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INTRODUCTION TO THE INTRODUCTION TO THE RESPIRATORY SYSTEMRESPIRATORY SYSTEM

OxygenOxygen and and Carbon Dioxide Carbon Dioxide are respiratory are respiratory gasesgases

Most cells require continuous Most cells require continuous oxygenoxygen supply supply for production of energy.for production of energy.

Without oxygen supply cells die.Without oxygen supply cells die.

Carbon dioxide Carbon dioxide is a waste product of cellular is a waste product of cellular metabolism. Its accumulation leads metabolism. Its accumulation leads to to acidosis.acidosis.

Exchange of respiratory gases Exchange of respiratory gases between between cellscells and their surrounding for homeostasis is and their surrounding for homeostasis is maintained by maintained by Respiration.Respiration.

IMPORTANT FACTS:IMPORTANT FACTS:

Phylogenesis of Respiratory SystemPhylogenesis of Respiratory System

In In ProtozoaProtozoa, (, (unicellular organism) oxygen and unicellular organism) oxygen and carbon carbon dioxidedioxide diffuse directly through cell diffuse directly through cell surfaces.surfaces.

MetazoaMetazoa (multicellular organisms) developed (multicellular organisms) developed specific specific respiratory areasrespiratory areas and liquid ( and liquid (blood) blood) transporttransport systems thus providing systems thus providing transportation of respiratory gases .transportation of respiratory gases .

MammalsMammals have highly developed respiratory have highly developed respiratory and circulatory systems. and circulatory systems.

RESPIRATORY TERMINOLOGYRESPIRATORY TERMINOLOGYRespirationRespiration:: is a complex process of exchange of is a complex process of exchange of respiratory gases (Oxygen & Carbon dioxide) between respiratory gases (Oxygen & Carbon dioxide) between an organism and external environment. It requires a an organism and external environment. It requires a constant supply of fresh air by Breathing in and out.constant supply of fresh air by Breathing in and out.

BreathingBreathing:: is a process of continuous ventilation of is a process of continuous ventilation of the lungs when a fresh atmospheric air will replace an the lungs when a fresh atmospheric air will replace an air used for the external (pulmonary) respirationair used for the external (pulmonary) respiration– Breathing includes two phases: Breathing includes two phases:

InspirationInspiration –– when air is taken into the lungs and when air is taken into the lungs and ExpirationExpiration –– when air is removed from these organs when air is removed from these organs

– Breathing involves skeletal components of thoracic Breathing involves skeletal components of thoracic cage and muscles of respiration, which produce cage and muscles of respiration, which produce respiratory movements.respiratory movements.

During ventilation of lungs a reciprocal During ventilation of lungs a reciprocal movement of air is caused by alternately movement of air is caused by alternately increasingincreasing and and decreasingdecreasing the volume of the the volume of the chest in breathing. chest in breathing.

Perfusion of lungs is achieved via branches of Perfusion of lungs is achieved via branches of pulmonary arteriespulmonary arteries, which bring , which bring deoxygenated deoxygenated bloodblood to the lungs for its to the lungs for its oxygenationoxygenation

Ventilation and PerfusionVentilation and Perfusion

RESPIRATION employs three processes:RESPIRATION employs three processes:External respirationExternal respiration involves the stage of involves the stage of taking taking oxygenoxygen from the air into the blood and from the air into the blood and returning returning carbon dioxide carbon dioxide to the air. It occurs to the air. It occurs through the Respiratory Membranes (air-blood through the Respiratory Membranes (air-blood barriers).barriers).Transport of respiratory gasesTransport of respiratory gases in the blood in the blood throughout the body via the circulatory system. throughout the body via the circulatory system. InternalInternal or or cellularcellular respiration is the process respiration is the process by which glucose or other small molecules by which glucose or other small molecules within the cell are oxidized to produce energy: within the cell are oxidized to produce energy: this requires this requires oxygenoxygen and generates and generates carbon carbon dioxidedioxide..

