Anatomy & Physiology

Anatomy & Physiology Study Guide secretions moisten the vaginal lining. The movement of water across the permeable epithelium provides some moisture. Throughout childhood the vagina and vestibule are usually separated by the hymen , an elastic epithelial fold of variable size that partially blocks the entrance to the vagina. An intact hymen is typically stretched or torn during first sexual intercourse. The External Genitalia The area containing the female external genitalia is the vulva. The vagina opens into the vestibule , a central space bounded by small folds known as the labia minora . Smooth, hairless skin covers the labia minora. Just anterior to the vaginal entrance, the urethra opens into the vestibule. Anterior to this opening, the clitoris projects into the vestibule. A small, rounded tissue projection, the clitoris is derived from the same embryonic structures as the penis in males. During sexual arousal, the clitoris becomes erect with the increased flow of blood. An ever-changing number of small, lesser vestibular glands release their secretions onto the exposed surface of the vestibule, keeping it moist. Bartholin glands secrete into the vestibule during sexual arousal. The mons pubis and labia majora establish the outer margins of the vulva. The outer margins of the labia majora and the mons pubis are covered with coarse hair, but the inner surfaces of the labia majora are relatively hairless. The Mammary Glands The maternal mammary glands secrete milk from which human infants can be nourished. Milk production, or lactation , occurs in mammary glands. In females, they are specialized organs of the integumentary system controlled by hormones of the reproductive system and by the placenta, a temporary structure that provides the embryo and fetus with nutrients. Each breast bears a nipple , a small conical projection where the ducts of the underlying gland open onto the body surface. The hyperpigmented skin around each nipple is the areola . The glandular tissue of a mammary gland consists of separate lobes, each containing several secretory lobules. The ducts of the lobules converge to become a single lactiferous duct for each lobe. Near the nipple, that lactiferous duct enlarges, forming an expanded chamber called a lactiferous sinus. Typically, 15–20 lactiferous sinuses open onto the surface of each. 25.7 Hormones and the Female Reproductive Cycle As in males, GnRH from the hypothalamus regulates reproductive function in females. FSH stimulation causes follicular development; each month some of the primordial follicles begin to develop into primary follicles. In addition, small quantities of estrogens are secreted by interstitial cells scattered throughout the ovarian stroma. Of the three estrogens circulating in the bloodstream– estriol, estradiol, and estrone–estradiol is most abundant and has the greatest effects on target tissues. It is the dominant hormone prior to ovulation. Estrogens affect the activities of many tissues and organs throughout the body. Among the important general functions of estrogens are stimulating muscle and bone growth; maintaining female secondary sex characteristics (such as body hair distribution and the location of adipose tissue deposits); maintaining functional accessory reproductive glands and organs; affecting central nervous system (CNS) activity (especially in the hypothalamus, where estrogens increase the sexual drive); and initiating the repair and growth of the endometrium. Achieve Page 348 of 368 ©2018