WEEK XIV (Gas exchange & Gas transport) Flashcards
Why is the partial pressure of gas in atmospheric air directly proportional to its % in the mixture?
Since the % of a gas in the mixture determines the pressure it contributes since each gas molecule exerts the same amount of pressure
How does Alveolar air differ from inspired atmospheric air?
- Saturation with water vapour (reduces partial pressure of other gases)
- Mixing with old air in the lungs (makes alveolar PO2 lower than atmospheric PO2)
How does ventilation maintain appropriate gradients in the alveoli?
By constantly replenishing alveolar O2 and removing CO2
What factors does Fick’s law state influences diffusion?
- Partial pressure gradient
- Surface area
- Thickness of the membrane
- Diffusion constant of the gas
How is Surface area for gas exchange increased during exercise?
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
What conditions decreases the lung surface area?
- Emphysema (loss of many alveolar walls)
- Lung cancer treatment (lung tissue surgically removes)
What conditions lead to increased thickness?
- 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
Why is the diffusion constant for CO2 20 times higher than that of O2?
because CO2 is more soluble in body tissues
Oxygen in the blood exists in which forms?
- Physically dissolved
- Chemically bound to haemoglobin (Primary mechanism)
What happens when PO2 increases and decreases?
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
How does the plateau portion of the O2-Hb curve ensure a good margin of safety in the oxygen-carrying capacity of the blood?
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
What can happen if PO2 falls below threshold (60 mmHg)?
Compromised oxygen delivery to tissues -> Hypoxia -> Potential adverse health effects
Haemoglobin has a much higher affinity for CO than for O2 (TRUE/FALSE)
TRUE
What is the Bohr effect?
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
What causes the oxygen-dissociation curve to shift to the right, decrease haemoglobin’s affinity to O2?
- CO2 and H+
- Increase in temperature
- 2,3 BPG
How is CO2 transported in the blood?
- Physically dissolved
- Bound to haemoglobin
- As Bicarbonate (HCO3-)
Describe what happens in the Chloride shift
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
Describe the Haldane effect
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]
What is Hypoxia?
Insufficient O2 at the cell level characterised by low arterial PO2 and inadequate Hb saturation
What are the different types of Hypoxia?
- 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)
What is Hyperoxia?
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]
What is Hypercapnia?
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]
What is Hypocapnia?
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]
What is Hyperpnea?
Increased ventilation matching an increased metabolic demand
