Embryology Flashcards
What is the first major system to function in the embryo?
The cardiovascular system
When does the primordial heart start functioning?
Beginning of the 4th week of development
Why does the primordial heart start functioning so early?
Nutrition received by diffusion is not enough to satisfy the growing embryo
What are the stages of development of the blood vessels?
Differentiation of mesenchymal cells
Angioblast formation
Blood island formation
Small cavities appear within blood islands
Endothelial lined cavities fuse to form endothelial channels
What is the difference between vasculogenesis and angiogenesis?
During vasculogenesis blood vessels form in situ
In angiogenesis vessels develop by sprouting and branching from the pre-existing vessels
Where do blood vessels first appear?
In the wall of the yolk sac, allantois, connecting stalk and chorion
When do the angioblastic cords first appear?
Around the 3rd week of development, first seen in the cardiogenic mesoderm
The angioblastic cords canalise to form
heart tubes
What does the tubular heart show?
Alternate dilatations and constrictions
What are the sections of the heart tube primordia?
Truncus arteriosus Bulbus cordis Ventricle Atrium Sinus venosus
Where do the two horns (left and right) of the sinus venous get their venous blood from?
Yolk sac, placenta and body of the embryo
What is the truncus arteriosus continuous with cranially?
Aortic sac
What arises from the aortic sac?
Aortic arches
Where do the aortic arches terminate?
Dorsal aorta
What controls the blood flow from the sinus venosus to the primordial atrium?
Sinoatrial valves
Blood passes through the atrioventricular canal into the
primordial ventricle
From the ventricle, blood is pumped through the
bulbus cordis and truncus arteriosus in the aortic sac, to the aortic arches
From the aortic arches, blood passes to the dorsal aorta for distribution to the
embryo, yolk sac and placenta
What are the layers of the heart?
Epicardium Myocardium Endocardium Pericardium Serous pericardium
What is the pericardium derived from?
Intra-embryonic coelom
What are the parietal layers of the serous pericardium and fibrous pericardium formed from?
Somatopleuric mesoderm
What is the visceral layer of the serous pericardium derived from?
Splanchnopleuric mesoderm
How is the bulboventricular loop formed?
The bulbus cordis and ventricle grow faster than other regions, forming a U-shaped loop called the bulboventricular loop
What is dextrocardia?
Where the heart tube bends to the left side instead of to the right
Most frequent positional abnormality of the heart
What might dextrocardia be associated with?
Situs inversus
During what week of development is the partitioning of the bulbus cordis and truncus arteriosus?
5th week
What changes occur in the mesenchymal cells during the 5th week of development?
Active proliferation of the mesenchymal cells in the walls of the bulbus cordis and truncus arteriosus
What results in the formation of the aortico-pulmonary septum?
180 degree spiralling of the bulbar and truncal ridges
What doe the aortico-pulmonary septum divide?
The bulbus cordis and truncus arteriosus into the aorta and pulmonary trunk
When does the formation of the cardiac septa occur?
Around 27th and 37th days of embryonic development
What is the method of formation of the cardiac septa?
Proliferation of the mesenchymal tissue
What is the cardiac septa formation followed by?
Endocardial cushion formation
When does partition of the primordial heart occur?
Begins around middle of 4th week and finishes by end of 5th week
How is the AV canal partitioned?
Endocardial cushions form on dorsal and ventral walls of AV canal
Develop from cardiac jelly
Endocardial cushions approach each other and divide the cavity into left and right AV canals
When is the partitioning of the primordial atrium?
Starts towards end of 4th week of development
What are formed during the partitioning of the primordial atrium?
Two septa and two foramen
What are the septa and foramen formed during partitioning of the primordial atrium?
Septum primum
Septum secundum
Foramen primum
Foramen secundum
What is the foramen ovale?
Septum secundum appears on the right of the septum premium and grows and overlaps the foramen secundum, to form an opening known as the foramen ovale
What is the role of the foramen ovale?
Before birth it allows most of the blood to pass from the right atrium to the left atrium and prevents the passage of blood in the opposite direction
Normally closes after birth, creating an increased pulmonary blood flow and shift of pressure to the left atrium
What is a remnant of the foetal oval foramen in the adult heart?
Oval fossa
What does non-closure of the foramen ovale result in?
Atrial septal defect
What does the interventricular septum develop from?
Muscular and membranous part of primordial ventricle
What does the muscular part of the primordial ventricle develop from?
Proliferation of the medial wall
Where is the interventricular septum formed?
Between the free edge of the muscular septum and the fused endocardial cushion
What does the interventricular foramen permit?
Communication between the left and right ventricles
How is the interventricular foramen closed?
By the fusion of the bulbar ridges with the endocardial cushion forming the membranous part of the interventricular septum
What do the aortic and pulmonary (semilunar) valves develop from?
Proliferation of subendocardial tissue
What do the tricuspid and mitral valves develop from?
Local proliferation of tissues around the atrioventricular canal
Where are the early pacemakers of the heart?
Primordial atrium then sinus venosus
When does the sinoatrial node develop?
During 5th week of development
Where is the location of the sinoatrial node in an adult?
