Human Reproduction

• 1. The zygote divides many times by cleavage (increase in number of cells by division but no overall increase in size) to double its cell number.
• A solid clump of about 100 cells called the morula is formed.
• 2. About 5 days after fertilisation the morula develops into a hollow ball called a blastocyst.
• The outer cells of the blastocyst form the trophoplast.
• This will become the membranes around the embryo.
• The inner cells called the inner mass will become the embryo.
• 3. The blastocyst is pushed down the Fallopian tube and into the uterus for implantation.

The zygote divides many times by cleavage (increase in cell no. but not in size) to double its cell number.

A solid clump of about 100 cells formed from the diploid zygote dividing many times by cleavage. (after 3 days).

A solid clump of about 100 cells called the morula is formed.

About 5 days after fertilisation the morula develops into a hollow ball called a blastocyst.

A hollow ball that the morula becomes 5 days after fertilisation.

Form the trophoblast and this will become the membranes around the embryo.

The outer cells of the blastocyst firm the trophoblast and thus will become the membranes around the embryo.

The inner cells (of blastocyst) called the inner mass will become the embryo.

The blastocyst is pushed down the Fallopian tube and into the uterus for implantation.

A primary layer of cells that forms during embryonic development.

• Mesoderm (middle) develops into muscles and blood.
• Endoderm (inside) develops into digestive tract and lungs.
• Ectoderm (outside) develops into skin, nerves and brain (CNS fully developed at 12 weeks)