Lecture 6

Question 1

Where does the heart evolve from?

Answer 1

Cardiogenic field
Cavity (pericardial)
Horseshoe shape in mesoderm

Question 2

What does folding of embryo have to do with the heart?

Answer 2

Lateral folding: creates the heart tube (pushes blood islands together towards the midline)
Cephalocaudal folding: brings the tube into the thoracic region (longitudinal region)
Folding occurs in the 4th week.
These foldings occur in unison.

Question 3

How is the primitive heart tube created?

Answer 3

Lateral folding allows two blood islands to coalesce to form a single heart tube. (Folding inwards)

Question 4

How is the primitive heart tube divided?

Answer 4

From bottom up: (same way as blood flow)

• sinus venosus
• atrium
• ventricle
• bulbus cordis
• truncus arteriosus
• aortic roots

Question 5

Where is the heart tube located?

Answer 5

Suspended in the pericardial cavity

Question 6

What is PDA?

Answer 6

Patent Ductus Arteriosus

• persistent communication b/w pulmonary trunk (artery) and aorta due to failure of physiological closure
• blood continues to flow from left to right from high to low pressure

Question 7

What is cardiac looping?

Answer 7

Tube elongates and runs out of room, but can moves laterally.
Twists and folds up (real left side folds down, right side folds up)
-places inflow and outflow vessels in the correct orientation and at the top
-large expansion of the ventricle and small expansion of the atrium, pushes the atrium upwards so it becomes posteriorly in line to ventricle/bulbus cordis

Question 8

How is the transverse pericardial sinus produced?

Answer 8

Via cardiac looping.

Inflow vessels folded behind the outflow vessels (veins behind the arteries)

Question 9

How is the sinus venosus developed?

Answer 9

Remodelling of symmetrical system

• right and left sinus horns equal in size
• venous return on the right shifts to right, left sinus horn recedes
• right sinus horn is absorbed by enlarging RA

Question 10

How is the oblique sinus formed?

Answer 10

As the left atrium expands, absorbing the pulmonary veins.

-put hand under apex of the heart and allow fingers to sit in the cul-de-sac

Question 11

How is fetal circulation different from mature circulation?

Answer 11

• lungs don’t work
• oxygenation and removal of carbon dioxide via placenta
• SHUNTS are required, which need to be reversible immediately as the baby is born

Question 12

What is the circulation system in a foetus?

Answer 12

• oxygenated blood from mother to placenta via umbilicus
• bypass the liver so oxygen not used up, as liver is very metabolically active (via ductus venosus-connects placenta to IVC)
• enters the RA
• blood shunted to LA via foramen ovale to bypass lungs
• some blood enters RV, so that the RV muscle doesn’t atrophise due to lack of work (from here the ductus arteriosus shunts blood from the pulmonary trunk to the aorta to bypass lungs)

Question 13

What connects the umbilical vein and the IVC?

Answer 13

Ductus venosus

Question 14

What links the right atrium and left atrium?

Answer 14

Foramen ovale (hole)

Question 15

What connects the pulmonary trunk and aorta?

Answer 15

Ductus arteriosus.

Question 16

What does the 4th arch give rise to?

Answer 16

L: Arch of the aorta
R: Proximal part of the right subclavian artery

Question 17

What does the 6th aortic arch give rise to?

Answer 17

R: Right pulmonary artery
L: Left pulmonary artery/ ductus arteriosus

Question 18

What is PDA? (Patent ductus arteriosus)

Answer 18

Maintaining the communication b/w descending aorta and pulmonary artery

• failure of closure of the ductus arteriosus
• increase in pO2 causes shunt to close via contraction to close lumen (failure of this leads to PDA)

Question 19

What is the atrioventricular canal?

Answer 19

Narrowing between the primitive atrium and ventricles (neck between them-they are joined)

Question 20

How does the ductus arteriosus normally close?

Answer 20

Physiological
-specific muscle type lining it, when exposed to high pO2, it contracts closing the vessel
Anatomical
-so you don’t require persistant contraction
-fibrosis (fibrotic chord)

Question 21

Which atria is developed mostly from the primitive atrium?

Answer 21

RA (receives venous return form vena cava & coronary sinus)
-LA is only a small portion of the primitive atrium

Question 22

How are the pulmonary veins formed?

Answer 22

• sprout pulmonary veins (left side)
• use the pulmonary vein tissue to become part of the atrial walls of the left atrium
• absorbs earliest branches of primitive pulmonary veins
• 4 openings now in aorta

Question 23

Which atria is smooth walled?

Answer 23

LA

RA has a rough, trabeculated wall

Question 24

Where is the highest pO2 in a foetal heart?

Answer 24

RA, so therefore it needs to be shunted to the LA

Question 25

What happens once the baby is born?

Answer 25

• respiration begins
• LA pressure increases closing foramen ovale
• ductus arteriosus contracts
• placental support removed
• ductus venosus closes due to lack of blood flow

Question 26

Why are more people living it’s congenital heart defects?

Answer 26

Because we can now treat many of these, therefore people are living with them and increasing the range of diseases/illnesses we face.

Question 27

What do the aortic arches give rise to?

Answer 27

Greater vessels of the head/neck

Question 28

What do the aortic arches look like?

Answer 28

-bilaterally symmetrical system of arched vessels (paired)
5 pairs
(1,2,3,4,6)

Question 29

Which is the smallest aortic arch and another name for it?

Answer 29

6

Pulmonary arch

Question 30

What is the nerve that becomes hooked around ductus arteriosus and why?

Answer 30

The aortic arches develop in the neck region so is near cranial nerves.
-Vagus, branch> left recurrent laryngeal nerve becomes hooked/looped and is very near the chest

Question 31

What can only hoarseness of the throat indicate?

Answer 31

Thoracic pathology with no association to the throat