The reproductive system
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The reproductive system is a collection of organs and a network of hormone production that work
together to create life.
The male reproductive system includes the testes (which produce sperm), penis, epididymis, vas
deferens, ejaculatory ducts and urethra.
The female reproductive system consists of the ovaries (which produce eggs or oocytes), fallopian
tubes, uterus, cervix, vagina and vulva.
Both the male and female reproductive systems must be functioning properly for a couple to conceive
naturally. A problem with the structure or function of either reproductive system can cause infertility.
Mechanism of reproductive system
The reproductive system is a collection of organs and a network of hormone production in men and women
that enable a man to impregnate a woman who gives birth to a child. In women, the ovaries produce the egg
cells, called the ova or oocytes. The oocytes are then transported to the fallopian tube where fertilization by a
sperm may occur. The fertilized egg then moves to the uterus, where the uterine lining has thickened in
response to the normal hormones of the reproductive cycle. In men, When the erect penis is stimulated,
muscles around the reproductive organs contract and force the semen through the duct system and urethra.
Semen is pushed out of the male's body through his urethra — this process is called ejaculation. Each time a
guy ejaculates, it can contain up to 500 million sperm. During conception, a sperm cell from the man fuses with
an egg cell in the woman, creating a fertilized egg (embryo) that implants and grows in the uterus during
pregnancy.
Abnormalities or damage to reproductive organs and malfunction of the hormone production and delivery
system that governs reproduction are common causes of infertility in men and women.
Brain centers play a key role in the regulation and control of the reproductive hormones and system. Hormones
are chemical messengers that affect the metabolism of other cells with receptors for the hormone. Hormones
may be produced in one part of the body and travel in the blood to another part of the body to initiate an action.
The reproductive brain centers are made up of the hypothalamus, located in the central part of the brain, and
the pituitary gland, located at the base of the brain just below the hypothalamus. Additional higher brain
regions influence activity in the hypothalamus.
The hypothalamus produces gonadotropin-releasing hormone (GnRH) to regulate the production and release
of FSH (follicle-stimulating hormone) and LH (luteinizing hormone) in the pituitary gland. FSH and LH are the
two gonadotropic hormones involved in both male and female reproduction. The rate and magnitude of GnRH
pulses from the hypothalamus regulate the release of FSH and LH from the pituitary gland.
Reproductive hormones in women
The menstrual cycle is regulated by the complex interactions of hormones produced in the hypothalamus,
pituitary and ovary. FSH released from the pituitary stimulates the ovarian follicles to begin maturation and
growth. Follicles are sac-like structures in the ovary containing eggs. As the follicle and egg develops, cells
within the follicle produce estrogen. Follicle cells produce another hormone called inhibin that circulates back to
the hypothalamus and pituitary to decrease the release of FSH.
The production of estrogen continues to rise under the influence of FSH as the follicle matures and increases
in size. When the follicle is mature, maximum production of estrogen occurs and this signals a rapid rise in LH
from the pituitary gland.
LH, along with the estrogen produced by the ovaries, helps in the maturation process of the egg. LH also
triggers ovulation – the release of a mature egg from one of the follicles in the ovary. After ovulation, the follicle
turns into a different structure, the corpus luteum, which produces progesterone.
Progesterone acts on the uterine lining (endometrium) causing it to thicken in preparation for implantation.
Progesterone is essential for implantation and pregnancy. If implantation does not occur, the thickened
endometrium will break down and be lost with menstrual bleeding.
Reproductive hormones in men
In men, FSH from the pituitary gland stimulates the testes to produce sperm by a process known as
spermatogenesis. LH from the pituitary gland signals the testes to produce testosterone, which enhances
sperm maturation. Testosterone is the primary male sex hormone.