Embryo Topic 6

Question 1

Somite

Answer 1

Somites are the result of the differentiation of the paraxial mesoderm. It is made up of blocks of the mesoderm and are located on each side of developing neural tube. The head mesoderm forms the muscles and connective tissues of the head and eyes. Somites are used as one of the criteria to know the age of the embryo.

Question 2

Sclerotome

Answer 2

Portion of the somite that gives rise to the vertebral and rib cartilage.

Question 3

Myotome

Answer 3

Portion of the somite that gives rise to the muscles of the back, rib cage, and abdomen.

Question 4

Dermamyotome

Answer 4

Portion of the somite that gives rise to the dermal cells and limb muscle.

Question 5

Syndetome

Answer 5

Subregion of the somite that is most dorsal and gives rise to the formation of tendons

Question 6

Arthrotome

Answer 6

Subregion of the somite that is most central and gives rise to the vertebral joints/discs and the proximal ribs.

Question 7

Somatic mesoderm

Answer 7

Portion of the lateral plate mesoderm that lines the body wall and is made up of the somatic mesoderm + the ectoderm to make the somatopleure.

Question 8

Splanchnic mesoderm

Answer 8

The portion of the lateral plate mesoderm. The splanchnic mesoderm and endoderm form the splanchnopleure.

Question 9

Somatopleure

Answer 9

The somatic mesoderm + the ectoderm make up the somatopleure.

Question 10

Splanchnopleure

Answer 10

The splanchnic mesoderm and endoderm form the splanchnopleure.

Question 11

Coelom

Answer 11

body cavity formed by lateral folding of the embryo

Question 12

Vasculogenesis

Answer 12

Blood vessels arise new from hemangioblasts that develop into blood cells and vascular tubes.

Question 13

Angiogenesis

Answer 13

Growth of new blood vessels from existing ones via branching

Question 14

Somitogenesis

Answer 14

There are 5 steps to somitogenesis. They are: (1) Establishment of periodicity, (2) fissure formation, (3) epithelialization, (4) specification, (5) differentiation.

Question 15

Notochord induction of sclerotome

Answer 15

Epithelial to mesenchymal transition causes them to migrate to form vertebral cartilage, leaves dermamyotome epithelium.

Question 16

There are several parts of segregation of the dermamyotome

Answer 16

Paraxial myotome: forms back and intercostal muscles
Abaxial myotome: forms abdominal muscle, tongue, limbs
Central myotome: proliferates madly and makes most cells

Question 17

Myogenesis

Answer 17

The myotome cells become dividing myoblasts, then the cells start to align and they stop proliferating, then the initial myotube formation occurs, then myotube maturation, then lastly you end up with a muscle fiber and stem cell.

Question 18

Osteogenesis

Answer 18

There are four different sources of bone and two different processes. For endochondrial ossification the sources are somites form the axial skeleton and the lateral plate mesoderm forms the limb skeleton. For the intramembraneous ossification the sources are the cranial neural crest forms the bones of the face and head and the mesodermal mesenchyme in the patella and the membrane of the bones.

Question 19

Tendon formation

Answer 19

Form from mesenchymal cells within the lateral plate mesoderm of the embryo with these cells differentiating into tendon progenitor cells that eventually become tendon. The last row of sclerotome is induced by the overlying myotome to differentiate into those connectors.

Question 20

Heart development: tube formation

Answer 20

The cardiogenic mesoderm migrates out of the mesodermal ayer towards the endoderm to form the endocardial tubes on either side. At the same time the endoderm is folding inward. The endoderm continues folding inwards until it forms its own tube, which drags two endocardial primordia close to each other. The endocardial tubes are surrounded by myocardial progenitors. When the endocardial tubes get close enough, they fuse together.

Question 21

Heart development: looping

Answer 21

Requires (1) cytoskeletal rearrangement, (2) extracellular matrix remodeling, and (3) asymmetric cell division.

Question 22

Heart development: chamber formation steps

Answer 22

1. endocardial cushions form and fuse.
2. septa grow towards cushion
3. valves form from myocardium

Question 23

Vasculogenesis steps

Answer 23

Endothelial progenitor cells —> coalescence of cells —> formation of lumen and vasculogenic networks —> blood vessel formation and stabilization

Question 24

Angiogenesis

Answer 24

Vessels sprout into adjacent areas by endothelial budding and fuse with other vessels called angiogenesis

Question 25

Hematopoiesis

Answer 25

Creation of all blood cells. There are two phases involved. The first phase is the embryonic phase and the blood cells arise from yolk sac mesoderm. The second phase is the definitive phase and the blood cells arise from lateral plate mesoderm in the AGM. Then they are delivered to liver, spleen, and

Question 26

Secondary Vasculogenesis

Answer 26

1. PEO forms from splanchnic mesoderm overlying the liver. 2. PEO contacts the ventricle and migrates as epicardium. 3. Subset of epicardial cells delaminate towards myocardium 4. These undergo MET to form coronary endothelium. 5. Coronary arteries then plug into the aorta where nerves are.

Question 27

Primitive organizer for kidney development

Answer 27

The nephric duct (Wolffian duct) matures into the collecting duct

Question 28

Pronephros

Answer 28

functional in fish, amphibians, not in mammals, then degenerates.

Question 29

Mesonephros

Answer 29

functional in some mammals, including humans, degenerates in females, forms epididymis and vas deferens.

Question 30

Kidney formation

Answer 30

The intermediate mesoderm 1st forms an organizer, the pronephric duct. This tissue then induces three stages of kidney. The first two are transitory, the third persists. (look on image on slides and put more details)