The reproductive system

The reproductive system is the group of organs that produces reproductive cells and provides pathways and supporting structures for reproduction. Female anatomy includes organs for fertilisation and development within the uterus; male anatomy includes organs that produce and transport sperm. Both systems have internal and external components closely related to the urinary organs.

Where are the reproductive organs located?

The pelvis is the bony region connecting the trunk to the lower limbs and enclosing the pelvic cavity. Many internal reproductive organs occupy this cavity, where they lie near the urinary bladder, which stores urine, and the rectum, the terminal part of the large intestine before the anal canal.

In female anatomy, the uterus lies between the bladder anteriorly, meaning towards the front, and the rectum posteriorly, meaning towards the back. The vagina descends behind the bladder and urethra, the tube carrying urine outside the body, and in front of the rectum.

In male anatomy, the prostate lies below the bladder, while the seminal glands lie behind it and in front of the rectum. Each testis lies outside the pelvic cavity in the scrotum, a pouch of skin and underlying tissues. The perineum, the region below the pelvic floor between the thighs, contains the external genital structures.

What are the ovaries and uterine tubes?

The ovaries are paired organs that contain developing oocytes, the female reproductive cells, and produce reproductive hormones. The left ovary usually lies near the left lateral wall of the pelvic cavity; the right ovary occupies the corresponding position on the right. Their positions vary with neighbouring organs and the attachments of the uterus.

Each uterine tube extends from the upper uterus towards an ovary. The left uterine tube has the same basic regions as its right counterpart:

• The infundibulum is the funnel-shaped lateral end, with fimbriae, finger-like projections beside the ovary.
• The ampulla is the wider region and the usual site of fertilisation, the union of sperm and an oocyte.
• The isthmus is the narrower segment approaching the uterus.
• The uterine part passes through the wall of the uterus.

The tube does not form a sealed connection with the ovary. Its lateral opening communicates with the peritoneal cavity, the potential space between the layers of the membrane lining the abdominal cavity and covering many organs. This arrangement allows an oocyte released from the ovary to enter the tube.

What are the fundus, body and cervix of the uterus?

The uterus is a hollow muscular organ. Its fundus is the rounded upper portion above the openings of the uterine tubes, and its body is the main central portion. The cervix is the narrower lower portion, with a supravaginal part above the vagina and a vaginal part projecting into it.

The uterine wall has a muscular layer, the myometrium, and an inner lining, the endometrium. The uterine cavity continues into the cervical canal, the passage through the cervix. The internal opening connects this canal to the uterine cavity; the external opening connects it to the vagina.

The uterus is commonly anteverted, meaning tilted forwards relative to the vagina, and anteflexed, meaning that its body bends forwards relative to the cervix. These describe orientation rather than separate structures. Uterine position varies, including with the filling of the bladder and rectum.

Which ligaments support the female reproductive organs?

Support comes from the pelvic floor, a muscular sheet closing the bottom of the pelvic cavity, and from connective tissue around the cervix and vagina. Several named ligaments help maintain position, but they do not all have the same supporting role.

• The cardinal ligaments are connective-tissue condensations extending from the cervix and upper vagina towards the lateral pelvic walls.
• The uterosacral ligaments extend backwards from the cervix towards the sacrum, the bone forming the posterior wall of the pelvis.
• The pubocervical ligaments extend forwards from the cervical region towards the pubis, the anterior part of the hip bone.
• The round ligaments extend from the uterus through the inguinal canals, passages in the lower abdominal wall, towards the labia majora.
• The ovarian ligaments connect the ovaries to the uterus.
• The suspensory ligaments of the ovaries connect them towards the lateral pelvic walls and carry ovarian vessels.

The broad ligament is a double fold of peritoneum extending between the uterus and pelvic walls. Its subdivisions are the mesometrium beside the uterus, mesosalpinx supporting the uterine tube and mesovarium attaching to the ovary. It is not the principal mechanical support of the uterus.

What are the vagina and female external genitalia?

The vagina is a muscular canal extending from the cervix to the vaginal opening in the perineum. Its upper end surrounds the projecting cervix, forming recesses called fornices. The posterior fornix is the deepest of these recesses.

The female external genitalia are collectively called the vulva. The mons pubis is the fatty prominence over the pubis, while the labia majora are the larger outer skin folds. The labia minora are the smaller inner folds bordering the vestibule, the space containing the urethral and vaginal openings.

The clitoris contains erectile tissue, which can become expanded by blood filling its vascular spaces. Most of it lies beneath the surface, with its glans, or rounded terminal part, situated externally and partly or wholly covered by the clitoral prepuce, a fold of skin. The bulbs of the vestibule are paired masses of erectile tissue beside the vaginal opening, and the greater vestibular glands lie posterolateral to that opening.

How are the testis, epididymis and deferent duct connected?

Each testis is a reproductive organ within the scrotum that produces sperm and reproductive hormones. Sperm develop in seminiferous tubules, tightly coiled tubes within the organ. Small channels carry sperm towards the epididymis, an organ along the posterior aspect of the testis containing a tightly coiled epididymal duct and, in its head, efferent ductules.

The epididymis has a head, body and tail. Its duct provides a passage in which sperm mature and are stored, and its tail continues into the deferent duct, also called the ductus deferens. This muscular tube ascends within the spermatic cord, a bundle containing the duct, vessels and nerves, and passes through the inguinal canal into the pelvis.

Within the pelvis, the deferent duct passes towards the back of the bladder. Its expanded terminal region, the ampulla, joins the duct of a seminal gland to form an ejaculatory duct, which passes through the prostate.

Where are the seminal glands, prostate and penis?

A seminal vesicle is a folded gland behind the bladder that contributes fluid to semen, the mixture of sperm and glandular secretions. These paired glands lie above the prostate, which surrounds the prostatic part of the male urethra below the bladder. The ejaculatory ducts open into the urethra within the prostate.

The penis has a root attached in the perineum and a body projecting externally. It contains paired corpora cavernosa, columns of erectile tissue, and a corpus spongiosum of penis, another erectile column surrounding the penile urethra. The corpus spongiosum expands distally, away from the root, to form the glans penis.

The male urethra carries urine from the bladder and also provides the final passage for semen. In the 3D model beside this article, rotate the view and fade the urinary bladder to explore its position relative to the reproductive organs.

Which female and male structures are homologous?

Homologous structures develop from corresponding embryonic tissues, the tissues present during early development. Their adult shapes and functions can differ substantially. Homology therefore describes developmental correspondence rather than identical anatomy.