SEHS - MOCK EXAM FLASHCARDS

What is partial pressure of a gas?

The pressure an individual gas in a mixture would exert if it alone occupied the whole volume. Dalton's law: total pressure = sum of the partial pressures.

Why does partial pressure of oxygen fall at altitude even though air is still 21% oxygen?

Barometric pressure decreases with altitude, so PO2= 0.21 × barometric pressure falls. Smaller pressure gradient = less oxygen diffusing into the blood.

What is hypoxia, and what specific form occurs at altitude?

Hypoxia = inadequate oxygen delivery for normal function. At altitude it is hypobaric hypoxia, caused by reduced partial pressure of oxygen in inspired air.

What happens to arterial oxygen saturation at altitude, and why does it matter?

It falls (e.g. from about 97% to 85-90% at 4000 m), because the diffusion gradient between alveoli, blood and tissues is reduced. This is the trigger for all acute responses.

Which receptors detect low arterial PO2 at altitude, and where are they located?

Peripheral chemoreceptors: carotid bodies (in the neck) and aortic bodies (in the aortic arch). They signal the medullary respiratory centre.

What is the short-term respiratory response to altitude, and what mechanism drives it?

Hyperventilation (increased ventilation), driven by peripheral chemoreceptors detecting low arterial PO2PO2​​, to maintain oxygen uptake.

Why does hyperventilation initially limit its own drive at altitude?

It blows off CO₂, so blood CO₂ falls and pH rises (respiratory alkalosis), which reduces the central chemoreceptor drive to breathe.

How do the kidneys compensate for altitude-induced respiratory alkalosis?

They excrete bicarbonate ions, restoring blood pH. This allows ventilation to rise further - ventilatory acclimatization (long-term respiratory adaptation).

What is the short-term cardiovascular response to altitude during submaximal exercise, and why?

Heart rate and cardiac output increase, to compensate for reduced arterial oxygen content and maintain oxygen delivery to working muscles

What happens to plasma volume at altitude (short-term), and what results from it?

Plasma volume decreases (altitude diuresis), which concentrates haemoglobin and increases its concentration per litre of blood.

What happens to stroke volume and submaximal heart rate at altitude (short-term)?

Stroke volume falls, so submaximal heart rate rises further to maintain cardiac output.

What is the pulmonary vascular response to altitude hypoxia?

Pulmonary blood vessels constrict (hypoxic pulmonary vasoconstriction), raising pulmonary arterial pressure and increasing the workload of the right side of the heart.

Which hormone drives the long-term cardiovascular adaptation to altitude, and what does it do?

Erythropoietin (EPO), released by the kidneys. It stimulates red blood cell production, increasing haemoglobin concentration and restoring arterial oxygen content.

What long-term blood and muscular adaptations improve oxygen delivery at the tissues?

Increased capillary density, myoglobin concentration and mitochondrial content; 2,3-DPG shifts the oxyhaemoglobin dissociation curve so oxygen is released more readily.

After acclimatization, what happens to heart rate and cardiac output at rest and submaximal intensity?

They gradually return toward sea-level values, because haemoglobin concentration (arterial oxygen content) has recovered.

Which performances remain impaired at altitude even after acclimatization?

Maximal oxygen uptake and prolonged aerobic events. Short anaerobic events are less affected because oxygen delivery matters less - so the impact depends on the nature of the activity.

What command-term structure earns full marks on "Explain" for this question?

A detailed account including reasons or causes: link each response to its trigger and effect, e.g. low PO2PO2​​ → chemoreceptors → increased ventilation. Roughly 10 marking points for 10 marks.

What should every answer to this question open with, before any responses?

The stimulus: lower barometric pressure → lower partial pressure of oxygen → reduced diffusion gradient → reduced arterial oxygen content (hypobaric hypoxia).

What tools should you reference in the exam for this topic?

The heart diagram in the SEHS data booklet, and a calculator if a PO2PO2​​ calculation appears (PO2 = 0.21 × barometric pressure).

What causes acute mountain sickness, and at what altitudes is it a concern?

Rapid ascent without acclimatization - hypoxia plus fluid imbalances (headache, nausea, fatigue). A risk above roughly 2500-3000 m; extreme altitude risks pulmonary and cerebral oedema.