3. Tissue Fluid Flashcards
What is tissue fluid
the fluid that surrounds cells in tissues
It is made up of substances that leave the blood eg oxygen, water and nutrients.
Cells then take in oxygen and nutrients and release metabolic wastes into it eg carbon dioxide and urea
Formation of tissue fluid
Contraction of the heart muscle sends blood along arteries, arterioles and capillaries which creates a pressure called hydrostatic pressure. This acts outwards, forcing tissue fluid out of the capillaries.
Red blood cells and large plasma proteins are too big to leave through the capillary walls.
Tissue fluid is formed at the arterial end of the capillary bed. As the blood is forced from the artery into narrower vessels hydrostatic pressure forces tissue fluid out of the plasma
hydrostatic pressure is opposed by 2 other forces
The hydrostatic pressure of the tissue fluid outside the capillaries.
The lower water potential of the blood. This is due to the plasma proteins which remain in the blood
Ultra-filtration
The overall effect of these forces is to force small molecules out of the capillaries leaving all the cells and proteins in the blood. Filtration occurs under pressure
Journey of tissue fluid relating to HSP
Tissue fluid is formed at the arterial end of the capillary bed. As the blood is forced from the artery into narrower vessels hydrostatic pressure forces tissue fluid out of the plasma
Tissue fluid vs plasma
Return of the tissue fluid
Once metabolites have been exchanged with the cells the tissue fluid has to be returned to the blood. This is done via the capillaries mainly.
Loss of tissue fluid from the capillaries reduces the hydrostatic pressure within them. Therefore by the time the blood reaches the venous end the pressure outside is greater than the pressure inside. Coupled with osmotic forces (due to the proteins in the blood) fluid moves back in.
The remainder of the tissue fluid is returned to the blood system via the lymphatic system.
The lymph is moved by
Hydrostatic pressure of the tissue fluid that has left the capillaries
Contraction of body muscles that squeeze the lymph vessels. These vessels contain valves to keep the lymph moving in the right direction.
Lymph
Water
Oxygen
Nutrients e.g glucose
White blood cells
Chylomicrons
It does not contain red blood cells (too big) or big protein molecules
Elephantiatis
If the lymph vessels are blocked, the flow of fluid in the lymph vessels will stop
The tissue fluid will build up in the tissues.
Explain how high blood pressure may cause oedema (4)
If blood pressure is high, the hydrostatic pressure at the arterial end of the capillary bed will be high.
This means that a lot of tissue fluid will be formed.
Not all of it will be able to return to the capillary
The rest will remain in the tissues and cause swelling
Describe and explain four ways in which the structure of a capillary adapts for the exchange of substances between blood and the suurrounding tissue
-Single cell thick so reduces diffusion distance
-small diameter so short diffusion distance
-narrow lumen so reduces flow rate so more time for diffusion
- red blood cells in contact with wall so more time for diffusion
Hypoalbuminemia is a condition where the level of a protein called albumen in the blood is very low. It causes an increase in tissue fluid, which can lead to swelling.
Explain how hypoalbuminemia causes an increase in tissue fluid. (2)
The water potential of the blood in the capillary is high because there is less albumin in the blood.
This means that less water is absorbed back by osmosis at the venule end of the capillary bed
This leads to an increase in tissue fluid.
