WEEK XIV (Gas exchange & Gas transport)

Question 1

Why is the partial pressure of gas in atmospheric air directly proportional to its % in the mixture?

Answer 1

Since the % of a gas in the mixture determines the pressure it contributes since each gas molecule exerts the same amount of pressure

Question 2

How does Alveolar air differ from inspired atmospheric air?

Answer 2

• Saturation with water vapour (reduces partial pressure of other gases)
• Mixing with old air in the lungs (makes alveolar PO2 lower than atmospheric PO2)

Question 3

How does ventilation maintain appropriate gradients in the alveoli?

Answer 3

By constantly replenishing alveolar O2 and removing CO2

Question 4

What factors does Fick’s law state influences diffusion?

Answer 4

• Partial pressure gradient
• Surface area
• Thickness of the membrane
• Diffusion constant of the gas

Question 5

How is Surface area for gas exchange increased during exercise?

Answer 5

Increased CARDIAC OUTPUT raises pulmonary blood pressure forcing previously closed pulmonary capillaries open -> Increases surface area available for exchange -> STRETCHING OF ALVEOLAR WALLS due to larger tidal volumes -> Increases surface area + decreases wall thickness

Question 6

What conditions decreases the lung surface area?

Answer 6

• Emphysema (loss of many alveolar walls)
• Lung cancer treatment (lung tissue surgically removes)

Question 7

What conditions lead to increased thickness?

Answer 7

• PULMONARY OEDEMA = excess accumulation of interstitial fluid between alveoli and pulmonary capillaries
• PULMONARY FIBROSIS = Replacement of delicate lung tissue with thick, fibrous tissue in response to chronic irritants
• PNEUMONIA = Inflammatory fluid accumulation within or around alveoli

Question 8

Why is the diffusion constant for CO2 20 times higher than that of O2?

Answer 8

because CO2 is more soluble in body tissues

Question 9

Oxygen in the blood exists in which forms?

Answer 9

• Physically dissolved
• Chemically bound to haemoglobin (Primary mechanism)

Question 10

What happens when PO2 increases and decreases?

Answer 10

PO2 increases -> Reaction is driven to the right -> Increased formation of OXYHAEMOGLOBIN

PO2 decreases -> Reaction is driven to the left -> Oxygen is released from haemoglobin

Question 11

How does the plateau portion of the O2-Hb curve ensure a good margin of safety in the oxygen-carrying capacity of the blood?

Answer 11

It allows the blood to efficiently transport oxygen even when the PO2 fluctuates, preventing significant changes in oxygen content and ensures adequate oxygen delivery to tissues

Question 12

What can happen if PO2 falls below threshold (60 mmHg)?

Answer 12

Compromised oxygen delivery to tissues -> Hypoxia -> Potential adverse health effects

Question 13

Haemoglobin has a much higher affinity for CO than for O2 (TRUE/FALSE)

Answer 13

TRUE

Question 14

What is the Bohr effect?

Answer 14

The influence of CO2 and H+ on the release of O2 from haemoglobin -> Causes a change in the molecular structure of haemoglobin which reduces its affinity for oxygen

Question 15

What causes the oxygen-dissociation curve to shift to the right, decrease haemoglobin’s affinity to O2?

Answer 15

• CO2 and H+
• Increase in temperature
• 2,3 BPG

Question 16

How is CO2 transported in the blood?

Answer 16

• Physically dissolved
• Bound to haemoglobin
• As Bicarbonate (HCO3-)

Question 17

Describe what happens in the Chloride shift

Answer 17

HCO3- diffuses out of the erythrocytes into the plasma -> HCO3- creates an electrical gradient leading to chloride ions from the plasma to diffuse into red blood cells to restore ELECTRIC NEUTRALITY

Question 18

Describe the Haldane effect

Answer 18

Haemoglobin binds with most of the H+ formed within erythrocytes -> Reduced haemoglobin has a greater affinity for H+ than oxygenated Hb -> Unloading of O2 from Hb facilitates the pickup of CO2 and CO2-generated H+ by Hb

[allows reduced Hb to pick up CO2 and H+ otw to lungs]

Question 19

What is Hypoxia?

Answer 19

Insufficient O2 at the cell level characterised by low arterial PO2 and inadequate Hb saturation

Question 20

What are the different types of Hypoxia?

Answer 20

• Hypoxic Hypoxia = Low arterial PO2 due to respiratory malfunction or exposure to high altitude or suffocating environments
• Anaemic Hypoxia = Reduced O2-carrying capacity of the blood due to a decrease in red blood cells, inadequate Hb or CO poisoning
• Circulatory Hypoxia = Insufficient oxygenated blood delivered to tissues caused by local vascular blockages, congestive heart failure or circulatory shock
• Histotoxic Hypoxia = Normal O2 delivery to tissues but cells cannot use available O2 (e.g cyanide poisoning)

Question 21

What is Hyperoxia?

Answer 21

Above-normal arterial PO2, typically not occurring with atmospheric air at sea level but can result from breathing supplemental O2

[too much oxygen can be toxic]

Question 22

What is Hypercapnia?

Answer 22

Excess CO2 in arterial blood caused by hypoventilation

[occurs in most lung diseases where both O2 and CO2 exchange between lungs and atmosphere are affected]

Question 23

What is Hypocapnia?

Answer 23

Below-normal arterial PCO2 levels caused by hyperventilation where CO2 is blown off more rapidly than is produced in the tissues

[can be triggered by anxiety states, fever, aspirin poisoning]

Question 24

What is Hyperpnea?

Answer 24

Increased ventilation matching an increased metabolic demand