2.4 Gas Exchange Flashcards
Gas exchange during respiration
*occurs between lungs and blood as well as blood and tissues
External respiration: diffusion of gases by the wayn blood and lungs
Internal respiration: diffusion of gases between tissues
*toal pressure exerted by mixture of gases = sum of pressures exerted by each gas (daltons law)
gas partial pressure
Pressure exerted by each gas in mixture
• Directly proportional to its percentage in mixture
daltons law: Total pressure exerted by mixture of gases is equal to sum of pressures exerted by each gas
partial pressure of oxygen and nitrogen
Oxygen makes up 20.9% of air
PO2 : 0.209 x 760 mm Hg =159 mm Hg
Nitrogen makes up ~78.6% of air
PN2 : 0.786 x 760 mm Hg = 597 mm Hg
What is Henry’s law
* for gas mxitures in cotneact w/ liquid
- each gas disolves in liquid proportion to its partial pressure
- at equilibrium, partial pressure of two phases are equal
- amount of each gas that will dssiolve depends on:
- > Solubility: CO2 is 20 more soluble in water than O2, and little N2 will dissolve
- > Temp: temperature of liquid rises, solubility decreases
what is external respiration?
what influences it?
External respiration (pulmonary gas exchange) involves the exchange of O2 and CO2 across respiratory membranes
influened by:
- > Partial pressure gradients and gas solubility
- > thickness and surface area of respiratory membrane
- > ventilation-perfusion coupling: mathcing of alveolar ventilation w/ pulmonary blood perfusion
describe exchange of CO2 and O2 during external respiration
- inspired air (O2:160, C02: 03) –mixes w/-> aleoli of lungs (O2 ↓ 104, CO2 ↑ 40)
– > pulmonary veins –> blood leaving lungs & entering tissue cap ( O2 ↓ 100, CO2 40)
*slight decrease here because lung tissue iteself is using a bit)
—> systemic arteries —> blood delivered to tissues (O2 ↓ 40, CO2 ↑ 45) —> Systemic veins
–> blood leaving tissues and entering lungs (O2 40, CO2 45) —–> pulmoanry arteries
–> inspired air and back to (O2:160, C02: 03)
describe the pressure gradient of O2 vs CO2
- O2
- steep gradient: venous blood is 40 mm Hg, aleolar is 104mmHg
- equilibrium is reached across resp memrbane in ~0.25 s, takes RBC ~0.75s to travel from start -> end fo capillary
- ensures adequate oxygenation even if bloodf lwo inc 3x
- CO2
- less steep gradient: venous blood 45 mmHg, alveolar 40 mmHg
- even tho not steep, CO2 still diffuses in equal amoutns w/ O2 bc CO2 is 20x mroe soluble
thickness of respiratory memrbane
– Respiratory membranes are very thin 0.5 to 1 um thick
– Large total surface area of the alveoli is 40X the surface area of the skin
what can cause effective thickness of respiratory memrbane
- if lungs become waterlogged and edematous
ex: pneumonia or left heart failure - the 0.75s RBC require to travel thru pulmonary capillaries may not be sufficient for adequate gas exchange resulting in oxygen deprivation
what is ventilation perfusion coupling
what does O2 control? what does CO2 control?
– Perfusion: blood flow reaching alveoli
– Ventilation: amount of gas reaching alveoli
- ventilation and eprfusion rates much be matched for optimal efficient gas exchange
- both are controlled b local autoregulatory mechanisms
*PO2 controls perfusion by changing arteriolar diameter
*PCO2 controls ventilation by changing bronchiolar diameter
What is the influence of local PO2 on perfusion
*Changes in PO2 in alveoli cause changes in diameters of arterioles
- > where alveolar O2 is high, arterioles dilate (INC perfusion aka blood flow)
- > where alveolar O2 is low, arterioles constrict
*diects blood to go to alveoli where oxygen is high so blood can pick up more O2
*OPP MECH SEEM IN SYSTEMIC ARTEROLES THAT DILATE WHEN OXYGEN IS LOW AND CONSTRICT WHEN HIGH
What is the influence of local PCO2 on ventilation
• Changes in PCO2 in alveoli cause changes in diameters of bronchioles
Where alveolar CO2 is high, bronchioles dilate
Where alveolar CO2 is low, bronchioles constrict
*Allows elimination of CO2 more rapidly
how is perfusion and ventilation balanced?
