Gas exchange in Gas exchange in MammalsMammals

Gas Exchange in MammalsGas Exchange in Mammals

Delivery of ODelivery of O2 2

to gas to gas exchange exchange surface surface (alveoli) and (alveoli) and removal of COremoval of CO22 from capillaries from capillaries and out of the and out of the body body (ventilation). (ventilation).

In Larger OrganismsIn Larger Organisms

Diffusion alone cannot meet the Diffusion alone cannot meet the needs of the inner-most cells of needs of the inner-most cells of larger organisms. They have a higher larger organisms. They have a higher demand for Odemand for O22 and removal of CO and removal of CO22..

Larger organisms must have some Larger organisms must have some form of internal transport system for form of internal transport system for gases. gases.

PathwayPathwayAir (outside) Air (outside) nasal passages (or mouth) nasal passages (or mouth)

pharynx pharynx larynx larynx trachea trachea bronchus bronchus bronchiole bronchiole alveoli alveoli bloodstream bloodstream

Nasal passagesNasal passages

- - Air is warmed and moistened. Dust and Air is warmed and moistened. Dust and bacteria removed by mucous and nasal hairs bacteria removed by mucous and nasal hairs (cilia).(cilia).

Cilia - creates wave-like movement to Cilia - creates wave-like movement to sweep mucous upwards to be expeled at sweep mucous upwards to be expeled at

the mouth/nose (along with trapped debris)the mouth/nose (along with trapped debris)

Cilia animationCilia animation

http://www.bioscope.org/taste/cd1/a0http://www.bioscope.org/taste/cd1/a0255a.htm255a.htm

TracheaTrachea Hollow tube held open by ‘C’ shaped

bands of cartilage. It branches into the two bronchi (one:

bronchus) which also have cartilaginous rings.

Alveolus

Bronchus then branch Bronchus then branch into smaller tubes into smaller tubes called called bronchiolesbronchioles which lead into grape-which lead into grape-like clusters of thin-like clusters of thin-walled air sacs called walled air sacs called alveoli alveoli (one: (one: alveolusalveolus) ) which are surrounded which are surrounded by by blood capillariesblood capillaries. .

Oxygen diffuses Oxygen diffuses across the moist across the moist lining of the alveoli lining of the alveoli into the capillaries.into the capillaries.

COCO22 diffuses out of diffuses out of the capillary and the capillary and into the air in the into the air in the alveoli. alveoli.

SurfactantSurfactant

Lipoprotein Lipoprotein produced by produced by alveolar cellsalveolar cells

Reduced surface Reduced surface tension tension (if no (if no surfactant – lung surfactant – lung cannot inflate cannot inflate normally)normally)

PigmentPigment Oxygen is picked up by a red pigment Oxygen is picked up by a red pigment

called haemogoblin (in red blood cells) called haemogoblin (in red blood cells) and is carried around the body in the and is carried around the body in the circulatory system . circulatory system .

As the blood carrying the oxygen As the blood carrying the oxygen (oxygenated blood) passes through the (oxygenated blood) passes through the body the haemoglobin releases oxygen body the haemoglobin releases oxygen which diffuses into the cells.which diffuses into the cells.

Other bitsOther bits

DiaphragmDiaphragm is a sheet is a sheet of muscle at bottom of muscle at bottom of these cavitiesof these cavities

Pleural membranePleural membrane lines each cavity and lines each cavity and covers each lung, and covers each lung, and encloses encloses pleural pleural space (which space (which contains fluid to help contains fluid to help membranes slide past membranes slide past each other during each other during breathing) breathing)

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Breathing/VentilationBreathing/Ventilation

Inhalation – Breathing InInhalation – Breathing In Diaphragm contracts Diaphragm contracts

(lowered), intercostal (lowered), intercostal muscles contract - muscles contract - lifts ribs up and out. lifts ribs up and out.

Increases volume of Increases volume of chest cavity chest cavity cause cause the air from outside the air from outside to rush in and fill up to rush in and fill up the increased space.the increased space.

Exhalation – Breathing outExhalation – Breathing out

Diaphragm and Diaphragm and intercostal muscles intercostal muscles relaxes relaxes

Diaphragm moves Diaphragm moves up and the ribs up and the ribs down down

Air is forced out as Air is forced out as the volume in the the volume in the chest cavity chest cavity returns to normal.returns to normal.

The breathing action (diaphragm The breathing action (diaphragm etc.) uses considerable energy but etc.) uses considerable energy but allows the animal to change the rate allows the animal to change the rate of gas exchange quickly to suit of gas exchange quickly to suit activity/environment requirements. activity/environment requirements.

Alveoli ↑’s surface Alveoli ↑’s surface area exposed for area exposed for diffusion of Odiffusion of O22 into into capillaries and COcapillaries and CO22 out into alveoli.out into alveoli.

300 million alveoli 300 million alveoli creates 40x the creates 40x the surface area of the surface area of the body.body.

Increased Surface Area for Gas Increased Surface Area for Gas ExchangeExchange

Moist SurfacesMoist Surfaces Moist surface within nasal passages, Moist surface within nasal passages,

alveoli and capillaries help Oalveoli and capillaries help O22 in air to in air to dissolve into the watery substance for dissolve into the watery substance for diffusion into capillaries.diffusion into capillaries.

Thin Exchange SurfaceThin Exchange Surface Thin surface of alveoli and capillaries ↓’s Thin surface of alveoli and capillaries ↓’s

barrier for diffusion of Obarrier for diffusion of O22 into capillaries and into capillaries and COCO22 out. out.

A more specialised system is required for the A more specialised system is required for the increased size of the animal to deal with:increased size of the animal to deal with:

→ → the inefficiency of diffusion over longer distancesthe inefficiency of diffusion over longer distances→ → higher demand for Ohigher demand for O2 2 and removal of COand removal of CO22..

Internal lungs are well protected from:Internal lungs are well protected from:→ → physical damage physical damage → → drying out in a dry environment. Enables drying out in a dry environment. Enables

mammals to have a wider range of habitats e.g. mammals to have a wider range of habitats e.g. dry, wet, water on land.dry, wet, water on land.

Lungs have a higher surface area to maximise rate Lungs have a higher surface area to maximise rate of diffusion of Oof diffusion of O2 2 into capillaries and removal of into capillaries and removal of COCO22..

Then the OThen the O22 and CO and CO22 is transported around the is transported around the body in the bloodstream of the circulation body in the bloodstream of the circulation system.system.

Blood vessels in the lungBlood vessels in the lung

Some more interesting Some more interesting info/picturesinfo/pictures

Warning – some pictures are a bit Warning – some pictures are a bit gory – so stop here if you are gory – so stop here if you are sensitive to blood and gore.sensitive to blood and gore.

Figure 23–8

Cross-section of the lung and Cross-section of the lung and heartheart

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Normal lung tissue

Smoker’s lung tissue

Cilia Cilia can be immobilized by can be immobilized by smokingsmoking

Cystic fibrosisCystic fibrosisFaulty chloride channel leads to thick mucus Faulty chloride channel leads to thick mucus

difficult to clear difficult to clear blockage and infection blockage and infection

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Normal lung tissue

Lung tissue from cystic fibrosis patient

Black lung diseaseBlack lung disease

An electron micrograph scan of coal dust (marked by dark patches) in lung tissue infected with black lung disease. A disease found primarily in older coal workers, black lung is characterized by thickening and scarring of lung tissue.

Pneumothorax: air trapped in the chest cavity.(Tension pneumothorax: life-threatening)

Pneumothorax: air trapped in the chest cavity.(Tension pneumothorax: life-threatening)