Capillaries II Flashcards
What is the importance of fluid exchange?
• Fluid exchange is important for normal physiological function, we need H2O for chemical reactions.
Give a simple reason as to why we have fluid re-absorption?
• Fluid re-absorption from tissues to blood can maintain circulation during haemorrhage.
If fluid filtration is damage what are the consequences?
• Abnormalities in fluid exchange can lead to oedema/tissue swelling. This is in the interstitial (between the basement membrane) space.
Describe the structures that surround the capillary in a body cell
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How does fluid move out of the capillaries and where does it move to?
- Capillary wall is a semi-permeable membrane.
* Fluid moves across membrane into interstitial space due to blood flow which exerts a hydraulic pressure.
What do large molecules create?
• Large molecules (eg. plasma proteins) cannot pass through membrane so they exert an osmotic pressure termed oncotic pressure which creates suction force to move fluid into capillary.
What does fluid movement across capillaries depend on?
• Fluid movement across capillary walls depends on the balance between hydraulic and oncotic pressures across the capillary wall.
Define oncotic and hydraulic/ hydrostatic pressure and why is one greater than the other?
Oncotic = reabsorption
Hydrostatic or Hydraulic = filtration
Hydrostatic pressure > oncotic pressure gradient – the essence of starlings law of capillary exchange
What four pressures determine filtration rate?
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Describe Starlings law for fluid exchange
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Starlings forces normally favour filtration
What factors promote filtration?
What factors promote reabsorption?
Capillary blood pressure and interstitial proteins
Plasma proteins
What develops if filtration is found in excess?
Oedema
How is excess fluid returned to the circulation?
• Excess fluid is returned to the circulation via lymphatic system.
Describe the pressure from the arteriole end to the venous end
• This diagram shows at the arteriole end there is a pressure of around 35mmHg. Continuing along the capillary pressure is lost. We have a declining gradient of hydrostatic pressure.
Does the osmotic pressure change?
• The osmotic pressure does not change and would give a horizontal line