There are various factors that will influence human reproduction and development: gene expression, hormones and the environment.
Some of these hormones that affect male and female reproduction
are:
testosterone: made by the testes in the male and stimulates
the development of male secondary sex characteristics (like facial hair
and deeper voice).
estrogen: made by the ovaries in the female and stimulates
the development of female secondary sex characteristics (wider hips and
mammary glands, starting the thickening of the uterus lining in preparation
for a possible pregnancy after the egg is released by the female each
month.
progesterone: made by yellow tissue called corpus luteum
in the empty ovarian follicle (place in ovary producing and releasing
the egg), the hormone maintains the thickness of the uterus lining in
case fertilization occurs and development of a fetus occurs.
Females: When reaching reproductive age the hormones interact in a cyclic manner, "menstrual cycle"
This process repeats every 28 days unless pregnancy occurs or other problems.
The process begins with the thickening of the uterus lining (estrogen controls the maintenance and thickness)
At the midpoint of the cycle the egg is released "ovulation,"
and the uterine lining thins "menstruation" and estrogen levees
decrease.
1. follicle stage (10-14 days average duration)
* production of ova/eggs occurs in tiny cavities in the ovary called follicles
* enlarging follicle produces estrogen which causes the uterus to get
ready for embryo implantation (uterus thickens its lining)
2. ovulation (1 day)
* follicle enlarges and ruptures ovary wall
* egg is released to the oviduct (usually only 1 is released at a time)
3. corpus luteum stage (10 -14 days average
duration)
* yellow tissue fills the follicle after ovulation called the corpus luteum
* "yellow body" secretes progesterone which maintains the thickness
of the uterus in case a pregnancy occurs
4. menstruation (3-5 days average duration)
* periodic shedding of the thickened lining of the uterus which occurs
if fertilization does not occur
