Embryology Flashcards
What are the functions of lateral and cephalocaudal folding in the development of the heart?
Lateral - brings the endocardinal tubes together to form the heart tube
Cephalocaudal folding - brings the tube into the thoracic region
What is the initial structure of the primitive heart tube?
Linear - receiving blood at the caudal pole through the sinus venosus and pumping blood from its cranial pole through the aortic roots. From cranial to caudal: (All The Best Vaginas Are Shaven) Aortic roots Truncus arteriosus Bulbus cordis Ventricle Atrium Sinus venosus
When does bending take place and what direction does each end of the primate heart tube move?
Day 23-28
Cephalic - ventrally, caudally and to the right
Caudal - dorsally, cranially and to the left
How does the atrium communicate with the ventricle after looping?
Via a constriction called the atrioventricular canal
What sinus does looping of the primitive heart tube form?
Transverse pericardial sinus
Anterior to superior vena cava
Posterior to ascending aorta and pulmonary trunk
Describe the fate of the sinus venosus
At first the left and right sinus horns are equal in size. As venous return shifts to the right, the left sinus horn recedes and the enlarging right atrium absorbs the right sinus horn.
Describe the development of the atria
The right atrium develops from most of the primitive atrium and absorbs the right horn of the sinus venosus.
The left atrium develops from a small portion of the primitive atrium and absorbs proximal parts of pulmonary veins (the smooth walled part of left atrium).
What sinus forms as a result of the left atrium absorbing the pulmonary veins?
Oblique pericardial sinus (“cut deep sac”)
Describe the development of the great vessels
Begins as a bilaterally symmetrical system of arched vessels that undergo extensive remodelling to create the major arteries leaving the heart.
4th aortic arch: Right -> proximal part of right subclavian artery. Left -> arch of aorta
6th aortic arch: Right -> right pulmonary artery. Left -> left pulmonary artery and ductus arteriosus. Inmervated by the recurrent laryngeal nerve.
What is the first step in septation?
The development of endocardial cushions on the dorsal and ventral sides of the atrioventricular canal. These grow upwards towards each other and divide the heart into right and left channels.
Describe the process of atrial septation
The division of the common atria involves the formation of two septa with three holes.
The septum primum grows down towards the endocardial cushions, forming the ostium primum before it reaches them.
Before the ostium primum closes, the ostium secundum appears in the septum primum (apoptosis).
Finally a crescent shaped septum, the septum secundum, grows - the hole in which is called the foramen ovale.
Describe the process of ventricular septation
The ventricular septum has a muscular and a membranous portion.
The muscular portion forms most of the septum and grows upwards towards the fused endocardial cushions. It leaves a hole at the top - the primary interventricular foramen.
The membranous portion of the interventricular septum fills the gap and closes the primary interventricular foramen. It is derived from the spiral septum that grows to separate the truncus arteriosus into outflow vessels.
What vessels does blood flow to and from the foetus?
The foetus receives oxygenated blood from the placenta and umbilical VEIN. This then bypasses the lungs and returns to the placenta via the umbilical ARTERY.
Describe what happens in the heart after birth
The baby takes its first breath, massively decreasing the pressure in the lungs. This results in more blood entering the lungs and more blood returning to the left atrium. When the pressure in the LA>pressure in the RA, the foramen ovale is closed. The ductus arteriosus contracts. Placental support has been removed and the ductus venosus closes.
What are the fates of the foetal shunts?
Foramen ovale -> fossa ovalis
Ductus arteriosus -> ligamentum arteriosus
Ductus venosus -> ligamentum venosus
Umbilical vein -> ligamentum teres