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In humans, blood passes from the post caval to the diastolic right atrium of heart due to:
A
stimulation of the sino auricular node
B
pressure difference between the post caval and atrium
C
pushing open of the venous valves
D
suction pull
Detailed Solution
Blood always flows from a region of higher pressure to a region of lower pressure.
During atrial diastole the right atrium is relaxed, so the pressure inside it falls to nearly zero.
The pressure of the blood in the great veins (the post caval or inferior vena cava) is low, but it is still higher than the pressure in the relaxed atrium.
Because of this pressure difference between the post caval and the atrium, blood flows passively from the vein into the right atrium.
The sino-auricular node initiates the contraction (systole) of the atria; it does not bring blood into the atrium.
There are no valves at the openings of the venae cavae that need to be pushed open, and the filling is due to the pressure gradient.
So blood passes into the diastolic right atrium due to the pressure difference between the post caval and the atrium.
During atrial diastole the right atrium is relaxed, so the pressure inside it falls to nearly zero.
The pressure of the blood in the great veins (the post caval or inferior vena cava) is low, but it is still higher than the pressure in the relaxed atrium.
Because of this pressure difference between the post caval and the atrium, blood flows passively from the vein into the right atrium.
The sino-auricular node initiates the contraction (systole) of the atria; it does not bring blood into the atrium.
There are no valves at the openings of the venae cavae that need to be pushed open, and the filling is due to the pressure gradient.
So blood passes into the diastolic right atrium due to the pressure difference between the post caval and the atrium.