PSC1002/L20 Adaptations to Altitude

Question 1

What is the partial pressure of a given gas determined by? (2)

Answer 1

Concentration of the gas within the mixture
Total pressure of the mixture

Question 2

Define Dalton’s Law.

Answer 2

Pressure exerted by a mixture of gases is equal to the sum of the partial pressures of each gas in the mixture

Question 3

What is the effect of altitude on gas exchange? (2)

Answer 3

Less O2 diffused into muscles
Less O2 diffused into blood

Question 4

What is the response of the body to a hypobaric environment? (3)

Answer 4

Increased rate and depth of ventilation
Chemoreceptors stimulated by low PO2
PO2 drives respiration due to hypoxia

Question 5

What is the role of the kidneys in high altitudes?

Answer 5

Maintaining pH homeostasis

Question 6

What are PaO2 and acid-base homeostasis in the context of chronic hypoxia? (2)

Answer 6

Hypoxic ventilatory response (HVR)
Renal excretion of bicarbonate (HCO3)

Question 7

What may be the result of an inadequate renal response to respiratory alkalosis via hypocapnia? (2)

Answer 7

Increased blood pH
Blunted HVR
Decreased oxygen saturation
Decreased cerebral blood flow

Question 8

Describe the hyperventilation cycle initiated by hypoxia. (5)

Answer 8

Hypoxia
Increased ventilation
Increased PO2
Decreased in PCO2 & increased pH
Decreased ventilation

Question 9

How does renal compensation to metabolic alkalosis work? (2)

Answer 9

Decrease in HCO3 in proximal tubule (excreted)
Decrease in H+ secretion by a-intercalated cells (acid retention)

Question 10

How does renal compensation improve ventilation? (4)

Answer 10

Reducing impact of respiratory induced alkalaemia
Decreased PCO2 detected by central chemoreceptors
Decreased respiration
Increased [H+] detected by peripheral chemoreceptors
Increased respiration

Question 11

What factors can increase oxygen affinity/left shift? (3)

Answer 11

Decreased temperature
Decreased 2-3 DPG
Decreased [H+]
CO

Question 12

What factors can decrease oxygen affinity/right shift? (3)

Answer 12

Increased temperature
Increased 2-3 DPG
Increased [H+]

Question 13

Describe the effect of increased 2-3 DPG.

Answer 13

Hb releases O2 at a higher PO2 making more O2 available to tissues during hypoxia

Question 14

Explain how short-term exposure to high altitude results in increased haematocrit. (3)

Answer 14

Increase in urination
Increase respiratory loss of H2O as Increased ventilation rate and dry air
Increased haematocrit

Question 15

Explain how long-term exposure to high altitude results in increased haematocrit. (4)

Answer 15

Increased haemopoiesis
Decrease O2 tension in kidney
Kidney releases erythropoietin
Increased haematocrit

Question 16

Describe how increased capillary numbers (angiogenesis) are beneficial to high altitude. (3)

Answer 16

Improved diffusion of oxygen by shortening diffusion distance
Increases SA for gas exchange both at alveoli and tissue
More mitochondria and cellular respiratory enzymes formed

Question 17

What does the incidence and severity of acute mountain sickness depend on? (3)

Answer 17

Rate of ascent
Altitude attained
Length of time at altitude
Degree of physical exertion
Individual’s physiological susceptibility

Question 18

What are the major symptoms of acute mountain sickness? (3)

Answer 18

Headache
Fatigue
Dizziness
Anorexia
Cyanosis

Question 19

What can acute mountain sickness progress into? (2)

Answer 19

HAPE - high altitude pulmonary edema
HACE - high altitude cerebral edema

Question 20

What occurs during HAPE? (5)

Answer 20

Alveolar hypoxia
Hypoxic pulmonary vasoconstriction
Increased capillary pressure
Increased hydrostatic pressure & damage to capillary wall
Oedema

Question 21

What are the symptoms of HACE? (3)

Answer 21

Severe headache
Confusion
Agitation/irritability
Nausea/emesis
Ataxia
Hallucinations
Seizures
Coma

Question 22

How does HACE occur? (3)

Answer 22

Cerebral hypoxia
Vasogenic oedema/cytotoxic oedema
Impaired brain function

Question 23

Define vasogenic oedema.

Answer 23

Movement of fluid into CNS across leaky blood brain barrier increases intracranial pressure

Question 24

Define cytotoxic oedema. (2)

Answer 24

Retention of fluid by cells in CNS
Cells swell and increases intracranial pressure

Question 25

What is the immediate response to HAPE and HACE? (2)

Answer 25

Descent
Place patient in Gamow bag