancy until birth, then returns to non-pregnant levels over the next few weeks.

Prolactin Regulation

• Prolactin secretion is controlled by an inhibitory factor, prolactin inhibitory hormone (dopamine), produced in the hypothalamus.
• Dopamine decreases prolactin secretion 10-fold.
• Nervous signals from the nipples to the hypothalamus during breast feeding cause a 10-20-fold surge in prolactin secretion that lasts for about 1 hour.

Other Lactotropes

• Chorionic somatomammotropin is a placental hormone with lactogenic properties, belonging to the growth hormone/prolactin gene family.
• Human placental lactogen is a placental hormone with key metabolic functions in pregnancy, mobilizing free fatty acids from lipids.

Effects of Lactogens on Mother's Mood

• Maternal behavior is influenced by lactogenic hormones, which may regulate postpartum mood in women.
• Low placental lactogen levels are associated with prenatal depression and postpartum depression.
• Maternal obesity is a risk factor for low placental lactogen production and postpartum depression and anxiety.

Suppression of Ovarian Cycles after Delivery

• Ovarian cycle (and ovulation) is blocked until a few weeks after cessation of nursing due to nervous signals from the breasts to the hypothalamus that inhibit secretion of gonadotropin-releasing hormone (GnRH).
• GnRH stimulates the formation of gonadotropic hormones, and its absence blocks ovarian cycle during several months of lactation.

Breast Development

• Estrogens stimulate the development of the mammary glands and the deposition of fat during puberty, known as thelarche.
• Polymastia is a common developmental abnormality of the breast, consisting of more than 2 mammary glands.
• Supernumerary breast tissue usually develops along the mammary line.

Hormonal Regulation of Breast Development

• Progesterone is required for full development of the lobule-alveolar system.
• Estrogen, progesterone, growth hormone, prolactin, adrenal glucocorticoids, and insulin develop the mature breast lobules.
• Estrogen stimulates growth of the ductal system of the breast, causing it to grow and branch, and increasing the stroma of the breasts.

Lactation

• Prolactin promotes lactation and is secreted by the mother's anterior pituitary gland.
• Prolactin concentration in the mother's blood rises steadily from the fifth week of pregnancy until birth.
• Once the baby is born, estrogen and progesterone levels decrease, and prolactin induces milk secretion.
• Other hormones necessary for milk formation include growth hormone, cortisol, parathyroid hormone, and insulin.

Effects of Lactogens on Mother's Mood

• Prolactin can be synthesized and released into the cerebrospinal fluid by epithelial cells in the choroid plexus.
• Prolactin binding to its receptors results in dimerization and activation of JAK2, triggering a signaling cascade.
• Latogenic hormones production during pregnancy and lactation regulates functions in the mother and the newborn, including pup retrieval, licking, and nurturing.

Suppression of Ovarian Cycles after Delivery

• In most nursing mothers, the ovarian cycle is blocked until a few weeks after cessation of nursing.
• Nervous signals from the breasts to the hypothalamus during suckling inhibit secretion of gonadotropin-releasing hormone (GnRH).
• GnRH stimulates the formation of the gonadotropic hormones, and its absence blocks ovarian cycle during several months of lactation.

Lobules' Evolution during Life

• Both type 3 and type 4 lobules are resistant to carcinogens.
• If a woman does not have pregnancy, she has an increased risk for breast cancer.
• Breastfeeding reduces estrogen exposure, misses menstrual cycles, and promotes breast tissue maturity to type 4 lobules.