IMMS - Embryology

Question 1

What are the stages of the early zygote?

Answer 1

1 cell -> 2 cell -> 4 cell -> 8 cell -> 16 cell morula

Question 2

Define ‘morula’

Answer 2

A solid ball of cells

Question 3

Division of the morula causes a cavity at one end of the morula. It is now known as the ____?

Answer 3

Blastocyst

Question 4

What is the cavity that has been created in the morula called?

Answer 4

Blastocoele

Question 5

What is the blastocyst made up of?

Answer 5

Embryoblast and trophoblast

Question 6

What does the embryoblast go on to form?

Answer 6

Embryo proper

Question 7

What dopes the trophoblast go on to form?

Answer 7

Placenta

Question 8

What is the embryoblast made up of?

Answer 8

Epiblast and hypoblast

Question 9

What are the epiblast and hypoblast known as?

Answer 9

Bilaminar disc

Question 10

What cells line the epiblast?

Answer 10

Columnar cells

Question 11

What cells line the hypoblast?

Answer 11

Cuboidal cells

Question 12

A new cavity called the ____ forms between the epiblast and trophoblast

Answer 12

Amniotic cavity

Question 13

What cells migrate to line the amniotic cavity and what are they then known as?

Answer 13

Epiblasts migrate and are known as amnioblasts

Question 14

What cells migrate to line the inner surface of the trophoblast (blastocoele), and what does this cavity become known as?

Answer 14

Hypoblast cells migrate. The cavity is then known as the primitive yolk sac

Question 15

How does the embryo initially receive nutrition?

Answer 15

By diffusion from the fluid it is travelling in

Question 16

Which part of the structure initially grows fastest?

Answer 16

The ‘placenta’

Question 17

What layers does the trophoblast develop into?

Answer 17

Outer syncytiotrophoblast and inner inner cytotrophoblast

Question 18

What are lacunae?

Answer 18

Spaces in the outer syncytiotrophoblast which form a lacunar network

Question 19

How is the primitive utero-placental circulation set up?

Answer 19

The outer syncytiotrophoblast erodes maternal sinuses, allowing maternal blood to enter the lacunar network

Question 20

What is the extraembryonic mesoderm?

Answer 20

A new layer of cells which develops between the cytotrophoblast and primitive yolk sac

Question 21

What happens to the extraembryonic mesoderm?

Answer 21

Spaces begin forming in it until they fuse together to form a cavity called the extraembryonic coelem (or chorionic cavity)

Question 22

What lines the extraembryonic coelem/chorionic cavity?

Answer 22

The chorionic plate

Question 23

What happens at around day 13 when part of the yolk sac is pinched off?

Answer 23

The remnant is the secondary yolk sac. An exocolemic cyst is also formed which is eventually eliminated

Question 24

The bilaminar disc also becomes joined to the ___ by the ___ which is the future ___

Answer 24

trophoblast, connecting stalk, umbilical cord

Question 25

What is gastrulation?

Answer 25

The rearrangement of cells in the bilaminar disc to form the trilaminar disc

Question 26

Briefly describe gastrulation

Answer 26

1) The primitive streak occurs along the caudal midline.
2) It expands towards the cranial end to form a primitive node with a circular depression called the primitive pit. The depression continues along the streak, forming the primitive groove.
3) Once the primitive streak is formed, cells of the epiblast migrate inwards, detach from the epiblast layer and slip into the gap between epiblast and hypoblast. The process is called invagination.
4) Invagination disrupts hypoblast cells until they are all replaced by a new layer called the endoderm.
5) Remaining cells of the epiblast are now the ectoderm, and some cells that remain in between epiblast and hypoblast layers form the mesoderm.

Question 27

What does the endoderm go on to differentiate into?

Answer 27

A tube forms in the endoderm, then flattens into the notochordal plate, then folds back into the notochord.

Question 28

What does the ectoderm go on to differentiate into?

Answer 28

Neuralation occurs. Tissue in the ectoderm thicken to form the neural plate, with two neural plate borders separating it from the ectoderm. The borders then fold towards each other, forming the neural crest. Eventually, they join and close to form the neural tube.

Question 29

What does the mesoderm go on to differentiate into?

Answer 29

Paraxial mesoderm, intermediate mesoderm and lateral mesoderm.

Question 30

What happens during the 4th week of development?

Answer 30

Embryonic folding in two planes - lateral and cephalic to caudal.

Question 31

What is embryonic folding a result of?

Answer 31

Differing rates of growth within the embryo

Question 32

What final structures does the ectoderm develop into?

Answer 32

Epidermis of skin, hair, nails, lens of eye, pituitary, mammary, sweat and sebaceous glands, CNS, PNS, enamel of teeth and sensory epithelia of nose, ear and eye

Question 33

What final structures does the paraxial mesoderm develop into?

Answer 33

Somites:

• Myotome: Muscle tissue.
• Scleratome: Bone and cartilage.
• Desmotome: Dermis of skin

Question 34

What final structures does the intermediate mesoderm develop into?

Answer 34

Urogenital system: kidneys, gonads, and their respective ducts

Question 35

What final structures does the lateral mesoderm develop into?

Answer 35

Somatic (parietal) layer: Future body walls
Splanchnic (visceral): Circulatory system, connective tissue for glands, muscle, connective tissue and peritoneal components of gut wall

Question 36

What final structures does the endoderm develop into?

Answer 36

Epithelial lining of GI, respiratory and urinary tract, parenchyma of thyroid gland, parathyroid gland, liver and pancreas, epithelial lining of tympanic cavity and auditory tube.