①The breast consists mainly of mammary glands, ducts, fat tissue, and fibrous tissue. ② The glands secrete milk, the ducts transmit milk to the nipple, while fat and fibrous tissue surround the mammary glands and ducts to play a supporting role. The physiological activities of the mammary glands are influenced and regulated by the endocrine secretions of the anterior pituitary gland, ovary and adrenal cortex. ④ During different stages of the menstrual cycle, the physiological state of the mammary gland also shows cyclic changes under the influence of various hormones. ⑤ Hormonal activity reaches its peak during pregnancy and lactation, when changes in the mammary gland are most pronounced.