Unlike the male, the female reproductive organs are sited entirely inside the body. Their function is to ripen and release an egg at regular intervals, and, if the egg is fertilized, to protect and nourish the embryo and fetus. No eggs are manufactured after birth – a female is born with a full set.
The female reproductive glands (ovaries) are located within the abdomen. From puberty, they mature and release the female sex cells (gametes), known as egg cells or ova. This release occurs roughly once a month as part of the menstrual cycle. The ripe egg travels along the fallopian tube to the uterus, the muscular sac in which it develops into an embryo and then fetus. Unfertilized eggs, and the uterine lining, leave via the vagina. The ovaries also make the female sex hormone oestrogen.
Both females and males have breasts (mammae), which contain modified sweat glands known as mammary glands. In females these are much larger and more developed than in males and produce milk at childbirth. Each breast contains 15–20 lobes of compound areolar glands, each lobe resembling a bunch of grapes on a long stalk. The cells of the glands secrete milk, which flows along merging lactiferous ducts towards the nipple. The breast also contains a widespread drainage system of lymph vessels (see section on Lymph and Immune Systems) .
An ovary contains thousands of immature egg cells. During each menstrual cycle, follicle-stimulating hormone (FSH) causes one egg to begin development; this takes place inside a primary follicle. The follicle enlarges as its cells proliferate, and begins to fill with fluid, becoming a secondary follicle that moves to the ovary’s surface. It also increases its production of the hormone oestrogen. A surge of luteinizing hormone (LH) causes the follicle to rupture and release the ripe egg–this is ovulation. The lining of the empty follicle thickens into a corpus luteum–a temporary source of hormones.
The external genital parts of the female are together known as the vulva. They are sited under the mons pubis, a mound of fatty tissue that covers the junction of the two pubic bones, the pubic symphysis. Outermost in the vulva are the flap-like labia majora, with the smaller, fold-like labia minora within them. Both are called “labia” due to their resemblance to lips. The labia majora contain fatty and connective tissue, sebaceous glands, smooth muscle, and sensory nerve endings. At puberty their exposed surfaces begin to grow hairs. Within the vulva are the openings to the vagina and the urethra. At the front end of the labia minora is the clitoris. Like the male penis, it is sensitive and engorges with blood during sexual arousal.