Cardiac Embryology Flashcards
Outline the timeline of cardiac development in the dog
Cardiac contractions and circulation
18-19 days – dog
28 days – humans
Slow at first and inc when atria and SV form
Cardiac partitioning
28 days – dog
35-49 days - humans
Describe structure of primitive heart tube
5 zones
Arterial trunk/truncus arteriosus
Bulbus cordis
Will form ventricles
Ventricle
Atrium
Sinus venosus
Outline the beginning of heart development
The growth of the primitive tube is quicker than the rest of the embryo and is also fixed at two ends. Meaning the proliferation of cell growth cause the tube to fold and fall to the right (this is known as D looping)
Can abnormally fall to the left
Right horn of sinus venosus becomes incorporated into atrial wall
Left horn not incorporated and will be known as the coronary sinus
Describe Formation & Development of AV cushions and the CR
Located within the atrio-ventricular (A-V) canal there are left and right A-V endocardial cushions which form chordae tendinea and the A-V valves
Clinical Relevance
Mitral/tricuspid dysplasia
+/- VSD
Present with a slight murmur (undeveloped valve)
Describe Formation & Development of the Interatrial Septa primum
Septa Primum
Left & right atria are separated by septum primum which grows towards the AV cushions.
The is a gap left within this growth which is known as the foramen primum (O1) where blood is able to flow from the right to the left atria
Quickest pathway for blood to be shunted
Describe Formation & Development of the Interatrial Septa secundum and the CR
Septa Secundum
To maintain the right to left blood flow a second septum develops. During this time, just before the septa primum closes the O1, a series of fenestrations occur which form a new opening known as the second foramen
The oblique passage created by the septa primum and septa secundum is know as the foramen ovale, where the second septum acts as a valve to this passage.
After birth the left atrial pressure becomes higher than the right, the valve moves back and closes the foramen ovale. The Septum Secundum and Septum Primum appose due to the decrease in pressure in RA and increased pressure in LA as blood inflow from lungs occurs and is now known as the interatrial septum
CR:
PFO (persistent foramen ovale) common in people and cattle
Other types of atrial septal defect (ASD)
Describe the cardiac blood flow within a fetus
Opening connects Right Atrium (RA) to Left Atrium (LA).
Blood at high pressure since it comes directly from umbilical vein - most will have bypassed capillary beds of liver.
Most of blood goes to left atrium via Foramen Ovale then Left Ventricle to aorta and not through the Right ventricle to the lungs. The blood that has accessed the pulmonary artery is shunted back to the aorta through the patent ductus arterioles
Oxygenated blood leaves from both the pulmonary trunk and aorta and goes straight up from heart to brain and back to heart.
The majority of the left ventricular output perfuses the upper body with a relatively small proportion to the lower body and placenta.
In comparison, the right ventricle receives relatively desaturated blood – it then ejects most of this blood not into pulmonary vasculature but through the ductus arteriosus to the lower body and placenta which helps to maximise the uptake of O2.
Describe Formation & Development of the Aorticopulmonary Septum and the CR
Within the Truncus arteriosus swellings develop known as truncal cushions
Within the Bulbis cordis swellings develop known as bulbar cushions
These grow towards one another in a spiral and contribute to the intraventricular septum
CR:
Persistent truncus arteriosus
VSD
Tetralogy of Fallot
Formation & Development of the Interventricular Septum and the CR
nce atrioventricular and truncobulbar cushions form and fuse the last step is the formation of two ventricles from a common chamber
The interventricular septum develops from caudal expansion & hypertrophy of the bulbus cordis and primitive ventricle, rather than ‘growth’ of a septum.
The bulbus cordis and ventricle grow in caudoventral direction which is known as trabeculation
Where mesenchymal and myocardial cells divide, and the endocardial cells under apoptosis.
This gives rise to the uneven surface of the ventricles and provides retention for the muscular papillary muscles which support AV valves
Closure of the Septum:
Apex develops muscular portion of the septum whilst the growth of atrioventricular cushion creates the membranous aspect. Both will meet and create the interventricular septum
CR:
Various types of ventricular septal defect
Ventricular septal defect VSD – Scarborough Flyer
Describe Formation & Development of the AV Valves
Mitral & Tricuspid
Form from reshaping and tissue loss within ventricular walls
Ventricle dilates, walls hypertrophy, trabeculation occurs and endodermal cell death
Strands of cardiac wall mesenchyme from Atrio-ventricular cushions to ventricular wall remain. These then form cusps of atrio-ventricular valves and chordae tendinea
Describe Formation & Development of the Semilunar Valves and the CR
Aortic and pulmonary semilunar valves
Following formation/ fusion of truncal ridges, there are three swellings in walls of Ao and PA trunks
These will expand into the lumen of each vessel
Very broad and then thin with cellular degeneration
CR
Aortic/pulmonic stenosis
Particularly in brachycephalic breeds
List the three key shunts of blood
- Ductus venosus
- Foramen ovale
- Ductus arteriosus
Outline the pathway of blood flow in the unborn baby
Oxygen and nutrients from the mother’s blood are transferred across the placenta and flows through the umbilical vein toward the baby’s liver.
There it moves through a shunt called the ductus venosus.
This allows some of the blood to go to the liver.
Most of this oxygenated blood flows to caudal vena cava and then into RA.
Most of the blood flows across to the LA through foramen ovale.
From the left atrium, blood moves to LV and then aorta to the body.
Blood returning to the heart from the body contains carbon dioxide and waste products as it enters the RA.
It flows down into the RV, and into PA.
Then flows through the ductus arteriosus into the descending aorta, which connects to the umbilical arteries into the placenta.
There the carbon dioxide and waste products are released into the mother’s circulatory system.
Explain the role of the ligamentum arteriosum
Once was the ductus arteriosus where blood would flow from the pulmonary artery into the descending aorta. It closes for when the animal is born.
CR: If this doesnt close then blood from the aorta will enter the pulmonary artery due to the pressure difference causing a condition such as Patent ductus arteriosus
Discuss the cardiac anatomy of fish and how it relates to development
Single circuit for blood flow and a two-chambered heart that has only a single atrium and a single ventricle.
The atrium collects blood that has returned from the body through the sinus venosus, and the ventricle pumps the blood to the gills, through the 6 arches of the aorta,where gas exchange occurs and the blood is reoxygenated; this is called gill circulation. The blood then continues through the rest of the body before arriving back at the atrium; this is called systemic circulation
