Questions and Answers
When does the cardiovascular system begin development after fertilization?
What is the first functional organ to develop in the embryo?
What are the two regions near the cranial end of the embryo where the cardiovascular system develops from?
What are the blood islands in the embryo?
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In which week of development does the embryo begin to fold?
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What is the result of the embryo folding in two directions?
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What are the two directions of the embryo's folding?
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How many days after fertilization is the primitive heart tube formed?
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What forms the smooth posterior wall of the right atrium?
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What forms the coronary sinus?
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What receives three veins: cardinal, vitelline, and umbilical?
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What forms the oblique vein of the left atrium?
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What forms the ductus venosus in the adult?
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What degenerates early in fetal life?
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What forms the ligamentum teres in the adult?
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What is bypassed in the fetal circulation?
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What is the result of the proximal parts of the pulmonary veins becoming absorbed into the wall of the left atrium?
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What is the correct sequence of events in the partitioning of the atria?
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How does the aorticopulmonary septum form?
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What are the five pairs of aortic arches that form the large arteries?
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What forms the dorsal aorta?
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What develops from the dorsal aorta?
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What is the result of the partitioning of the atria?
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What happens to the blood that doesn't pass through the foramen ovale?
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What is the result of the ductus arteriosus remaining open in a newborn?
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What is the effect of an atrial septal defect on the pulmonary circulation?
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What is the outcome of untreated atrial septal defect?
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What is the ligament that forms after the ductus arteriosus closes?
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What is the characteristic of cyanotic congenital heart defects?
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What is an example of an acyanotic congenital heart defect?
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What happens to the umbilical vein after birth?
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What is the result of the membranous portion of the septum failing to develop properly?
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What is the common complication in patients with Atrioventricular Septal Defect?
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What is the characteristic presentation of a patient with Coarctation of the Aorta?
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What is the consequence of Transposition of the Great Arteries?
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What is the result of Pulmonary Stenosis in Tetralogy of Fallot?
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What is the function of the overriding aorta in Tetralogy of Fallot?
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What is the purpose of giving prostaglandins in Transposition of the Great Arteries?
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What is the consequence of Ventricular Septal Defect?
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Study Notes
Embryology of the CVS
- The cardiovascular system begins development around the 10th day after fertilization.
- The heart is the first functional organ to develop, with the heartbeat able to be heard on sonography by around the 6th week.
Formation of the Primitive Heart Tube
- The cardiovascular system exists as two regions near the cranial end of the embryo, called cardiogenic fields, derived from the lateral splanchnic mesoderm.
- The cardiogenic fields consist of blood islands, which develop further and fuse to form two tubes called endocardial tubes, one on each side of the embryo.
- In the fourth week of development, the embryo begins to fold, and the heart tissue is positioned to form the primitive heart tube surrounded by the pericardial sac.
Development of the Left Atrium
- The proximal parts of the pulmonary veins become absorbed into the wall of the left atrium.
- The contribution of the pulmonary veins is shown in blue, and the primitive left atrium is shown in pink.
Partitioning of the Atria
- Endocardial cushions develop in the dorsal and ventral aspects of the developing heart, acting as targets for the developing septum.
- The sequence of events is:
- Septum primum
- Ostium primum
- Ostium secundum
- Septum secundum
- Ostium of septum secondum
- Formation of foramen ovale
Partitioning of the Ventricle
- Takes place in two steps:
- Formation of the muscular portion – primary interventricular foramen
- Formation of the membranous portion
Septation of the Outflow Tract
- The bulbus cordis and truncus arteriosus form one tube allowing outflow from the heart.
- Splitting of the common tube forms the aorta and pulmonary trunk.
- 2 lines of proliferations of neural crest cells appear on the inner walls of the outflow tract, which spiral around and grow towards each other to form the aorticopulmonary septum.
Formation of the Great Vessels
- Head and neck vessels arise from the truncus arteriosus as aortic arches.
- There are five pairs of arches, numbered I, II, III, IV, VI (arch V doesn't form in humans, so there are 5 arches numbered between 1-6 without a number 5).
Further Arterial Development
- In the rest of the body, the arterial patterns develop mainly from the right and left dorsal aortae.
