Mod 13 - Gas Exchange & O2 Transport

4 Physical principles of gas exchange

Membrane thickness

Diffusion coefficient of gas

Surface area

Partial pressure

Respiratory Membrane thickness

Simple squamous epithelium

alveoli and Capillary beds

only changes with clinical conditions

Diffusion coefficient of gas

Measure how easily a gas diffuses through a liquid or tissue

CO2 is 20 times more diffusible than O2

based on solubulity and gas molecule size

Respiratory membrane surface area

More surface area = Easier to get gas into blood

remains constant unless by lung cancer or other conditions

Partial pressures difference in respiratory membrane

Gas moves from area of higher partial pressure to area of lower partial pressure

Dalton's Law of partial pressures

Total pressure is sum of all partial pressures

Partial pressure of O2 at sea level

159 mmHg

gas moves from area of higher partial prssure to area of lower partial pressure

Henry's Law

Concentration of a gas in a liquid is determined by its partial pressure and its solubility coefficient

[dissolved gas] = pressure gas x solubility coefficient

Decompression sickness

Deep diving & increased pressure forces more N2 to dissolve in blood

How is oxygen transported in the blood

Moves from alveoli into blood (External respiration)

Moves from tissue capillaries into tissues (Internal respiration)

How is CO2 transported in the blood

Moves from tissues into tissue capillaries

Moves from pulmonary capillaries into alveoli

more soluable

3 modes of transport

dissolved = 7%

RBC bound to hgb = 23%

bicarbonate = 70%

How does O2 partial pressure change in the body

High during inspiration

Decreases when in alveoli because of loss of O2 to blood

Decreases again in pulmonary veins because of mixing with deoxygenated blood

How does CO2 partial pressure change is the body

High in body tissue

Decreases in alveoli

Decreases to 0.3 mmHg in atmospheric air

What is saturated hemoglobin

Hemoglobin is carrying 4 oxygen molecules (Max)

Oxygen-hemoglobin dissociation curve

Describes the percentage of hemoglobin saturated with oxygen at any given PO2

What cause a right shift in the oxygen-hemoglobin dissociation curve

Decrease pH

Increase CO2

Increase temp

Exercising ((heats up muscle so temp increase)

@levels of tissue: take sat from 75 to 25%, causes rightward shift, decrease in sat. of oxygen)

What cause a left shift in the oxygen-hemoglobin dissociation curve

Increase pH

Decrease CO2

Decrease Temp

Going to altitude

pH effects on oxygen affinity for hemoglobin

As acidity increases, O2 affinity decreases

Bohr effect

CO2 effects on oxygen affinity for hemoglobin

CO2 converts to carbonic acid & becomes H+ and bicarbonate

Lowers pH

Temperature effects on oxygen affinity for hemoglobin

Metabolism = heat as by-product

As temp increases, more O2 is released

hypothermia = matabolism slows, less O2 released

BPG effects on oxygen affinity for hemoglobin

Released by RBCs as they break down glucose for energy

Binds to hemoglobin and increases release of oxygen

gas exchange

pressure of individual gases in air @ sea level

percentage of each gas are constant

humitity levels changes

@altitude: closer to earth - densly packed molecules

• percentage of eacg of the hases make up per volue doesnt change

• to bakance levels increase percentage of oxygen breathing

ozygen transport in blood

• moves from alveoli into blood

• oxygen moves from tissue capillares into tissue

2 modes of transport:

• dissolved (1.5%)

• rbc round to hgb (98.5%)

CO2 effects on oxygen affinity for hemoglobin

CO2 converts to carbonic acid & becomes H+ and bicarbonate

Lowers pH

pulmonary veins

PO2 = 95 mm Hg

decrease bc mixing with deoxt blood from bronchiol veins (blood vessels serving bronchioles and outside)

inspired air

PO2 = 160 mm hg

alveolar air

PO2 = 104 mm hg

decrease bc reaching a door way

lobe p.p oxygen in blood reaches doorway equalizing high partial pressure in equilibrium

Body tissue pressure

46 mm hg

alveolar air

40 mm hg

atmospheric air

0.3 mmHg

oxygen transport

heme group on Hgb can carry up to 4 O2 molecules

when 4 O2 bound, Hgb 100% saturated

oxygen hemoglobin dissociation curve

% of hemoglobin sat w O2 at any given PO2

curve S shape affected by pH, Pco2, temp

2,3-bisphosphoglycerate (BPG) affects sat. of Hgb

shape change = reduce affinity for oxygen there easier to pull O2 off