[7.6] (2/2) tissue fluid and its formation Flashcards
what does tissue fluid contain?
- glucose
- oxygen
- amino acids
- fatty acids
- ions in solution
what is the role of tissue fluid?
- to receive carbon dioxide and other waste materials from the tissues in return for supplying useful substances to tissues
- means by which materials are exchanged between blood and cells
what relationship does tissue fluid have with cells?
- bathes all cells of the body
- immediate environment of cells ie. where they live
how does tissue fluid provide a mostly constant environment for the cells it surrouds?
composition of blood plasma is controlled by various homeostatic systems
what is tissue fluid formed from?
blood plasma
how is tissue fluid formed as blood passes through capillaries?
- some plasma leaks out through gaps in walls of capillary to surround cells of body
- this forms TF
how does the composition of plasma and tissue fluid compare?
- virtually the same
- TF contains far fewer proteins
why does tissue fluid contain fewer proteins than blood plasma?
proteins are too large to fit through gaps in the capillary walls and so remain in the blood
what is hydrostatic pressure?
pressure created from the pumping of the heart
what happens at the arterial end of the capillary?
- higher hydrostatic pressure at the arterial end
- tissue fluid moves out of blood plasma
what happens at the venule end of the capillary?
- lower hydrostatic pressure at venule end
- less fluid is pushed out of capillary
what does how much liquid leaving the plasma to form tissue fluid depend on?
two opposing forces:
- hydrostatic pressure of TF outside capillaries, which resists outward movement of liquid
- lower water potential of blood due to plasma proteins. water moves back into blood in capillaries
what happens when there is no water potential gradient?
- ie. ψ of capillary and TF are the same
- water goes back to arterial end of capillary from TF
- overall, more TF leaves capillary than returns so TF can bathe cells
when does tissue fluid return to the blood plasma?
once it has exchanged metabolic materials with the cells it bathes
how does most tissue fluid return to the blood plasma?
directly via the capillaries
how does tissue fluid return to the circulatory system via the capillaries?
- loss of TF from capillaries lowers hydrostatic pressure in them
- once blood has reached venous end of the capillary, its hydrostatic pressure is lower than the TF outside it
- TF is forced back into capillary due to higher hydrostatic pressure outside them
- plasma has lost water but still contains proteins so has a lower ψ than TF
- water leaves tissue by osmosis down a ψ gradient
what happens to the tissue fluid that does not return through the capillaries?
carried back via the lymphatic system
describe the lymphatic system
- contain lymph capillaries, which are like capillaries but have dead ends
- lymph capillaries are gradually merged into larger vessels that form a network in the body
- larger vessels drain their contents back into the bloodstream via 2 ducts that join veins close to the heart
how are plasma proteins returned to the blood?
any plasma proteins that have escaped from the blood are returned to the blood via the lymph capillaries
what happens if plasma proteins are not removed from the tissue fluid?
- lower ψ of TF
- reabsorption of water into blood in capillaries is prevented
what happens to large molecules that are not able to pass through the capillary wall?
- enter lymphatic system as lymph
- lymph capillaries have closed ends and large pores that allow large molecules to pass through
how are the contents of the lymphatic system moved?
- hydrostatic pressure of TF that has left capillaries
- contraction of body muscles squeeze lymph vessels - valves in lymph vessels ensure fluid inside them moves away from tissues towards heart
