1. Production of gametes. Specialized organs of the reproductive system produce gametes: sperm cells in males and oocytes (eggs) in females.

2. Fertilization. The reproductive system enables fertilization of the oocyte by the sperm.

3. Development and nourishment of a new individual. The female reproductive system nurtures a new individual in the uterus until birth and provides nourishment (milk) after birth.

4. Production of reproductive hormones. Hormones produced by the reproductive system control its development and the development of the gender-specific body form.

The testes are small, ovoid organs, each about 4–5 cm long, within the scrotum. They function as both exocrine and endocrine glands. Their major exocrine secretion is sperm cells, and their major endocrine secretion is the hormone testosterone. The outer part of each testis is a thick, white capsule consisting mostly of fibrous connective tissue called the tunica albuginea. Extensions of the tunica albuginea enter the testis and form incomplete septa. 

 primary spermatocytes divide by meiosis. Spermatogenesis begins when the primary spermatocytes divide. Each primary spermatocyte passes through the first meiotic division to become two secondary spermatocytes. Each secondary spermatocyte undergoes a second meiotic division to produce two even smaller cells called spermatids. Each spermatid contains one of each of the homologous pairs of chromosomes. Therefore, each sperm cell contains 22 autosomes and either an X or a Y chromosome. Each spermatid undergoes the last phase of spermatogenesis, called spermiogenesis, to form a mature sperm cell.

At the base of the penis, the corpus spongiosum expands to form thebulb of the penis, and each corpus cavernosum expands to form the crus of the penis. Together, these structures constitute the root of the penis, and the crura attach the penis to the pelvic bones. Skin is loosely attached to the connective tissue that surrounds the erectile columns in the shaft of the penis. The skin is firmly attached at the base of the glans penis, and a thinner layer of skin tightly covers the glans penis. The skin of the penis, especially the glans penis, is well supplied with sensory receptors. A loose fold of skin called the prepuce, or foreskin, covers the glans penis.

The seminal vesicles are sac-shaped glands located next to the ampullae of the ducta deferentia. Each gland is about 5 cm long and tapers into a short excretory duct that joins the ampulla of the ductus deferens to form the ejaculatory duct. The prostate gland, consisting of both glandular and muscular tissue. The prostate gland is composed of a fibrous connective tissue capsule containing distinct smooth muscle cells and numerous fibrous partitions, also containing smooth muscle, that radiate inward toward the urethra. Fifteen to 30 small prostatic ducts carry these secretions into the prostatic urethra. The bulbourethral glands, are a pair of small glands located near the membranous part of the urethra. Each bulbourethral gland is a compound mucous gland. The small ducts of each gland unite to form a single duct, which then enters the spongy urethra at the base of the penis.

Testosterone is the major male hormone secreted by the testes. It is classified as an androgen because it stimulates the development of male reproductive structures and male secondary sex characteristics. The testes secrete other androgens, but they are produced in smaller concentrations and are less potent than testosterone. In addition, the testes secrete small amounts of estrogen and progesterone. Testosterone has a major influence on many tissues. It plays an essential role in the embryonic development of reproductive structures, their further development during puberty, the development of secondary sex characteristics during puberty, the maintenance of sperm cell production, and the regulation of gonadotropin secretion. It also influences behavior.

When erection occurs, the penis becomes enlarged and rigid. Erection is the first major component of the male sex act. Emission is the accumulation of sperm cells and secretions of the prostate gland and seminal vesicles in the urethra. Sympathetic centers in the spinal cord (T12–L1), which are stimulated as the level of sexual tension increases, control emission. Sympathetic action potentials cause peristaltic contractions of the reproductive ducts and stimulate the seminal vesicles and the prostate gland to release their secretions resulting in ejaculation. Sensations that are normally interpreted as pleasurable occur during the male sex act and result in a climactic sensation, called orgasm, associated with ejaculation. After ejaculation, a phase called resolution occurs, which is characterized by a flaccid penis, an overall feeling of satisfaction, and the inability to achieve erection and a second ejaculation for a period that can range from many minutes to many hours or longer.

The formation of female gametes begins in the fetus. By the fourth month of development, the ovaries contain 5 million oogonia (egg generation), the cells from which oocytes develop. By the time of birth, many of the oogonia have degenerated, and the remaining ones have begun meiosis.  Meiosis stops, however, during the first meiotic division at a stage called prophase I. The cell at this stage is called a primary oocyte,and at birth there are about 2 million of them. From birth to puberty, the number of primary oocytes decreases to around 300,000–400,000. Only about 400 primary oocytes will complete development and give rise to the secondary oocytes that are eventually released from the ovaries. Ovulation is the release of a secondary oocyte from an ovary. Just before ovulation, the primary oocyte completes the first meiotic division to produce a secondary oocyte and a polar body.

When amature follicle forms a lump on the surface of the ovary. During ovulation, the mature follicle ruptures, forcing a small amount of blood, follicular fluid, and the oocyte, surrounded by the cumulus cells, into the peritoneal cavity. The cumulus cells resemble a crown radiating from the oocyte and are thus called the corona radiata. Usually, only one mature follicle reaches the most advanced stages of development and is ovulated. Happens about every 28 days. Primary follice-->secondary follicle-->mature follice-->ovulation. 

