Download Comparative Vertebrate Physiology

Human Anatomy and
Physiology
Respiration: Gas exchange
Gas transfer systems
Components:
1. Breathing
2. Respiratory diffusion
3. Bulk transport
4. Cellular diffusion
External
respiration
Internal
respiration
Dalton’s Law



PT = P1 + P2 + P3 etc.
Therefore each gas has a partial pressure
(pgas)
Pgas = % of total mixture
Dalton’s Law
Atmospheric air
Gas
N2
O2
CO2
H2O
%
78.6
20.9
0.04
0.46
Partial pressure
597
159
0.3
3.7
760
Henry’s Law


Gases dissolve into liquid in proportion to
their partial pressure
Equilibrium will be reached (e.g. gases in
the lung)
Gas state
Liquid state
(lung)
(blood)
300
100
(fast)
250
150
200
(slower)
(no movement)
200
Gas solubility
Factors effecting:
 Temperature (not in humans)
 Solubility of gas


Air: CO2 > O2(20th) > N2 (1/2)
Would humans survive if air had more CO2
than O2?
Alveolar gases
Gas
N2
O2
CO2
H2O
Partial pressure
569
104
40
47
%
74.9
13.7
5.2
6.2
Atm.
78.6
20.9
0.04
0.46
760
At any point in time air in alveoli contains:
Less O2, more CO2 & H2O
Why is gas composition
different?




O2 diffuses into blood, CO2 in opposite
direction
Humid air in conductive pathway
Air in alveoli a mixture of air from more
than one breath
How can humans alter gas composition?

Increase rate and depth of breathing
Vascular circuits




Systemic
Coronary
Pulmonary
Bronchial – to lungs from heart
Gas pressure gradients
Pressure gradients
Oxygen


pO2 in deoxygenated blood is 40 mmHg
pO2 in alveoli is 104 mmHg
Pressure gradients
Carbon dioxide
pCO2 in alveoli is 40 mmHg
pCO2 in deoxygenated blood is 45 mmHg


Alveoli
40
PCO2
O2
P
104
Deoxygenated blood
45
5
40
64
Pressure gradients

Relatively the same amount of O2 and
CO2 are exchanged. Why?
Answer: Solubility
Surface area



Why is surface area important?
Surface area in a human lung is 70m2
Factors decreasing surface area

Emphysema (volume unchanged)

Tumors, mucus
Ventilation-perfusion coupling
vasoconstriction
Low ventilation
Well perfused
Poor ventilation
Poor perfusion
vasodilation
High ventilation
Poor perfusion
High ventilation
High perfusion
Gas transport in blood

Methods of transport



Dissolved in plasma (3 ml per liter)
Problem: C.O. would need to be 80 l/min
Bound to a respiratory pigment (Hb)
(200 ml per liter)
Solution: Hb carries both O2 and CO2
simultaneously
Hemoglobin structure
O2
CO2
Oxy vs. deoxyhemoglobin
Oxygen transport in blood


The term percent saturation
Deoxyhemoglobin: Hb is 75% saturated
Hb-O2 affinity

Decreasing affinity




Decrease in pH (Bohr effect)
Binding to 2,3 diphosphoglycerate
Elevated temperature
Increase in pCO2
75%
55%
pO2
Oxygen transport

Hypoxia: inadequate O2 to tissues




Anemic: few RBC’s
Ischemic: impaired or blocked blood
circulation
Histotoxic: body cells unable to use O2 even
though enough delivered (cyanide)
Hypoxemic: reduced arterial pO2 (CO2
poisoning)
CO2 transport

Ways to transport



Dissolved in plasma (7 - 10%)
Bound to Hb (20 - 30%)
Bicarbonate ion (60 - 70%)
CO2 transport from tissue
CO2 transport into lungs