General Embryology 2

Question 1

Subdivision of mesoderm

Answer 1

• Intraembryonic mesoderm proliferates between the ectoderm and endoderm
• 3 regions develop

Question 2

3 regions of mesoderm subdivision

Answer 2

• Paraaxial mesoderm
• Intermediate mesoderm
• Lateral mesoderm

Question 3

Paraaxial mesoderm

Answer 3

• Head mesenchyme

- Somites

Question 4

Intermediate mesoderm

Answer 4

• Urogenital organs

Question 5

Lateral Mesoderm

Answer 5

• Split by the formation of the intraembryonic coelom
• Somatic mesoderm (somatopleure)
• Splanchnic mesoderm (splanchnopleure)

Question 6

Somites

Answer 6

• Block-like condensations of paraxial mesoderm

- Form on the sides of the neural tube

Question 7

Somatogenesis

Answer 7

• Somite pairs begin formation on day 20
• Progresses in a cranial to caudal pattern
• 42-44 pairs form, most caudal disappear leaving 37 pairs

Question 8

First 4 pairs of somites

Answer 8

• Contribute to head

Question 9

8 pairs of somites

Answer 9

• Contribute to the cervical region

Question 10

12 pairs of somites

Answer 10

• Contribute to the thoracic region

Question 11

5 pairs of somites (two sets of 5)

Answer 11

• Contribute to the lumbar region

- Contribute to the sacral region

Question 12

3 pairs of somites

Answer 12

• Contribute to coccyx

Question 13

Somites subdivide into

Answer 13

• Sclerotome

- Dermamyotome

Question 14

Sclerotome forms

Answer 14

• Meninges
• Vertebrae
• Ribs

Question 15

Dermamyotome forms

Answer 15

• Dermis of the neck and back

- Muscle

Question 16

Dermamyotome differentiates into

Answer 16

• Dermatome

- Myotome

Question 17

Myotome splits into

Answer 17

• Epimere, located dorsally

- Hypomere, located ventrally

Question 18

Epimere gives rise to

Answer 18

• Epaxial muslces of the back

- Deep back muscles

Question 19

Hypomere gives rise to

Answer 19

• Hypaxial muscles
• Muscles of the abdominal and thoracic wall
• Limb muscles

Question 20

Lateral plate divides into

Answer 20

• Somatic mesoderm

- Splanchnic mesoderm

Question 21

Somatic mesoderm

Answer 21

• Lines body wall

Question 22

Somatopleure

Answer 22

• Somatic mesoderm + ectoderm

- Forms body wall with ectoderm

Question 23

Splanchnic mesoderm

Answer 23

• Covers endoderm

Question 24

Splanchnopleure

Answer 24

• Splanchnic mesoderm + endoderm

- Forms gut wall with endoderm

Question 25

Coelom

Answer 25

- Body cavity formed by lateral folding of the embryo

Question 26

Folding of the embryo

Answer 26

- Lateral folds fuse at the ventral midline | - Forms intraembryonic coelom

Question 27

Intraembryonic coelom eventually divides into 3 principal body cavities:

Answer 27

- Pericardial - Pleural - Peritoneal cavities

Question 28

Craniocaudal and lateral folding

Answer 28

- Draw in the yolk sac (purse string) - Close off body wall (except at umbilicus) - Flat trilaminar embryonic disc -> cylindrical embryo

Question 29

Ectopia cordis

Answer 29

- Failure of the thoracic body wall to close

Question 30

Gastroschisis

Answer 30

- Failure of the abdominal body wall to close

Question 31

Early development of the cardiovascular system

Answer 31

- Vasculogenesis begins during 3rd week | - Hemangioblast cells develop in the extraembryonic splanchnic mesoderm of the yolk sac

Question 32

Hemabgioblast development gives rise to

Answer 32

- Hematopoietic cell progenitors - Endothelial precursor cells - Endothelial cells surround blood cell aggregates (blood islands)

Question 33

Yolk sac involved in erythropoiesis until

Answer 33

- About day 60

Question 34

Vasculogenesis

Answer 34

- Differentiating endothelial cells organize into small capillary vessels - Fuse to form channels

Question 35

Vasculogenesis events

Answer 35

- Vascularizes the yolk sac, connecting stalk, and chorionic villi - Vessels from extraembryonic mesoderm -> placenta -> join embryo blood vessels (from intraembryonic splanchnic mesoderm) -> establish circulation

Question 36

Intraembryonic vessels begin to develop on

Answer 36

- Day 18

Question 37

Hematogenesis does not begin within the embryo until about

Answer 37

- 4th week

Question 38

2 major phases of hematopoiesis

Answer 38

- Embryonic (weeks 1-4) | - Definitive (weeks 4-term)

Question 39

Embryonic phase of hematopoiesis

Answer 39

- Blood cells arise from yolk sac extraembryonic mesoderm

Question 40

Definitive phase of hematopoiesis

Answer 40

- Hematopoietic stem cells (from extraembryonic/intraembryonic mesoderm) -> seed the spleen, liver, and then bone marrow

Question 41

Liver is major site of

Answer 41

- Fetal hematopoiesis until bone marrow takes over

Question 42

Vasculogenesis definition

Answer 42

- Blood vessels arise de novo from “hemangioblasts” that develop into blood cells and vascular tubes

Question 43

Angiogenesis

Answer 43

- Growth of new blood vessels from existing ones

Question 44

Segmentation of endoderm

Answer 44

- Foregut - Midgut - Hindgut

Question 45

Foregut

Answer 45

- Trachea - Esophagus - Stomach - Duodenum - Liver - Pancreas

Question 46

Midgut

Answer 46

- Small intestine - Ascending colon - Proximal 2/3 of transverse colon

Question 47

Hindgut

Answer 47

- Distal 1/3 of transverse colon - Descending colon - Rectum - Upper anal canal

Question 48

Weeks 4-8

Answer 48

- Organogenetic period: all main organ systems have begun to develop - Critical period of many organ systems

Question 49

Teratogen exposure

Answer 49

- Can cause major congenital birth defects during organogenetic period (weeks 4-3)

Question 50

Teratogens

Answer 50

- Agents that can disturb the development of an embryo (or fetus) - Radiation, drugs, infections, chemicals