Longitudinal ridges called columns extend the length of the anterior and posterior vaginal walls, and several transverse ridges called rugae extend between the anterior and posterior columns. The superior, domed part of the vagina, the fornix, is attached to the sides of the cervix, so that a part of the cervix extends into the vagina. The wall of the vagina consists of an outer muscular layer and an inner mucous membrane. The muscular layer is smooth muscle that allows the vagina to increase in size to accommodate the penis during intercourse and to stretch greatly during childbirth. The mucous membrane is moist stratified squamous epithelium that forms a protective surface layer. The vaginal mucous membrane releases most of the lubricating secretions produced by the female during intercourse.

On each side of the vestibule, between the vaginal opening and the labia minora, is an opening of the duct of the greater vestibular gland. Additional small mucous glands, the lesser vestibular glands, are located near the clitoris and urethral opening. They produce a lubricating fluid that helps maintain the moistness of the vestibule.

Each adult female mammary gland usually consists of 15–20 glandular lobes covered by a considerable amount of adipose tissue. It is primarily this superficial adipose tissue that gives the breast its form. The lobes of each mammary gland form a conical mass, with the nipple located at the apex. Each lobe has a single lactiferous (milk-producing)duct, which opens independently of other lactiferous ducts on the surface of the nipple. Just deep to the surface, each lactiferous duct enlarges to form a small, spindle-shaped lactiferous sinus, where milk accumulates during milk ejection. The lactiferous duct supplying a lobe subdivides to form smaller ducts, each of which supplies a lobule. Within a lobule, the ducts branch and become even smaller. In milk-producing, or lactating, mammary glands, the ends of these small ducts expand to form secretory sacs called alveoli. Myoepithelial cells surround the alveoli and contract to expel milk. In non-lactating mammary glands, only the duct system is present.

Elevated rates of estrogen and progesterone secretion by the ovaries are primarily responsible for the changes associated with puberty. Before puberty, estrogen and progesterone are secreted in very small amounts, and LH and FSH levels remain very low. The low secretory rates are due to a lack of GnRH released from the hypothalamus. At puberty, not only are GnRH, LH, and FSH secreted in greater quantities than before puberty, but also the adult cyclic pattern of FSH and LH secretion is established.

FSH and LH stimulate follicular growth and maturation. They also cause an increase in estrogen secretion by the developing follicles. FSH exerts its main effect on the granulosa cells, whereas LH exerts its initial effect on the theca interna cells and later on the granulosa cells. LH stimulates the theca interna cells to produce androgens, which diffuse from these cells to the granulosa cells. FSH stimulates the granulosa cells to convert androgens to estrogen. In addition, FSH gradually increases LH receptors in the granulosa cells. Estrogen produced by the granulosa cells increases LH receptors in the theca interna cells. Consequently, theca interna cells and granulosa cells cooperate to produce estrogen. After LH receptors in the granulosa cells have increased, LH stimulates the granulosa cells to produce progesterone, which diffuses from the granulosa cells to the theca interna cells, where it is converted to androgens.

The gradual increase in estrogen levels, especially late in the follicular phase, begins to have a positive-feedback effect on LH and FSH release from the anterior pituitary. Consequently, as the estrogen level in the blood increases, it stimulates greater LH and FSH secretion. The sustained increase in estrogen is necessary for this positive-feedback effect. In response, LH and FSH secretion increases rapidly and in large amounts just before ovulation. The increase in blood levels of both LH and FSH is called the LH surge, and the increase in FSH is called the FSH surge. The LH surge occurs several hours earlier and to a greater degree than the FSH surge, and the LH surge can last up to 24 hours. The LH surge initiates ovulation and causes the ovulated follicle to become the corpus luteum. FSH can make the follicle more sensitive to the influence of LH by stimulating the synthesis of additional LH receptors in the follicles and by stimulating the development of follicles that may ovulate during later ovarian cycles.

The LH surge causes the primary oocyte to complete the first meiotic division just before or during the process of ovulation.

The term uterine cycle refers to changes that occur primarily in the endometrium of the uterus during the menstrual cycle. Other, more subtle changes also take place in the vagina and other structures during the menstrual cycle. Cyclic secretions of estrogen and progesterone are the primary cause of these changes. The endometrium of the uterus begins to proliferate after menses. The remaining epithelial cells rapidly divide and replace the cells of the functional layer that were sloughed during the last menses. A relatively uniform layer of low cuboidal endometrial cells is produced. The cells later become columnar, and the layer of cells folds to form tubular spiral glands. Blood vessels called spiral arteries project through the delicate connective tissue that separates the individual spiral glands to supply nutrients to the endometrial cells. After ovulation, the endometrium becomes thicker, and the spiral glands develop to a greater extent and begin to secrete small amounts of a fluid rich in glycogen.

When a woman is 40–50 years old, menstrual cycles become less regular, and ovulation often does not occur consistently. Eventually, menstrual cycles stop completely. The cessation of menstrual cycles is called menopause. The time from the onset of irregular cycles to their complete cessation, which is often 3 to 5 years, is called the female climacteric. Menopause is associated with changes in the ovaries. The number of follicles remaining in the ovaries of menopausal women is small. In addition, the follicles that remain become less sensitive to stimulation by LH and FSH; therefore, fewer mature follicles and corpora lutea are produced. Older women experience gradual changes in response to the reduced amount of estrogen and progesterone produced by the ovaries.