Ventilation and Diffusion

Question 1

What does Dalton’s Law state?

Answer 1

Total pressure of a mixture of gases is the sum of their individual partial pressure

Question 2

Describe what will change partial pressure?

Answer 2

If atmospheric pressure changes or if the preportion of gas changed.

Question 3

How do you calculate the partial pressure of a gas?

Answer 3

Percentage of gas you have X atmospheric pressure

Question 4

What does Henry’s law state?

Answer 4

The concentration of oxygen dissolved in water is proportional to the partial pressure (PO2) in the gas phase.

Question 5

How do you calculate the concentration of oxygen dissolved?

Answer 5

s x PO2 (s = solubility of O2 in water.

Question 6

What is the partial pressure of Nitrogen in air and then in alveoli?

Answer 6

Air - 593.48mmHg ( 79 pKa)

Alveoli - 556.78mmHg ( 74 pKa)

Question 7

Define partial pressure

Answer 7

the pressure that would be exerted by one of the gases in a mixture if it occupied the same volume on its own at the same temperature.

Question 8

What is the partial pressure of oxygen in air and in the alveoli

Answer 8

Air - 159.22mmHg (21 pKa)

Alveoli - 149.37mmHg (20 pKa)

Question 9

What is the partial pressure of carbon dioxide in air and in the alveoli

Answer 9

Air = 0.23mmHg (0.03pKa)

Alveoli = 6.63mmHg (0.88pKa)

Question 10

Before oxygen can pass the barrier it must do what?

Answer 10

• Dissolve in aqueous layer, diffuse across the membranes and then entre the blood.

Question 11

The rate of diffusion is proportional to what?

Answer 11

• Partial pressure difference,
• Surface area,
• Solubility,
• Molecular mass
• Inversely proportional to tissue thickness

Question 12

What allows for oxygen to exchange between alveolar and blood easily

Answer 12

• Lungs have large surface area,
• Large number of alveoli,
• Thickness is small
• Large concentration gradient

Question 13

What is the oxygen pressure for arterial and venous alveolar blood

Answer 13

Arterial - 100

Venous - 40

Question 14

What is the most soluble gas

Answer 14

CO2 is the most soluble, then oxygen and nitrogen is barely soluble at atmospheric pressure

Question 15

Describe the process of carbon dioxide moving from blood to alveolar air

Answer 15

Carbon dioxide is dissolved easily in blood which means it can easily diffuse across the membrane along the small concentration gradient. However due to the greater solubility diffusion is 20x more rapid than O2

Question 16

What are some diffusion limitations of gas exchange?

Answer 16

• Oedema, as the thickness of the barrier increases so gas exchange is reduced.
• Emphysema, surface area is reduced due to tissue breakdown so gas exchanged is reduced.
• Pulmonary fibrosis, Thickness is increased due deposition of fibrotic tissue.
• Mucus, inflammation of airway, tumours and reduced gas entry (gas exchange reduced)

Question 17

Describe what occurs with reduced altitude

Answer 17

Atmospheric pressure is reduced and hence PO2 is reduced

Question 18

What is the acute response to physiological adaptation to altitude

Answer 18

Hypoxia sensed by chemoreceptors. Ventilatory drive increases initially but is then blunted by chemoreceptors responding to the decreased PaCO2 due to initial increased ventilation. CO increases.

Question 19

What is the adaptive response to physiological adaptation to altitude?

Answer 19

Central chemoreceptors adapt so ventilation rate continues to increase. PaCO2 drops leads to respiratory alkalosis and the kidneys compensate by reducing acid secretion so blood pH normalises. The alkalosis stimulates release 2,3 DPG

Question 20

What are the changes in acclimation response to physiological adaptation to altitude

Answer 20

Blood, Vasculature and cardiopulmonary system

Question 21

What changes in blood in response to adaptations to altitude

Answer 21

Erythropoietin release stimulated and Hb conc increases

Question 22

What changes in vasculature in response to adaptations to altitude

Answer 22

Hypoxia stimulates angiogenesis and capillary density increases throughout body

Question 23

What changes in cardiopulmonary system in response to adaptations to altitude

Answer 23

• Vascular and ventricular remodelling,
• Smooth muscle growth increases vascular wall thickness,
• Right ventricular hypertrophies.

Question 24

How does diving effect atmospheric pressure?

Answer 24

It increases it by 1 atmosphere (760mmHg) every 10m depth

Question 25

Describe the effects of depth

Answer 25

• Increase in partial pressure and nitrogen and oxygen dissolve into blood at lethal excess.
• Volume decreases.

Question 26

Describe the effects of gas toxicity

Answer 26

• Nitrogen narcosis
• Oxygen poisoning
• At high pressure oxygen dissolves in blood
• Heilox - nitrogen is replaced by helium and percentage of oxygen tailored to reduce harm.
• Helium is less readily dissolves in body tissues and less narcotic