Embryology and Development 4

Question 1

What day does the development of the circulatory system begin?

Answer 1

day 15-16
right after gastrulation

Question 2

describe the process of how blood vessels form

Answer 2

happens in yolk sac and embryo, but happens faster in yolk sac
- ANGIOBLASTS: mesoderm cells in wall of yolk sac differentiate into angioblasts
- BLOOD ISLANDS: angioblasts proliferate
- ENDOTHELIAL CELLS + BLOOD CELLS: under blood islands, little pockets lined with endothelium appear. Pluripotent cells that create blood proliferate. Inside space is lumen.
- ENDOTHELIAL TUBES: pockets fuse to create tubing networks

Question 3

role of angioblast cells

Answer 3

build walls of the blood vessels

Question 4

Does the embryo get its blood supply from its mother?

Answer 4

No! It creates its own.

Question 5

describe development of the heart

Answer 5

• Day 20: 2 endothelial tubes located in CARDIOGENIC REGION (“heart-genesis”) specialize into ENDOCARDIAL TUBES
• Day 21: these 2 endocardial tubes fuse together to make the PRIMITIVE HEART TUBE with 4 main dilations at day 22
• Day 23: complete fusion and bending (via pericardial cavity)
• contractions (non-neural) begin at end of 3rd week

Question 6

Name the 4 main dilations of the primitive heart tube and when they form

Answer 6

Day 22
1. Sinus venosus
2. Ventricle
3. Atrium
4. Bulbus cordis

Question 7

Describe structure and function of endocardial tubes

Answer 7

development starts day 20
- ARTERIAL END: exit point for blood
- VENOUS END: entry point for blood

Question 8

Describe the process of heart folding, what causes it?

Answer 8

Cause: pericardial cavity
- ventricles move forward and down
- atria move backwards and up
(gotta flip ‘em)

• sinus venosus -> part of R atrium and SA node (pacemaker)
  -primitive atria -> L and R atrium
• ventricles -> L and R ventricles
• bulbous cordis -> R ventricle, arteries that leave heart

Question 9

tissue between L and R ventricles in pre-natal heart

Answer 9

interventricular septum

Question 10

Name the tissues that separate the 2 sides of the pre-natal heart

Answer 10

top: Interarterial septum
R: septum secondum
L: septum primum

bottom: interventricular septum

Question 11

Name the hole in the interarterial septum, what it does and how it works

Answer 11

FORAMEN OVALE
- diverts blood flow
- high pressure in R atrium pushes blood directly to L atrium and into the body

Question 12

Why does blood bypass fetal lungs and liver? What are the mechanisms that allow this to happen?

Answer 12

• lungs deflated (passes through foramen ovale and ductus arteriosus)
• placenta is doing the liver’s job filtering blood (passes through ductus venosus)

Question 13

what is the closed foramen ovale called?

Answer 13

FOSSA OVALIS

Question 14

degraded ductus arteriosis

Answer 14

LIGAMENTUM ARTERIOSUS

Question 15

degraded ductus venosus

Answer 15

LIGAMENTUM VENOSUM

Question 16

What happens the the fetal circulatory system when a newborn takes its first breath?

Answer 16

lungs inflate
foramen ovale closes
- pressure in L atrium increases, pushing together the septum secundum and septum primum
- now called FOSSA OVALIS
ductus arteriosus - LIGAMENTUM ARTERIOSUM
ductus venosus - LIGAMENTUM VENOSUM
umbilical vein - LIGAMENTUM TERES (round ligament of liver)
umbilical arteries - MEDIAL UMBILICAL LIGAMENTS (cords of the umbilical arteries)

Question 17

Describe fetal blood flow through circulatory system, starting at the right artium

Answer 17

• right atrium
• right ventricle
  can also bypass to L atrium via foramen ovale
• pulmonary arteries
  can bypass to aorta via DUCTUS ARTERIOSUS
• lungs (only to supply O2 to tissues, lungs are deflated)
• pulmonary veins
• left atrium
• left ventricle
• aorta
• umbilical arteries
  picks up O2 from maternal blood
• umbilical cord -> umbilical vein via DUCTUS VENOSUS
• inferior vena cava (this is where O2 rich and O2 low blood coming back from fetal veins will mix)

Question 18

what region of the gut produces the lung evaginations?

Answer 18

foregut

Question 19

Describe development of the lungs

Answer 19

Day 28
- begins as single mid-line evagination from foregut: TRACHEAL BUD
- lung buds branch off of developing trachea. first two buds are BRONCHIAL BUDS.
- Week 5: trachea as base, PRIMARY BRONCHI and then SECONDARY BRONCHI branch
Week 6: TERTIARY BRONCHI
Week 7: 3 lobes on R, 2 on left. SUPERIOR, MIDDLE and INFERIOR lobes
- branching continues up to 17 times