LEC 15: Embryology IV - 08.27.14

Question 1

notochordal process

Answer 1

mesenchymal cells from primitive node migrate cranially in the midline to form notochordal process

Question 2

How does the notochordal process grow

Answer 2

notochordal process grows cranially between endoderm and ectoderm until it reaches the prechordal plate

Question 3

Characteristics of the notochord

Answer 3

• primary inductor of the embryo
• defines cranial-caudal axis
• formation of vertebral column
• induces overlying ectoderm to form neural plate

Question 4

What induces the neural plate

Answer 4

neural plate is induces by underlying notochord

• thickened embryonic ectoderm
• neurectoderm gives rise to CNS

Question 5

neurulation

Answer 5

formation of the neural tube (induced by underlying notochord)

Question 6

How does the neural tube form

Answer 6

• neural groove (day 18) and neural folds fuse to form a neural tube
• fusion begins cranially
• neural tube pinches off from surface ectoderm

Question 7

When does the neural tube close

Answer 7

• anterior neuropore (day 24-25)
• posterior neuropore (day 27)

Question 8

Fate of the neural tube (forebrain)

Answer 8

cerebral hemispheres

Question 9

Fate of the neural tube (embryonic midbrain)

Answer 9

Adult midbrain

Question 10

Fate of the neural tube (hindbrain)

Answer 10

• pons
• cerebellum
• medulla oblongata

Question 11

Fate of the neural tube (not forebrain, midbrain, or hindbrain)

Answer 11

spinal cord

Question 12

Neural Crest Cells

Answer 12

• neuroectodermal cells at the crest of each neural fold detach as the neural tube separates from the surface ectoderm
• neural crest cells migrate to each side of the neural tube

Question 13

What derives from neural crest cells

Answer 13

• dorsal root ganglia
• ganglia of autonomic nervous system
• cranial nerves (V, VII, IX, X)
• peripheral nerve sheaths
• melanocytes
• adrenal medulla
• facial muscles and bones

Question 14

embryonic mesoderm

Answer 14

• mesenchyme from primitive streak and notochordal process migrates laterally and cranially
  
  • becomes continous with the extraembryonic (splanchnic) mesoderm
• eventually becomes embryonic (somatic) mesoderm

Question 15

What does embryonic (somatic) mesoderm derive from

Answer 15

extraembryonic (splanchnic) mesoderm

• mesenchyme from primitive streak and notochordal process migrates laterally and cranially
• becomes continuous with extraembryonic (splanchnic) mesoderm

Question 16

Where does cardiogenic mesoderm derive from

Answer 16

Cardiogenic mesoderm derives from embryonic mesoderm

Question 17

embryonic mesoderm separates ectoderm and endoderm everywhere except

Answer 17

1. oropharyngeal membrane (prechordal plate) - mouth
2. cloacal membrane - anus

Question 18

Somites

Answer 18

embryonic mesoderm on both sides of the notochord proliferates to form a longitudinal column of paraxial mesoderm

• paraxial mesoderm divides into paired blocks of mesoderm (somites)
• somites appear first cranially (end of week 3)
• 42-44 pairs of somites by end of week 5

Question 19

How many pairs of somites are eventually formed, and where are they formed initially

Answer 19

• somites initially appear cranially at end of week 3
• 42-44 pairs of somites by end of week 5

Question 20

Somites give rise to…

Answer 20

• axial skeleton (vertebral column, sternum, skull, ribs)
• skeletal muscles
• dermis

Question 21

formation of embryonic body cavity

Answer 21

• coelomic spaces form in lateral mesoderm and cardiogenic mesoderm
• spaces coalesce into horseshoe-shaped intraembryonic coelom (body cavity)

Question 22

What does the embryonic coelom become

Answer 22

1. pericardial cavity (heart)
2. pleural cavity (lungs)
3. peritoneal cavity (abdominal organs)

Question 23

fetal circulation (angiogenesis)

Answer 23

• begins at start of week 3
• begins in:
  
  • extraembryonic mesoderm
  • yolk sac
  • connecting stalk
  • chorion
• primordial uteroplacental circulation begins in week 3

Question 24

angioblasts

Answer 24

• mesenchymal cells in yolk sac (angioblasts)
• angioblasts aggregate to form blood islands

Question 25

Describe the formation of blood vessels from blood islands formed by angioblasts

Answer 25

* small cavities appear within blood islands * angioblasts flatten to form endothelium of blood vessels * endothelial-lined cavities fuse to form vessels

Question 26

hemocytoblasts

Answer 26

blood cells initially formed from endothelial cells of angioblasts

Question 27

What do heart and great vessels form from

Answer 27

heart and great vessels mesenchyme in cardiogenic area

Question 28

Heart tube

Answer 28

* paired endocardial tubes form during week 3 * endocardial tubes fuse to form heart tube * heart tube joins with vessels to form primitive cardiovascular system * heart begins to beat by end of week 3

Question 29

allantois

Answer 29

out-pouching of yolk sac into connecting stalk; associated with the development of the urinary bladder

Question 30

neural tube defects

Answer 30

result from failure of closure of neural tube * spina bifida (caudal neural tube doesn't close) * anencephaly (cranial neural tube doesn't close)