Capillaries II- Fluid Exchange Flashcards
What can maintain circulation during haemorrhage?
Fluid reabsorption from tissues to blood
How does fluid move at the capillary wall (tissue -> capillary)?
- Fluid moves across into interstitial space due to blood flow which exerts a hydraulic pressure
- large molecules cannot pass through the membrane so exert an osmotic pressure which creates a suction force to move fluid into capillary
What does fluid movement across capillary walls depend on?
The balance between hydraulic and oncotic pressures across the capillary wall
What essentially are starlings forces?
The interaction of two forces
What does hydrostatic pressure tend to favour?
Filtration
What are Lp and A in starlings forces at normal conditions?
Constants
What does overall control of extracellular fluid balance depend on?
Capillary filtration/ reabsorption and the lymphatic system
What do starlings factors determine changes in?
Fluid balance in circulation, the interstitial fluid and the lymphatic system
What is hypovolemia
Low capillary pressure
What happens when there is hypervolemia?
Cardiac output is increased which increases blood pressure and therefore more blood flow
What is hypervolemia caused by?
Sympathetic nerve-induced vasoconstriction of pre-capillary arterioles leading to a drop in downstream pressure
What does an increase in capillary pressure lead to?
An increase in venous pressure and an increase in filtration (which leads to oedema)
What are the four causes of oedema?
Increased capillary pressure
Decreased plasma protein oncotic pressure
Inflammatory response
Lymphatic problems
What are the clinical applications of increased capillary pressure?
Standing up for long periods of time
DVT
Cardiac failure
What does increased venous pressure cause?
Backup of pressure leading to increased capillary pressure across capillaries and increased filtration
