17. Veins, Capillaries and Lymphatics Flashcards
What is filtration of capillaries and what main 2 force determine the rate?
Net movement of fluid
- Capillary blood pressure
- Plasma protein colloid osmotic pressure
What is the average outward force of capillaries?
17mmHg
What is the average inwards force of plasma protein colloid osmotic pressure in capillaries?
28mmHg
Why might a capillary become more permeable?
Histamine, bacterial infection, prolonged ischaemia or burns
What is hydrostatic pressure?
Weight of a column of water
Pressure increases as you go beneath heart level
Effects of gravity below heart level
Veins distend due to increased transmural pressure
Temporary fall in venous return
Muscle pump and valves break up columns of blood when moving
Effect of gravity above heart level
No effect as deep veins in brain stay open due to non-collapsable structure even at negative pressure
What happens when you stand up?
Immediate pooling of blood in legs
Fall in venous return
Fall in cardiac output
Baroreceptors detect fall in BP
Describe the postural adaptation response
Baroreceptors detect fall in BP
Increase HR and cardiac output
Vasoconstrict to mobilise venous blood
What is postural hypotension?
Veins constrict less, causing pooling of blood
Results in fainting due to decreased CO and BP
What happens at positive G forces?
Black out
Blood pools in feet resulting in a lack of cerebral flow
What happens at negative G forces?
Red out
Blood rushes to the head
What happens after prolonged exposure to zero gravity?
Weakened heart and atrophy
What does Central Venous Pressure measure?
Right atrial pressure
Shows right cardiac function and dehydration
What does the Jugular Venous Pressure give an estimate of?
Central Venous Pressure
