MDDE

Question 1

What is compaction?

Answer 1

→ change in shape of the embryo

Question 2

What is a morula?

Answer 2

→ blastomeres begin to form tight junctions with one another, leading to deformation of their round shape and formation

Question 3

How old is a morula?

Answer 3

→ 12-16 days

Question 4

How is the site of implantation sealed?

Answer 4

→ by a fibrin plug

Question 5

What does the bilaminar germ disk consist of?

Answer 5

→ epiblast

→ hypoblast

Question 6

When is the amniotic cavity formed?

Answer 6

→ 9 days

Question 7

What displaces the hypoblast?

Answer 7

→ by involuting cells that become definitive endoderm, and mesoderm

Question 8

When does gastrulation occur?

Answer 8

→ 3rd week

Question 9

What does gastrulation allow?

Answer 9

→ the two cell layers become three germ cell layers,

→ the bodily axes observed in the mature adult are created

Question 10

What lies in the primitive streak?

Answer 10

→ a primitive node at the cranial end, and within the primitive node lies the primitive pit.

Question 11

What happens to cells of the epiblast?

Answer 11

→ epiblast layer break off and migrate toward the primitive pit
→ detach and penetrate through the epiblast layer to form three new germ cell layers

Question 12

How is the endoderm formed?

Answer 12

→ by epiblast cells that migrate through the primitive pit and displace the hypoblast cells

Question 13

How is the mesoderm formed?

Answer 13

→ formed by epiblast cells that migrate through the primitive pit and lie between the epiblast layer and the newly created endoderm.

Question 14

How is the ectoderm formed?

Answer 14

→ formed by the epiblast cells that remain in position

Question 15

What does the endoderm give rise to?

Answer 15

→ Epithelial lining of digestive and respiratory tracts,

→ Lining of urethra, bladder and reproductive System

→ Liver and pancreas

Question 16

What does the mesoderm give rise to?

Answer 16

→ Notochord

→ Musculoskeletal system

→ Muscular layer of stomach, intestine etc

→ Circulatory system

Question 17

What does the ectoderm give rise to?

Answer 17

→ Epidermis of skin

→ Cornea and lens of eye

→ Nervous system

Question 18

Describe the neurulation process?

Answer 18

→ectoderm differentiate to form a neural plate
→neural plate then bends dorsally, folding inwards to form a groove flanked by a neural crest
→infolded groove closes off and separates from the neural crest to form the neural tube

Question 19

What does the neural tube elongate into?

Answer 19

→form the central nervous system (brain and spinal cord)

Question 20

What do the the cells of the neural crest differentiate into?

Answer 20

→peripheral nervous system

Question 21

How does the neural tube close?

Answer 21

starts at hindbrain and then progresses anteriorly and posteriorly

Question 22

Describe the cloth purse model of folding

Answer 22

→ septum and heart move from margin to centre
→yolk sac, allantois and stalk make umbilical cord
→prochordal and cloacal plates delimit gut tube

Question 23

What happens during folding?

Answer 23

→Heart and other structures move from margin of embryo to the centre

Question 24

Describe the folding process

Answer 24

→amnion and embryonic disc grow vigorously but the yolk sac does not.
→ the expanding disk balloons into a 3D, cylindrical shape.
→The dorsal structures of notochord, brain and somites stiffen this axis
such that the flexion takes place at the thin, flexible outer rim of the disc

Question 25

What do malformations in the cleavage, implantation, and gastrulation result in?

Answer 25

→death

Question 26

What is involved in organogenesis?

Answer 26

→Differentiation of somitic derivatives 
→Development of sensory organs 
→Limb formation
→Formation of face structures 
→Formation of genital structures