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Cardiorespiratory Science > Diffusion and Convection > Flashcards

Diffusion and Convection Flashcards

1
Q

What determines the fluid filtration in the glomerular capillaries?

A

Starling Forces

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2
Q

What maintains glomerular capillary hydrostatic pressure?

A

Arrangement of afferent and efferent arterioles maintain the glomerular capillary hydrostatic pressure which results in filtration along the length of the capillary

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3
Q

What are the main roles of the major vessels in the systemic circulation?

A

(Elastic) Arteries - Distribution of blood to tissues, Conversion of intermittent to continuous flow.

Arterioles - Resistance

Capillaries - Exchange

Venules & eins - Capacitance

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4
Q

What influence does gravity have on systemic circulation?

A

Gravity influences hydrostatic pressure. (P)

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5
Q

What is the equation to work out Hydrostatic pressure using gravity?

A

P = pgh

p= density g= gravity constant h= height

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6
Q

For every meter below the level of the heart (0mmHg) how much does the pressure change?

A

Pressure increases by 74mmHg for every meter below the level of the heart

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7
Q

Whilst lying down, why does gravity have no effect on pressure?

A

Since everything in the body (eg. head, heart limbs) are all at the same level.

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8
Q

What happens to pressure above the level of the heart?

A

The blood pressure decreases from about 95 mmHg to roughly 53mmHg

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9
Q

What happens to pressure below the level of the heart?

A

Blood pressure increases from 95mmHg to roughly 185mmHg

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10
Q

What is the pressure drop through the elastic arteries?

A

5mmHg

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11
Q

What are the driving pressures

A

Pressure between the arteriole and venous pressure remains the same as gravity has the same effect on venous pressure.

(Pa - Pv)

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12
Q

Why do we get fluid filtration across the entire length of the capillary down at the feet?

A

At the level of the feet:
MAP = 185mmHg

There is a pressure of 60mmHg used to overcome arteriolar resistance so blood enters capillaries with a pressure of Pc = 125mmHg.

Pc falls by 15mmHg to 110mmHg as blood passes through them to the venous end of the capillaries.

The interstitial oncotic pressure is constant at 25mmHg

Therefore we have a greater force favouring filtration along the entire length of the capillary since:

At the Arteriolar end net filtration is 125 - 25 =100mmHg favouring fluid filtration out of the capillary.
At venous end net filtration is 110 - 25 = 85mmHg favouring fluid filtration out of the capillary.

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13
Q

What are the types of flow in the cardiovascular and respiratory systems?

A 
Convection
Diffusion
Laminar
Turbulent
Filtration
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14
Q

What is convection (bulk flow)?

A

Bulk flow of fluid (blood or gas) from an area of high pressure to an area of low pressure

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15
Q

Where does convection occur in the cardiorespiratory systems?

A

Large airways (conducting zone) and blood vessels

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16
Q

What is diffusion?

A

Movement of molecules from an area of higher concentration to an area of lower concentration
eg. O2 and CO2 between alveoli and pulmonary capillaries.

17
Q

Where does diffusion occur in the cardiorespiratory system?

A

Respiratory zone between alveoli and pulmonary capillaries and between systemic capillaries to tissues

18
Q

Why does convection occur within the trachea (respiratory system)?

A

Small cross sectional area
Higher velocity
Relies on pressure gradient
Therefore transport via convection.

19
Q

Why does diffusion occur within the bronchioles (respiratory system)?

A 
Large cross sectional area
lower velocity
Relies on partial pressure gradient
alveoli appear in walls of bronchioles
Therefore transport via diffusion
20
Q

Why does convection occur within the Aorta (cardiovascular system)?

A

Small cross sectional area
Higher velocity
Relies on pressure gradient
therefore transport via convection

21
Q

Why does diffusion occur within the capillaries (cardiovascular system)?

A

Large cross sectional area
Low velocity
relies on concentration gradient or partial pressure gradient
Therefore transport via diffusion

22
Q

What factors determine diffusion?

A 
Surface area
Diffusibility
Partial pressure gradient
Thickness of diffusion barrier
Partial pressure gradient
23
Q

How is the respiratory system adapted for diffusion?

A

Large surface area packed into a relatively small volume

Thickness of diffusion barrier is very small (0.2 - 0.6 um)

24
Q

What is important about CO2 being more diffusible than O2?

A

CO2 is 20x more diffusible than O2 which can therefore lead to problems seen with O2

25
Q

What is crucial to drive diffusion?

A

Partial pressure gradient

26
Q

Where does equilibration occur within the pulmonary capillaries

A

About 1/3 rd of the way along the capillary (0.25s) sees a 13kPa of O2

27
Q

Why does the fact that it only takes up to 1/3rd of the capillary to reach equilibration important?

A

Allows us to have a large diffusion reserve.

28
Q

Why is having a large diffusion reserve important?

A

During exercise blood flow is increased and therefore having a large diffusion reserve, this allows us to still achieve full equilibration (but decreased diffusion reserve)

29
Q

What effect does a thickened diffusion barrier have on the diffusion reserve?

A

The thickened barrier means that the exchange of gases takes longer and therefore there is a decreased diffusion reserve. Hence equilibration is not achieved until much later along the capillaries.
This means that in exercise (or when there is increased blood flow) means that full equilibration is not achieved

30
Q

What happens when there is a decreased partial pressure gradient?

A

Eg. at altitude
Less O2 available and therefore lower inspired Pi O2 and therefore this leads to a decreased partial pressure gradient.
This means that diffusion takes longer and means that equilibration of O2 occurs but at a lower PO2.

31
Q

Why is having a higher number of capillaries in the cardiovascular system important?

A

Minimises the diffusion distance by having a large number of capillaries.
Higher metabolic tissues will have more capillaries.

32
Q

How is a concentration/partial pressure gradient maintained in the cardiovascular system?

A

Can be maintained by having adequate blood flow.

As long as new fresh blood flows between vessels and capillaries ensures that the concentration gradient is maintained

Cardiorespiratory Science (15 decks)

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