Respiratory System 3

Question 1

Factors that govern the exchange of gases among the air, blood and tissues

Answer 1

Membrane thickness - the thinner the membrane, the faster the rate of diffusion.

Membrane surface area - the larger the surface area, the faster the rate of diffusion.

Pressure difference across the membrane (Difference in partial pressure between two membrane) - the smaller the different, the faster the rate of diffusion.

Question 2

Identify normal partial pressures of O2 and CO2 in air, blood and tissue

Answer 2

Partial pressure of O2
Air and water = 104 mmHg
Arterial Blood = 95 mmHg (75 mmHg to 100 mmHg)
Venous Blood = 30 to 40 mmHg
Tissue = 40 mmHg (or less)

Partial pressure of CO2
Air = 0.25 mmHg
Arterial Blood = 40 mmHg
Venous Blood = 46 mmHg (Around or more)
Tissue = Around 45 mmHg

Question 3

Describe O2 and CO2 transport

Answer 3

Air travels through the upper and then the lower respiratory structures

Oxygen enters the blood at alveolar-capillary interface and crosses into the capillaries by the process of diffusion

Oxygen is transported in blood dissolved in plasma or bound to hemoglobin inside RBC

Oxygen diffuses into the cells

Cellular respiration determines metabolic CO2 production

CO2 diffuses out of cells

CO2 is transported dissolved bound to haemoglobin

CO2 enters the alveoli at alveolar-capillary interface.

Question 4

Describe the function of haemoglobin

Answer 4

Most O2 in blood transported bound to haemoglobin

Haemoglobin produces oxygen which supply to tissue more efficiently

Haemoglobin Increases Oxygen Transport

Hemoglobin must reversibly bind O2

• loading O2 in the lungs
• unloading O2 at the tissues

One O2 bound → induces conformational change in other subunits → bind O2 with greater affinity

Question 5

Describe the physiological significance of the oxyhaemoglobin dissociation curve

Answer 5

A biochemical relationship indicating that the higher the partial pressure of O2 in the blood, the more O2 haemoglobin it can bind.

Haemoglobin can bind oxygen with high affinity at the alveoli but at the tissues it has low affinity for O2 enabling it to unload the oxygen where it is required.

Not a linear relationship but a sigmoidal relationship = initial binding is slow but the rate of binding of O2 to Hb increases, as the affinity of Hb for O2 increases until the Hb becomes saturates (plateu region) - known as cooperative binding

Question 6

The concentration and movement of O2 and CO2 between air, lungs, the blood & tissues? (Fick’s, Dalton’s & Henry’s Law)

Answer 6

Exchange of O2 and CO2 between alveolar air and blood occurs via passive diffusion

Fick’s Law
Diffusion proportional to surface area, concentration (or partial pressure) gradient & permeability and inversely proportional to distance

Dalton’s Law
Each gas in a mixture exerts it own pressure, i.e. the partial pressure, proportional to its concentration in the mixture

Henry’s Law
Quantity of gas that dissolves in a liquid is proportional to the partial pressure and solubility coefficient

Question 7

How O2 and CO2 are transported in the blood?

Answer 7

At lungs, diffusion of:
O2 from alveoli to blood
CO2 from blood to alveoli

At tissues, diffusion of:
O2 from blood to tissues
CO2 from tissues to blood

Oxygen enters the blood at alveolar-capillary interface and crosses into the capillaries by the process of diffusion

Oxygen is transported in blood dissolved in plasma or bound to hemoglobin inside RBC

Oxygen diffuses into the cells

Cellular respiration determines metabolic CO2 production

CO2 diffuses out of cells

CO2 is transported dissolved bound to haemoglobin

CO2 enters the alveoli at alveolar-capillary interface.

Question 8

The physical and chemical factors that influence the haemoglobin-oxygen dissociation curve?

Answer 8

Effect of pH - known as the Bohr effect (mainly due to CO2)
Effect of temperature
Effect of Pressure of Carbon dioxide

Shifting of curve to right (Lower pH, Higher temperature, Higher PCO2)

• Reduced Hb-O2 affinity
• increasing unloading of O2 from Hb

Shifting of curve to left (Higher pH, Lower temperature, lower PCO2)

• Higher Hb-O2 affinity
• decreasing unloading of O2 from Hb

Question 9

The relationship between CO2 and pH and the role of carbonic anhydrase?

Answer 9

Carbonic anhydrase is an enzyme that balances the pH of the blood and enables the breathing out of carbon dioxide.

In red blood cells carbonic anhydrase catalyzes the reaction

Convert carbon dioxide and water into into carbonic acid, which further breaks down into bicarbonate ions and protons (H+)

Carbon Dioxide + Water (Favoured at lungs) → Carbonic Acid → Bicarbonate ions and protons (H+) (Favoured at tissues)