development of the heart - session 3

Question 1

congenital birth defects

Answer 1

• can be
  
  • strucutural abnormalities
  • complete absence of a structure
• Result from interference with/ interruption of normal developmental processes
• causes can be
  
  • genetic
  • Exposure to chemicals/ drugs/ infectious agents
  • unexplainable

Question 2

congenital heart defects

congenital heartdefects = most common birth defect

Answer 2

Developing heart is subject to same vulnerabilities as all other systems, occurs when there is:

• a structural defect of chambers or vasculature
• there is an obstruction
• communication between pulmonary + circulatory systems

These occur due to additional complexity due to differing circulatory needs of foetus compared to a newborn

Question 3

cardiogenic field and cardiovascular system (CVS)

Answer 3

• embryo folds in 4th week - cardiogenic field appears -> zone within mesoderm - has capacity to differentiate into cvs in its entirety - heart, vessels, cells etc.

Question 4

primitive heart tube

Answer 4

• heart develops from precursor= primitive heart tube
  
  • it’s a modified blood vessel with an inlet and outlet
• must be divided into 4 chambers
• blood enters through sinus venosus + moves through without being pumped

Question 5

cardiac looping

Answer 5

• primitve heart tube undergoes looping as it elongates in order to fit into space of pericardial sac
• twists + folds up which places inflowand outlow tubes in correct orientation with respect to each other
• atrium pushed superiorly and posteriorly

Question 6

development of the atria

Answer 6

• RA develops mainly from primitve atrium + sinus venosus - RA has rough surface
  
  • recieves venous blood from body (vena cava) + the heart (coronary sinus)
• LA develops mainly from proximal parts of pulmonary vein + a small portion from primitive atrium
  
  • recieves oxygenated blood from lungs + has a smooth surface

Question 7

conflicting circulatory requirements 1

Answer 7

in mature circulation:

• deoxygenated blood collected frombody - pumped to lungs for reoxygenation +removal of CO₂
• reoxygenated blood returned from lungs to heart - pumped around body

but in foetus:

• lungs dont work - oxygenation + CO₂ removal occur at placenta - shunts required to maintain foetal life
• these must be reversible at birth

Question 8

conflicting circulatory requirements 2

Answer 8

• blood enters via umbilical vein- passes through liver
• then shunted into inferior vena cava leading blood to RA
• blood needs to be in LV to be pumped around body so shunted into LV
  
  • some blood shunted to RV for development

Question 9

fetal circulatory shunts

Answer 9

• Ductus venosus shunts blood from placenta to IVC then into RA
• Foramen ovale shunts blood from RA to LA
• Ductus arteriosus shunts blood from Pulmonary trunk to aorta

At birth, respiration begins increasing left atrial pressure + causing foramen ovale to close. Ductus aretriosus also closes. As the placental support is removed, the ductus venosus closes

Question 10

aortic arches - aortic development

Answer 10

• early arterial system begins as bilaterally symmetrical system of arched vessels
• undergo extensive remodelling to create the major arteries of the heart

4th arch develops into - left side into arch of aorta

• right side into proximal part of right subclavian artery

6th arch = pulmonary artery - right into right pulmonary artery

• L into L pulmonary artery + ductus arteriosus

Question 11

Patent Ductus Arteriosus (PDA)

Answer 11

• congenital condition where DA doesn’t close after birth
• means there is persistent cimmunication between aorta + pulmonary artery/ pulmonary trunk
• blood flows from aorta to PA leading to increased vol. + pressure inside the PA

Question 12

The Foramen Ovale

Answer 12

• 2 walls form between atria; septum … primum + septum secundum - each wall has ostiums (holes) -these don’t line up - allows blood to flow from RA into LA - this is the foramen ovale
• at birth pressure in LA rises above pressure in RA- causes septum primum to push against septum secundum - thus closing flow of blood

Question 13

atrial septal defect

Answer 13

• There can be a defect in the ostium secundum caused by either the septum primum being too short or resorbed.
• The septum secundum can be too small causing the defect.

Question 14

Hypoplastic Left Heart Syndrome

Answer 14

• exact cause unknown
• could be from defect in development of mitral + aortic valves which leads o atresia leading to limited flow
• Could be that the ostium secundum Is too small so there’s inadequate flow from right to left in utero – left heart is underdeveloped

Question 15

the ventricles

Answer 15

• muscular component of ventricular wall grows upwards towards endocardial cushions but leaves small hole called 1º interventricular foramen
• connective tissue from endocardial cushions fills gap
  
  • in ventricular septal defect the CT portion doesn’t form leavinggap in septum

in diagram - endocardial cushions in red

Question 16

dividing the outflow tract - routing oxygenated and deoxygenated blood appropriately

Answer 16

• blood pumped out of truncus arteriosus (TA) - need to be separated into 2 vessels
• endocardial cushions also appear in TA
• as they grow towards eachother they twist around each other - forming a spiral septum

Question 17

transposition of great arteries and ventricular septal defect

ventricular septal defect - most commonly membranous portion of intraventricular septum involved

Answer 17

transposition of great arteries

• aorta comes out of the RV and pulmonary artery comes out of the LV.
  
