L30 Gases & respiration 1: Introduction to respiration & gas laws

Question 1

Define internal and external respiration.

Answer 1

Respiration = Internal respiration + External respiration

Internal respiration:

• Cellular respiration
• Intracellular process: O₂ used by mitochondria to generate ATP
• CO₂ and H₂O produced as waste product

External respiration:

- the exchange of gases between the atmosphere and the cells of the body

Question 2

4 processes of external respiration

Answer 2

1. ventilation (by bulk flow)

2. Gas exchange across respiratory membrane

(by diffusion, from region of high to region of low partial pressure )

3. O₂ and CO₂ transport in the blood (by bulk flow)

by simple diffusion across the respiratory surface

4. Gas exchange in tissue (by diffusion)

Question 3

Explain the four factors that influence the rate of gas diffusion across a respiratory membrane. *Fick’s law

Answer 3

1. surface area (larger faster) *human lung and fish gills

2. Diffusion coefficient (larger faster)

- constant for each gas

• high soluble gases have a larger diffusion coeficient and diffuse more quickly (CO₂ more soluble than O₂ in water)

3. Partial pressure gradient (larger faster)

• O₂ and CO₂ diffuse passively along their individual partial pressure gradient
• from high to low (partial pressure)

4. diffusion distance (larger slower)

• thinner the respiratory membrane, faster rate of diffusion
• must be thin

Question 4

Briefly describe conditions that pathological conditions that affect diffusion.

Answer 4

1. pulmonary oedema 肺水肿

• fluid in the lung increase diffusion distance
• fluid collecting in the interstitium and eventually the alveoli
• obstructs normal exchange of gases across respiratory membrane

2. Emphysema 肺气肿

• progressive destruction of alveoli wall
• caused by smoking
• lead to decrease surface area of gas exchange

Question 5

Recall the value of atmospheric pressure at sea level (mm Hg) and describe the effect of altitude on air pressure.

Answer 5

Atmospheric pressure

• pressure measured in mmHg (millimeters of mercury)
• pressure exerted by atmospheric air can push a column of mercury (Hg) to a height of 760mm.

Effect of altitude on pressure

• air pressure decreases with increasing altitude
• higher attitudes, less gas molecule in a given volume and air pressure decrease
• less compression occurs and air is less dense

Question 6

Describe the factors affecting the bulk flow of air.

Answer 6

- Bulk flow occurs when all gas molecules move together in the same direction (e.g. wind, ventilation)

• allow rapid movement over long distances

air flow = pressure gradient / resistance

resistance (R) is the frictional force between air and the wall of the airway that opposes airflow

-determined mainly by the radius of airways (radius increase R increase)

airway resistance - refers to resistance of entire system of airways

airway branching increase the total cross sectional area, reducing the total resistance in that particular area of the respiratory system

e.g. mammals: resistance lowest at bronchioles (smallest airways, but numerous

Question 7

Explain the relationship between flow, resistance and airway diameter.

Answer 7

Flow rate decrease with higher resistance

Resistance increase with smaller diameter.

flow rate decrease with smaller diameter

Question 8

Explain Boyle’s Law and how this can be applied to lung ventilation.

( inspiration and expiration rely on Boye’s law)

Answer 8

P_{<strong>1</strong>}V₁= P₂V₂

volume increase, gas pressure decrease, give temp remain constant.

- pressure of gas defined as the force that gas exerts on the wall of container

• during inspiration, muscle contraction expands thoracic cavity ( V increase)

Question 9

Explain Dalton’s Law of Partial Pressures, how this relates to air and the effect of altitude on partial pressures in the air.

Answer 9

1. partial pressure is the pressure exerted by an individual gas in a mixture

• depends on the % of the gas within the mix
  2. total pressure of air (760 mm Hg at sea level) is the s_um of the partial pressures_ of the individual gases within it

* increased water vapor pressure (ie.humidity) decrease the contribution of the other gases

3. partial pressure in high altitudes
   - at high altitude, atmospheric pressure (total air pressure is less)
   - % composition of each gas does not change
   - partial pressure of each gas is less

Question 10

Explain Henry’s Law and the implications of differing solubility levels of CO₂ and O ₂ in respiration.

Answer 10

The amount of gas will dissolve in a liquid is determined by its partial pressure and solubility

[gas] = P_gas * solubility coeficient

high solubility → low partial pressure required to dissolve the gas

low solubility → high partial pressure required

* any given partial pressure, CO₂ conc higher

• when gas contact with liquid, net movement will occur between states IF a pressure gradient exists
• this will occur until equilibrium is reached

P₀₂ in air = P_O2 in liquid (pressure same, doesn’t imply conc / # of gas molecules in air and liquid same)

* final concentration of gas in liquid at equilibrium depend on its solubility

* partial pressure tell how gas will behave in solution (not conc)