Embryology Flashcards
Which organ in the embryo is the 1st to undergo functional differentiation?
the heart!
What changes occur to the embryo disc to start the formation of the heart?
Begins with a change in the mesoderm in the area called the cariogenic plate. This is in the most cranial aspect of the embryo disk, above where the brain will form.
What are blood islands?
These form as the cariogenic plate forms, they are two tubes running along the embryo disk that will join together ventrally during embryo folding to form the cardiogenic tube (this becomes the heart).
How does the heart end up in the thorax if it first develops above the brain?
During embryo folding the embryo folds at its cranial and caudal regions so the cardiogenic tube is folded down ventrally into the thorax region.
What is D-looping?
What is L-looping?
D-looping is when the heart folds to the right side as it is growing faster than the embryo.
This is when the heart abnormally folds to the left side.
Label the 5 zones of the primitive cardiac tube:
What aspens to the left and right horn of the sinus venous during cardiac looping?
Right horn becomes incorporated into the atrial wall
Left horn isn’t incorporated, it instead becomes the coronary sinus on the atrial surface of the heart
What are endocardial cushions?
They grow out of the sides of the cardiac heart to divide the primitive atria from ventricles. This process is called partitioning and it makes the AV valves and the chordae tendinae.
They also pinch in as they divide staring to form the coronary groove.
What happens if the endocardial cushions don’t develop correctly?
Mitral/tricuspid valve dysplasia
(abnormal growth of valves)
+/- VSD
What are the 4 stage in interatrial separation?
- at end of w4, septum primum grows towards the endocardial cushions
- it divides the L & R atria but leaves a gap called the foramen primum so blood can pass from R to L
- a second septum grows, the septum secundum which partly separates the ratio
- the two form the foramen ovale with the septum primum acting like a flap, and the pressure in the RA keeping it open
What are the 2 steps involved in interventricular separation?
What can go wrong?
- Septum forms in ventricles to create left and right
- septum grows towards the endocardial cushions and should be complete in dogs by day 32
Interventricular septum defects can occur due to incomplete closure! he septum doesnt quite meet the endocardial cushion
Once the atria and ventricles have formed, how does the blood flow in the fetal heart?
Blood enters right atria from caudal vena cava.
It pushes to the left through the foramen ovale.
It then goes into the left atrium and into the aorta.
Some blood may go into the right ventricle and then into the pulmonary artery to the ductus arterioles and then joining back into the aorta as there is no need of blood to go to the lungs.
What happens to the foramen ovale at birth?
It closes within minutes of birth, right atrial pressure drops and left increases leading to the foramen being permanently closed. There is also now a need for blood to be travelling to and from the lungs.
What is a potential defect with the inter-atrial septa after birth?
- PFO persistent foramen ovale, it does not close after birth so blood still flows through from the right atrium to the left (common in people and cattle)
- Other types of atrial septal defect (ASD)
What causes the ventricles insides to look corrugated?
Why is this thought to be beneficial?
Endocardial cell undergoing apoptosis and mesenchymal and myocardial cells dividing.
Prevents turbulent blood flow within the ventricle
Why are the papillary muscle maintained in the heart?
They support the AV valves and stop them from everting
How are the (mitral and tricuspid) AV valves formed?
Formed from the reshaping and tissue loss occurring in the ventricular walls.
(V walls dilate, cells get larger, trabeculation, cell death)
How are the aortic and pulmonic valves formed?
What can go wrong?
Swelling/fibres grow out of the sides of the walls of the trunks of the aorta and pulmonary artery. They expand into the lumen getting thinner as they grow due to cellular degeneration.
Vessels become too narrow causing aortic/pulmonic stenosis
So how are the aorta and pulmonary vessels separated during development?
Septation of the cranial end of the cardiac tube
What is the cardiac skeleton and what is its purpose?
Marks the line of the coronary groove, separating the atria and ventricles and insulating and isolating them electrically from each other so that controlled and co-ordinated contractions can occur.
Also provides as an attachment site for myocardial muscle cells so that when they contract they pull on the skeleton wringing out the heart.
What is the trabeculum septomarginalis?
It is a piece of meat in the right ventricle that has conducting fibres so that more remote regions of the right ventricle receive the electrical signals and contract properly.
What are ossa cordis?
A bone in the cardiac skeleton found in animals that usually have very large valves. It helps to support them and keep them open when they need to be.
The Ox has this bone.
Explain what the following terms and statements are referring to:
“theory of recapitulation”
“Embryological parallelism”
“Ontogeny recapitulates phylogeny” - Haeckel
Early mammal embryos are very similar to fish, the stages it goes through during organ development represents the stages of evolution of the animals remote ancestors
Where do mammals and other animas differ when it comes to embryo development?
In the later stages of development (ventricles, truncous arteriousus dividing into Ao + PA, vena cava)
