Foetal Circulation Flashcards
what is the function of foetal circulation?
function of foetal circulation is to supply oxygen-rich blood preferentially to heart and brain
what is foetal circulation in the placenta?
- from placenta = oxygen-rich blood passes in umbilical vein
- some blood from umbilical vein passes through liver but majority bypasses liver parenchyma to join caudal vena cava via ductus venous
Where does blood entering right atrium come from?
does so from two sources
= oxygen rich blood in caudal vena cava = 68%
= oxygen poor blood returning from foetal tissues cranial to heart via cranial vena cava = 32%
How does blood pass into the left atrium?
because foramen ovale is directed towards caudal vena cava = most oxygen rich blood passes through foramen ovale between septum I and septum II and through foramen II into left atrium
How does blood pass to the aorta?
- some blood passes through high-resistance vascular bed of pulmonary circulation but three quarters passes directly from pulmonary artery to aorta via ductus arteriosus bypassing the lungs
- the aorta given off most oxygen rich blood supply to heart = coronary arteries and to brain = brachiocephalic artery before it is joined by less well-oxygenated blood in ductus arteriosus
What happens to blood after returning from the lungs?
- small amount of blood returning from foetal lungs via pulmonary vein having received no oxygenation enters left atrium
- it does not significantly alter content of oxygen rich blood reaching left atrium via foramen ovale
- from left atrium as in adult circulation, blood passes from left atrium to left ventricle and aorta giving branches to heart and brain
what changes occur in foetal circulation directly at birth?
- diaphragm contracts
- external intercostal muscles lower pressure within thoracic cavity
- draw air into lungs
- pulmonary capillaires dilate
- resistance in pulmonary bed reduced to about tenth of resistance
= increase blood flow through lungs - increases pulmonary venous pressure + left atrial pressure
- rise in L atrial pressure + fall in R atrial pressure = cause septum I and II be pushed together tightly
= forming interatrial septum = prevent backflow
what changes occur in foetal circulation soon after birth?
- closure of ductus arteriosus = lungs received adequate flow of unoxygenated blood from pulmonary trunk
- at birth = first breath = increased oxygenated blood in ductus causing smooth muscle in wall within few hours or days
- proliferating connective tissue eventually closes ductus permanently forming ligamentum arteriosum
what changes occur in foetal circulation in relation to umbilical arteries at birth?
- umbilical arteries similarly constrict at birth cutting off foetal blood supply to placenta + remnants are retained as round ligaments of bladder
- venous return from placenta also stops + umbilical veins cease to function
- remnants are seen in adult as falciform + round ligaments of liver
- thus main source of blood flowing through ductus venosus ceases and diminishes until no longer functional vessel
- remnant of ductus venosus may remain asligamentum venosum within liver
What are some congenital cardiovascular problems?
- septal defects
- patent ductus arterosus
- valvular deformities
- tetralogy of fallot
- vascular ring anomaly
- portosystem shunts
define septal defects
- atrial = failure of closure of foramen ovale
- > increased load on right side of heart as left atrial pressure is higher = results in pulmonary congestion and relative pulmonic stenosis- ventricular
- > results in increased pulmonary blood flow and left ventricular dilation and failure
- ventricular
define patent ductus arteriosus
- in foetus lungs are high resistance vascular bed + blood flows through ductus from right to left
- failure of closure of ductus arteriosus at birth results in left to right flow as pulmonary vascular resistance + right heart pressure both decrease while left heart pressure increases
- this produces pulmonary congestion + characteristic machinery murmur heard continuously throughout cardiac cycle
define vulvular deformities
- stenoses
- > narrowing often seen in conjunction with post stenotic dilation
- > pulmonic stenosis = results in right ventricular hypertrophy and failure with accompanying high pitched seagull murmur
- > aortic stenosis = less common, results in poor coronary blood supply and often results in sudden death following myocardial damage- Incompetencies (leakage or insufficiency)
- > congenital AV valve problems are unusual in dog though common genetic occurrence
- > congenital AV valve deformities commoner in cats
- Incompetencies (leakage or insufficiency)
define tetralogy of fallot
- called because of four simulataneous problems = ventricular septal defect, pulmonic stenosis, aortic override and right ventricular hypertrophy
- results in stunting + cyanosis and is usually terminal
define vascular ring anomaly
- occurs when abnormal development of aortic arches in relation to gut tube
- normally left IV arch develops as aorta + left VI arch forms ductus arteriosus
- in vascular ring anomaly = right IV arch develops instead of left + connection with left IV arch forms constricting band around oesophagus = results in mega oesophagus
- occasionally similar constriction caused by normal left IV arch development into aorta but anomalous right subclavian branching from aorta instead of from brachiocephalic trunk