High in the right atrium near the entrance of the superior vena cava
What do the atrioventricular node and Bundle of His develop from?
Cells of atrioventricular canal and sinus venosus
What is transposition of the great vessels associated with?
Cyanotic heart disease in newborns
Atrial septal defects
Ventricular septal defects
What is the cause of transposition of the great vessels?
Failure of the aorticopulmonary septum to take a spiral course and effective migration of neural crest cells
What are the two methods of development of the blood vessels?
Vasculogenesis
Angiogenesis
What are the first arteries to appear in the embryo?
Primitive aortae
What are the parts of the primitive aortae?
Ventral part and dorsal part
When do the pharyngeal arches develop?
During 4th and 5th week of development
How many pairs of aortic arches normally develop?
Six pairs
What happens to the 5th pair of aortic arches in the embryo?
In 50% they are rudimentary
In 50% they do not develop
What is the adult derivative of the first aortic arches?
Maxillary arteries
What is the adult derivative of the second aortic arches?
Hyoid and stapedial arteries
What is the adult derivative of the third aortic arches?
Common carotid and first pair of internal carotid arteries
What is the adult derivative of the fourth aortic arches?
Arch of aorta from left common carotid to left subclavian arteries (left side)
Right subclavian artery (right side)
What is the adult derivative of the sixth aortic arches?
Left pulmonary artery and ductus arteriosus (left side)
Right pulmonary artery (right side)
What is the function of the vitelline arteries?
Supply yolk sac in the embryo
What are the adult derivatives of the vitelline arteries?
Celiac artery
Superior mesenteric artery
Inferior mesenteric artery
When do the vitelline arteries merge with the dorsal mesentery?
During the development of the gut tube
What happens to the umbilical arteries after birth?
Proximal portion persists as the internal iliac and superior vesical arteries
Distal portion degenerates and forms the medial umbilical ligaments
What are the coronary arteries derived from?
Migration of pro-epicardial cells
Cells of the epicardium
What is the function of the vitelline veins in the embryo?
Carry blood from the yolk sac to the sinus venosus
What is the function of the umbilical veins in the embryo?
Carry oxygenated blood to the embryo
What is the function of the cardinal veins in the embryo?
Drains body of embryo
What are the adult derivatives of the vitelline veins?
Portal vein
Hepatocardiac part of inferior vena cava
Hepatic sinusoids
Superior mesenteric vein
What happens to the umbilical veins in the adult?
Right umbilical vein degenerates completely
Left umbilical vein obliterates and forms ligamentum teres of the adult liver
What happens to the ductus venosus in the adult?
Obliterates and forms ligamentum venosum
What is the main venous drainage system of the embryo?
Cardinal veins
When does the embryonic lymphatic system develop?
At the end of the 6th week of development
How many lymph sacs develop at the end of the embryonic period?
Six primary lymph sacs - two jugular, two iliac, one retroperitoneal and one chyle cistern
What does the thoracic duct develop from?
Caudal part of the right thoracic duct
Anastamosis between the thoracic ducts and the cranial part of the left thoracic duct
What are lymphocytes initially derived from?
Stem cells in the yolk sac membrane, latterly in the liver, spleen and bone marrow
What is good respiration in the newborn dependent on?
Normal circulator changes at birth
What is the function of the ductus venosus?
Bypasses blood from the umbilical vein to the IVC
Becomes ligamentum venosum of the liver
What is the function of the oval foramen?
Diverts blood from the right atrium to the left atrium
Closes after birth by tissue proliferation and adhesion of septal structures
What is the function of the ductus arteriosus?
Diverts blood from the pulmonary trunk to the descending aorta
Obliterates to form ligamentum arteriosum
What percentage of live births are affected by congenital heart disease?
1%
What sex is generally more affected by CHD?
Male
What CHD are more common in females than males?
Atrial septal defect
Patent ductus arteriosus
What are some possible causes of CHD?
Maternal rubella infection in pregnancy Maternal alcohol abuse Maternal drug treatment and radiation Genetics Chromosomal abnormalities
What are the clinically significant types of atrial septal defect?
Ostium secundum defect
Endocardial cushion defect with ostium premum defect
Sinus venosus defect
Common atrium
What is the most common type of congenital heart disease and what percentage of defects does this account for?
Ventricular septal defect - 25% of defects
What is the most common type of ventricular septal defect?
Membranous type
Tetralogy of Fallot is made up of what cardiac defects?
Pulmonary stenosis
Ventricular septal defect
Dextroposition of the aorta
Right ventricular hypertrophy
What is the cause of Tetralogy of Fallot?
Unequal division of the conus due to anterior displacement of the conotruncal septum
What are the common venous system defects?
Double inferior vena cava
Absence of the inferior vena cava
Left SVC
Double SVC
What are the anomalies of the lymphatic system?
Congenital lymphoedema
Cystic hygroma
What is patent ductus arteriosus associated with?
Maternal rubella infection in early pregnancy
What is the cause of patent ductus arteriosus?
Failure of muscular wall to contract, respiratory distress syndrome, lack of surfactant in the lungs
What are the forms of coarctation of the aorta?
Preductal, extensive preductal or postductal
