Heart Development

Question 1

heart beat begins in ___ week

septation occurs during ___ week

Answer 1

Heart beat begins in 3rd week.
Septation during 4th week.

Must continue to pump blood as it rearranges/develops

Question 2

causes of heart defects

Answer 2

1) single gene mutations
2) Chromosomal aberrations
3) Neural crest defects/ deficits
4) teratogens
5) diseases

Question 3

___________ provides tissue for the heart

Answer 3

lateral plate mesoderm

Question 4

lateral plate mesoderm divides into ________ layer & _________ layer
[+ what they will form]

Answer 4

Lateral plate mesoderm divides into Somatic layer (parietal pericardium) & Splanchnic Layer (cardiac muscle, visceral pericardium)

Separated by intraembryonic coelom (will form pericardial cavity)

Question 5

two pathways of cardiogenic induction

Answer 5

1) vasculogenesis (medial): condensation of mesenchyme to form vessels, blood cells
2) myogenesis (lateral): gives rise to heart muscle

Question 6

lateral folding of embryo

Answer 6

~3 weeks

Brings 2 heart tubes together to form single tube

Question 7

rostro-caudal folding of embryo

Answer 7

~3 weeks
Moves developing heart into neck, thorax. Takes nerve supply with it.
Driven by rapid growth of neural tissue.

Question 8

dorsal mesocardium

Answer 8

Suspends the heart after embryonic folding. Needs to be broken down to:

1) allow heart looping
2) form adult transverse pericardial sinus

Question 9

absent cilia during heart looping causes

Answer 9

dextrocardia or situs inversus totalis

Question 10

embryonic veins

Answer 10

1) common cardinal vein
2) vitelline veins
3) umbilical vein

Question 11

rightward shift of venous flow

Answer 11

Sinus horn becomes coronary sinus.

Left umbilical vein persists.

Vitelline veins become liver sinusoids.

Cardinal veins go elsewhere.

Right umbilical vein becomes ductus venosus to allow maternal blood to join IVC.

Now all blood enters R side of heart

Question 12

intussusception

Answer 12

Uses wall of sinus venosum (smooth, becomes sinus venarum) to grow R atrial wall (rough pectinate muscles).

Joined at crista terminalis.

Growing pulmonary veins incorporated into L atrial wall.

Question 13

septation (general)

Answer 13

Endocardial cushions contribute to atrial septa, ventricular septa, aorticopulmonary septum, AV heart valves, AV node.

Question 14

septum intermedium

Answer 14

Separates 2 AV canals.
Also forms part of interventricular and interatrial septums too (crux).

From inferior/superior endocardial cushions.

Question 15

Ways to bypass fetal lungs

Answer 15

1) foramen ovale: right atrium to left atrium

2) ductus arteriosus: pulmonary trunk to aorta (for whatever did get to RV)

Question 16

atrial septation

Answer 16

1) Growth of septum primum from atrial roof toward septum intermedium. Ostium primum (opening) remains.
2) Opening in upper septum primum (ostium secundum) forms. Ostium primum seals. by fusion with septum intermedium.
3) Septum secundum grows to cover ostium secundum, forming foramen ovale (closed by change in pressure at birth)

Question 17

ventricular septation

Answer 17

1) myocardial growth forms muscular ventricular septum

2) endocardial cushion tissue growth forms membranous septum

Question 18

if membranous and muscular ventricular septum do not meet, causes —

Answer 18

atrioventricular septal defect

Question 19

conotruncal septation

Answer 19

Produces aortic and pulmonary trunks.

Aorticopulmonary septum creates a spiral division.

Spiraling –> 180 degreee twist, essential to connect aorta w/ LV and pulmonary trunk w/ RV

Question 20

craniofacial defects at birth might indicate:

Answer 20

neural crest problem

Aorticopulmonary defects also caused by lack of neural crest.

Question 21

change in blood pressures after birth

Answer 21

Maternal blood is stopped: decrease pressure in RA.
First breath: increases pressure in LA.

Both: shut foramen ovale (forms fossa ovalis)

Question 22

persistent truncus arteriosus

Answer 22

Interventricular septal defect

Failure of conotruncal ridges to fuse, so no divided aorticopulmonary septum.
Causes IV septum defect.
Mixture of venous/arterial blood –> cyanosis
Tx: surgery, implant shunt between RV and pulmonary trunk

Question 23

transposition of great vessels

Answer 23

Due to failure of conotruncal septum to SPIRAL.

LV empties into pulmonary trunk and RV empties into aorta

Not immediately fatal bc usu assoc w/ parent ductus arteriosus and/or patent foramen ovale (some arterial blood can get distributed systemically and oxygenated blood can get out through right)

Tx: prostaglandins to keep ductus arteriosus open, surgery

Question 24

tetralogy of Fallot

Answer 24

Primary defect: anterior displacement of conotruncal septum (unequal division of conotruncus)

Secondary defects: 
Misalignment of aorticopulmonary + membranous IV septum (IV septal defect).
Overriding aorta (mixes oxygenated/deoxygenated blood).
Hypertrophy of R ventricle.

Question 25

Key step for correct formation of interventricular septum formation

Answer 25

septum intermedium and outflow tract have to be in midline for correct formation of interventricular septum formation

Question 26

Fetus - ___ pressure is higher than ___ because

Answer 26

RA>LA pressure, because maternal blood coming in

Question 27

As fetal lungs become inflated, resistance to pulmonary blood flow is _____

Answer 27

reduced

constriction of ductus arteriosus diverts entire R ventricular output into pulmonary circulation