Embryology

Question 1

When does the blastocyst and small conceptus present and how big are they

Answer 1

epiblast and hypoblast (blastocyst) - 9 days, around 0.1cm wide.
Conceptus - ~5-6 weeks, around 1cm wide.

Question 2

What 4 processes are repeated to achieve embryology

Answer 2

Proliferate
Move
Differentiate
Cell loss

Question 3

What are the signalling methods used in regulation of cells

Answer 3

Paracrine (adjacent cells)
Autocrine (to oneself)
Concentration signalling (strongest signals are received by cells located closest to the source)

Question 4

Why is there little endocrine regulation in embryology

Answer 4

there isn’t much vasculature made so this doesn’t occur much

Question 5

What occurs to the zygote/embryo after fertilisatipn

Answer 5

1. Embryo attaches to endometrial endothelium
2. Formation of bilaminar disc
3. Bilaminar disc formed of epiblast and hypoblast
4. STB invade the decider and CTB move forward
5. CTB in contact with capillaries

Question 6

Describe the appearance of the conceptus from day 9 of embryology

Answer 6

Conceptus is a bilaminar disc in a blastocyst, consisting of an epiblast and hypoblast

Question 7

What occurs in gastrulation (9-16)

Answer 7

1. Gastrulation forms a 3 layer conceptus - ectoderm, mesoderm and endoderm
2. Epiblast undergoes proliferation forms a group of cells and differentiate into mesoderm cells
3. Mesoderm cells move into a gap (primitive streak) between epiblast and hypoblast.
4. Mesoderm cells differentiate again to replace and form endoderm cells
5. Mesoderm actively cause apoptosis of hypoblasts and differentiate to form endoderm

Question 8

What organs originate from the endoderm

Answer 8

gut
liver
lungs

Question 9

What organs originate from the mesoderm

Answer 9

Skeleton
Muscles
Kidney
Heart 
Blood

Question 10

What organs originate from the ectoderm

Answer 10

Skin

CNS

Question 11

What occurs in day 17-21 of embryology

Answer 11

1. After gastrulation has formed 3 layers, the ectoderm proliferates to form the neural plate
2. There is no proliferation at the neural groove – notochord is acting as a negative regulator to prevent prolif
3. The neural fold’s fold over and form the neural canal.
4. After day 21, the body cavity then closes by day 28 and pinches off the yolk sac into the umbilical cord (allantois).

Question 12

What occurs in the second month of development

Answer 12

Limbs develop – days 28-56.
Face develops.
Internal tissues develop – heart, lungs and gut.

Question 13

When will the conceptus look human by

Answer 13

day 56

Question 14

Describe the development of the CNS

Answer 14

22-23, tissues fuse down the midline to leave 2 openings at the anterior and posterior neuropore

Question 15

Describe the development of the

Answer 15

1. The two endocardial tubes fuse into a primitive heart tube
2. Blood flow begins day 21
3. The heart then undergoes a turning action (anti-clockwise) to form the primitive heart and the 4 chambers form.

Question 16

Explain how the endocardial tubes fuse in the development of the heart

Answer 16

1. Endocardial tubes develop in the mesoderm and come together as the body cavity closes around day 21.
2. The primitive heart tube is joined at the cranial end in a horseshoe (MacDonald’s arc shape) which is them split to form the muscular tube.