OVERVIEW : THE BIOLOGY OF REPRODUCTION
FEMALE REPRODUCTIVE ANATOMY
Eggs develop and are stored and matured in
the ovaries. The fallopian tubes carry the eggs that are released
from the ovaries during ovulation to the uterus. Fertilization of an egg by a
sperm usually occurs in the fallopian tube. If an egg is fertilized, it will
develop into a fetus in the uterus. The uterus has a specialized lining
called the endometrium that allows an embryo to implant into the wall
providing the developing baby with nutrients and support.
MENSTRUAL CYCLE AND OVULATION
The entire menstrual cycle is controlled
by the brain in concert with the ovaries. There are five main hormones involved
in reproduction. Follicle stimulating hormone (FSH), luteinizing
hormone (LH), and prolactin are produced by the pituitary gland in
the brain. FSH stimulates the growth of the egg within the ovary, while LH
stimulates ovulation or the release of the egg. Estrogen and
progesterone are produced in the ovary and help prepare the lining of the
uterus so it will accept a fertilized egg. The menstrual cycle is measured in
days, starting with Day 1 as the first day of the menstrual period. Ovulation
usually occurs at approximately Day 14. If the released egg is not fertilized,
the lining of the uterus (the endometrium) is sloughed off as the menstrual
period. Although a 28 day cycle is shown in the picture above, most women’s
cycles vary in length.
MALE REPRODUCTIVE ANATOMY
Millions of sperm are produced every
day in the testes. It takes approximately 2 months for sperm to develop
and mature. The vas deferens carry the sperm from the testicles to the
urethra where the seminal vesicles and prostate gland add fluid to
form semen. Semen moves out of the body through the urethra in the
penis. Although approximately 40 million sperm are released at
ejaculation, sperm are very small and most of the semen consists of fluid that
provides nutrients and enzymes to nourish the sperm.
MEN OR WOMEN?
Infertility problems are associated equally with both
men and women. (Female 35%, Male 35%, Male and Female 25%, unexplained
infertility 5%).
MALE FACTORS
Men are most likely to have a problem with their sperm
(volume, count, shape, movement). Sometimes infertility can also be due to
problems with testicles, prostate, varicocele (large vein), illness,
medications, or hormones.
FEMALE FACTORS
Infertility can be caused by egg quality, ovulation
factors, cervical factors, tubal factors, pelvic factors, or even weight. Both
hormone functioning and reproductive anatomy must be "normal" for fertilization
and fetal growth to occur.