Pulmonary ventilation ensures that alveoli are supplied Pulmonary ventilation ensures that alveoli are supplied with with oxygenoxygen, and it removes , and it removes carbon dioxide carbon dioxide arriving arriving from bloodstream.from bloodstream.

The actual process of gas exchange occurs between The actual process of gas exchange occurs between the blood and alveolar air the blood and alveolar air across the respiratory across the respiratory membranemembrane..

The driving force for exchange of respiratory gases is The driving force for exchange of respiratory gases is defined by a difference of Partial Pressure of Gases in defined by a difference of Partial Pressure of Gases in the air and blood and an ability of their molecules to the air and blood and an ability of their molecules to diffuse from a gas into a liquid and vice versa. diffuse from a gas into a liquid and vice versa.

During gas exchange between air & blood During gas exchange between air & blood molecules molecules of each gas diffuse from area with higher pressure to of each gas diffuse from area with higher pressure to area with lower pressurearea with lower pressure (Henry’s Law) (Henry’s Law)

GAS EXCHANGE AT RESPIRATORY MEMBRANE:GAS EXCHANGE AT RESPIRATORY MEMBRANE:

Inspired air:Inspired air:– Nitrogen – 597 (78.6%)Nitrogen – 597 (78.6%)– Oxygen – 159 (20.8%)Oxygen – 159 (20.8%)– Carbon Dioxide – 0.3 (0.04%)Carbon Dioxide – 0.3 (0.04%)– Water Vapor – 3.7 (0.5%)Water Vapor – 3.7 (0.5%)

Alveolar air:Alveolar air:– Nitrogen – 573 (75.4%)Nitrogen – 573 (75.4%)– Oxygen – 100 (13.2%)Oxygen – 100 (13.2%)– Carbon Dioxide – 40 (5.2%)Carbon Dioxide – 40 (5.2%)– Water Vapor – 47 (6.2%)Water Vapor – 47 (6.2%)

Expired air:Expired air:– Nitrogen – 569 (74.8%)Nitrogen – 569 (74.8%)– Oxygen – 116 (15.3%)Oxygen – 116 (15.3%)– Carbon Dioxide – 28 (3.7%)Carbon Dioxide – 28 (3.7%)– Water Vapor – 47 (6.2%)Water Vapor – 47 (6.2%)

Partial Pressure & Normal Gas Concentration in AirPartial Pressure & Normal Gas Concentration in Air

Exchange & Transport of GasesExchange & Transport of Gases

Diffusion of Gases-Fick's LawDiffusion of Gases-Fick's Law Transfer of gases across cell membranes or capillary walls Transfer of gases across cell membranes or capillary walls

occurs by occurs by simple diffusionsimple diffusion. For gases, the rate of transfer by . For gases, the rate of transfer by diffusion (X) is directly proportional to the driving force, a diffusion diffusion (X) is directly proportional to the driving force, a diffusion coefficient, and the surface area available for diffusion; it is coefficient, and the surface area available for diffusion; it is inversely proportional to the thickness of membrane barrier. Thus,inversely proportional to the thickness of membrane barrier. Thus,

VX - Volume of gas transferred per unit time D - Diffusion coefficient of the gas A - Surface area ΔP - Partial pressure difference of the gas ΔX - Thickness of the membrane

Diffusion of Gases-Fick's LawDiffusion of Gases-Fick's Law

The driving force for diffusion of a gas is the The driving force for diffusion of a gas is the partial pressure difference of the gas partial pressure difference of the gas (ΔP)(ΔP) across the membrane, across the membrane, notnot the concentration the concentration difference. difference.

Thus, if the PO2 of alveolar air is 100 mm Hg Thus, if the PO2 of alveolar air is 100 mm Hg and the PO2 of mixed venous blood that enters and the PO2 of mixed venous blood that enters the pulmonary capillary is 40 mm Hg, then the the pulmonary capillary is 40 mm Hg, then the partial pressure difference, or driving force, for partial pressure difference, or driving force, for O2 across the alveolar/pulmonary capillary O2 across the alveolar/pulmonary capillary barrier is 60 mm Hg (100 mm Hg - 40 mm Hg).barrier is 60 mm Hg (100 mm Hg - 40 mm Hg).

