Early embryonic development and implantation

Early embryonic development and implantion

• - The zygote, the single cell that results from the fertilisation of an egg by a sperm has the potential to grow into a new individual human
• - After fertilisation the zygote travels down the Fallopian tube and begins to divide by mitosis which results in the formation of two cells exactly the same as the original parent cell. These cells divide again by mitosis into four, then eight, then sixteen and so on.
• - By about 6 days after fertilisation, the original zygote has reached the uterus and developed into a blastocyst
• - The blastocyst is a hollow ball of cells called the inner cell mass (embryo blast)
• - The inner cell mass will develop into the embryo and the cells that compose it are called stem cells
• - These stem cells are able to produce any of the different types of body cells
• - The blastocyst remains free within the cavity of the uterus for two to three days, then sinks into the soft endometrium (uterine lining) to become firmly attached to the wall of the uterus
• - This process is called implantation, and enables the blastocyst to gain nourishment for growth and development by absorbing nutrients from the glands and blood vessels of the uterine lining
• - In-vitro fertilisation (IVF) is when an embryo can be placed in the female's uterus where it can implant in the lining, this can help couples who have been unable to achieve pregnancy by natural methods

Cell Differentiation

• The cells that make up the inner cell mass of the blastocyst are stem cells
• Stem cells are; not specialised for any particular function; capable of repeated mitosis; differentiate into specialised cells
• When cells replicate themselves it is called proliferation
• Differentiation is the process when unspecialised cells develop the characteristics and functions of a particular type of cell, eg -bone, nerve, blood, muscle
• The stem cells develop into the types of cells that make up the mature human body
• These are known as tissues. A tissue is a group of cells that have a similar structure and work together to perform a certain function
• Mitosis ensures that each daughter cell receives the same genetic information that is contained in the parent cell
• As stem cells proliferate different genes become activated which results in differentiation into specialised cells
• The external signals for cell differentiation include chemicals secreted by other cells, physical contact with neighbouring cells, and certain molecules in the cell's immediate surroundings, called its microenvironment

Stem cells and the process of differentiation