Heart Development

Question 1

What are the stages of heart development

Answer 1

1 cardiac progenitors
2 linear heart tube
3 looping of heart tube - rearranges the chambers
4 making heart chambers

Question 2

What are the two stages of forming the linear heart tube

Answer 2

1 cardiac crescent - cardiac progenitors first recognisable as a crescent shaped epithelium
2 linear heart tube - heart progenitors form linear heart tube

There is an outer layer myocardial cells and endothelial cells on the inside

Question 3

What is cardiac jelly

Answer 3

Gelatinous acellular matrix secreted by myocardium

Question 4

What is the organisation of the early heart tube

Answer 4

Blood flows in past the sinus venosus then primitive atrium then primitive ventricle then to the bulbus cordis then past the truncus arteriosus

This moves blood cranially

Question 5

What is the process of folding/looping of the heart

Answer 5

1- heart progenitors form the linear heart tube
2 - tubular heart adopts spiral shape, inflow portion, common atrium is forced dorsally and cranially

During folding atrium are displaced dorsally and cranially

Question 6

What does the looping of the heart do?

Answer 6

Brings 4 chambers of future heart into their positions

Remodelling of these chambers = development of septa and valves between them

Question 7

What was seen in the zebra fish experiment

Answer 7

If blood flow was blocked, there was a failure to develop the outflow tract (bulbus), it does not loop and the walls of the inflow and outflow tracts collapse and fuse

Question 8

What is left right patterning of the heart

Answer 8

Begins at gastrulation
The nodal gene is transcribed in cells on the LEFT of the primitive streak
Important in determining the left right orientation of the embryo

Question 9

Inversion of turning

Inversus viscerum

Answer 9

1- reversal looping, nodal gene on right side

2- randomised l/r orientation due to random transcription of nodal gene on

Question 10

What are the late stages of heart development ?

Answer 10

Forming the definitive chambers - remodelling of the heart where the atria and ventricles are separated into the right and left.
The inter atrial septum, AV septum and inter-ventricular septum are also formed

Question 11

What is the atrioventricular canal

Answer 11

The atrial chambers are separated by the ventricles by this canal.
The AV CANAL IS POSITIONED TO THE EMBRYOS LEFT SO THAT ONLY THE LEFT ATRIA AND LEFT VENTRICLE ARE CONNECTED DIRECTLY

Question 12

What is the repositioning of the AV canal

Answer 12

1- growth of the right ventricle region
2 - pulls the av canal more centrally
3 - septation of canal divides the canal into 2 separate canals
4 - supported by fusion of endocardial cushions that form septum intermedium&raquo_space;> divides av canal

Question 13

What is atrial separation

Answer 13

1- septum primum grows, there is an initial gap
2 - ostium primum allows flow
3 - cell death gives rise to hole in septum primum = ostium secundum
4 - septum secundum grows to the left of the septum primum
5 - higher blood pressure in RA, blood pushes on septum primum and pushes it away from septum secundum

Question 14

What is ASD

Answer 14

Atrial septal defect

• hole forms in right atrium but small holes may close with no need of surgery
• in boxer Doberman and English sheep dog

Question 15

What is ventricular separation?

Answer 15

Growth of the muscular part of the septum from membrane of ventricles
The spiral septum is the separation of the outflow tract which produces two outflow tracts = the pulmonary and aorta

Question 16

What is VSD

Answer 16

Ventricular septal defect
Blood flow from left ventricle out into pulmonary trunk and into the pulmonary circulation
Many cases in horses and English bull dogs
The heart has to work hard to get enough blood into the circulation
VSD can occur in the muscular septum or in the membraneous part of it

Question 17

What is tetralogy of fallot

Answer 17

Blood travels from right ventricle into the aorta

Failure in the spiral septum formation
Failure in formation of ventricular septum
Pulmonary stenosis - obstructed blood flow to the lungs
Hypertrophy - thickening of right ventricle as it has to work harder to get enough blood into the lungs to compensate
Over riding aorta

Question 18

What is the circulation before birth

Answer 18

Blood previously flows from the placenta from the mother into the right atrium, the flat valve called the foramen ovale is open between the atria that allows blood to flow into the left atria
Ductus arteriosus is a shunt that pushes blood any blood going into the pulmonary circulation into the aorta as blood is already oxygenated from the mother

Question 19

What is the circulation after birth

Answer 19

Foramen ovale closes and seals up due to high pressure in the chambers
The ductus arteriosus closes between the pulmonary trunk and aorta as the lungs no need to be bypassed (closes due to prostaglandin levels)

Question 20

What is PDA

Answer 20

Patent ductus arteriosus

The ductus artiosus shunt does NOT close therefore blood from the aorta goes into the pulmonary artery

Treatable with prostaglandin inhibitors during first few weeks of life or by surgery

If untreated, high risk of heart failure