Transport of GasesTransport of Gases

Transport of Carbon DioxideTransport of Carbon Dioxide

Conditions for Oxygenation of Blood:Conditions for Oxygenation of Blood:

Sufficient surface areas Sufficient surface areas (Respiratory Areas) for (Respiratory Areas) for gaseous exchange between Atmospheric air gaseous exchange between Atmospheric air and Bloodand Blood

Presence of Respiratory Membranes Presence of Respiratory Membranes (air-blood (air-blood barriers) with a very short diffusion path barriers) with a very short diffusion path between Atmospheric air and Bloodbetween Atmospheric air and Blood

Concentration gradients Concentration gradients for diffusion of Oxygen for diffusion of Oxygen and Carbon dioxide between the air and bloodand Carbon dioxide between the air and blood

Conditions for Oxygenation of Blood:Conditions for Oxygenation of Blood:

The surface area available in adult lungs for The surface area available in adult lungs for gaseous exchange is around gaseous exchange is around 140m²140m², which is , which is about the area of a single tennis court. about the area of a single tennis court.

The blood in the alveolar capillaries is The blood in the alveolar capillaries is separated from alveolar air by a thin (0.6* in separated from alveolar air by a thin (0.6* in many places) many places) respiratory membranerespiratory membrane (1* = one (1* = one thousandth of a mm). thousandth of a mm).

Respiratory Membrane includes:Respiratory Membrane includes:

1. 1. Cell membrane & Cytoplasm of the Cell membrane & Cytoplasm of the covering alveolar epithelial cellcovering alveolar epithelial cell, lined with , lined with a layer of a layer of SurfactantSurfactant, which has contact , which has contact with an air with a high Oxygen content.with an air with a high Oxygen content.2. 2. Cell membrane & Cell membrane & Cytoplasm of Cytoplasm of endothelial cell of the adjacent blood endothelial cell of the adjacent blood capillarycapillary, containing red blood cells with a , containing red blood cells with a high Carbon Dioxide content.high Carbon Dioxide content.3. 3. Fused basal laminae Fused basal laminae of the above two of the above two epithelial cells. epithelial cells.

Components of Respiratory MembraneComponents of Respiratory Membrane

Alveolar Air

Diffusion gradients are maintained by:Diffusion gradients are maintained by:

VentilationVentilation (breathing) which renews alveolar (breathing) which renews alveolar air, maintaining oxygen concentration near that air, maintaining oxygen concentration near that of atmospheric air and preventing the of atmospheric air and preventing the accumulation of carbon dioxide.accumulation of carbon dioxide.

The The flow of blood flow of blood in alveolar capillaries which in alveolar capillaries which continually brings blood with low oxygen continually brings blood with low oxygen concentration and high carbon dioxide concentration and high carbon dioxide concentration to the respiratory membranes.concentration to the respiratory membranes.

Sites For External Respiration:Sites For External Respiration:

Areas of the body, which may have a Areas of the body, which may have a ppresence of Respiratory Membranes with resence of Respiratory Membranes with a very short diffusion path between a very short diffusion path between atmospheric air and blood & appropriate atmospheric air and blood & appropriate concentration gradients of oxygen and concentration gradients of oxygen and carbon dioxide in the air and blood, may carbon dioxide in the air and blood, may perform External Respiration.perform External Respiration.

Three Types of External Respiration:Three Types of External Respiration:

Lungs, Skin and Alimentary Canal have Lungs, Skin and Alimentary Canal have conditions for External Respirationconditions for External Respiration

Pulmonary respiration - 85%; Pulmonary respiration - 85%;

Cutaneous respiration - 10%; Cutaneous respiration - 10%;

Intestinal respiration - 5%.Intestinal respiration - 5%.

