Venous Return Flashcards
What is venous return ?
The volume of blood that returns to the right side of the heart via the venues and the veins
How does an increase in VR affect ventricular contraction ?
- Increase in blood to right atrium
- Strengthens the right atrium chamber
- This increases the SA node firing rate
- Causes HR to increase
What is starling’s law ?
A decrease in VR = a decrease in SV which = a decrease in Q
- same with increase
VR at rest
Sufficient to maintain SV and Q to meet the demand for O2
VR during exercise
Blood pressure in the veins is too low to maintain VR, so SV and Q decreases
Why does the body need extra help to push the blood
The push the blood against gravity and to increase VR and SV
What are the mechanisms aiding venous return ?
- Pocket Valves
- Muscle Pump
- Respiratory Pump
- Smooth Muscle
- Gravity
+ starling’s law
What do Pocket Valves do ?
Prevent back flow of blood and direct it towards the heart
What does the muscle pump do ?
The veins are situated between skeletal muscles - when the muscles contract this helps to push or squeeze blood back to the heart
What does the respiratory pump do ?
During exercise breathing becomes deeper and faster - this causes pressure changes in the thorax and abdomen, squeezing large veins and thus blood back to the heart
During exercise how does breathing change
During exercise breathing becomes deeper and faster
What does smooth muscle do ?
Contraction and relaxation of smooth muscle in the middle layer of the vein walls helps push the blood towards the heart
What does gravity do ?
Blood from the upper body is aided by gravity
