L8.2 Capillaries Flashcards
describe the blood flow through capillaries
- capillaries are arranged into capillary beds
- blood supply to a capillary bed can be controlled (precapillary sphincters)
- bloods still flow through metarteriole (bypass capillary beds)
see notes for diagram of blood flow through capillaries
see notes for diagram of blood flow through capillaries
why are capillaries good for diffusion?
- small diffusion distance: thin capillary walls, small capillary diameter, large network of capillaries
- large surface area available for exchange
- slow blood flow
describe the exchanges through the capillary wall:
- lipid-soluble substances pass through the ________
- small water-soluble substances pass through the _______
- _______ generally cannot cross the capillary walls
- exchangeable proteins are moved across by ________
- lipid-soluble substances pass through the endothelial cells
- small water-soluble substances pass through the pores (makes it easier for the molecules to pass from the blood supply and then out into the interstitial fluid around)
- plasma proteins generally cannot cross the capillary wall
- exchangeable proteins are moved across by vesicular transport
describe solute exchange
- down concentration gradients
- plasma- interstitial fluid- tissue cells
- active tissues increase concentration gradients = increase rate of diffusion
describe bulk flow
- continuous flow of fluid and solutes between capillaries and interstitial fluid
- interstitial fluid = plasma minus plasma proteins
- fluid movement is controlled by: hydrostatic pressure and osmotic pressure
- filtration: pushing fluid out of capillary
- reabsorption: drawing fluid into capillary
describe the forces driving bulk flow
- capillary hydrostatic pressure (CHP)
- hydrostatic pressure of blood flowing into capillaries
- pushes fluid out of capillaries
- higher at arteriolar end than venular end - blood colloid osmotic pressure (BCOP)
- plasma proteins too large to exit capillary
- more solutes in the capillary than the interstitial fluid
- osmosis draws the fluid back into the capillary
what is net filtration pressure?
NFP is the difference between the capillary hydrostatic pressure and blood colloid osmotic pressure
- positive NFP favours filtration (when CHP higher)
- negative NFP favours reabsorption (when BCOP higher)
where is the cardiovascular control centre located? what is its function?
located in the medulla oblongata
- receives sensory info about blood pressure (baroreceptors)
- regulates sympathetic and parasympathetic activity to heart and vessels
what are baroreceptors? types?
mechanoreceptors that respond to stretch
- carotid sinuses: monitor blood flow to the brain
- aortic arch: monitor blood flow to systemic circulation
describe what the baroreceptors do when blood pressure falls below normal
blood pressure falls below normal -> decrease carotid sinus and aortic arch receptor potential -> decrease rate of in afferent nerves -> cardiovascular centre -> increase sympathetic cardiac nerve activity, increase sympathetic vasoconstrictor nerve activity, decrease parasympathetic nerve activity -> increase HR, increase SV and arteriolar and venous vasoconstriction -> increase CO, increase TPR -> blood pressure increased toward normal
see notes for haemorrhage
see notes for haemorrhage
describe what the baroreceptors do when blood pressure become elevated above normal
blood pressure becomes elevated above normal -> increase carotid sinus and aortic arch receptor potential -> increase rate of in afferent nerves -> cardiovascular centre -> decrease sympathetic cardiac nerve activity, decrease sympathetic vasoconstrictor nerve activity, increase parasympathetic nerve activity -> decrease HR, decrease SV and arteriolar and venous vasodilation -> decrease CO, decrease TPR -> blood pressure decreased toward normal
