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*List 3 factors that influence pulmonary ventilation.

Airway resistance, Alveolar surface tension, Lung compliance


Airway resistance

Friction encountered by air in the airways.


As a rule, airway resistance is insignificant. Why?

1. Airway diameters in the first part of the conducting system are huge and air low viscosity. 2. As airway get smaller more branches are present. Compliance is the most important factor - airway resistance and surface tension are not factors in healthy people.


Where does the greatest resistance to air flow occur?

Medium sized bronchi.


Alveolar surface tension

Water in the alveoli acts to draw the walls of the alveoli together.


Lung compliance

Determined by two factors:
1. distensibility of lung tissue and surrounding thoracic cage
2. alveolar surface tension.

Distensibility is high and surfactant keeps surface tension low, so lungs are high compliance. Compliance can be decreased by scar tissue or ↓ surfactant.


What factors increase airway resistance?

.↓ diameter of bronchioles. Histamine, cold air, irritants, parasympathetic


What factors decrease airway resistance?

.↑ diameter of bronchioles. Epi, sympathetic



Infant respiratory distress syndrome - lack of surfactant. Synthetic surfactants can be used.


**Tidal volume - TV

The amount of air that moves in and out of the lungs with each breath during quiet breathing (500ml)


**Vital capacity

Tidal + Inspiratory reserve + Expiratory reserve. The total amount of exchangeable air.


Total lung capacity

Sum of all lung volumes


Dead space

Volume of the conducting zone conduits - a volume that never contributes to gas exchange. A significant amount of air simply fills up the volume of the conducting zones (tidal volume of 500 - 350 reaches the alveoli, 150 in trachea/bronchi/ect.)


Charles law

The volume of a given quantity of gas is directly proportional to its absolute temperature.

This helps keep the lungs inflated.


Percentages of O2 transported in blood (by different methods)?

1.5% dissolved in plasma, 98.5% bound to Hb


Dalton's law of partial pressures

Partial pressures; each gas in a mixture of gases exerts its own pressure as if all the other gases were not present. (total pressure exerted by a mixture of gases is the sum of the pressures exerted by each gas individually)

PB = PN2 + PO2 + PCO2 + PH20
760 = 597 + 159 + 0.3 + 3.7


Henry's law

States that when a mixture of gases is in contact with a liquid, each gas will dissolve in the liquid in proportion to its partial pressure.

This explains how the plasma concentration of a gas such as oxygen relates to its partial pressure - CO2 is about 20x more soluble in blood than is O2.


Compare atmospheric and alveolar air composition.

O2 - 20.9% - 159mm hg,
CO2 - 0.04% - 0.3mm hg,
H2O - 0.46% - 3.7mm hg

O2 - 13.7% - 104mm hg,
CO2 - 5.2% - 40mm hg,
H2O - 6.2% - 47mm hg.


What causes the differences in composition between alveolar and atmospheric air?

O2 - Lower in alveoli because of diffusion.

CO2 - Higher in alveoli because of diffusion.

H2O - Humidification of air by conducting passageways.

Also, differences in CO2/O2 are caused by a mixture of newly inspired gases and gases remaining in the respiratory passageways between breaths.


Relate Dalton’s and Henry’s laws to events of external respiration.

Dalton's law: Co2's partial pressure gradient (45 in blood/40 in alveoli) makes it flow out of blood into alveoli, O2's partial pressure gradient (40 in blood/104 in alveoli) causes O2 to flow into the blood.

Henry's law: Co2, with only a small gradient, flows just as easily as O2, which has a steep gradient, because it is 20x more soluble.


Relate Dalton’s and Henry’s laws to events of internal respiration.

Dalton's law: Co2's partial pressure gradient (40 in blood/>45 in tissue) makes it flow out of tissue into blood, O2's partial pressure gradient (less 40 in tissue/100 in blood) causes O2 to flow into tissue.

Henry's law: Co2, with only a small pressure gradient, flows easily because of its solubility.


3 factors influencing external respiration

1. Thickness and surface area of respiratory membrane

2. Partial pressure (dalton) and gas solubility (Henry)

3. Ventilation-perfusion coupling


PP inspired air

O2 160 CO2 0.3


PP alveoli

O2 104 CO2 40


PP blood leaving lungs

O2 100 CO2 40


PP tissues

O2 less than 40 CO2 greater than 45


PP blood entering lungs

O2 40 CO2 45


Ventilation/perfusion coupling - O2

(Breathing/blood supply to tissue)

Influence of O2 on perfusion: If alveolar ventilation if inadequate, local pO2 is low because blood takes away O2 more quickly than ventilation can replenish it.

As a result, terminal arterioles constrict redirecting blood flow to respiratory areas where pO2 is high.

