Embryology Flashcards
Where does the primitive heart receive blood from?
At its caudal pole (inflow) and the blood flows out (outflow) from the cranial pole
When is the cardiogenic field created?
During gastrulation and initially it lies at the cranial end of the embryo.
Describe the segments of the primitive heart
Aortic roots A
Truncus arteriosus Tad
Bulbus cordis Bit
Primitive ventricle Vicious
Primitive atrium and sinus venosus Allan
How is the heart tube created?
How is the tube brought into the thoracic region?
Lateral folding
Cephalocaudal folding
What is the point of looping?
It puts the primordium of the right ventricle closest to the outflow tract, primordium of the left ventricle closest to inflow tract and atrium dorsal to the bulbus cordis. (i.e. inflow is dorsal to outflow)
Baso - places inflow & outflow cranially with the inflow dorsal to outflow
What does the primitive atrium form?
Small component of each atrium (muscular/rough parts)
What does the bulbus cordis form?
Gives rise to the smooth part of the right ventricle
What does the primitive ventricle form?
Muscular/rough part of the left ventricle
What does the truncus arteriosus form?
Gives rise to roots and proximal portions of the pulmonary trunk and aorta
Describe the development of the sinus venosus
Right and left sinus horns initially equal in size. Venous return shifts to RHS, L sinus horn recedes. Right sinus horn is absorbed by enlarging RA.
What gives rise to the left atrium?
As well as the primitive atrium, the left atrium is partly formed by absorbed primordial pulmonary vein tissue
What is the oblique sinus?
The oblique pericardial sinus is formed as the left atrium expands, absorbing the pulmonary veins.
How does the foetus receive oxygenated blood?
From mother via placenta and umbilical vein. Blood by-passes the foetal lungs (they aren’t functional at this point) and returns to the placenta via umbilical arteries but foetal heart needs to work to develop muscular tone
What is the purpose of the aortic arches?
They are the basis of the vessels. Begins as a bilaterally symmetrical system of arched vessels. Undergoes extensive remodelling to create the major arteries leaving the heart.
What is the sixth arch of the aortic arches and what does it create?
Pulmonary arch.
R - R pulmonary artery
L - L pulmonary artery and Ductus Arteriosus
Which nerve supplies the sixth aortic arch?
Recurrent laryngeal nerve
Describe the recurrent laryngeal nerves position and explain how it got like that
As the aortic arches are remodelled to create the mature formation, the heart ‘descends’ and the nerve hooks around the 6th aortic arch. It therefore turns back on itself when returning. Left recurrent laryngeal nerve becomes hooked around the shunt between the pulmonary trunk and the aorta.
Define septation
Process in which the primitive heart tube divides into chambers and the outflow tract is subdivided into pulmonary trunk and the aorta
How is the atrioventricular canal formed?
Junction between the atrium and the ventricles becomes constricted, creating a narrow channel
How is the heart divided?
Endocardial cushions form in the region of the atrioventricular canal and provide a platform toward which the septa grow inferiorly or superiorly, dividing the heart into left and right hand sides.
What is the foramen ovale?
A right to left shunt which is needed in utero but must be instantly sealed after birth (fossa ovalis)
Describe the division of the common atrium
Septum primum grows towards the fused endocardial cushions. Ostium primum is the hole present before the septum primum does so. A second hole, ostium secondum, appears in the septum primum before the atrium primum closes. A second, crescent shaped septum (septum secundum) grows.
What are the auricles?
An area derived from the primitive atrium, present on both the left and right atria.
Describe ventricular septation
Two components –> muscular and membranous. Muscular - forms most of the septum and grows up towards the fused endocardial cushions, leaving a small gap (primary interventricular foramen). Membranous - connective tissue derived from endocardial cushions to ‘fill the gap’.
What does the foramen ovale become in an adult?
Fossa ovalis
What does the ductus arteriosus become in an adult?
Ligamentum arteriosum
What does the ductus venosus become in an adult?
Ligamentum venosum
What does the umbilical vein become in an adult?
Ligamentum teres (hepatis)
What is the function of the umbilical vein?
Provides oxygenated blood to the foetus
What are the layers of heart muscle?
Endocardium (endothelial and subendothelial lining)
Myocardium
Epicardium (serous layer of visceral pericardium)
Pericardial cavity
Parietal layer of serous pericardium
Fibrous pericardium
Which germ layer does the heart originate from?
The mesoderm
What can cause heart murmurs during systole?
Aortic stenosis, mitral regurgitation
MRSAS - mitral regurgitation, systole, aortic stenosis
What causes murmurs in diastole?
Aortic regurgitation and mitral stenosis
DARMS - diastole, aortic regurgitation and mitral stenosis
Describe the right atrium’s composition
Sinus vinera - smooth –> SVC/IVC (from sinus venosus)
Fossa ovalis (remnant of foramen ovale) - round depression in septum between atria
Muscular portion of RA - auricle
What does the sinus venosus form?
Smooth part of right atrium
Describe the route of the recurrent laryngeal nerve
The route is slightly different on both sides of the body. On the right side, the nerve loops under the right subclavian artery before its ascent to the larynx whereas the left recurrent laryngeal nerve loops beneath the aorta.
How are the primitive ventricles separated?
The primitive ventricle becomes divided by a septum (the septum inferius or ventricular septum) which grows upward from the lower part of the ventricle, its position being indicated on the surface of the heart by a furrow.
What are the three shunts present in the embryo?
Foramen ovale
Ductus arteriosus
Ductus venosus
What is the role of the ductus arteriosus?
It connects the pulmonary artery to the proximal descending aorta, by passing the lungs.
What is the role of the ductus venosus?
Shunts most of the left umbilical vein blood flow directly to the inferior vena cava. Thus, it allows oxygenated blood from the placenta to bypass the liver.
What is the role of the foramen ovale?
It allows blood to enter the left atrium from the right atrium.
