Venous and lymphatic systems Flashcards
What are the 2 functions of veins?
- Transport of blood back to the heart
2. Store blood and mobilise when required
What site are arterioles ?
The principle site of resistance to blood flow within the vascular tree
Velocity of flow is _______ proportional to the total ________ _________ area
Inversely
Cross-sectional
What is venous return?
The volume of blood returning to heart from systemic veins
How is venous return determined ?
- Pressure gradient
2. Venous resistance
What is the average pressure of the venous system and the right atrial pressure ?
Pressure system - 18mmHg
Right atrial pressure - 0mmHg
How do other factors promote venous return?
Increase the pressure gradient
What are the factors that facilitate venous return?
Venous valves Cardiac suction effect Pressure of blood due to cardiac contraction Skeletal muscle pump Respiratory muscle pump Increase in blood volume Increase in venous tone
What is the cardiac suction effect ?
Pressure in the heart decreases and therefore increases the pressure gradient
What does Venus tone refer to?
The degree of contraction of smooth muscle within the veins
What are the factors that increase venous tone?
- Sympathetic stimulation
- Activated venous stretch receptors
- Hormones (catacolamines)
And increase venous return will cause an increase in the ________________, _____________ and _____________.
End-diastolic volume
Stroke volume
Cardiac output (should equal the venous return)
What is venous compliance ?
The rate of change in volume (V) with changing pressure (P)
How can venous compliance be calculated ?
Change in volume / change in pressure
Does arteries or veins have a higher vascular compliance?
Veins
Why can veins be used as an arterial bypass grafts?
At high pressures, the compliance of veins and arteries are the same and if you take a segment of vein and remove the valves you can use this as a bypass as arteries are always under high amounts of pressure.
How much of the TBV is present in the systemic venous system at rest?
64%
What senses a drop in central blood volume due to haemorrhage?
Atrial volume receptors
What are the 4 large sites of venous blood?
The spleen
The liver
Large abdominal veins
Venous plexus
What are the 2 components of venous pressure?
- Pressure generated by heart
2. Hydrostatic pressure
Why are the veins above the heart collapsed?
The pressure in the veins are less than atmospheric pressure (negative hydrostatic pressure)
What causes hydrostatic pressure ?
Gravity
What is central venous pressure ?
Pressure in the thoracic vena cava near right atrium
What does central venous pressure depend on ?
1) Venous return
2) Right ventricular function
