Reproduction of living organisms: Reproduction in humans
Textbook reference: PP 257-261
Objective:
All mammals begin their life as a tiny fertilized egg. In this
chapter, we will look at sexual anatomy, development of
a foetus, contraceptive methods and sexual transmitted
infections (STI’s).
1. The reproductive system: a system that produces and combines
male and female gametes in order to
reproduce. Reproduction occurs by
internal organization.
Gametes:
males and female sexual cells: Sperm in
males and egg in females.
Males sex cell: Sperm
Female sex cell : egg
Hormones:
chemical messengers that travel in the body though the
bloodstream and tell the testicles (in boys) and ovaries (in
girls) when to begin producing gametes (sperm and egg).
Puberty:
a period that begins when hormones cause changes in
the bodies of boys and girls. These changes are designed
to prepare them for reproduction.
1. Pituitary gland:
2.
3.
4.
5.
6.
a gland located at the base of the brain. In
humans, it is about the size of a pea. It releases
sex hormones.
In males, the sex hormone is testosterone (Released by the
testicles).
In females, the sex hormones are progesterone and estrogen.
(Released by the ovaries).
Testosterone triggers the testicles to produce spermatozoa (Sperm).
Progesterone and estrogen trigger the ovaries to produce ova (Eggsplural). There is a period in each month where a menstrual cycle
occurs. In this cycle, an ovum (Egg-singular) develops and is released
by the ovaries.
Puberty also leads to other physical changes.
Puberty
Boys
Girls
Pubic hair and other body hair begins to grow

Larynx changes which
triggers the deepening of
voices

Breasts develop
b) Male reproductive organs: produces a large number of spermatozoa.
c) Female reproductive organs: produce ova.
d) The menstrual cycle:
a cycle that lasts about 28 days. It causes
changes to the female reproductive
organs:
1)
The lining of the uterus thickens to help the uterus
implant and begin development.
2)
A woman’s body temperature increases during ovulation.
3)
If an ovum is not fertilized by a sperm after a few days, it
is expelled from the body along with the cells that lined
the uterus, this is called menstruation..
2. Pregnancy: A male gamete meets and fertilizes a female gamete.
a)
Steps of fertilization:
1.
2.
3.
4.
Fertilization occurs when spermatozoa are
deposited in the vagina during intercourse.
The sperm then swims in the fallopian tubes until
they reach an ovum.
Of the several million spermatozoa released only
a few thousand will reach the ovum.
Only one will succeed in fertilizing the ovum.
5. When a sperm fertilizes an egg, it now becomes a zygote.
6. The zygote then moves from the fallopian tube into the uterus.
7. As it travels down to the uterus, it undergoes cell division. By the
time, it reaches the uterus, it is now a clump of 16 cells, and hence it
is divided three times.
8. Just before depositing in the uterus, the zygote now looks like a
fluid-filled sac. It has a group of cells called embryoblast.
9. External cells become the placenta.
10.The embryoblast become the embryo.
4. Family planning:
Factors that affect animal production of gametes
are seasons (Climatic change), quantity and
quality of food available. As for humans, females
produce an ovum every month and males
produce spermatozoa every day.
Contraception:
Contraception causes temporary or permanent
sterility in men and women. Certain methods of
contraception prevent fertilization, or the union
of a spermatozoon with an ovum. Others prevent
the zygote from implanting in the uterus.
The following (Next slide) is a table that describes different
contraceptive methods and devices: