THE HUMAN REPRODUCTIVE
SYSTEM
All the topics in Human Biology which have been covered so far - the body systems and
their functioning - apply equally to males and females.
However, in the case of the reproduction process, two different systems are required, of
different sexes, male and female. This is, of course, why the process is called sexual
reproduction.
Use the mouse to label these diagrams of the male and female reproductive systems,
showing the biological names of the various parts.
What structure is connected to the point marked X above? > bladder
In addition, both the male and the female reproductive systems do not perform their
function continuously from birth onwards in the same way as, for instance, the
respiratory system and the digestive system! In fact, the reproductive organs do not start
to function until puberty. When this happens, the reproductive system also has effects on
other systems, all round the body - secondary sexual characteristics. Obviously, these
changes are different in the two sexes, but there are some similarities.
Complete this table summarising the physical changes in boys and girls at this time.
n.b. These may be accompanied by emotional changes as well.
Boys
11-16
Girls
8-15
Change no 1:
voice deepens
breasts enlarge
Change no 2:
hair on face and body
hips more rounded
Change no 3:
muscles develop
hair in groin and armpits
Age range:
Change no 4:
testes produce sperms ovaries produce eggs (ova)
Changes caused by
hormone called:
testosterone
oestrogen
produced by:
testes
ovaries
Most of the changes at puberty can be seen as preparation for the process of reproduction,
and for the eventual role of parenthood.
THE MENSTRUAL CYCLE
From puberty ( age roughly 8 - 15 ) until the menopause (age roughly 45 - 55 years),
the female reproductive system normally goes through a series of regular changes which
are called the menstruan cycle, because it is repeated month after month. In fact, the cycle
normally lasts about 28 days, although there is some variation from one woman to
another.
Most of the changes involve the buildup of the lining of the uterus, to coincide with the
release of an egg (ovulation) so as to provide an environment to accept a fertilised egg,
followed by the breakdown of this tissue if the egg is not fertilised. When the lining of
the uterus is got rid of, it results in a flow of blood and tissue. This phase, which lasts
only about 4-5 days, is called menstruation. Counting from the first day of bleeding, an
egg is normally released at about day 14 (i.e. in the middle of the cycle), although there is
some variation, and the cycle length may also vary.
Hormonal regulation of the menstrual cycle
After menstruation, follicle stimulating hormone (FSH), from the pituitary gland, causes
a follicle in the ovary to develop, and before releasing the egg the follicle produces
several oestrogen hormones. Under the influence of oestrogens, the lining of the uterus
gradually grows thicker. After ovulation, rising levels of progesterone from the corpus
luteum (remains of the follicle) support this lining, and cause blood vessels in it to
become more developed (vascularisation) - in preparation to receive an egg, if it is
fertilised. As the production of progesterone decreases in the next few days, support for
the thickened uterine lining is lost, and eventually menstruation occurs, usually on the
28th day.
SEXUAL INTERCOURSE
This is also called making love, because it is a very intimate act between a man and a
woman, and it should be a pleasurable experience for both. In the process, a liquid called
semen, containing sperms, passes out of the end of the man's penis - a process called
ejaculation - and these may be deposited inside the woman's vagina.
CONCEPTION
In order for a woman to become pregnant, several events must occur.
- Sperms must swim through the cervix, through the uterus and along the Fallopian tube,
and meet an egg which has just been released from the ovary, and which is travelling in
the opposite direction along the Fallopian tube.
- One sperm must enter the egg and both cells must join together, so that their nuclei fuse
- the process of fertilisation.
- The fertilised egg (zygote) then starts to divide to produce more cells, but the ball of
cells produced must become attached to the lining of the uterus (implantation), in order
to develop further. It will also continue to produce progesterone which stabilises
conditions inside the uterus until birth.
Use the mouse to identify the regions within the female reproductive system where
Ejaculation, Fertilisation, and Implantation may occur.