L17- diffusion and convection in CVRS Flashcards
how does the gravity influence the hydrostatic pressure
increases the pressure so in this case, its the arterial pressure
how does the influence of gravity affect the flow of blood and air
the flow would be faster the closer to the gravity
how to calculate hydrostatic pressure using gravity
Pressure = density x g x height
how is the hydrostatic pressure or arterial blood determined when lying down
- not affected by gravity so the pressure is determined by the work of heart so around 93mmHg
- for the head and feet, the pressure slightly changes
what happens to the hydrostatic pressure from the point of the head
decreases due to less effect of gravity
what doesnt change even the pressure is affected by the gravity
the driving pressure (Pa - Pv)
below the level of the heart, what will happen to capillary hydrostatic pressure (Pc)
increases
explain the effect of gravity on the capillaries filtration
Pc is 125 mmHg as MAP is 185mmHg and 60mmHg of MAP is used to overcome the arteoilar resistance
- there’s net filtration at arterial and venous end out of the capillary
what is convection
bulk flow of fluid or gas from an area with higher pressure to lower pressure like in airways and blood vessels
what part of the RS relies on transport of gas by convection
- trachea because it has small CSA so there’s a high velocity and relies on pressure gradient
what part of the RS relies on the transport of gas by diffusion
respiratory bronchioles because it has large CSA so low velocity and relies on partial pressure gradient (conc gradient)
what part of the CVSrelies on transport of blood by convection
aorta - small CSA and high velocity
what part of the CVS relies on the transport of gas by diffusion
capillaries - high CSA and low velocity
eqn for law of diffusion
Vdot = SA x (1/thickness of membrane) x diffusibility x partial pressure graident (P1-P2)
factors affecting diffusion
SA
- thickness of diffusion barrier
- diffusibility of the gases depending on Mw and solubility
- partial pressure graident of the metabolic gases
components making up diffusion barrier
alveolar epithelium
basal laminar
capillary endothelium
how does the O2 equilibrate
enters the venous blood at 5kPa
-PO2 in alveoli is 13kPa so diffusion takes place so PcapO2 is now 13kPa
what is diffusion reserve
capacity of O2 once it reached EQB
-around 70%
what happens to the diffusion reserve durinf exercise
-decreases but still reached at the end
what happens to diffusion reserve when the barrier is thickened at rest and during exercise
rest- reserve decreased but full EQB of O 2 reached
exercise - full EqB not reached
what happens to diffusion reserve when the partial pressure of O2 is decreased at rest and during exercise
rest - decreased reserve but full EQB reached at lower arterial partial pressure
how is diffusion distance minimised
- large no of capillaries
- max SA by capillaries
- high diffusibility due to channels and transporters
- conc gradient maintained by enough blood flow
