Session 3 Flashcards
In which week of embryonic development does folding occur?
4th week
The cardiogenic field is an area of what type of embryonic tissue?
Mesoderm
What happens in the cardiogenic field to begin the development of the heart?
The beginnings of differentiation start and blood islands appear
What are blood islands?
Areas of differentiating cells in the cardiogenic field that have the capacity to make blood cells/vessels/heart muscle
How is the primitive heart tube formed?
2 endocardial tubes with blood islands exist in the embryo before it folds.
As the embryo folds, the tubes meet at the midline and fuse to from a single primitive heart tube
What are some possible causes of congenital heart defects?
Genetic
Exposure to chemicals/drugs/infectious agents
Describe the basic structure of the primitive heart tube
Effectively a modified blood vessel with an inlet and outlet
Describe the different parts of the primitive heart tube from inlet to outlet
Sinus venosus Atrium Ventricle Bulbus cordis Truncus arteriosus Aortic roots
What does the sinus venosus consist of?
4 inlet tubes
How does blood flow in the primitive heart tube?
Straight from inlet to outlet with nothing to regulate the flow - simple contractile tube
When does cardiac looping take place? What is cardiac looping? What is its function?
When the primitive heart tube elongates and runs out of room
The twisting and folding up of the primitive heart tube
Places the inflow and outflow of the heart in the correct orientation
What part of the primitive heart tube does the right atrium develop form?
Most of the primitive atrium and a small part of the sinus venosus
What part of the primitive heart tube does the left atrium develop from?
A small portion of the primitive atrium and absorbs proximal parts of the pulmonary veins
Which atrium has smooth walls? Why?
Left atrium
Absorbs parts of the proximal pulmonary veins
Do the lungs work in a foetus?
No - no gas exchange can take place
Where does oxygenation and removal of carbon dioxide from the blood take place in a foetus?
At the placenta
What structures are required to maintain fetal life with regards to the blood circulation in a foetus?
Shunts
Name three shunts found in a foetus
Foramen ovale
Ductus arteriosus
Ductus venosus
Blood enters the foetus through which vessel?
The umbilical vein
What is the first shunt encountered by the blood entering the umbilical vein?
Ductus venosus
Describe what happens to the blood at the ductus venosus. What is the purpose of this?
It is shunted around the liver to the inferior vena cava
The liver is highly metabolically active in fetal life so could easily consume all of the oxygenated blood
What is the function of the foramen ovale?
Shunts blood from the right atrium across to the left atrium to be pumped around the body
Does any blood enter the right ventricle?
A small amount to allow for its development
What is the function of the ductus arteriosus?
Shunts blood from the pulmonary trunk to the aorta
When do the foetal shunts close?
At birth
What causes the foramen ovale to close at birth?
First breath taken, increasing LA pressure, closing the foramen ovale
What causes the ductus arteriosus to close at birth?
Muscular contraction
What causes the ductus venosus to close at birth?
Removal of placental support
Describe the layout of the early arterial system
Bilateral symmetrical system of arched vessels - aortic arches
Which aortic arch forms the the proximal part of the right subclavian artery ?
The right side of the 4th arch
Which aortic arch forms the arch of the aorta?
The left side of the 4th arch
Which aortic arch forms the right pulmonary artery?
Right side of the 6th arch
Which aortic arch forms the left pulmonary artery and ductus arteriosus?
The left side of the 6th arch
Where in the foetus does the heart begin to develop? What happens to this?
Embryonic neck
Descends into the chest as it develops
The left recurrent laryngeal nerve innervates the…
Larynx
What happens to the left recurrent laryngeal nerve as the developing heart descends from the embryonic neck to the chest?
It becomes hooked around the 6th aortic arch - around the shunt between the pulmonary trunk and aorta (ductus arteriosus)
What happens in patent ductus arteriosus? Where is it most common? What effect will this have on blood in the heart?
The ductus arteriosus doesn’t close immediately at birth
Premature infants
Will shunt from left to right
Describe the structure of the foramen ovale and how blood is shunted through it
Consists of two wedges of tissue - septum secundum and septum primum with misaligned holes
The high pressure of blood in the right atrium compared to the left atrium shunts blood from right to left through both holes
What happens to close the foramen ovale at birth?
At birth, the pressure in the left atrium rises greater than the pressure in the right atrium
Septum primum is pushed against septum secundum, stopping the flow of blood as the holes are misaligned
What can result from either septum primum or septum secundum defects?
Atrial septal defects
What happens in hypoplastic left heart syndrome?
Left ventricle is not normally developed due to inadequate blood supply during development
What is the name given to the process that develops and separates the ventricles?
Ventricular septation
Ventricular septum has both ________ and _________ components
Which portions forms most of the septum?
Muscular
Membranous
The muscular portion
Describe the process of ventricular septation
Muscular portion grows upwards towards the fused endocardial cushions leaving a small gap called the primary interventricular foramen
Membranous portion formed from connective tissue derived from endocardial cushions fills the gap
What is the most common cause of a ventricular septal defect?
No closure of the primary interventricular foramen by the membranous portion of the septum
How is the common outflow tract of the developing heart split into the distinct aorta and pulmonary trunk?
Endocardial cushions in the truncus arteriosus grow and twist around each other to form a spiral septum
What is transposition of the great arteries?
Congenital heart defect, where the aorta arises from the right ventricle and the pulmonary trunk arises from the left ventricle
What symptom is commonly seen in transposition of the great arteries?
Cyanosis
What is cyanosis?
Bluish discolouration of the skin, nail beds and mucous membranes due to deoxygenated Hb in arteries
What is tetralogy of fallot?
Ventricular septal defect where you get an overriding aorta which straddles both ventricles
What can result from tetralogy of fallot? What causes tetralogy of fallot?
RV hypertrophy as RV outflow tract is blocked
Defect in normal formation of spiral septum in the truncus arteriosus
What specific type of embryonic cells play an important role in septation? What are they derived from? What are they particularly sensitive to?
Neural crest cells
Neuroectoderm
Alcohol
What is the typical % saturation of Hb with oxygen in the…
I) arterial system
II) venous system
~100%
~67%
Give an example of a maternal infection that can cause congenital heart disease
Rubella
Toxoplasmosis
What sorts of congenital heart defects are commonly seen in Down’s syndrome?
Atrio-ventricular septal defects
What is tricuspid atresia?
Congenital heart defect where there is no RV inlet so there is a right to left shunt of entire venous return and blood is pumped to the lungs via ventricular septal defect
What is pulmonary atresia?
Where there is no RV outlet, there is right to left shunt of the entire venous return and blood flows to the lungs via patent ductus arteriosus