  • blood that goes to the lungs returns and goes back into the lungs again.
  • blood that goes to the body comes back and then is returned to the body. The blood isn’t oxygenated.

Question 18

tetralogy of fallot

Answer 18

• overriding aorta means that the blood doesn’t leave through the pulmonary artery causing an obstruction.
• Other defects seen are ventricular septal defect, right ventricular hypertrophy or pulmonary stenosis

Question 19

the recurrent laryngeal nerves

Answer 19

• each aortic arch has corresponding nerve
• nerve corresponding to 6th is laryngeal nerve
  
  • right descends to T1-T2, + left descends to T4-T5
• 2 factors influence course of nerve on L + R sides
  
  • caudal shift of developing heart + expansion of the developing neck region
  • need for a fetal shunt between pulmonary trunk + aorta

Question 20

understanding congenital heart defects

aetiology

Answer 20

Aetiology (the causes of a disease) of Congenital Heart Defects::

• Genetic (Down’s, Marfan’s, Turner’s, etc. syndromes)
• Environmental – teratogenicity from drugs, alcohol etc
• Maternal infections – Rubella, Toxoplasmosis etc

A teratogen is an agent that can disturb the development of the embryo or fetus. Teratogens halt the pregnancy or produce a congenital malformation (a birth defect).

Question 21

Pathophysiology

Answer 21

Pathophysiology – when physiology goes wrong in injury/illness. By understanding normal anatomy physiology, pathological findings become logical

considerations of congenital heart defect pathophysiology:

• RV pumps deoxygenated blood to lungs
• Pulmonary circulation has low resistance
• LV pumps oxygenated blood at systemic blood pressure to Aorta
• Each ventricle is morphologically adapted for its task

Question 22

Cyanosis

Answer 22

cyanosis - bluish discoloration of skin due to poor circulation or inadequate oxygenation of the blood

• presence of deoxygenated haemoglobin in arterial circulation
• Cardiac cyanosis – deoxygenated blood bypasses lung
• Respiratory cyanosis – inadequate oxygenation of blood

Question 23

acyanotic heart defects

Answer 23

• blood shunted from left to right
• This can also refer to obstructive lesions such as; aortic, pulmonary, mitral stenosis.
• requires hole, blood from left heart returned to lungs instead of body
• Increased lung blood flow by itself is not damaging but increased pulmonary artery or pulmonary venous pressure is

Question 24

cyanotic heart defects

Answer 24

right to left shunts - much more complex

• requires hike + distal hole + obstruction
• deoxygenated blood bypasses lungs

examples of both acyanotic and cyanotic in image

Question 25

atrial and ventricular septal defects

Answer 25

atrial can be Acyanotic. leads to increased pulmonary blood flow - more blood in the RV. can lead to LV hypertrophy + failure or sometimes pulmonary hypertension. ventricular can be Acyanotic. leads to LV overload - increases the pressure in the pulmonary venous system. This eventually leads to pulmonary hypertension.

Question 26

tetralogy of fallot

Answer 26

As heart is forming, LV + RV separate from each other + the arteries rotate around each other. In tetralogy of Fallot, they haven’t gone quite far enough so pulmonary artery is still slightly over to the right and the aorta is sitting above the ventricular septum which doesn’t close. Thus, the upper part of the heart is rotated to the right a bit effects; pulmonary stenosis, ventricular septal defect, RV hypertrophy, over-riding aorta

Question 27

tricuspid atresia

Answer 27

form of congenital heart disease where there is a complete absence of the tricuspid valve --there is an absence of right atrioventricular connection. This leads to a Hypoplastic (undersized) or absent right ventricle * No RV inlet * R to L atrial shunt of entire venous return * Blood flows to the lung via Ventricular septal defect or Patent Ductal Arteriosus

Question 28

hypoplastic left heart

Answer 28

left heart under-formed * LV underdeveloped * Ascending aorta very small * RV supports systemic circulation * Obligatory R to L shunt

Question 29

pulmonary atresia

Answer 29

* no pulmonary valve - no RV outlet * R to L shunt of entire venous return * blood flows to lungs via PDA

Question 30

Natural History of Common Congenital Heart Diseases

Answer 30

see image