tissue fluid Flashcards
How is tissue fluid formed?
- As blood passes through capillaries some plasma leaks out through gaps in the walls of the capillary to surround cells of the body. This results in formation of tissue fluid.
What does tissue fluid do?
- Bathes almost all the cells of the body that are outside the circulatory system.
- Exchange of substances between cells and blood occur via tissue fluid.
What does the volume of liquid that leaves the plasma to form tissue fluid depend on?
- Depends hydrostatic pressure and oncotic pressure.
What is hydrostatic pressure?
- This is the pressure exerted by a fluid e.g blood.
- The hydrostatic pressure in this fluid sample is the blood pressure, generated by the contraction of the heart muscle.
What is oncotic pressure?
- This is the osmotic pressure exerted by plasma proteins within a blood vessel.
- Plasma proteins lower the water potential within the blood vessel, causing water to move into the blood vessel by osmosis.
What happens when blood is at the arterial end?
- When the blood is at the arterial end of a capillary the hydrostatic pressure is great enough to force fluid out of the capillary.
- Proteins remain in the blood as they are too large to pass through the pores in the capillary wall.
- The increased protein content cerastes a water potential gradient between the capillary and the tissue fluid.
What pressure is greater than the other at the arterial end and what is the result of this?
At the arterial end the hydrostatic pressure is greater than the osmotic pressure so the net movement of water is out of the capillaries into the tissue fluid.
At the venous end what happens to the hydrostatic pressure?
- At the venous end of the capillary the hydrostatic pressure within the capillary is reduced due to increased distance from the heart and the slowing of the blood flow as it passes through the capillaries.
- The water potential gradient between the capillary and the tissue fluid remains the same as at the arterial end.
At the venous what pressure is higher than the other and what is the result of this?
- At the venous end the osmotic pressure is greater than the hydrostatic pressure and water begins to flow back into the capillary from the tissue fluid.
Roughly how much fluid is reabsorbed at the venous end and what happens to the other fluid?
- Roughly 90% or the fluid lost at the arterial end of the capillary is reabsorbed at the venous end.
- The other 10% remain as tissue fluid and is eventually collected by lymph vessels and returned to the circulatory system.
What is edema?
- When blood pressure is high then the pressure at the arterial end is even greater, this pushes more fluid out of the capillary and fluid begins to accumulate around the tissues.
How is lymph formed?
- Larger molecules that are not able to pass through the capillary walls enter the lymphatic system as lymph.
- Small valves in the vessel walls are the energy point to the lymphatic system.
How does lymph reenter bloodstream?
- Through veins located close to the heart.
How does plasma proteins that have escaped from the blood return to blood and what happens if plasma protein is not removed from tissue fluid?
- Any plasma proteins that have escaped from the blood are returned to blood via lymph capillaries.
- If plasma proteins were not removed from the tissue fluid they could lower the water potential of tissue fluid and prevent re absorption of water into blood in capillaries.
Describe three ways in which the composition of tissue fluid is different to composition of plasma.
In plasma and here is:
- A higher conc of glucose.
- A higher conc of plasma proteins.
- A higher conc of glycerol.
- A lower water potential.
- A higher oxygen and lower CO2 conc.
In tissue fluid there is:
- A higher conc of the substance secreted by cells e.g insulin.
