L17- diffusion and convection in CVRS

Question 1

how does the gravity influence the hydrostatic pressure

Answer 1

increases the pressure so in this case, its the arterial pressure

Question 2

how does the influence of gravity affect the flow of blood and air

Answer 2

the flow would be faster the closer to the gravity

Question 3

how to calculate hydrostatic pressure using gravity

Answer 3

Pressure = density x g x height

Question 4

how is the hydrostatic pressure or arterial blood determined when lying down

Answer 4

• 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

Question 5

what happens to the hydrostatic pressure from the point of the head

Answer 5

decreases due to less effect of gravity

Question 6

what doesnt change even the pressure is affected by the gravity

Answer 6

the driving pressure (Pa - Pv)

Question 7

below the level of the heart, what will happen to capillary hydrostatic pressure (Pc)

Answer 7

increases

Question 8

explain the effect of gravity on the capillaries filtration

Answer 8

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

Question 9

what is convection

Answer 9

bulk flow of fluid or gas from an area with higher pressure to lower pressure like in airways and blood vessels

Question 10

what part of the RS relies on transport of gas by convection

Answer 10

• trachea because it has small CSA so there’s a high velocity and relies on pressure gradient

Question 11

what part of the RS relies on the transport of gas by diffusion

Answer 11

respiratory bronchioles because it has large CSA so low velocity and relies on partial pressure gradient (conc gradient)

Question 12

what part of the CVSrelies on transport of blood by convection

Answer 12

aorta - small CSA and high velocity

Question 13

what part of the CVS relies on the transport of gas by diffusion

Answer 13

capillaries - high CSA and low velocity

Question 14

eqn for law of diffusion

Answer 14

Vdot = SA x (1/thickness of membrane) x diffusibility x partial pressure graident (P1-P2)

Question 15

factors affecting diffusion

Answer 15

SA

• thickness of diffusion barrier
• diffusibility of the gases depending on Mw and solubility
• partial pressure graident of the metabolic gases

Question 16

components making up diffusion barrier

Answer 16

alveolar epithelium
basal laminar
capillary endothelium

Question 17

how does the O2 equilibrate

Answer 17

enters the venous blood at 5kPa

-PO2 in alveoli is 13kPa so diffusion takes place so PcapO2 is now 13kPa

Question 18

what is diffusion reserve

Answer 18

capacity of O2 once it reached EQB

-around 70%

Question 19

what happens to the diffusion reserve durinf exercise

Answer 19

-decreases but still reached at the end

Question 20

what happens to diffusion reserve when the barrier is thickened at rest and during exercise

Answer 20

rest- reserve decreased but full EQB of O 2 reached

exercise - full EqB not reached

Question 21

what happens to diffusion reserve when the partial pressure of O2 is decreased at rest and during exercise

Answer 21

rest - decreased reserve but full EQB reached at lower arterial partial pressure

Question 22

how is diffusion distance minimised

Answer 22

• large no of capillaries
• max SA by capillaries
• high diffusibility due to channels and transporters
• conc gradient maintained by enough blood flow