- Changing diameters of local arterioles and bronchioles synchronizes ventilation-perfusion
- If ventilation < Perfusion
- will get ↑ PCO2 and ↓ PO2
- O2 regualres arteriolar diameter
- Pulmonary arterioles serves alveoli constrict
- get a match of ventilation and perfusion (corrects the ratio)
- will get ↑ PCO2 and ↓ PO2
- If ventilation > Perfusion
- ↓ PCO2 and ↑ PO2
- bc of INC O2, arterolies serving alveoli DILATE
- get inc in both ventilation and perfusion
why is ventilation and perfusion never balanced for all alveoli
- > Regional variations may be present, due to effect of gravity on blood and air flow
- > Occasionally, alveolar ducts plugged with mucus cause unventilated areas
describe gas exchange in internal respiration
in alveoli of lungs: (O2: 104, CO2: 40) —-> pulmonary veins (O2 100)
—> Blood leaving lungs and entering tissue capillaries (O2 100, CO2 40)
—> Systemic arteries —> tissues (O2 40, CO2 45) —> systemic veins
—> Blood leaving tissues and enting lungs (40 mmHg 45 mmHg)
—> pulmonary arteries —> Inspired air (O2 160, CO2 0.3)
what is internal respiration
describe the partial pressues of O2 and CO2
Internal respiration involves capillary gas exchange in body tissues
- Partial pressures and diffusion gradients are reversed compared to external respiration
- Tissue PO2 always lower than in arteriol blood PO2 (40 vs 100 mmHg)
- oxygen moves from blood to tissue
- Tissue PCO2: always higher than arterial blood PCO2 (45 vs 40 mmHg)
- CO2 moves from tissues into blood
- Venous blood returning to heart has PO2 of 40 mmHg and PCO2 of 45
how is oxygen carried in blood
2 ways
- 1.5% if dissolved in plasma
- 98.5% is bound to each iron of hemoglobin (Hb) in RBCs
structure of hemoglobin
Hb molecule is composed of four polypeptide chains, each with a iron-containing heme group
- each Hb can transport four oygen molecules
- Oxyhemoglobin (HbO2): hemoglobin-O2 combination
- Reduced hemoglobin (deoxyhemoglobin (HHb): hemoglobin that has released O2
*Rate of loading and unloading of O2 is regulated to ensure adequate oxygen delivery to cells
What happens to hemoglobin as oxygen binds and is released
- O2 binds: Hb changes shape, increasing its affinity for O2
As O2 is released, Hb shape change causes a decrease in affinity for O2
*when all 4 heme groups have O2 bound it is fuly saturated
*partially saturated when onle 1-3 hemes carry O2
what factors that influence hemoglobin saturation:
- PO2
• Other factors: Temperature, Blood pH, PCO2, Concentration of bisphosphoglycerate (BPG, from glycolysis)
how does PO2 influence hemoglobin saturation
- PO2 influences binding and release of O2 with hemoglobin
- % Hb saturation can be plotted against PO2 concentrations
* Resulting graph is not linear, but an S-shaped curve called the oxygen-hemoglobin dissociation curve
Saturation of Hb in arterial vs venous blood
- Arterial blood
- PO2 is 100 mmHg and contains 20mL of O2/100mL blood
- Hb is 98% saturated and durther increases in PO2 (depp breath) produce minimal increases in O2 for binding
- Venous blood
- PO2 is 40 mmHg
- Hb is still 75% saturated
- venous reserve: oxygen remaining in venous blood that can still be used
Describe the Oxygen Hemoglobin dissocaition curve
- A: In metabolically active tissues (e.g. exercising muscle)
- the PO2 is even lower
- At a PO2 of 20mmHg, Hb is only 40% Saturated.
- B: in tissues PO2 is low (40 mmHg)
- Hb is less saturated (75%) with O2
- C: At high altitude, ther eis less O2
- at a Po2 in lugs of only 80 mmHg, Hb still 9% saturated
- D: if more O2 present, more O2 is bound
- bc of Hb’s properies O2 binding strength changes with saturation
- E: in lungs where PO2 is high (100 mmHg) Hb is almost fully saturated (98%) with O2
