The human gas exchange system consists of the nasal passages, the pharynx or throat, the larynx or...
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Transcript of The human gas exchange system consists of the nasal passages, the pharynx or throat, the larynx or...
The human gas exchange systemconsists of the nasal passages, thepharynx or throat, the larynx orvoice box, the trachea, the rightand left bronchus and the lungs
Larynx
Trachea(with rings of cartilage)
Left lung
Ribs
Diaphragm(a powerful sheet of muscle
separating the thorax from the abdomen)
Intercostalmuscles
Section throughribs
Rightbronchus
Bronchioles
The Human Gas Exchange SystemThe Human Gas Exchange System
The bronchioles dividemany times forming
respiratory bronchioles,which in turn divide toto form alveolar ducts
that terminate in groupsof sacs – the alveoli
Respiratorybronchioles
Alveolarduct
Alveoli
A single alveolus
Each alveolus is ahollow, thin-walled
sac that is surroundedby a dense network ofcapillaries and is thesite of gas exchange
in the lungs
The Gas Exchange SurfaceThe Gas Exchange Surface
Gases are exchanged across the alveoli by diffusion
According to Fick’s Law...
Rate of diffusion =surface area x difference in concentration
thickness of exchange surface
Maximum rate of diffusion of respiratory gases is achieved by:
• the large surface area presented by the alveoli (there are about 350 millionalveoli in the two lungs presenting an enormous surface area of
approximately 90 square metres – about the area of a tennis court)
• the large differences in concentration of metabolites between the alveoli and the blood capillaries
• the thinness of the diffusion barrier (alveolar and capillary walls providea total thickness of only 0.005 mm)
As deoxygenated blood from the body tissues flows through the network ofcapillaries surrounding each alveolus, oxygen diffuses into the blood and carbondioxide diffuses from the blood into the alveolus; oxygenated blood travels from
the lungs to the left of the heart for delivery to the body tissues
The Gas Exchange SurfaceThe Gas Exchange Surface
The exchange of gases between the lungs and the circulating blood takes placeacross the thin-walled alveoli whose walls consist of squamous epithelium
This photomicrograph shows the thin walls and large surface area displayed by the alveoli in human lung tissue
ALVEOLI
Gas Exchange occurs across the Alveolar EpitheliumGas Exchange occurs across the Alveolar Epithelium
The wall of the alveolus is composed of squamous epithelium together withits basement membrane
squamouscells
basement membrane
This thin wall is surrounded by an extensive network of capillaries whosewalls are also composed of flattened,
squamous epithelium
Gas Exchange occurs across the Alveolar EpitheliumGas Exchange occurs across the Alveolar Epithelium
capillary
The thinness of the capillary and alveolar walls, togetherwith their basement membranes, provides a barrier
between the alveolar air and the blood in the capillaries of approximately 0.3 m
The thinness of this barrier is one of the features thataids rapid diffusion of gases into and out of the blood
Gas Exchange occurs across the Alveolar EpitheliumGas Exchange occurs across the Alveolar Epithelium
capillary and alveolar wallsThis electron micrograph shows
a portion of human lung
Alveolarwall
Capillarywall
Red bloodcell
Nucleus ofcapillary
The short diffusionpath for efficientexchange of gasesbetween the air inthe alveoli and the
blood in the capillariesis provided by the thinsquamous epitheliumlayers of these tissues
O2
CO2
Gas Exchange occurs across the Alveolar EpitheliumGas Exchange occurs across the Alveolar Epithelium