Lecture 7

Question 1

What are the outflow tracts?

Answer 1

• aorta

- pulmonary trunk (artery)

Question 2

What connects the atria and the ventricle?

Answer 2

Atrioventricular canal-after looping

Still doesn’t have 2 pumps in series, just inflow/outflow

Question 3

When does the heart tube start contracting?

Answer 3

3 weeks after conception, so is beating early- when woman may not even realise she is pregnant so is susceptible to risk factors

Question 4

How are the primitive atrium & ventricle divided?

Answer 4

Septation (creates 4 chambers, all events occur at same time)

• interatrial septum (b/w atria)
• interventricular septum (b/w ventricle)
• septation of ventricular outflow tract (to separate into aorta/pulmonary trunk)

Question 5

How is the interatrial septum formed?

Answer 5

• endocardial cushions (wedges of tissue) in atrioventricular canal
• on dorsal/ventral side of canal which grow into the canal and meet at midline (looks like a dot in the middle of the atrium as coronal cross section)
• creating left and right hand channels
• septum primum grows down from roof of primitive heart tube towards fused endocardial cushions

Question 6

Why is atrial septation complex?

Answer 6

-we need something compatible for fetal & adult life (require shunt between the 2 atria, which can resolve immediately after birth)

Question 7

How many septa & holes are formed throughout atrial septation?

Answer 7

• 2 septa (septum primum, septum secundum)
• 3 holes (ostium primum- hole present before septum primum fuses with the endocardial cushions, ostium secundum is punched in the septum primum, hole in the septum secundum due to C shape is foramen ovale)

Question 8

How does atrial septation occur?

Answer 8

• septum primum grows down from the roof of the primitive atria towards the endocardial cushions (blood can flow from right to left atria as septum is not complete)
• just below this septum is about to obliterate flow from right to left, you punch a second hole forming the ostium secundum-allowing blood flow to left atria:without this foetus would die
• septum secundum grows in a C shape leaving a gap called the foramen ovale
• higher pressure of right side, forcing the two septum leafs apart (because the 2 holes are staggered)

ALLOWS A RIGHT TO LEFT SHUNT

Question 9

What is the fossa ovalis?

Answer 9

Adult remnant of foramen ovale

Question 10

How do the holes in the atrial septum close after birth?

Answer 10

The left atria increases in pressure, rather than the right one in birth, which causes the two leaflets together (physiological change)
Over time the leaves will fully fuse (anatomical closure)

-due to the staggered holes, you will create a single impermeable membrane between the 2 chambers

Question 11

What are some atrial septal defects?

Answer 11

• septum primum is resorbed
• septum primum is too short
• absence of septum secundum/septum primum
• septum secundum too short

Question 12

What is hypoplastic left heart syndrome?

Answer 12

• cause not known (could be defect in development of valves, ostium secundum too small to allow enough blood to the left side)
• left heart doesn’t develop fully

Question 13

How does ventricular septation occur?

Answer 13

• muscular portion grows upwards from base of ventricle towards the endocardial cushions
• muscle makes it most of the way, it then needs to be fixed with membranous tissue growing down from endocardial cushions (primary interventricular foramen)

Question 14

What are the 2 components of the ventricular septum?

Answer 14

• muscular

- membranous (smaller)

Question 15

What is a ventricular septal defect?

Answer 15

-membranous portion involved with this

Question 16

How does septation of the outflow tract occur?

Answer 16

Endocardial cushions appear in truncus arteriosus in a staggered arrangement up the truncus arteriosus
-as they grow towards each other they twist upwards around each other
(Causing vessels to wind round each other)

Allowing connection of left ventricle to aorta, and right ventricle to pulmonary trunk: divides into L/R pulmonary arteries

Question 17

How do congenital heart defects form?

Answer 17

-structural abnormalities
-complete absence of a structure
Results from interruption of a normal developmental programme

Question 18

What are some causes of congenital heart defects?

Answer 18

• genetic
• exposure to chemicals/drugs-warfarin, anti-convulsants/infectious agents- rubella, toxoplasma
• unexplained

Question 19

When do congenital heart defects occur?

Answer 19

• there is an obstruction e.g. failure of a valve to form normally blocking it
• communication between pulmonary and systemic flow
• structure defect in chambers/vasculature

Question 20

What are the most common birth defect?

Answer 20

Congenital heart defects
1% worldwide incidence, 90% survive to adulthood

Meaning many people living with the repaired congenital defects
-adding on complexity in pregnancy

Question 21

What is a teratogenic drug?

Answer 21

Teratogen that can disturb the development of an embryo/foetus. (Some can be used to manage heart disease))

Question 22

What is the transposition of the great arteries?

Answer 22

• aorta arises from right ventricle
• pulmonary trunk arises from left ventricle

Related to placement/spiralling or septum within truncus arteriosus

(Deoxygenated blood from body enters right side of heart, leaves via aorta back to the body, oxygenated blood from lungs enters left side and leaves via pulmonary trunk back to lungs)

Question 23

What will you see in transposition of the great arteries?

Answer 23

Cyanosis (blue skin due to low oxygen levels in blood)

Question 24

What is the tetralogy of Fallot?

Answer 24

Combination of 4 distinct defects

• large ventricular septal defect
• overriding aorta (sits across both ventricles)
• stenosis of pulmonary trunk: stenosis, limiting flow to pulmonary circulation
• right ventricle hypertrophy as right ventricle tries to push against obstruction

Due to truncal septum not forming correctly

Question 25

What cells are responsible for creating endocardial cushions?

Answer 25

Neural crest cells