- The right and left dorsal aortae fuse to form the dorsal aorta, which then sprouts posterolateral arteries, lateral arteries, and ventral arteries (vitelline and umbilical).
Fate of Sinus Venosus
- The right horn of the sinus venosus forms the smooth posterior wall of the right atrium.
- The left horn and the body of the sinus venosus atrophy and form the coronary sinus.
- The left common cardinal vein forms the oblique vein of the left atrium.
Development of the Venous Vasculture
- Each horn of the sinus venosus receives 3 veins:
- Cardinal vein from the fetal body
- Vitelline from the yolk sac
- Umbilical from the placenta
Embryonic and Adult Venous Vasculture
| Embryonic | Adult |
|---|---|
| Vitelline veins | Portion of the IVC, a hepatic veins and sinusoids, ductus venosus, portal vein, inferior mesenteric vein, superior mesenteric vein, splenic vein |
| Umbilical veins | Right: degenerates early in fetal life, Left: Ligamentum teres |
| Cardinal veins | Anterior: SVC, internal jugular veins, Posterior: Portion of IVC, common iliac veins |
| Subcardinal | Portion of IVC, renal veins, gonadal veins |
| Supracardinal | Portion of IVC, intercostal veins, hemiazygos vein, azygos vein |
Fetal Circulation
-
- Umbilical vein
-
- IVC -> DV
-
- RA -> FO -> LA (Pulmonary bypass)
-
- LV -> AORTA
-
- Blood that doesn't pass through the FO enters the RV and is pumped into the pulmonary trunk to fetal systemic circulation via the DA
Circulation After Birth
- a. The ductus arteriosus closes - Ligamentum arteriosum
- b. The oval foramen closes - Foramen ovale fuses with septum secundum to form solid interatrial septum
- c. The umbilical vein closes - Ligamentum teres hepatis
- d. The ductus venosus closes - Ligamentum venosum
- e. The umbilical arteries close - The medial umbilical ligaments
Congenital Heart Defects
- Cyanotic defects:
- Tetralogy of Fallot
- Transposition of the great arteries
- Acyanotic defects:
- Atrial septal defects
- Coarctation of the aorta
Acyanotic Congenital Heart Defects
- Patent Ductus Arteriosus (PDA):
- The ductus arteriosus remains open, allowing blood under higher pressure in the aorta to flow into the pulmonary artery.
- Leads to a higher afterload for the right ventricle, which can eventually result in right-sided heart failure.
- Atrial Septal Defect (ASD):
- Caused by underdevelopment of the septum primum or secundum, resulting in a hole in the atrial septum.
- Allows blood in the left atrium to flow into the right atrium, leading to a higher volume of blood being pumped around the pulmonary circulation.
- Ventricular Septal Defect (VSD):
- The membranous portion of the septum fails to develop properly, primary IV foramen remains open.
- Blood in the LV will flow into the RV, causing pulmonary hypertension and right-sided heart failure.
- Atrioventricular Septal Defect:
- Caused by failure of the endocardial cushions to develop properly, resulting in a hole in the middle of the heart with one common atrioventricular valve, instead of a mitral and a pulmonary valve.
- Common in Down's syndrome.
- Coarctation of the Aorta:
- Congenital narrowing of part of the aorta, causing high blood pressure upstream and weak pulses and cramping in the legs downstream.
Cyanotic Heart Defects
- Transposition of the Great Arteries:
- The aorticopulmonary septum forms, but does not spiral, therefore when the baby is born the aorta arises from the right ventricle, and the pulmonary trunk arises from the left ventricle.
- A neonatal emergency, requiring prostaglandins to maintain the PDA and allow some oxygenated blood into the systemic circulation until surgery can be performed.
- Tetralogy of Fallot:
- Pulmonary Stenosis: the pulmonary artery or the pulmonary valve is narrowed, so less blood can enter.
- Overriding Aorta: aorta is large and situated right next to the VSD, so most of the blood in the heart flows through it.
- Ventricular Septal Defect: allows blood from the right ventricle which cannot be pumped through the stenosed pulmonary artery/valve to move into the left ventricle and be pumped around the body via the aorta.
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Description
This quiz covers the development of the cardiovascular system from fertilization to the formation of the primitive heart tube. Learn about the cardiogenic fields and the first functional organ to develop.
