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Carbon monoxide poisoning causes tissue hypoxia. Which type of hypoxia does it produce?
- A Anaemic hypoxia due to reduced oxygen-carrying capacity of blood You picked ✓
- B Histotoxic hypoxia due to failure of cells to use oxygen You picked ✕
- C Hypoxaemic hypoxia due to low arterial oxygen partial pressure You picked ✕
- D Ischaemic hypoxia due to reduced blood flow to tissues You picked ✕
- E Stagnant hypoxia due to inadequate blood circulation You picked ✕
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Incorrect
The answer is A: Anaemic hypoxia due to reduced oxygen-carrying capacity of blood
Explanation
Why A is correct
See Hypoxic Cell Injury. Option A is correct. Hypoxia means too little oxygen reaching a tissue, and there are four types. In anaemic hypoxia the blood cannot carry enough oxygen, as in anaemia, where there is too little haemoglobin, and in carbon monoxide poisoning. Carbon monoxide is a colourless, odourless gas from incomplete burning of fuel, and it binds to haemoglobin with about 240 times the affinity of oxygen to form carboxyhaemoglobin. Oxygen therefore cannot bind, and the blood's oxygen-carrying capacity falls even though the lungs are working and the blood is flowing normally. Symptoms include headache, dizziness, nausea, tiredness and confusion. The other types are hypoxaemic (low arterial oxygen), ischaemic (too little blood flow) and histotoxic (cells cannot use oxygen, as in cyanide poisoning). A memory aid: carbon monoxide takes the seats on the oxygen bus.
- Type: carbon monoxide causes anaemic hypoxia, because the blood cannot carry enough oxygen.
- Mechanism: it binds haemoglobin with about 240 times the affinity of oxygen, forming carboxyhaemoglobin.
- Lungs and flow: the lungs work and blood flow is normal, but oxygen-carrying capacity falls.
Why the other options are incorrect
- B. Histotoxic hypoxia due to failure of cells to use oxygen: Histotoxic hypoxia means the cells cannot use the oxygen they receive, classically because cyanide blocks cell enzymes. In carbon monoxide poisoning the problem is oxygen carriage in the blood. Your answer
- C. Hypoxaemic hypoxia due to low arterial oxygen partial pressure: Hypoxaemic hypoxia comes from a low oxygen level in arterial blood, for example at altitude or in lung disease. In carbon monoxide poisoning the oxygen pressure in the lungs and blood is normal. Your answer
- D. Ischaemic hypoxia due to reduced blood flow to tissues: Ischaemic hypoxia comes from reduced blood flow, for example from a blocked artery or heart failure. In carbon monoxide poisoning the flow is usually preserved but the blood carries less oxygen. Your answer
- E. Stagnant hypoxia due to inadequate blood circulation: Stagnant hypoxia comes from slow or pooled blood flow, so tissues are starved because too little blood arrives. Carbon monoxide does not slow the flow of blood. Your answer
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1
Which morphological change is most characteristic of reversible cell injury?
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2
Which feature best distinguishes apoptosis from oncosis (necrotic cell death) at a cellular level?
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