Lecture 6 Flashcards
Where does the heart evolve from?
Cardiogenic field
Cavity (pericardial)
Horseshoe shape in mesoderm
What does folding of embryo have to do with the heart?
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.
How is the primitive heart tube created?
Lateral folding allows two blood islands to coalesce to form a single heart tube. (Folding inwards)
How is the primitive heart tube divided?
From bottom up: (same way as blood flow)
- sinus venosus
- atrium
- ventricle
- bulbus cordis
- truncus arteriosus
- aortic roots
Where is the heart tube located?
Suspended in the pericardial cavity
What is PDA?
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
What is cardiac looping?
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
How is the transverse pericardial sinus produced?
Via cardiac looping.
Inflow vessels folded behind the outflow vessels (veins behind the arteries)
How is the sinus venosus developed?
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
How is the oblique sinus formed?
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
How is fetal circulation different from mature circulation?
- 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
What is the circulation system in a foetus?
- 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)
What connects the umbilical vein and the IVC?
Ductus venosus
What links the right atrium and left atrium?
Foramen ovale (hole)
What connects the pulmonary trunk and aorta?
Ductus arteriosus.
What does the 4th arch give rise to?
L: Arch of the aorta
R: Proximal part of the right subclavian artery
What does the 6th aortic arch give rise to?
R: Right pulmonary artery
L: Left pulmonary artery/ ductus arteriosus
What is PDA? (Patent ductus arteriosus)
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)
What is the atrioventricular canal?
Narrowing between the primitive atrium and ventricles (neck between them-they are joined)
How does the ductus arteriosus normally close?
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)
Which atria is developed mostly from the primitive atrium?
RA (receives venous return form vena cava & coronary sinus)
-LA is only a small portion of the primitive atrium
How are the pulmonary veins formed?
- 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
Which atria is smooth walled?
LA
RA has a rough, trabeculated wall
Where is the highest pO2 in a foetal heart?
RA, so therefore it needs to be shunted to the LA
What happens once the baby is born?
- respiration begins
- LA pressure increases closing foramen ovale
- ductus arteriosus contracts
- placental support removed
- ductus venosus closes due to lack of blood flow
Why are more people living it’s congenital heart defects?
Because we can now treat many of these, therefore people are living with them and increasing the range of diseases/illnesses we face.
What do the aortic arches give rise to?
Greater vessels of the head/neck
What do the aortic arches look like?
-bilaterally symmetrical system of arched vessels (paired)
5 pairs
(1,2,3,4,6)
Which is the smallest aortic arch and another name for it?
6
Pulmonary arch
What is the nerve that becomes hooked around ductus arteriosus and why?
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
What can only hoarseness of the throat indicate?
Thoracic pathology with no association to the throat
