tissue fluid Flashcards
(16 cards)
what is tissue fluid?
the fluid that all cells are surrounded by
the cells exchange substances with fluid by taking up substances such as ions, glucose and water from the tissue fluid and returning substances such as urea
what is something that is present in plasma but not tissue fluid?
plasma proteins because they are too big to leave the capillary
what process is tissue fluid formed by?
ultrafiltration
fluid (NOT YET TISSUE FLUID) is forced out under pressure from the capillary through gaps between capillary cells
which end of the capillary does blood enter and how does this lead to formation of tissue fluid?
blood enter arterial end of capillary
here the hydrostatic pressure is high
this is due to ventricular contraction and closeness to the heart
the hydrostatic pressure is greater than the force of osmosis (the water potential gradient is not steep)
therefore fluid (water) from the plasma moves out of the capillary in the direction of the greater force via ultrafiltration
dissolved substances leave the capillary in the water
how does pressure at the venous end of the capillary differ to the arterial end?
hydrostatic pressure is lower
due to…
1. the loss of fluid as tissue fluid is formed along the capillary
2. the greater distance away from the heart
3. the narrowness of the capillary that provides resistance to flow
how does the force of osmosis at the venous end compare to the arterial end and what does this mean for the return of tissue fluid?
force of osmosis is greater because the plasma proteins were unable to leave capillary
the water potential gradient is much steeper because the proteins are dissolved in only the small amount of water that is left in the capillaries after the tissue fluid was formed
water moves into the capillary by osmosis
what is oedema?
accumulation of tissue fluid
why does not as much tissue fluid returned as is formed?
the difference between the two forces at arterial end is greater than at the venous end
what is done to prevent oedema?
excess tissue fluid is drained away into lymph vessels
the lymph fluid moves along the vessels of the lymphatic system when the tube are compressed as local skeletal muscles and smooth muscles contract
valves prevent backflow of fluid
the lymph fluid drains into the subclavian vein in the neck to return fluid to blood
what are the three things that lead to oedema? why?
- high hydrostatic pressure- this will cause more tissue fluid to form and less water can return
- the loss of plasma proteins- without these the water potential gradient for water to return via osmosis is less steep
- failure of the drainage of excess tissue fluid- there is a problem with the lymph vessels
how could an infection from a parasitic worm lead to serious oedema?
-parasite blocks lymph vessel
-excess tissue fluid cannot be drained away
-tissue fluid accumulates because more fluid moves out of capillary than what is returned
-because the difference between the hydrostatic pressure and force of osmosis is higher at arterial end than venous.
why does increased blood pressure lead to oedema?
-means hydrostatic pressure is higher
-more fluid leaves the capillary (because there is a greater difference between hydrostatic pressure and force of osmosis)
-filtration rate is higher
-less fluid/ water returns because there is less difference between the force of osmosis and the hydrostatic pressure at venous end
how might starving individuals end up with oedema?
-plasma proteins are broken down to provide a source of energy/ amino acids
-the water potential gradient between the tissue fluid and the capillary is less steep
-less water returns via osmosis
why are diuretics used to treat oedema? (they cause the production of large quantities of urine)
-loss of water in urine decreases the hydrostatic pressure
-so less fluid leaves the capillary at the arterial end (the difference between hydrostatic pressure and force of osmosis is smaller)
-OR YOU CAN SAY; more water is returned at the venous end (the difference between the force of osmosis and hydrostatic pressure is greater)
why might patients be given albumin (plasma protein) to treat oedema?
-water potential of plasma lowered
-water potential gradient between the tissue fluid and the capillary is steeper
-more water returns via osmsois
why might increased permeability of capillary walls lead to oedema?
-plasma proteins lost from the capillary into the tissue fluid
-the water potential of the capillaries is higher
-the water potential gradient between the tissue fluid and the capillary is not as steep
-less water returns to capillary via osmosis
