RP - Gas Transport: Carbon Dioxide Transport by Blood Flashcards
Describe the bicarbonate buffer system:
Primary buffer system in blood
CO2 + H20 ↔ H2CO3 ↔ H+ + HC03-
Prevents large pH changes by shifting equilibrium between CO₂, carbonic acid (H₂CO₃), and bicarbonate
Lungs remove CO₂ to regulate acidity, while kidneys excrete H⁺ and reabsorb HCO₃⁻
Haemoglobin buffers the H+ so that an acidic environement doesn’t form, H+ reaches lung and is expired
What is the chlorine shift in the bicarbonate buffering system ?
Chloride shift is the exchange of bicarbonate and chloride ions across the red blood cell membrane
It maintains electrical neutrality during CO₂ transport
Cl⁻ ions enter RBC from plasma to compensate for negative charge.
* Reverse occurs in lungs, bicarbonate re-enters RBCs and is converted back to CO₂.
* Chloride shift maintains ionic and pH stability during CO₂ transport.
* Essential for maintaining CO₂ carriage as bicarbonate.
Describe the defence of H+ concentration:
Buffer systems - immediate response to pH changes, primarily through the bicarbonate buffer system
Respiratroy regulation:
- The lungs adjust ventilation to regulate CO₂ levels, influencing blood pH
- Increased ventilation removes CO₂, reducing H⁺ concentration and raising pH
Renal regulation:
- The kidneys excrete H⁺ and reabsorb HCO₃⁻ to maintain acid-base balance
- This process is slower but provides long-term pH regulation
Compare oxygen and carbon dioxide transport:
Carbon dioxide:
- high solubility in plasma
- main transport form as bicarbonate ions
- binding to haemoglobin forms carbaminohaemoglobin
- pH influences CO₂ transport and buffering
- transport mechanism via bicarbonate, plasma and Hb
Oxygen:
- low solubility in plasma
- main transport form by Hb
- binding to Hb = oxyhemoglobin
- pH influences haemoglobin’s O₂ affinity
- main transport mechanism is Hb
Describe the Fick principle for carbon dioxide:
The Fick principle relates the rate of CO₂ production to blood flow and the arteriovenous CO₂ content difference
Carbon dioxide output = arterio-venous difference × cardiac output
What is the Haldane effect ?
The Haldane effect describes how deoxygenated haemoglobin has a higher affinity for CO₂, facilitating CO₂ uptake in tissues
Mechanism:
- in tissues haemoglobin releases O₂ and binds CO₂ more readily
- In the lungs, oxygenation of haemoglobin reduces its affinity for CO₂, promoting CO₂ release
What is the Bohr effect ?
Defined as the reduction of haemoglobin’s oxygen affinity due to increased CO₂ and lower pH
Mechanism:
- in tissues CO₂ stabilises the tense state of haemoglobin, favouring O₂ unloading
- in the lungs CO₂ shifts haemoglobin to an resting state, increasing O₂ affinity for oxygen loading
CO₂ shifts haemoglobin to an R state, increasing O₂ affinity for oxygen loading
Quantified by the Bohr coefficient, reflecting the change in hemoglobin’s oxygen saturation with pH or CO₂ changes
Describe the carriage of carbon dioxide by blood:
Dissolved in blood - around 5%, more soluble than oxygen s higher % dissolves
Haemoglobin - binds at N-terminus of chain and causes the Bohr effect by reducing Hb affinity for oxygen causing right shift, around 10%
Bicarbonate - carbon dioxide + water > bicarbonate < H+ and HCO3-, facilitated by carbonic anhydrase
What is acidosis and alkalosis ?
Acidosis:
- where blood pH falls below 7.35
- respiratory acidosis caused by caused by hypoventilation leading to CO₂ retention
- metabolic acidosis caused by excessive lactate production and bicarbonate loss during intense exercise
Alkalosis:
- blood pH increases above 7.35
- respiratory alkalosis caused by hyperventilation causing CO₂ loss
- metabolic alkalosis caused by excessive bicarbonate or loss of acids
Describe the pulmonary circulation of carbon dioxide:
Transport: CO₂ is carried from tissues to lungs via venous blood
Exchange: In pulmonary capillaries, CO₂ diffuses into alveoli to be exhaled
Mechanism:
- Bicarbonate in plasma re-enters red blood cells.
- Carbonic anhydrase converts bicarbonate back to CO₂
- CO₂ diffuses into alveoli for exhalation
