Respiratory System - C02 Carriage Flashcards
What is the role of carbon dioxide in acid/base balance?
Production of carbonic acid catalysed by carbonic anhydrase, H2O + CO2 = H2CO3
Carbonic acid dissociates into bicarbonate ions (HCO3-) and hydrogen ions (H+):
Release of H+ ions contributes to the acidity of the blood
Through gas exchange in the lungs and regulation of breathing rate by the respiratory system, CO2 is removed from the body, helping to maintain the pH of the blood within a narrow physiological range
Discuss the partial pressure of oxygen.
160 mmHg at sea level
As air is inspired into the lungs, oxygen enters the alveoli and equilibrates with the partial pressure of oxygen in the alveolar air, which is around 100 mmHg
Oxygen diffuses across the alveolar-capillary membrane into the pulmonary capillaries, where it binds to haemoglobin
In arterial blood, the partial pressure of oxygen (PaO2) is typically around 80-100 mmHg
Oxygen is then transported by haemoglobin to tissues where its partial pressure is lower, around 40 mmHg
This partial pressure gradient facilitates oxygen release from haemoglobin and diffusion into tissues for cellular respiration
Discuss the partial pressure of carbon dioxide.
In venous blood returning to the lungs, the partial pressure of carbon dioxide is 45 mmHg
In the alveoli CO2 is expired reducing the partial pressure of carbon dioxide in the alveolar air to around 40 mmHg
What is Dalton’s law and Henry’s law?
Dalton’s Law states that the total pressure exerted by the mixture of inert (non-reactive) gases is equal to the sum of the partial pressures of individual gases in a volume of air
Henry’s Law states that the number of molecules dissolving in a liquid is directly proportional to the partial pressure of the gas
Discuss the oxygen dissociation curve and its key features.
The oxygen dissociation curve illustrates the relationship between the partial pressure of oxygen (PO2) and the saturation of haemoglobin with oxygen (SO2)
* Sigmoidal shape - at low partial pressures of oxygen, haemoglobin has a lower affinity for oxygen, resulting in a slower initial rate of oxygen binding, however as the partial pressure of oxygen increases, haemoglobin’s affinity for oxygen increases, leading to rapid saturation.
* Plateau region - haemoglobin nearly saturated with oxygen, ensures a small change in oxygen partial pressure has a significant effect on oxygen content in blood
* Steep slope - allows for efficient unloading of oxygen in tissues, small decreases in PO2 result in significant decreases in haemoglobin saturation, facilitating oxygen release to tissues
* Factors affecting the curve - Bohr effect, temperature, CO2 concentration
Discuss the carbon dioxide dissociation curve and its key features.
Illustrates the relationship between the partial pressure of carbon dioxide (PCO2) and the amount of CO2 dissolved in plasma or bound to haemoglobin
Linear relationship - allows for easy prediction of the amount of CO2 carried in the blood at different partial pressures
Solubility of CO2 - CO2 highly soluble in plasma, majority of carbon dioxide is transported in the form of bicarbonate ions (HCO3-)
Role of haemoglobin - haemoglobin can bind to CO2 facilitating its removal from the blood
Bohr effect - lower pH enhances the release of oxygen from haemoglobin and facilitates the binding of carbon dioxide.
What is foetal blood’s key features ?
Foetal haemoglobin (HbF) has a higher affinity for oxygen than adult haemoglobin (HbA) which allows it to extract oxygen from maternal blood in placenta efficiently
Oxygen diffuses from the maternal blood to the foetal blood across the placental membrane, facilitated by the high oxygen affinity of foetal haemoglobin
What is an anaemic blood’s key features?
Reduced haemoglobin content therefore reducing the blood’s oxygen carrying capacity potentially leading to hypoxia
The oxygen dissociation curve, which illustrates the relationship between oxygen saturation and partial pressure of oxygen, may shift to the right in anaemia
This means that haemoglobin has lower affinity for oxygen, making it easier for oxygen to dissociate from haemoglobin and be released to tissues
This adaptation helps to compensate for reduced oxygen carrying capacity.
What is haemoglobin ?
Haemoglobin (Hb) is a protein found in the red blood cells that carries oxygen in your body
Hb + O2 ⬄ HbO2
Oxygen capacity - max amount of oxygen that can combine with haemoglobin
Oxygen saturation =
Volume of oxygen bound to Hb (mL/L)
——— x100
Total oxygen capacity (mL/L)
What are the key features of oxygen carriage ?
Low solubility so transported by haemoglobin.
Transportation - 98% haemoglobin, 2% plasma
Regulation - O2 dissociation curve and factors affecting haemoglobin’s affinity for oxygen
Binding affinity - Hb has high affinity for oxygen, binding is cooperative
What are the key features of carbon dioxide carriage?
Solubility - high
Transportation - Plasma, bicarbonate ions
Regulation - pH changes, enzyme activity and carbonic anhydrase reaction
Binding affinity - Haemoglobin exhibits low affinity for CO2, binding is non-cooperative
