Gastrulation and Trilaminar disc

Question 1

Describe monozygotic twins

Answer 1

Twins that are identical because they both come from the same zygote

Question 2

Describe dizygotic twins

Answer 2

Twins that are non identical as they come from two separate zygotes

Question 3

What is Sesquizygosity

Answer 3

Twins that are genetically identical WRT one parent but approx 50% different with the DNA from the other parent. Potentially as a result of 2 sperm penetrating Zona Pellucida

Question 4

Outline the formation of the primary yolk sac

Answer 4

Occurs in week 2. The floor = Heuser’s membrane, the ceiling = hypoblast.

Question 5

Outline the formation of the secondary yolk sac

Answer 5

Formed from the extra-embryonic mesoderm separates to form the extra embryonic coelom. Cells from the mesoderm pinch off an area of the yolk sac and what remains is the secondary yolk sac.

Question 6

Outline the formation of the final yolk sac

Answer 6

Week 4 - Part of the yolk sac is surrounded by endoderm and incorporated into the embryo as the gut. The bits that remains is the final yolk sac.

Question 7

Where does the amniotic cavity form?

Answer 7

It forms in the space between the epiblast and the cytotrophoblast

Question 8

How and where does the chorionic cavity form

Answer 8

Extra-embryonic mesoblast cells, derived from epiblast cells grow into the extra-embryonic reticulum. Beginning of the reticular vacuole formation that with form the chorionic cavity. It forms inside the extra-embryonic mesoblast.

Question 9

What is gastrulation?

Answer 9

Gastrulation is the formation of the three germ layers: Endoderm, Ectoderm and Mesoderm. The bilaminar disc is converted into a trilaminar disc.

Question 10

When does Gastrulation occur?

Answer 10

Week 3

Question 11

How does gastrulation begin?

Answer 11

It begins with the formation of the primitive streak.

Question 12

What does the primitive streak include?

Answer 12

The Primitive groove, the Primitive Pit and the Primitive Node (AKA Hensen’s Node)

Question 13

Label the diagram about the primitive streak.

Answer 13

on iPad.

Question 14

What do the invading epiblast cells form?

Answer 14

The mesoblast

Question 15

What replaces the hypoblast?

Answer 15

Endoblast.

Question 16

How are the three layers generated?

Answer 16

The epiblast cells roll over into the Primitive Groove and migrate towards the centre. They they undergo the EMT (Epithelial - Mesenchymal Transition). The first cells through displace the hypoblast and become the endoderm. The next cells that remain in the middle become the mesoderm and the cells that remain in the epiblast become the ectoderm.

Question 17

Compare and contrast Epithelial to Mesenchymal cells.

Answer 17

Epithelial - Cell polarity, Cell adhesion, Stationary, High levels of E-cadherin, Low levels of N-cadherin.

Mesenchymal are the complete opposite.

Question 18

Give the derivatives of the endoderm.

Answer 18

epithelial lining of the GIT, respiratory tract bladder and urethra; thyroid and parathyroid glands, liver, pancreas.

Question 19

Give the derivatives of the mesoderm.

Answer 19

connective tissue (cartilage, bone, blood); striated and smooth muscles; heart; blood and lymphatic vessels; kidneys; ovaries and testes; spleen; serous membranes lining the body cavities (pericardial, pleural, peritoneal).

Question 20

Give the derivatives of the ectoderm

Answer 20

CNS (brain and spinal cord); PNS; sensory epithelia of the eye, ear, nose; epidermis and its appendages (hair and nails); mammary glands; pituitary gland.

Question 21

What are formed as a result of gastrulation

Answer 21

The three germ layers and the creating of body axis, Anterior-Posterior, Dorsal-Ventral, and Left-Right