AlveolusandRespiratoryMembrane• thinmembranewheregasexchangeoccursin

thelungs,• simplesquamousepithelium(Squamouscells

havetheappearanceofthin,flatplates.Theyfitcloselytogetherintissues;providingasmooth,low-frictionsurfaceoverwhichfluidscanmoveeasily)liningthealveoli,theendotheliumofthepulmonarycapillarywallsandthefusedbasementmembrane

• Oxygenandcarbondioxidecandiffuseeasilyacrossthethinmembrane.Inmanyregionswheretherearenointerstitialfluid.

• basement Membrane is Extracellularmaterialconsistingofabasallaminasecretedbyepithelialcellsandareticularlaminasecretedbyunderlyingconnectivetissuecells.

Alveolus and Respiratory basement Membrane

• a thin, fibrous, non-cellular region of tissue that separates the epithelium (e.g.,skin, respiratory tract, gastrointestinal tract, etc), mesothelium (pleural cavity,peritoneal cavity, pericardial cavity, etc) and endothelium (blood vessels, lymphvessels, etc) from underlying connective tissue.

• Basement membrane is not actually a membrane; rather, it is a matrix.

Gas ExchangeHenry’s Law:

The amount of gas dissolved in a liquid is determined by the pressure of the gas and its solubility in the liquid.

n If the temperature stays constant, increasing the pressure will increase the amount of dissolved gas.

Pgas = KC (T = const)K: Henry’s Constant

C:concentration of the dissolved gasNote that: C1 / P1 = C2 / P2

Oxygen-Hemoglobin dissociation curve

Gas Exchange

O2 and CO2 exchange by passive diffusionPO2 is 105 mmHg in alveoli and 40 in alveolar capillariesPCO2 is 45 mmHg in alveolar capillaries and 40 in alveoli

Gas Exchange

Henry’s Law:

The amount of gas dissolved in a liquid is determined by the pressure of the gas and its solubility in the liquid.

n If the temperature stays constant, increasing the pressure will increase the amount of dissolved gas.

Pgas = KC (T = const)K: Henry’s Constant

C:concentration of the dissolved gasNote that: C1 / P1 = C2 / P2

Gas TransportHemoglobin structure and functionAhemoglobinmoleculecanbinduptofouroxygenatoms

Gas TransportOxygen Dissociation Curve. Affinity for O increases after the first O adsorption until saturation.This curve is controlled by, the pH (acidity, or alkalinity), Temperature in partial pressure of CO2 )

GasTransportFactorsaffectingoxygendissociationcurve(inlungsmembrane).Thisleftwardshiftindicatesthatthehemoglobinunderstudyhasan

increasedaffinityforoxygensothathemoglobinbindsoxygenmoreeasily,butunloadsitmorereluctantly.

Leftshiftofthecurveisasignofhemoglobin'sincreasedaffinityforoxygen(e.g.atthelungs).

GasTransportFactors affecting oxygen dissociation

curve (e.g. near tissue)• Arightwardshiftindicatesthatthe

hemoglobinunderstudyhasadecreasedaffinityforoxygen.Thismakesitmoredifficultforhemoglobintobindtooxygen(requiringahigherpartialpressureofoxygentoachievethesameoxygensaturation),butitmakesiteasierforthehemoglobintoreleaseoxygenboundtoit.

• Theeffectofthisrightwardshiftofthecurveincreasesthepartialpressureofoxygeninthetissueswhenitismostneeded,suchasduringexercise,orhemorrhagicshock

Bohr effect

ABG ResultsArterialBloodGasValuestest

Controlfactors decrease increaseTemperature leftshift rightshift2.3-DPG leftshift rightshiftp(CO2) leftshift rightshiftpH(Bohreffect) rightshift(acidosis) leftshift(alkalosis)

2.3-DPG(bisphosphoglycerate)Acid:bindswithgreateraffinitytodeoxygenatedhemoglobin

Itsproductionincreasesduringhypoxaemia,chroniclungdisease,anaemia,andcongestiveheartfailure

Pulmonary Emphysemaabnormal permanent enlargement of the airspaces distal to the

terminal bronchioles (The end of the nonrespiratory conducting airway) accompanied by destruction of the alveolar wall and without obvious fibrosis (excess fibrous connective tissue in an organ ) and

lost elasticity

Lung Injury - X-Ray

Haemothoraxcollection of blood in the space between the chest wall and the lung (the pleural cavity

Pneumothoraxabnormal collection of air or gas in the pleural space that separates the lung from the chest

Respirators and Ventilators

• When a patient has difficulty breathing because of paralysis, neurological insufficiency, or other causes

• It is usually sufficient to aid only inspiration process, since the elastic contractions of the chest walls and lung are sufficient to accomplish expiration.

• Iron lung type respirator create negative pressure over the patient entire body except for the head thus aid the chest expansion and inspiration.

• Positive pressure ventilators are better . It works by entering oxygen wit pressure greater than atmospheric pressure.

Exercise The air in a sealed container with constant volume has apressure of 1 atm at 0 oC. What will be its pressure at 100 oC? Atwhat temperature will the pressure be 2 atm?

(Pf = 1.37 atm, 546.3 K=273.15 oC)

Exercise Given 1000 cm3 volume of gas at 27 oC, whattemperature would be required for that gas to occupy a volume of500 cm3, if the pressure were constant?

(150 K)

Exercise Iftheabsolutepressureinsideaballoon(closedcontainer)is90mmHgwith75%ofhelium,5%ofCO2 and20%ofO2findthepartialpressuresofO2,CO2 andheliumgasses