Lecture 12: Venous Blood Flow and the Heart Flashcards
Where is most of the blood in our body found?
Systemic veins
Why can’t we store extra blood in our pulmonary circuit?
It is too small
Why can’t we store extra blood in our systemic arteries?
It would raise our blood pressure
Why can’t we store extra blood in our capillaries?
They are too small
How are veins able to store more blood in them?
They have a higher compliance
What allows veins to have a higher compliance?
They have a thin tunica media which allows room for compliance
What doesn’t allow arteries to have a higher compliance?
Thick tunica media forming a more rigid structure
What is compliance?
The extent to which a vessel allows deformation in response to an applied force
What is the equation for compliance?
Delta V/P
What does it mean for compliance if it takes more pressure to change the volume of a vessel?
The less compliant it is
What allows arteries to maintain their shape even under low pressure?
A thick tunica media
What happens to veins under low pressure?
They collapse as pressure conforms shape
What does a small portion of pressure do to the volume of a vein?
It causes a large change in volume
What is meant by veins having survival value?
They can move blood over to arteries in an emergency situation
What is venoconstriction?
contraction of veins pushing blood stored there into the arteries
What can happen as a consequence of an arterial puncture?
2
- Loss of arteriole blood
- Life-threatening fall in arterial pressure
What controls venoconstriction?
Neural control
What does supine mean?
Lying down
What happens to venous volume whilst supine?
It is uniform
What happens to venous volume whilst standing up?
2
- Venous volume below the heart increases
- Venous volume above the heart decreases
What is larger venous or arterial volume?
Venous
What does gravity pulling blood down cause the veins to do?
Causes the veins to bow
Where does venous pooling mainly occur?
Legs/feet
What helps counteract venous pooling?
2
- Venous valves
- Tone of surrounding tissue
What does muscle tone do?
Acts to stiffen the veins, making them less compliant and less prone to pooling
What do some people prone to fainting possess?
Low muscle tone and excessive pooling
What do skeletal muscle contractions do to blood?
Increase venous return to the heart
What do venous valves superior to the contracting muscle do?
Open, allowing blood to move towards the heart
What do venous valves inferior to the contracting muscle do?
They are forced closed, preventing back flow of blood to the capillaries
What does breathing do to the intercostal muscles and intern blood?
Pushes intercostal muscles against veins pumping blood towards the heart
What is Starling’s law of the heart?
The more stretched muscles fibres are before a contraction, the stronger the contraction will be
What does an increased venous return mean?
An increased stroke volume
What does a larger stretch of cardiac muscles do to the maximum contraction of the heart?
Larger maximum contraction