GROSS ANATOMY OF GROSS ANATOMY OF THE RESPIRATORY THE RESPIRATORY

SYSTEMSYSTEM(OVERVIEW)(OVERVIEW)

THREE COMPONENTS OF THE THREE COMPONENTS OF THE RESPIRATORY SYSTEM:RESPIRATORY SYSTEM:

RESPIRATORY TRACTRESPIRATORY TRACT– Conducting portionConducting portion– Respiratory portionRespiratory portion

LUNGS & PULMONARY CIRCULATIONLUNGS & PULMONARY CIRCULATION

ADDITIONAL STRUCTURES INVOLVED IN ADDITIONAL STRUCTURES INVOLVED IN PULMONARY VENTILATIONPULMONARY VENTILATION

RESPIRATORY SYSTEM

RESPIRATORY TRACT RESPIRATORY TRACT (AIRWAY)(AIRWAY)

Its conducting portionIts conducting portion is composed of is composed of interconnected hollow organs, thus forming a interconnected hollow organs, thus forming a branching out passageway, which has branching out passageway, which has hard hard elementselements (bones, cartilages, ligaments) (bones, cartilages, ligaments) in its in its walls. Those elements maintain to keep walls. Those elements maintain to keep lumina of hollow organs patent, because they lumina of hollow organs patent, because they prevent collapsing of walls of air passages. prevent collapsing of walls of air passages.

Two Major Subdivisions of Two Major Subdivisions of Conducting Portion:Conducting Portion:

a)a) Upper part/airwayUpper part/airway (nasal cavity with (nasal cavity with paranasal air sinuses, oral cavity, nasopharynx, paranasal air sinuses, oral cavity, nasopharynx, oropharynx and upper portion of oropharynx and upper portion of laryngopharynx);laryngopharynx);

b)b) Lower part/airwayLower part/airway (larynx, trachea, (larynx, trachea, extrapulmonary bronchi, intrapulmonary extrapulmonary bronchi, intrapulmonary bronchi, regular and terminal bronchioles). It bronchi, regular and terminal bronchioles). It includes bronchial trees. includes bronchial trees.

Subdivisions of Respiratory Tract

Upper & Lower AirwayUpper & Lower Airway

4

5

6

Nasal Cavity

Pharynx

OralCavity

Larynx

Trachea

RESPIRATORY TRACT RESPIRATORY TRACT (AIRWAY)(AIRWAY)

Its respiratory portion – “Respiratory Tree”:Its respiratory portion – “Respiratory Tree”: consists of functional units “Acini”, which consists of functional units “Acini”, which include respiratory bronchioles, alveolar ducts, include respiratory bronchioles, alveolar ducts, alveolar atria or vestibules and alveolar sacs alveolar atria or vestibules and alveolar sacs with alveoli. Acini are attached to the smallest with alveoli. Acini are attached to the smallest elements of the bronchial tree – the terminal elements of the bronchial tree – the terminal bronchioles.bronchioles.

Lowest part of Conducting Portion & Respiratory PortionLowest part of Conducting Portion & Respiratory Portion

Outside air:Outside air:Varies in temperature. Varies in temperature. At the alveolarAt the alveolar surface it must surface it must be at body temperaturebe at body temperatureVaries from very dry to very humid. Varies from very dry to very humid. At the alveolar At the alveolar surface it must be saturated with water vapoursurface it must be saturated with water vapourContains dust and debris. Contains dust and debris. These must not reach the These must not reach the alveolar wallalveolar wallContains micro-organisms, Contains micro-organisms, which must be filtered out which must be filtered out of the inspired air and of the inspired air and disposed,disposed, before they reach the before they reach the alveoli, enter the blood and cause possible problems.alveoli, enter the blood and cause possible problems.It is easy to see that the temperature and humidity of It is easy to see that the temperature and humidity of inspired air will increase as it passes down a long inspired air will increase as it passes down a long series of tubes lined with a moist mucosa at body series of tubes lined with a moist mucosa at body temperature. The mechanisms for filtering are not so temperature. The mechanisms for filtering are not so obvious though the turbulence of inspired air could obvious though the turbulence of inspired air could play some role in it.play some role in it.

Functions of Nasal CavityFunctions of Nasal Cavity

It is also filtered & cleaned there.

