M13: Respiratory System - Gas Exchange

Question 1

diffusion of gases through respiratory membrane depends on 4 factors

Answer 1

1. Membrane thickness
2. Diffusion coefficient of gas
   - how easily a gas diffuses through a liquid or tissue
   - CO2 is 20x more diffusable than O2
3. Surface area
4. Partial pressure differences (BIGGEST FACTOR)

*but diffusion coefficient and surface don’t really change unless there’s a clinical condition

Question 2

Dalton’s Law

Answer 2

• each gas in a mixture of gasses exerts its own pressure
• total pressure is the sum of all partial pressures

Question 3

Henry’s Law

Answer 3

• concentration of a gas in a liquid is determined by its partial pressure and its solubility coefficient

[dissolved gas] = pressure of gas * solubility constant

Question 4

If nitrogen is in the air, why don’t we breathe it in?

Answer 4

• N2 has very low solubility, would need very high partial pressures to breathe it in
  (Henry’s Law)
• EXCEPTION: deep sea diving creates pressures great enough for us to breathe in N2. Causes decompression sickness (the bends), where dissolved N2 in blood turns into a gas if diver surfaces too fast

Question 5

2 modes of transportation for oxygen, 3 modes of transport for CO2 in the body

Answer 5

OXYGEN
- dissolved in blood (1.5%)
- carried on RBC (bound to iron on hemoglobin) (98.5%)

CO2
- dissolved in blood (7%)
- RBC (bound to GLOBIN in hemoglobin) (23%)
- bicarbonate (70%)

Question 6

right shift in oxygen-hemoglobin disassociation curve

Answer 6

• decrease in blood pH
• increase CO2
• increase temperature

Causes
- exercise (increases heat, alters pH, increases CO2 production)
- benefit of right shift -> greater O2 offloading to tissues

Question 7

what is more soluble, CO2 or O2?

Answer 7

CO2 is 24x more soluble than O2! Greater pressure difference needed to bring oxygen in

Question 8

O2 PP changes in the body

Answer 8

INSPIRED AIR = 160
ALVEOLUS = 104
why the drop? addition of water and loss of O2 to blood
PULMONARY CAPILLARY = 104
PULMONARY VEINS = 95
why the drop? mixing with deoxygenated blood from bronchiole veins
TISSUE CAPILLARIES = 95
INTERSTITIAL FLUID = 40 (equalized between 95 and 20)
TISSUE CELLS = 20
VENOUS BLOOD TO LUNGS = 40

(all mmHg)

Question 9

CO2 PP changes in the body

Answer 9

BODY TISSUES = 46
INTERSTITIAL FLUID = 45
TISSUE CAPILLARY = 40
VENOUS BLOOD = 45
ALVEOLUS = 40

INSPIRED AIR = 0.3
EXPIRED AIR = 27

ARTERIOLE BLOOD = 40

Question 10

% hemoglobin O2 saturation at different PPs

Answer 10

LUNGS (104mmHg) = 98%
most hemoglobin have 4 O2 bound
BODY TISSUES AT REST (40mmHg) = 75%
most hemoglobin have 3 O2 bound

Question 11

left shift in oxygen-hemoglobin disassociation curve

Answer 11

• increase in blood pH
• decrease CO2
• decrease temperature

Causes
- going to altitude (colder and PP O2 drops which stimulates breathing and lowers C02, low C02 increases pH)
- benefit of left shift -> increase O2 uptake in lungs, BUT makes it harder to drop of O2 to tissues

Question 12

Bohr effect + effect of pH on O2 affinity for Hgb

Answer 12

-high amount of C02 will dissacociate into H+ ions
- decrease in pH (means more H+)
- H+ bind to hemoglobin, change its shape
- increases oxygen offloading

Question 13

temperature effects on O2 affinity for Hgb

Answer 13

HIGH TEMP
- high metabolism, heat as byproduct
- increased heat = more O2 released from Hgb

LOW TEMP
- metabolism slows, less O2 released from Hgb

Question 14

BPG effect on O2 affinity for Hgb

Answer 14

• released by RBC as they break down glucose for energy
• BPG binds to Hgb and increases O2 release

Question 15

Boyle’s Law

Answer 15

the pressure and volume of a system are inversely proportional

Question 16

where is the highest PP C02 in the body and why?

Answer 16

body tissues
46 mmHg
because they produce C02 as a byproduct of metabolism