human anatomy and physiology respiration: gas exchange
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Human Anatomy and Physiology
Respiration: Gas exchange
Gas transfer systems
Components:1. Breathing
2. Respiratory diffusion
3. Bulk transport
4. Cellular diffusion
Externalrespiration
Internalrespiration
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
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 (lung)
Liquid state (blood)
300 100
250 150
200 200
(fast)
(slower)
(no movement)
Gas solubilityFactors 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
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 gradientsOxygen pO2 in deoxygenated blood is 40 mmHg
pO2 in alveoli is 104 mmHg
Pressure gradientsCarbon dioxide pCO2 in alveoli is 40 mmHg
pCO2 in deoxygenated blood is 45 mmHg
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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
Low ventilationWell perfused
High ventilationPoor perfusion
Poor ventilationPoor perfusion
High ventilationHigh perfusion
vasoconstriction
vasodilation
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
Oxy vs. deoxyhemoglobin
O2
CO2
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
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