L32 Gases & respiration 3: Respiration in Mammals

Question 1

Define 4 pressures involved in ventilation and explain the changes that occur to each during ventilation

Answer 1

1. Atmospheric pressure (P_atm)

• pressure outside the air
• assume constant at 760mmHg at sea level
• also referred to as o mmHg as other pressures quoted relative to P_atm

2. Alveolar pressure (P_alv)

• also called intra-alveolar pressure, the pressure of air within the alveoli.
• pressure change during breathing due to
  1) changes in the lung Volume
  2) airflow into / out of the lungs
• Varies with phases of respiration, driving bulk air flow
• At rest (not breathing in/out), P_alv=P _atm
• as P_atm quiet constant, P_alv determines air flow into and out of the lungs

3. Intra-pleural pressure (P_ip)

• varies with stage of the respiratory cycle, but usually < P_{alv (at rest =756mmHg)}
• during quiet (unforced) breathing, P_ip is negative sue to
  1) inward recoil of lungs (inherent elastic properties)

2) outward recoil of the rib cage (compressed at rest)
3) pleural membranes “held together” by pleural fluid

- can be positive during forced expiration

4. Transpulmonary pressure (P_tp)

• the difference between P_alv and P_ip. (P_tp=P_{alv -} P_ip)
• represent the force that keeps the lungs distended
• an increase in P_tp creates a larger distending force across the lungs and the l_ungs expand_
• always positive under normal condition, positive during forced expiration

Question 2

List the muscles involved in inspiration and explain how bulk air flow occurs as a result of muscle contraction

Question 3

Explain the difference between quiet and active expiration

and list the muscles that are used for each

Question 4

Define hypo- and hyper-ventilation and explain the changes they cause to blood gases

Question 5

Explain the importance of pressure gradients in the gas diffusion

Question 6

Define the 3 types of dead space

Answer 6

1. Anatomic dead space

-volume of conducting zone *trachea and bronchi

2. Alveolar dead space

• dead space within respiratory zone
• alveoli unavailable for gas exchange

3. Physiologic dead space

• anatomic + alveolar dead space
• in normal animals:

* alveolar dead space minimal

Question 7

List the partial pressure of oxygen and carbon dioxide in the alveoli and in the different parts of the circulation

Question 8

How Oxygen bind to haemoglobin

Answer 8

• Oxygen is poorly soluble in blood, most oxygen transported bound to haemoglobin (Hb) inside the RBCs *binding is reversible
• the amount of O2 bound to Hb depends on the partial pressure of O2
• CO competes with O2 （bind the Hb at the same site)
• CO2 binds in a non-competitive manner

Question 9

Describe how oxygen transported in the blood

Answer 9

O₂ move from Alveolus to capillaries:

high P_O2 in alveolar faciliates O₂ binding to Hb

O2 move from Hb to tissue cell:

low PO2 in tissue faciliates O2 release from Hb