LUNGSLUNGS

Lungs Lungs areare paired parenchymatous organs, paired parenchymatous organs, which consist of which consist of lobeslobes, , bronchopulmonary bronchopulmonary segmentssegments and and lobuleslobules..They also include intrapulmonary bronchi, They also include intrapulmonary bronchi, bronchioles and numerous bronchioles and numerous Respiratory Trees Respiratory Trees or or functional units: functional units: AciniAcini, , which contain which contain Respiratory Membranes Respiratory Membranes (air-blood barriers)(air-blood barriers).. Latter serve for gas exchange between Latter serve for gas exchange between atmospheric air and blood. Transport of gases atmospheric air and blood. Transport of gases with the blood to and from lungs is provided via with the blood to and from lungs is provided via the pulmonary circulation.the pulmonary circulation.

ADDITIONAL STRUCTURES ADDITIONAL STRUCTURES INVOLVED IN PULMONARY INVOLVED IN PULMONARY

VENTILATIONVENTILATIONThey include the: They include the:

– Visceral and parietal Visceral and parietal pleurae pleurae

– Two plural cavities (right & left)Two plural cavities (right & left)

– Bones and joints of the thoracic cage Bones and joints of the thoracic cage

– Muscles of respiration with their blood and Muscles of respiration with their blood and nerve supply)nerve supply)

Mechanism of breathing.Mechanism of breathing. In order to grasp the way in which we breathe we have In order to grasp the way in which we breathe we have to grasp the following facts:to grasp the following facts:– Each lung is surrounded by a pleural cavity or sac, except Each lung is surrounded by a pleural cavity or sac, except

where the plumbing joins it to the rest of the body, rather like where the plumbing joins it to the rest of the body, rather like a hand in a boxing glove. a hand in a boxing glove.

The glove has an outer and inner surface, separated by a layer of The glove has an outer and inner surface, separated by a layer of padding. The pleura, similarly, has two surfaces, but the padding is padding. The pleura, similarly, has two surfaces, but the padding is replaced by a thin layer of fluid. replaced by a thin layer of fluid.

– Each lung is enclosed in a cage bounded below by the Each lung is enclosed in a cage bounded below by the diaphragm and at the sides by the chest wall and the diaphragm and at the sides by the chest wall and the mediastinum. mediastinum.

– Breathing works by making the cage bigger: the pleural Breathing works by making the cage bigger: the pleural layers slide over each other and the pressure in the lung is layers slide over each other and the pressure in the lung is decreased, so air is sucked in. Breathing out does the decreased, so air is sucked in. Breathing out does the reverse, the cage collapses and air is expelled. reverse, the cage collapses and air is expelled.

Arrangement of PleuraArrangement of Pleura

Ribs, Respiratory Muscles, Lungs & PleuraeRibs, Respiratory Muscles, Lungs & Pleurae

Parietal Pleura Visceral Pleura

Mechanism of breathing.Mechanism of breathing. Breathing movements are sometimes divided into:Breathing movements are sometimes divided into:– Pump handle movementsPump handle movements, the sternal end of rib is elevated , the sternal end of rib is elevated

or depressed on its vertebral joints or depressed on its vertebral joints – Bucket handle movementsBucket handle movements, the rib rotating on its axis , the rib rotating on its axis

around anterior and posterior attachments.around anterior and posterior attachments.

With more and more effort put into deeper and deeper With more and more effort put into deeper and deeper breathing the scalene muscles of the neck contract, breathing the scalene muscles of the neck contract, raising the first rib and hence the rest of the cage, raising the first rib and hence the rest of the cage, then other neck muscles and even those of the upper then other neck muscles and even those of the upper limb become involved. limb become involved.

A patient with difficulty in breathing often grips a table A patient with difficulty in breathing often grips a table edge in order to stabilize the limbs so that their edge in order to stabilize the limbs so that their muscles can be used to help in moving the thoracic muscles can be used to help in moving the thoracic wall.wall.

Expansion of Thoracic Cage (Bucket handle action)Expansion of Thoracic Cage (Bucket handle action)

Expansion of Thoracic Cage (Pump handle action)Expansion of Thoracic Cage (Pump handle action)

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