Lecture 10 Flashcards
What is the rough distribution of blood in the body? How does the largest occur?
5% in capillaries, 15% for the arteries, heart -lungs and large veins. 50% in the small veins in venules.
This means 65% (2/3rds) or blood is in the veins. This is because the veins have low pressure and high volume, allowing for a large amount of blood storage.
What part of vein structure allows for storing more blood at lower pressure than arteries?
The veins have a thinner wall and are more compliant as well as a larger radius due to that thinner wall.
What is compliance in terms of blood vessels?
The extent to which a vessel allows deformation in response to an applied force. The equation is change in volume / change in pressure = compliance.
How does change in shape with pressure vary in the veins and arteries?
Arteries have very little change in volume due to pressure (low compliance), veins have huge change in volume in response to pressure (even collapsing do not even circular if very low).
Why do veins have survival value besides returning blood to the heart? What processes can it use (under what control?) to do this?
The veins store spare blood, this allows us to maintain enough blood to stay alive even if we lose some.
The veins can venoconstrict under neural control to push more blood into the system in the event of an accident.
What does the high vascular compliance mean tends to happen to veins due to gravity? How is this counteracted
Blood tends to pool in veins near the bottom, this is counteracted through the actions of venous valves, meaning the blood can only pool within the valves. It is also counteracted by the ‘tone’ of surrounding tissue, this is because the surrounding tissue helps to provide pressure for the vein to prevent large amounts of pooling in the bottom of veins. When laying down (supine) the venous volume will be uniform.
What makes a person prone to fainting in regards to veins?
Venous pooling, either due to low muscle tone or non functioning valves.
How does skeletal muscle aid in venous blood flow?
The contraction of skeletal muscle combined with venous valves can push the venous blood towards the heart.
What is Starling’s Law of the heart? What other factor can increase stroke volume?
The more stretched muscle fibres are before a contraction, the stronger the contraction will be. This means the more volume in the heart the more it will pump out. The exception is if the stretching is very large the actin and myosin fibres will be too far apart and won’t be able to form cross bridges. Leading to no contraction.
Increased contractility can also increase stroke volume.
What values change when going from lying down to upright?
Stroke volume decreases (less blood returning due to gravity.
cardiac output lowers
Heart rate increases heavily
Venous resistance increases
Mean arterial pressure goes down slightly.
