Lecture 14 - Capillary exchange Flashcards
Why do we need capillary exchange?
To obtain nutrients and oxygen
Remove metabolic wastes
What are 3 adaptations capillaries have for efficiency?
Short diffusion distance
Slow blood flow
Large SA
Why and how does short diffusion distance help capillaries?
Gases can move around faster
Thin walls, small diameter
Close to cells
Why and how does slow blood flow help capillaries?
More time for gases to fully exchange
Have a large cross sectional area
Why and how does a large surface area help capillaries?
More opportunity for gas exchange
There are 10 billion + capillaries
What are the three transport mechanisms in capillary exchange?
Diffusion
Bulk flow
Transcytosis
What is diffusion in capillary exchange?
Occurs directly through the endothelial cell membrane, ion channels, or clefts and pores
Occurs down conc grad
What is bulk flow in capillary exchange?
Occurs through clefts and pores
By filtration/osmosis
Down pressure gradient
Can be a two way process
What is transcytosis in capillary exchange?
Occurs by vesicular transport
How is bulk flow between capillaries and interstitial fluid determined?
By the net pressure difference across capillary walls
What are the four forces that influence fluid and solute movement in capillaries?
Capillary hydrostatic pressure
Interstitial fluid hydrostatic pressure
Blood colloid osmotic pressure
Interstitial fluid colloid osmotic pressure
What is capillary hydrostatic pressure?
Pushes
The pressure exerted on capillary walls pushing fluid out
What is interstitial fluid hydrostatic pressure?
Pushes
The pressure exerted on outer capillary walls by interstitial fluid pushing the fluid inW
What is blood colloid osmotic pressure?
Pulls
Plasma osmotic pressure pulling fluid in
What is interstitial fluid colloid osmotic pressure?
Pulls
Osmotic pressure of interstitial fluid pulling fluid out
What is the equation for net filtration pressure?
Net filtration pressure = net hydrostatic pressure - net osmotic pressure
What is the equation for net hydrostatic pressure?
Capillary hydrostatic pressure - interstitial fluid hydrostatic pressure
Favours filtration, pushing fluid out
What is the equation for net oncotic pressure?
Blood colloid osmotic pressure - interstitial fluid colloid oncotic pressure
Favours reabsorption, pulling fluid into capillary
What happens to filtration when there is hypertension?
The CHP will increase
This increases NFP and filtration
What happens to filtration when there is a haemorrhage?
CHP will decrease
This decreases NFP
Reabsorption is increased
What happens to filtration when there is dehydration?
BCOP increases
This decreases NFP
Reabsorption increases
What happens to filtration when there is tissue damage?
ICOP increases
This increases NFP
Filtration increases
What is the difference in pulmonary circulation and capillary exchange?
In lungs arterioles constrict in regions of low O2 to move blood flow to O2 rich areas. O2 absorption increases
In other organs vessels dilate when O2 falls which enhances O2 delivery
What is the difference in coronary circulation and capillary exchange?
Adrenaline promotes coronary artery vasodilation
Coronary flow increases when there is vasoconstriction somewhere else
CF is restricted during systole
CF is high during diastole
What is different in cerebral circulation and capillary exchange?
In emergencies theres vasodilation of cerebral vessels
There is vasoconstriction in the periphery
Neurons have bad metabolic reserves
There are 4 arteries to support the brain
