The embryonic period

Question 1

What 4 stages are there in the embryonic period?

Answer 1

Gasturlation, Neurulation, segmentation and folding.

Question 2

What occurs in gastulation?

Answer 2

the primitive streak forms in the upper surface of the epiblast and the mesoderm forms between a ecto and endoderm (at the start of embryonic period these were called epiblast and hypoblast)

Question 3

Give examples of teratogens which are most damaging in embryonic period

Answer 3

warfarin, isotetrion

Question 4

there are two holes in the mesoderm what are they for?

Answer 4

One will become the mouth the other will become the anus

Question 5

How does the mesoderm and primitive streak from?

Answer 5

Cell migration from sides of the epiblast inwards to the middle and then downwards (invagination)

Question 6

What will the ectoderm become?

Answer 6

Organ and structures that maintain contact with outside world (skin, nervous system)

Question 7

What will the mesoderm become?

Answer 7

supporting tissues (muscle, cartilage, vascular system)

Question 8

What will the endoderm become?

Answer 8

Internal structures (epithelial lining of GI tract, respiratory tract, parenchyma of gands)

Question 9

What is sinus inversus? How does it arise?

Answer 9

where viscera in body swap sides (heart points to the right), normally no morbidity associated. Occurs as ciliated cells in node that normally waft certain signals to the left no longer work or work in opposite direction.

Question 10

What occurs in Neurulation?

Answer 10

The notochord develops which converts the overlying ecotoderm into neuroectoderm. The ectoderm thickens to make slipper shaped neural plate and the ends curl towards each other to create the neural tube.

Question 11

What is a somite? How many are there?

Answer 11

Regular blocks of mesoderm cells arranged around a small cavity on either side of the notochord, 31

Question 12

What happens after the somites form?

Answer 12

they undergo organised degeneration into sclerotome (will become bones), myotome (will become muscle) and dermatome (will become skin)

Question 13

What are the implications of segmentation?

Answer 13

organises mesoderm into repeating structures (ribs, spinal segments ect)
Guides innervation

Question 14

How does the trilaminar disc fold?

Answer 14

sides of ectoderm fold down followed by the ends, this pinches part of the endoderm to go on to create the GI tract and put cardiogenic areas (originally above mouth) in correct places. Also means embryo is suspended in amniotic sac