Embryology 2 Flashcards
What are the 2 methods by which blood vessels develop?
- Vasculogenesis
- Angiogenesis
Vasculogenesis
The new formation of a primitive vascular network
Angiogenesis
The growth of new vessels from pre-existing blood vessels
Where is the aortic sac formed from?
Extension of truncus arteriosus of primordial heart tube
What are the first arteries to appear in the embryo?
Right and left primitive aorta
What does each primitive aorta have?
A ventral part (ventral aorta) and a dorsal part (dorsal aorta)
When do the two ventral aorta partially fuse to form the aortic sac?
After the fusion of 2 endocardial tubes
What arise from the aortic sac?
Aortic branches
How many arches are on either side?
6
What are the 3 sub-circulations?
- Cardinal
- Vitelline
- Umbilical
When do the pharyngeal arches develop?
During weeks 4+5
What does each pharyngeal arch receive?
Its own nerve and artery (pharyngeal arteries)
hat do the pharyngeal arteries communicate with?
Aortic branches
What do the aortic branches become?
Aortic arches
What are the 6 aortic arches on each side all in communication with?
Dorsal aortae
How are the aortic arches formed?
Pharyngeal arch arteries join aortic branches
What usually develops from aortic branches and pharyngeal arch arteries ?
6 pairs of aortic arches
Where do the aortic arches terminate?
Dorsal aorta
What are the fates of arches 1 + 2?
- Disappear early
- Remnant of 1st arch forms part of the maxillary artery (branch of ext. carotid artery)
What is the fate of arch 3?
-Constitutes the commencement of the internal carotid artery and is therefore named the carotid arch
What is the fate of the 4th right arch?
Right subclavian artery
What is the fate of the 4th left arch?
Constitutes the distal part of the aortic arch
What is the fate of arch 5?
Either never forms or forms incompletely and then regresses
What is the fate of the 6th right arch?
The proximal part persists as the proximal part of the right pulmonary artery
What is the fate of the 6th left arch?
Gives off the left pulmonary artery and forms the ductus arteriosus.
What happens to the ductus arteriosus within 1-3 months?
The ductus is obliterated and becomes the ligamentum arteriosum
What do most defects of the great arteries arise as a result of?
Persistence of aortic arches that normally should regress or regression of arches that normally shouldn’t
Aberrant subclavian artery
- With regression of the right aortic arch 4 and the right dorsal aorta, the right subclavian artery has an abnormal origin on the left side.
- To supply blood to the right arm, this forces the right subclavian artery to cross the midline behind the trachea and oesophagus, which may constrict these organs.
What is the symptoms of aberrant subclavian artery?
Usually no clinical symptoms
Double aortic arch
Occurs with the development of an abnormal right aortic arch in addition to the left aortic arch, forming a vascular ring around the trachea and oesophagus which usually causes difficulty breathing and swallowing
Patent ductus arteriosus
- A condition wherein the ductus arteriosus fails to close after birth.
- Early symptoms are uncommon, but in the 1st year of life include increased work of breathing and poor weight gain.
What is the outcome of an uncorrected patent ductus arteriosus?
May lead to congestive heart failure with increasing age
Coarctation of the aorta
A congenital condition wherein the aorta is narrow, usually in the area where the ductus arteriosus inserts.
Where are coarctations most common?
Aortic arch
Where can coarctations occur
- Proximal to ductus arteriosus (preductal)
- Distal to ductus arteriosus (postductal)
What arteries supply the yolk sac in the embryo?
Vitelline arteries
What are the vitelline arteries represented by in the adult?
- Celiac artery (artery of the foregut)
- Superior mesenteric artery (artery of the midgut)
- Inferior mesenteric artery (artery of the hindgut)
What is the fate of the umbilical arteries before birth?
Paired branches of the dorsal aorta to placenta
What happens to the proximal portion of the umbilical arteries after birth?
Persists as internal iliac and superior vesical branches ( to urinary bladder)
What happens to the distal portion of the umbilical arteries after birth?
Degenerates to form obliterated umbilical arteries and forms medial umbilical ligaments
Where do vitelline veins transport blood?
Carry blood from the yolk sac to the sinus venosus
Where do umbilical veins originate?
Chorionic villi of the placenta
Where do the umbilical veins carry oxygenated blood to?
Embryo
What do cardinal veins do?
- Drain the body of the embryo
- Carry the blood from the head and the lower body into the heart
What are the fates of the vitelline veins?
- Portal vein
- Hepatocardiac (liver to heart) part of the inferior cava
- Liver sinusoids
- Superior mesenteric vein
What is the fate of the right umbilical vein?
Degenerates completely
What is the fate of the left umbilical vein?
Obliterates and forms ligamentum teres of adult liver
What is the fate of the ductus venosus?
Obliterates and forms ligamentum venosum
What does the ductus venosus do in the foetus?
Shunts a portion 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 are the cardinal veins ancestors of?
All intraembryonic vasculature
What is the main venous drainage system of the embryo?
Cardinal veins
What does the cardinal venous system consist of?
Anterior, posterior and common cardinal veins draining to sinus venosus
What do the cardinal veins form?
Vena cave (SVC+IVC) system by anastomosis among the veins
What venous system abnormalities are there?
- Double IVC
- Absence of IVC
- Left SVC
- Double SVC
When does the lymphatic system develop?
End of the 6th week around the main veins
What part of the lymphatic system develops at the end of the embryonic period?
Six primary lymph sacs
What is good respiration in a neonate dependent on?
Normal circulatory transition at birth (placental circulation to pulmonary circulation)
What vascular structures are important in the transitional circulation
- Ductus venosus
- Oval foramen
- Ductus arteriosus
What does the ductus venosus do?
- Shunts left umbilical vein blood flow directly to IVC
- Allows oxygenated blood from the placenta to bypass the liver
What does the oval foramen do?
- Allows blood to enter the left atrium from the right atrium
- Allows blood to bypass the lungs
What does the ductus arteriosus do?
Allows blood that still escapes to the right ventricle to bypass the lungs
What is the foetal circulation system?
- Aorta
- Descending aorta
- Abdominal aorta
- Common iliac artery
- Umbilical arteries
- Placenta
- Umbilical vein
What does the ductus venosus become?
Ligamentum venosum of the liver
What happens to the oval foramen?
- Closes after birth by tissue proliferation and adhesion of septal structures
- Becomes fossa ovalis
What does the ductus arteriosus become?
Obliterates to form ligamentum arteriosum
Who does patent ductus arteriosus more commonly effect?
Females
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 and lack of surfactant in the lungs
What are the main theories of the cause of coarctation of aorta?
- Incorporation of muscle tissue of ductus arteriosus into arch of aorta. When ductus arteriosus contracts after birth, part of the arch also constricts
- Genetic/ environmental factors
Where do most cases of coarctation occur?
Opposite the ductus arteriosus