Where ventilation is maximal in pulmonary circ, caps dilate.

This is opposite in systemic circulation!!


Ventilation/perfusion coupling - CO2

Bronchioles servicing areas where alveolar CO2 levels are high dilate allowing CO2 to be eliminated more rapidly.

Bronchioles serving areas where CO2 is low constrict.












Carbonic Acid





Equation of loading and unloading o2

HHb + O2 -->.


The rate at which Hb binds or unbinds to O2 is influenced by?

Po2, Temp, pH, Pco2, BPG


Describe how O2 is transported in the blood

1.5% dissolved in plasma, 98.5% bound to hemoglobin


Influence of Po2 on hemoglobin saturation?

At higher plasma partial pressures of O2, hemoglobin unloads little O2, but if plasma partial pressure falls dramatically (exercise) much more O2 can be unloaded.

(high Po2/lungs facilitates binding of O2, low Po2/tissues facilitates release of O2.)

Most important factor...


Plateau in oxygen-hemoglobin dissociation curve

Represents a safety net - Po2 from 100 down to about 60 results in only a small drop in saturation (100 down to 90)


Steep region in the oxygen-hemoglobin dissociation curve

Po2 is lower here, representing the tissues.

O2 saturation drops off steeply here because more O2 is dropped in the needy tissues.


How is O2 loading and unloading affected by pH?

Increase in H+/decline in PH lowers affinity/shifts to right/drops off more o2


How is O2 loading and unloading affected by temperature?

Increase in temp lowers affinity/shifts to right/drops off more o2


How is O2 loading and unloading affected by PCO2?

Increase in Pco2 lowers affinity/shifts to right/drops off more o2, more carbaminohemoglobin made


O2 release and CO2 pickup at the tissues

98.5% O2 and 70% CO2 do this:

HbO2 --> O2 + Hb (Influenced by PP and incoming CO2), O2 diffuses to tissue.

Incoming CO2 + H2O --> H2CO3 (carbonic acid via carbonic anhydrase) then --> HCO3- (bicarbonate) + H+. HCO3- is transported into plasma.

H+ binds with Hb leftover from HbO2 (neutralizing H+).

Cl- is protein transported into RBC to maintain pH (Chloride shift).

10% CO2 diffuses in and is dissolved in plasma.

1.5% O2 that was dissolved in plasma diffuses out.

20% entering CO2: CO2 + Hb --> HbCO2 (carbaminohemoglobin).


O2 pickup and CO2 release in the lungs

98.5% O2 and 70% CO2 do this:

O2 + HHb --> HbO2 + H+ (Hb arrives carrying H, but when it reaches the lungs the high Po2 decreases the affinity of Hb for H - it drops off and O2 binds).

H+ + HCO3- (H+ is picked up by bicarbonate) --> H2CO3 (carbonic acid ) --> H2O + CO2 (driven by carbonic anhydrase). CO2 exits to lungs.

CL- REVERSE shifts out of RBC to counterbalance.

1.5% O2 diffuses in and is dissolved in plasma.

10% CO2 that was dissolved in plasma diffuses out.

Accounting for 20% of CO2, Carbaminohemoglobin/HbCO2 ---> CO2 + Hb, CO2 released into alveoli.


Haldane effect

Effect of oxygen saturation on the binding of CO2.

Reflects the greater ability of reduced hemoglobin to form carbaminohemoglobin.


Bohr effect

Effect of pH on Hb-O2 (more hydrogen ions)

Declining blood pH/↑H+ (and increasing Pco2) weaken the Hb-O2 bond.

This enhances oxygen unloading where it is needed most.


Leftward and Rightward shifts

Right - lowers affinity of o2, Left - raises affinity for O2


What 3 ways is carbon dioxide is transported in the blood?

10% in dissolved in plasma, 20% carbaminohemoglobin, 70% as bicarbonate


What catalyzes the bicarbonate reaction?

carbonic anhydrase


Carbamino effect

Increased presence of CO2 weakens the Hb-O2 bond


How much is O2 is dropped off in resting conditions? Exercising?

25%, 75%


Carbonic anhydrase-Bicarbonate and Hemoglobin as buffers

Hemoglobin picks up H+ in the tissues, HCO3- picks it up at the lungs


Carbonic anhydrase-bicarbonate buffer system

Resists shifts in blood ph.

Slow breathing allows Co2 to accumulate in the blood, Rapid/deep breathing flushes out Co2

If H+ rises, H+ is combined with HCO3- to form bicarbonate (H2CO3). If H+ drops, Carbonic acid dissociates from H2CO3 releasing H+.


Carbamino effect

Effect of co2 effect on O2 binding affinity.

In the presence of co2, hemoglobins affinity for O2 goes down.

Enhances unloading of O2