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Ps Respiratory System > L16 Respiratory Physiology > Flashcards

L16 Respiratory Physiology Flashcards

1
Q

What factors affect the diffusion of gas?

A

Movement of gas is directly proportional to:
1) pressure gradient of the gas
2) solubility of the gas in liquid
3) temperature

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2
Q

What does Dalton’s law state about total pressure (P) ?

A

The total pressure is exerted by a mixture of gases is equal to the sum of the pressures exerted by the individual gases

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3
Q

How is the pressure exerted by an individual gas determined?

A

By its relative abundance in the mixture and is independent of the molecular size or mass of the gas

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4
Q

What is the equation for the partial pressure of a gas?

A

atmospheric pressure X % of gas

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5
Q

What does the partial pressure of gas in air depend on?

A

Depends on the water vapour present

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6
Q

What is Henry’s law?

A

About the solubility of gas
- at constant temperature, the amount of gas that dissolves in a liquid depends on the solubility of the gas in the liquid and the partial pressure of the gas

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7
Q

Explain the diffusion of gases at alveolar surface

A

Movement of gas is directly proportional to:
Pressure gradient of gas
- Po2 alveolar air > Po2 blood
- Pco2 alveolar air < Pco2 blood

Solubility of the gas in liquid
- both co2 and o2 are soluble
- co2 solubility > o2 solubility

Temperature
- alveolar air is at core, body temperature

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8
Q

What are the characteristics of pulmonary circulation?

A
  • low pressure system
  • high flow
  • parallel to the lower respiratory tract
  • close association of capillaries and alveoli
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9
Q

What is the route for pulmonary circulation?

A

Right ventricle -> pulmonary trunk -> pulmonary arteries -> lungs -> pulmonary veins -> left atrium

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10
Q

What cells does the alveolar consist of?

A

1) Type I alveolar cell - 90% of alveolar cells, very thin, gas exchange

2) Type II alveolar cell - smaller, thicker, produce surfactant

3) Macrophages - protect alveolar structures from non-filtered, small particles

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11
Q

How is the diffusion distance reduced in alveoli?

A

The basal laminae of Type I alveolar cells and endothelial cells of capillary are fused

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12
Q

What is the equation for Fick’s law of diffusion?

A

For gas diffusion across the respiratory membrane

Flux = (P x change in C) / X

P = permeability of barrier x surface area
C = concentration gradient across the membrane barrier
X = distance to diffuse (minimised by fused basement membranes)

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13
Q

What is gas exchange in the alveoli driven by and give examples

A

By concentration gradients
Po2 alveoli > blood - o2 movement into capillaries
Pco2 blood > alveoli - co2 movement into alveoli

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14
Q

What effect does the change in ventilation ave on Po2 and Pco2?

A

They are inversely related during changes in ventilation
- as alveolar ventilation increases, alveolar Po2 increases and alveolar Pco2 decreases

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15
Q

What does hyperventilation result in?

A

Increased alveolar Po2 and decreased alveolar Pco2

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16
Q

What does hypoventilation result in?

A

Decreases alveolar Po2 and increased alveolar Pco2 and hypoxemia

17
Q

Define hyperbaric

A

Higher than normal partial pressure of oxygen

18
Q

What is hyperbaric oxygen therapy?

A

A person is placed in a chamber and exposed to higher than normal Po2 which leads to increased alveolar Po2 levels and o2 exchange
-> dissolved in plasma and delivered in tissues

19
Q

What is hyperbaric oxygen therapy used to treat?

A

Conditions that benefit from increased oxygen delivery such as:
- severe blood loss
- crush injuries
- anaemia
- chronic wounds

Used for decompression sickness

20
Q

How does hyperbaric oxygen therapy work to treat decompression sickness?

A
  • this sickness is caused by dissolved gases in the blood coming out of the solution and forming bubbles in the bloodstream
  • the therapy forces gases back into the solution which eliminates bubbles
21
Q

What pathological changes that adversely affect gas exchange cause hypoxia?

A

SURFACE AREA
- decrease in amount of aleveoar surface area e.g. emphysema

DIFFUSION BARRIER PERMEABILITY

  • increase in thickness of alveolar membrane e.g. fibrotic lung disease
    DIFFUSION DISTANCE
  • increase in diffusion distance between alveoli and blood e.g. pulmonary edema
22
Q

What causes emphysema?

A

The alveoli are destructed which means less surface area for gas exchange
- alveoli Po2 is normal/low
- po2 in the blood is low

23
Q

What causes fibrotic lung disease?

A

Gas exchange is slowed due to thickened alveolar membrane
Loss of lung compliance may decrease alveolar ventilation
- Po2 in alveolar is normal/low
- Po2 in blood is low

24
Q

What causes pulmonary edema?

A

Fluid in the interstitial space increases diffusion distance
The arterial Pco2 may be normal due to higher co2 solubility in water
- Po2 in alveoli is normal
- Po2 in blood is low

25
Q

What causes asthma?

A

Increased airway resistance decreases alveolar ventilation so the bronchioles are restricted
- Po2 in alveoli is low
- Po2 in blood is low

26
Q

What is hypoxia pulmonary vasoconstriction?

A
  • it redirects blood flow to ventilated alveoli
  • improves gas exchange
  • contrast with systemic circulation
27
Q

What is bronchiole diameter mediated by?

A

By CO2 levels in exhaled air

28
Q

What does the total oxygen content of arterial blood depend on ?

A

Depends on the amount of oxygen dissolved in plasma and bound to haemoglobin

29
Q

Why is ventilation-perfusion matching beneficial?

A

Perfusion of blood past alveoli is matched to alveolar ventilation which maximises gas exchange

30
Q

How is ventilation-perfusion mismatch caused?

A

Caused by under-ventilated alveoli

31
Q

What are the consequences of ventilation-perfusion mismatching?

A
  • if ventilation decreases in a group of alveoli, Pco2 increases and Po2 decreases
  • blood flowing past those alveoli does not get oxygenation
32
Q

What is the mechanism which keeps ventilation and perfusion matched?

A

Decreased tissue Po2 around underventilated alveoli which constricts their arterioes
-> diverts blood to better ventilated alveoli

33
Q

What does the regional variation of inspired air depend on?

A
  • posture
  • rate of inspiration
  • amount of air inspired
34
Q

Where in the lung is lung perfusion greater than alveolar ventilation?

A

At the base of the lungs

35
Q

Where in the lungs is the lung perfusion less than alveolar ventilation?

A

At the apex of the lungs

36
Q

What happens when lung perfusion and alveolar ventilation are mismatched?

A

Blood is shunted from the right to the left side of the heart without adequate oxygenation

Ps Respiratory System (3 decks)

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