Human Reproduction


Living organisms all reproduce in order to make a new generation of organisms . As seen earlier, there are two types of reproduction that living organisms do:-

  1. Sexual Reproduction.

  2. Asexual Reproduction.

Humans reproduce through sexual reproduction. A male sperm cell fuses with a female egg cell inside the female's reproductive system. From fertilisation to birth, the process takes approximately 9 months.

Female Reproductive System

The diagram below shows the main parts of the female reproductive system:-

Function of parts:

  1. Ovary - Contains hundreds of undeveloped egg cells or ova. The female is born with all the ova she will ever have.

  2. Oviduct - Connects the ovaries to the uterus. They are covered in thousands of cilia cells to move the ovum towards the uterus. Fertilisation occurs in the oviduct.

  3. Uterus - The uterus is where the baby will develop over approximately 9 months until birth.

  4. Cervix - The cervix is a ring of muscle which acts as the entrance to the uterus.

  5. Vagina - The vagina is a tube of muscle that connects the cervix to the outside of the female body. The vagina is where the male sex cells enter the female's body.

The diagram below shows the main parts of the male reproductive system:-

Function of parts:-

  1. Testes - The male sex cells (Sperm) are continuously made here. Hormones are also produced here.

  2. Sperm Duct - Carries the sperm cells to the urethra. The sperm cells mix with fluid from the glands to make semen.

  3. Urethra - Carries the semen from the glands to outside of the male body. This is the same tube which carries urine from the bladder, but a ring of muscle prevents these from mixing.

  4. Penis - Enters the female body during sexual intercourse to pass semen into the vagina.

Menstrual Cycle

In order to ensure that the fertilised egg has the best possible environment to develop in, the entire lining of the uterus (called the Endometrium) is replaced every 28 days in a process known as the Menstrual Cycle.

The diagram below shows the (approximately) 28 day menstrual cycle:-

The process of the menstrual cycle is as follows:-

  1. Day 1 - The endometrium breaks down and is lost from the body through the vagina. In the ovary, a new ovum starts to develop.

  2. Day 7 - By this point, the endometrium starts to thicken again and the ovum is almost fully mature.

  3. Day 14 - The ovum is released from the ovary in a process called ovulation. Cilia cells in the oviduct move the ovum towards the uterus.

  4. Day 21 - The endometrium has reached full thickness and is ready for implantation if the female becomes pregnant.

  5. Day 28 / 1 - If the female is not pregnant, The endometrium breaks down and is lost from the body through the vagina.


The process of fertilisation takes place within the oviduct of the female reproductive system. To do this, the male sperm cells must be placed within the female through sexual intercourse.

Image result for fertilisation sperm egg

The sperm cells 'swim' from the vagina, through the cervix and uterus to the oviduct to reach the ovum.

The video below shows the journey and difficulties a sperm cell must endure to fuse with the ovum.

Stages of Pregnancy

Once fertilisation has occurred, the process of pregnancy can begin. The single fertilised cell goes through a huge amount of change before the baby is ready to be born:-

Note - The diagrams above are not to scale, the actual sizes of the early stages are too small to show clearly on the scale of a full grown baby.

The videos below show short explanations of the three Trimesters of pregnancy.

First Trimester ( Week 1 to 12 )

Second Trimester ( Weeks 13 to 28 )

Third Trimester ( Weeks 29 to 40 )

Note - The above video links will open a new window to the TWIG website. These Require a GLOW login to be accessible.


After 37 to 40 weeks, the foetus is counted as being full term, and if born would be expected to survive without specialist treatment.

The diagram below shows the main stages of childbirth:-