Thorax 7: Foetal Circulation Flashcards
How does blood circulate through the foetal heart?
enters the Right atrium, bypasses pulmonary circulation and enters the left atrium, enters the left ventricle, goes up into the aorta to the systemic circulation
What is the function of the placenta?
Nutrients and metabolites diffuse across the placental barrier from mother to foetus and vice versa
Describe the composition of placenta
formed of foetal tissue which thins as pregnancy progresses
Explain the structure of the placenta
- membrane between 2 circulations= foetal and maternal
- endothelium of foetal capillaries is covered by syncitiotrophoblast presenting a huge surface area of microvilli
- maternal capillaries break down and maternal blood bathes foetal microvilli directly
How is oxygenated blood transported from the placenta to the foetus?
1 Umbilical vein
what vessels carry deoxygenated blood from the foetus? how many are there?
2 umbilical arteries
What happens to blood in the placenta?
blood is oxygenated and picks up nutrients from maternal blood across the placental membrane
What are the 2 adaptations of the foetal circulation?
- no need for pulmonary circulation since blood is oxygenated at the placenta
- no need for a hepatic circulation since nutrients already modified by maternal liver
How does blood pass from the Right atrium to the left atrium in the foetal heart?
blood is directed by a valve through the foramen ovale
what is the function of the foramen ovale?
bypasses the right ventricle and pulmonary trunk hence the pulmonary circulation
What is the purpose of the Ductus Arteriosus?
bypass the pulmonary circulation, carries venous blood directly into the aorta after the arch and its branches
where is the Ductus A. situated?
connects the pulmonary trunk to the inferior aspect of the arch of the aorta
what happens to blood that reaches the foetal lungs?
10% of right ventricle blood passes into the pulmonary circulation to provide the developing lungs with oxygenated blood
What is the purpose of the Ductus venosus?
oxygenated blood from the mother entering the foetus via the placenta must bypass the liver, this is done by the Ductus V.
Where does the Ductus V. drain to?
Drains into the IVC
What is the blood composition of the foetal IVC?
- oxygeanted, nutrient rich blood from Ductus V.
- deoxygenated blood with waste products returning from the foetal systemic circulation
how is the pulmonary circulation established at birth?
- first breath pulls blood into the pulmonary circulation
- sudden increase in pressure in the Left atrium pulls the inter-ventricular septum shut closing the foramen ovale
- blood is returned from pulmonary circulation and Left A pressure=Right Atrium pressue
How many phases is the ductus arteriosus destroyed in?
2
what happens in the first phase of destruction of the Ductus A. ?
- due to smooth muscle contraction
- oxygen is a potent constrictor of Ductus A. and the oxygen tension of blood in aorta and PT increases after 1st breath
- drop in prostaglandins since no longer produced by placenta= Ductus A. closure
What happens in the second phase of destruction of the Ductus A.?
-thickening of tunica intima that occurs over a period of 1-3 months
What artefact is left behind from the Ductus A.?
ligamentum arteriosum
What happens to the Ductus Venosus?
- with delivery of placenta the umbilical vessels contract and get obliterated over a period of days
- hepatic circulation becomes established and the Ductus Venosus becomes the Ligamentum Venosum
What structure does the umbilical vein develop into?
Ligamentum teres
what do the 2 umbilical arteries develop into?
medial umbilical ligaments
