Embryonic development

Question 1

Define embryology

Answer 1

The branch of medicine concerned with the study of embryos and their development

Question 2

What does development involve?

Answer 2

1. the division and differentiation of cells
2. the changes that produce and modify anatomical structures

Question 3

What periods can embryonic development be divided into?

Answer 3

1. pre-embryonic (0-2 weeks)
2. embryonic (3-8 weeks)
3. foetal period (8 weeks - 9 months)

Question 4

What is the pre-embryonic period?

Answer 4

1. 1-2 weeks
2. Early cell division and implantation
3. formation of a bilaminar

Question 5

What is the embryonic period?

Answer 5

1. 3-8 weeks
2. trilaminar structure forms
3. rudiments of most organs and tissues develop

Question 6

What is the foetal period?

Answer 6

1. 8 weeks - 9 months
2. rudiments grow and mature

Question 7

What kind of cell is a fertilised ovum?

Answer 7

totipotent stem cell

Question 8

What is cleavage?

Answer 8

a series of cell divisions thet subdivide the cytoplasm of the zygote

Question 9

What is a morula?

Answer 9

A ball of 16 cells in pre-embryonic development

Question 10

How many cells does a blastocyst have?

Answer 10

70-100

Question 11

What is the order of the pre-embryonic stage?

Answer 11

1. ovum
2. zygote
3. morula
4. blastocyst

Question 12

How is the bilaminar disk formed?

Answer 12

1. after implantation, some cells in the inner cell mass differentiate into a new type of cell layer
2. new layer is the hypoblast
3. original layer is epiblast

Question 13

What is is the hypoblast?

Answer 13

The new layer of cells formed by the blastocyst to create the bilaminar disk

Question 14

What is the epiblast?

Answer 14

The original layer of cells that remains as part of the bilaminar disk

Question 15

What are the important changes at the start of week 3?

Answer 15

1. gastrulation
2. neurulation

Question 16

What is gastrulation?

Answer 16

The process by which the three germ layers are formed

Question 17

What are the stages of gastrulation?

Answer 17

1. epiblast cells form a primitive streak
2. they move down into the hypoblast layer and displace it
3. this forms the endoderm layer
4. some epiblast cells move inbetween the epiblast and endoderm to form the mesoderm
5. the epiblast becomes known as the ectoderm

Question 18

When does gastrulation occur?

Answer 18

day 14-20

Question 19

What are the three germ layers?

Answer 19

1. ectoderm
2. mesoderm
3. endoderm

Question 20

What type of cells are the germ layers?

Answer 20

multipotent stem cells

Question 21

What is the three germ layer structure known as?

Answer 21

the embryo

Question 22

What process forms the organs?

Answer 22

Organogenesis

Question 23

What forms the notochord?

Answer 23

A central tube of mesoderm cells

Question 24

What will the notochord become?

Answer 24

the vertebral discs

Question 25

What does the notochord stimulate?

Answer 25

stimulates the ectoderm to thicken, which forms a neural plate made of neuroectoderm cells

Question 26

What does the neural plate do?

Answer 26

1. forms 2 ridges
2. fuse to form neural tube

Question 27

What are the cells on the neural crest called?

Answer 27

Neural crest cells

Question 28

What will the neural tube eventually become?

Answer 28

the brain and spinal cord

Question 29

What forms over the neural tube?

Answer 29

Ecotoderm layer, which will form the outer skin of the developing embryo

Question 30

What does the ectoderm give rise to?

Answer 30

1. nervous system
2. skin
3. lens and cornea

Question 31

What happens by day 25?

Answer 31

the neural tube closes at the cranial end (brain) and the caudal end (spinal cord)

Question 32

What happens if the neural tube does not close?

Answer 32

1. spina bifida if caudal neuropore doesn’t close
2. anencephaly if cranial neuropore

Question 33

Where do neural crest cells migrate to?

Answer 33

the mesoderm, where they differentiate into different cell types

Question 34

What do neural crest cells differentiate into?

Answer 34

craniofacial cartilages and bones

Question 35

What is ectomesenchyme

Answer 35

The neural crest cells which have migrated into the mesoderm

Question 36

What happens at the start of week 4?

Answer 36

the pharyngeal arches arise

Question 37

What will the endoderm develop into?

Answer 37

1. epithelial lining of GI and digestive tract
2. lining of urethra, bladder, and reproductive system
3. pancreas

Question 38

What will the mesoderm form?

Answer 38

1. circulatory system
2. muscular layer of stomach and intestines
3. musculoskeletal system
4. vertebral discs of spinal cord