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