Chapter 17 - Deveolpment Of A Human Embryo

Question 1

What is implantation?

Answer 1

• as the zygote travels down the Fallopian tube it begins to divide via mitosis
• after multiple divisions, the zygote is referred to as a blastocyst
• one side of the blastocyst is a group of roughly 30 cells that make up the inner cell mass (embryoblast)
• the blastocyst remains free in the uterus for 2-3 before implanting itself into the endometrium

Question 2

What are 3 main abilities of stem cells found in the embryoblast?

Answer 2

1. The cell is not specialised for a specific function.
2. The cell can undergo repeated division (proliferation)
3. The cell can differentiate into a specialised cell type (tissues)

Question 3

What are some external signals for cell differentiation to occur?

Answer 3

• chemicals secreted by other cells
• physical contact with other cells
• it’s microenvironment

Question 4

What are the 3 types of stem cells and where are their purpose?

Answer 4

1. Totipotent stem cells
   - can give rise to all cell types that make up the body (including placenta)
   - lining cells of the blastocyst
2. Pluripotent stem cells
   - can give rise to all the cell types that make up the body but NOT the cell types that make up the embryonic membranes
   - inner cell mass
3. Multipotent stem cells
   - can develop into more than one type of specialised human body cell (not all cells)

Question 5

What are the three primary germ layers?

Answer 5

Ectoderm

• hair, nails
• epidermis of skin
• muscles of the eye
• sensory organs
• entire nervous system
• enamel of the teeth

Mesoderm

• connective, cardiac and skeletal tissue
• bone, cartilage, blood
• epithelium of the ovaries, testes and other sex organs

Endoderm

• epithelium of the alimentary canal, liver and pancrease
• epithelium of the pharynx, larynx, trachea, bronchi and lungs
• epithelium of the vagina and associated Glands.

Question 6

What are the 4 different embryonic membranes?

Answer 6

1. The amnion membrane
   - first membrane to develop
   - surrounds the embryo into a cavity in which it secretes amniotic fluid
   - when it ruptures before birth, it is known as the breaking of waters.
2. The chorion membrane
   - surrounds the embryo and the three other membranes
   - fuses with the inner layer of the chorion, eventually becoming the main part of the foetal portion of the placenta.

The other two membranes are not important is humans but become a part of the umbilical cord.

Question 7

What is the purpose of the placenta?

Answer 7

• supplies nutrients to and removes waste from the foetus
• by the end of the third month of pregnancy, the placenta is completely formed
• serves as an endocrine organ producing a number of hormones necessary to maintain pregnancy.
• the placenta is attached to the foetus by the umbilical cord
• Single umbilical vein and two umbilical arteries

Question 8

What is Chronic Villi?

Answer 8

• Chronic villi grow from the outer layer of cells on endometrium
• the villi penetrate the endometrium and are surrounded by the mother’s blood
• the maternal and foetal blood are separated by thin layers cells
• the exchange of materials take place by active transport and diffusion