Week 7 - Respiration during exercise (p3)

Question 1

What is Dalton’s law?

Answer 1

total pressure of a gas mixture is equal to the sum of the pressure that each gas would exert independently

Question 2

How is the partial pressure of a gas worked out?

Answer 2

fraction of gas within air x barometric pressure (x 750mmHg at sea level)

Oxygen 159 mmHg
Carbon dioxide 0.3 mmHg
Nitrogen 600.7 mmHg
(Inspired air)

Question 3

Identify the difference between arterial partial pressure of oxygen and alveolar partial pressure of oxygen.

Answer 3

Arterial PO2 (100mmHg) is slightly less than alveolar PO2 (105mmHg) due to a very small gas exchange impairment.

Question 4

Identify the difference between arterial PCO2 and alveolar PCO2.

Answer 4

both 40mm Hg

Question 5

At rest, what is PO2 and PCO2 in deoxygenated blood?

Answer 5

PO2 40mmHg
PCO2 46mmHg

Venous PO2 is decreases whereas venous PCO2 is increases as tissues consume oxygen but produce CO2.

Question 6

What happens to partial pressure of O2 and CO2 in the alveolar when inspired?

Answer 6

PO2 decreases to 105mmHg (from 159)
PCO2 increases to 40mmHg (from 0.3)

Question 7

What are the four steps of pulmonary circulation?

Answer 7

1. Pulmonary artery carries deoxygenated blood from
   the right ventricle to the lungs
2. Gas exchange between the alveoli and pulmonary
   capillaries occurs
3. Oxygenated blood is returned to the left atrium via
   the pulmonary vein
4. Oxygenated blood is pumped around the systemic
   circulation to systemic cells

Question 8

What is the pressure and resistance of the pulmonary circuit like?

Answer 8

low pressure, low resistance

mean pulmonary artery pressure is 15mmHg

Question 9

What is the mean pulmonary artery pressure compared to systemic arterial pressure?

Answer 9

15mmHg compared to 100mmHg

Question 10

Why is the pulmonary circulation low resistance?

Answer 10

its thin walled and has little smooth muscle - this is it accepts the entire cardiac output so it doesn’t need to redistribute the blood.

Question 11

During exercise, what happens to pulmonary vascular resistance?

Answer 11

decreases due to recruitment and distension (enlarge) of pulmonary capillaries which increases flow and decreases resistance

Question 12

What does gas exchange require a matching of?

Answer 12

Ventilation to blood flow (V/Q)

• The ideal V/Q is 1
• V/Q > 1 = under perfused (apex of lung)
• V/Q < 1 = over perfused (base of lung)

Question 13

Upon exercise, why does V/Q improve?

Answer 13

o Increased tidal volume
o Increased pulmonary artery pressures

In some cases, V/Q worsens, especially during heavy exercise

Question 14

What are the two forms in which oxygen is carried in the blood?

Answer 14

1. Dissolved into plasma (2%)
2. Bind with haemoglobin (98%)

Question 15

What is Henry’s law?

Answer 15

the amount of gas dissolved in blood is proportional to the partial pressure of that gas

o The amount of O2 dissolved is 0.003 mL O2/100 mL blood/mmHg.
o At an arterial PO2 of 100 mmHg, this results in 0.003*100=0.3 mL O2/100 mL blood.

Question 16

Each molecule of haemoglobin (Hb) can transport how many molecules of oxygen?

Answer 16

4

Question 17

How many mL of oxygen do we have per gram of haemoglobin?

Answer 17

1.34mL per gram of Hb

Question 18

How many grams of haemoglobin do you have per 100mL of blood?

Answer 18

15

Question 19

How do you work out arterial oxygen content?

Answer 19

1.34 x haemoglobin mass x oxygen saturation/100 + (0.003 x PO2)

1.34 x 15 x 1 + (0.003 x 100) = 20.3mL O2/100ml of blood

Question 20

What is the total oxygen content in venous blood?

Answer 20

15

less than oxygen content in arterial blood which is 20

Question 21

When venous P02 decreases during exercise, what is the effect?

Answer 21

the amount of 02 unloaded to tissues becomes significantly greater

Question 22

What is the “Bohr effect”?

Answer 22

exercise causes an increase in H+, CO2 and core body temperature, causing a rightward shift of the oxyhemoglobin dissociation curve (ODC) - so haemoglobin is less saturated with oxygen which facilitates the unloading of O2 to active tissue

Question 23

What is the protein that carries oxygen in the muscle?

Answer 23

Myoglobin - an oxygen binding protein found in skeletal muscle

Question 24

What is the role of myoglobin?

Answer 24

• High O2 affinity; unloads at very low PO2 (less than 20)
• Shuttles O2 from muscle cell membrane to mitochondria for aerobic respiration
• Provides intramuscular O2 storage for when its needed during exercise (its a reserve)

Question 25

What are the 3 forms in which carbon dioxide is carried in the blood?

Answer 25

1. Dissolved in plasma (10%)
2. Bound to deoxygenated haemoglobin to form carboamino haemoglobin (20%)
3. Bicarbonate (70%)

Question 26

What is the principal way that carbon dioxide is transported?

Answer 26

by bicarbonate

Question 27

Is CO2 more soluble or is O2 more soluble?

Answer 27

CO2 20x more soluble than 02

Question 28

Carbon dioxide binds with oxygen to form carbonic acid which dissociates into bicarbonate and a hydrogen ion. What happens next?

Answer 28

bicarbonate leaves the RBC and chlorine moves into the cell to maintain neutrality

Question 29

What is the equation for bicarbonate and hydrogen ion?

Answer 29

CO2 + water –> carbonic acid –> bicarbonate + H+

Question 30

How does CO2 production during exercise stimulate breathing via a feedback loop?

Answer 30

causes an increase in H+ and thus a decrease in arterial pH - this stimulates breathing

Question 31

What form is most of the oxygen contained in blood?

Answer 31

oxyhemoglobin as oxygen binds to hemoglobin