Embryology

Question 1

What 4 processes are repeated in order to achieve embryonic development

Answer 1

Proliferation
Movement (chemotaxis)
Differentiation
Loss (apoptosis)

Question 2

What is the key difference in the repeated processes that occur in embryonic development compared to the adult

Answer 2

Mature somatic cells show characteristics one at a time, whereas in an embryo, cells may show the first 3 characteristics simultaneously (Proliferation, movement and differentiation)

Question 3

What basic processes is embryonic development regulated by

Answer 3

Autocrine and paracrine effects

Changes in receptor expressoin

Question 4

Why are there no endocrine effects in embryo development

Answer 4

Absence of a vascular system

Question 5

What does regulation in factors and response in embryo development involve

Answer 5

Gradient
Combination
Spatial
Temporal

Question 6

What are the basic steps in the general timeline of embryonic development

Answer 6

1. Fertilisation
2. Preimplantation development (day 0-6)
3. Implantation
4. Gastrulation
5. Neurulation

Question 7

Describe what occurs in pre-implantation development

Answer 7

Day 0-3 = cleavage, 1 cell to 2,4,8

Day 4 - morula formation as the 8-cell compacts and differentiates

Day 5-6 - blastocyst formation

Question 8

Describe the blastocyst at day 6

Answer 8

Inner cell mass (embryo), fluid-filled blastocyst cavity and trophectoderm (placenta)

Question 9

What occurs in implantation

Answer 9

1. Hatching of the blastocyst to remove the zona pellucida
2. Blastocyst begins to implant into the uterine lining (primed endometrium/decidua)
3. The inner cell mass becomes a bilayer disc containing the epiblast and hypoblast

Question 10

What areas that implantation can occur in may cause harm/fatality to the mother

Answer 10

Fallopian tube
Intraperitoneal space
Ovary

Question 11

What is the overall change that occurs in gastrulation

Answer 11

Formation of the trilaminar disc (ectoderm, mesoderm, endoderm) from the bilayer

Question 12

Explain the process of gastrulation

Answer 12

1. Proliferation of the epiblast
2. Differentiation of the epiblast into mesoderm
3. Cells move into the space between epiblast and the hypoblast
4. Mesoderm cells replace the hypoblast as they undergo apoptosis
5. Mesoderm differentiates into the endoderm
6. Epiblast differentiates into the ectoderm

Question 13

What does the endoderm differentiate into

Answer 13

Gut
Liver
Lungs

Question 14

What does the mesoderm differentiate into

Answer 14

Skeleton 
Muscle
Kidney 
Heart 
Blood

Question 15

What does the ectoderm differentiate into

Answer 15

Skin

Nervous system

Question 16

What occurs in neurulation, when does it occur and what is it controlled by

Answer 16

The differentiation of the ectoderm to form the CNS

Occurs before gastrulation is complete (up to 4 weeks) and under the control of the notochord in the mesoderm

Question 17

Explain the process of neurulation

Answer 17

1. Formation of the neural plate from the ectoderm
2. Development of the neural folds (day 20)
3. Increase in size
4. Meet over the neural groove and fuse to form the neural tube
5. 4 weeks - more complex structure at the cranial end and brain development starts

Question 18

When does the anterior pore neuroclose

Answer 18

25 days

Question 19

When does the posterior neuropore close

Answer 19

28 days

Question 20

What occurs in the yolk sac in week 3

Answer 20

Outside the embryo proper the primordial germ cells are in the yolk sac endoderm at the caudal end of the embryo
Cardiac and vascular progenitors in the primary heart field are at the cranial end of the embryo

Question 21

Describe the folding of the embryo

Answer 21

Anterio-posterior direction
Folds the PGCs into the hind gut, and the developing heart progenitors under the head of the embryo
Folding laterally - fuses the ventral midline (chest and abdomen) of the embryo