Class 8 Science |  Human Body

The Human Reproduction System

What is reproduction

- Reproduction is the process of giving rise to young ones (offsprings) of the same kind.
- The Male reproductive cell is known as a sperm (plural: sperms). It is produced in the testes.
- A female reproductive cell is known as an ovum (plural: ova). It is produced in the ovaries.

Fertilization

Fertilization is the union of a sperm cell and an ovum
During sexula intercourse, the penis (male organ) deposits sperms in the vagina (female organ)
The sperms swim up to the oviduct via the uterus where they get to the ovum.
Fusion process (where the sperm enters the ovum forming a zygote.

Development of the foetus

After fertilization, the sperm and the ovum form a single cell called a zygote.
The zygote undergoes cell division changing into a cell called an embryo.
The embryo (which is a growing cell) moves down to the uterus (womb) developing fingerlike structures called placenta.
The embryo attaches itself to the uterine wall in a process called implantation.
The embryo then grows to become a foetus

Functions of the Placenta

Facilitates production of necessary hormones to mainain the pregnancy
Enhances exchanges of oxygen from mother's body to the foetus
Enhances the exchange of carbon dioxide from the foetus to the mother's body
Prevents disease causing germs from reaching the foetus.

Functions of the umbilical cord

- Joins the placenta to the foetus
- It passes oxygen and nutrients from the placenta to the foetus' blood stream
- It passes carbon dioxide and nitrogenous wastes from the foetus to the placenta.

Amniotic fluid

It is found within the amnion sac of the mother. Functions of the amniotic fluid
- Cushions the foetus from shock
- Allows easier foetal movement
- Controls the temperature to allow for safe groth of the foetus
- Lubricates the foetus
- Prevents dehydration by provding moisture.

The process of birth

(The birth process occurs during the gestation period - 9 months)
1) The uterine wall contracts - also known as labour
2) Following the contraction of the uterine wall, the amnion breaks, releasing fluids. The head of the foetus is pushed down the cervix
3) Cervix enlarges (dilates) allowing the passage of the foetus down to the vagina
4) The enlarged vagina allows the foetus, to come out, head first
5) When the baby is out, the umbilical cord is tied and cut to separate the baby from the mother
6) the afterbirth - part of the umbilical cord and placenta comes out.

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The Human Excretory System

Excretion is the removal of waste products from the body
In humans, the major waste products are urea, carbon dioxide, excess water and excess salts
The organs responsible for the removl of waste are:

• Skin - Removes excess water and salts in the form of sweat
• Lungs - Removes carbon dioxide and water vapout through exhalation
• Kidneys - Removes urea and excess water in the form of urine

The Skin

Below is a picture of the skin, as an excretory system

The Kidney

Below is a labelled diagram of the kidney, as an excretory system

The Lungs (Respiratory System)

Below is a labelled diagram of the respiratory system.