9. the respiratory system

8/13/2019 9. the Respiratory System

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classification

Anatomical classification

Upper( nose, nasal cavity, sinuses,&pharynx.)

Lower ( larynx,trachea,bronchi,broncheoles,alveoles.)

Physiological classification

Conducting zone from the nose tobronchioles except respiratory bronchioles.

Respiratory zone.


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Airway anatomy.


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Airway anatomy the trachea.


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airway

There are two openings to the human

airway.

1.the nose which leads to the

nasopharynx .

2. the mouth which leads to the

oropharynx. These passages are

separated anteriorly the palate , but they

join posteriorly in the pharynx.


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The pharynx.

The pharynx is a U shaped fibro muscular

structure that extends from the base of the

skull to the cricoids cartilage.

It opens anteriorly in to the nasal cavity,

the mouth, the larynx.


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The larynx

The larynx is a cartilaginous skeleton held

together by ligaments & muscle.

It is composed of nine cartilages.

The opening of the larynx is called glottis.

The epiglottis prevents aspiration by

covering the glottis.


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Dead space

Areas of ventilation without perfusion.

Each inspired breath is composed of gas thatcontribute to alveolar ventilation ( VA) & gasthat become dead space( VD).

Thus tidal volume( VT) = VA + VD.

In the normal , spontaneously breathingperson, the ratio of alveolar-to-dead space

ventilation for each breath is 2:1. Physiologic dead space consists of anatomic& alveolar dead space.


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Anatomic dead space.

It arises from ventilation of structures that

do not exchange respiratory gases; the

oronasopharynx to the terminal &

respiratory bronchioles.

It is approximately 2ml/kg.


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Alveolar dead space

It arises from ventilation of alveoli where there islittle or no perfusion to the alveoli.

physiologic dead space is primarily influenced bychanges in alveolar dead space.(because disease

changes anatomic dead space little.) Rapid changes in physiologic dead space

ventilation most often arise from change inpulmonary blood flow, resulting in decreasedperfusion to ventilated alveoli.

The most common etiology of acutely increasedphysiologic dead space is an abrupt decrease inCO( shock), pulmonary embolism.


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Shunt. Areas of perfusion without ventilation.

Physiologic shunt occurs in lung that is perfused but poorly

ventilated( the portion of the total cardiac out put that returns to theleft heart & systemic circulation without receiving oxygen in the

lung.)

A small % of venous blood normally bypasses the right ventricle &

empties directly in to the left atrium.

this anatomic, absolute shunt arises from the venous return from the

pleural, bronchiolar,& thebesian veins( this venous drainage

accounts for 2 to 5% of the cardiac output.)

Anatomic shunts of greatest magnitude are usually associated with-

- congenital heart disease that cause right to left shunt.

-extensive acute lung injury.

-consolidated pneumonia.


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Function of the respiratory system.

Gas exchange between air & blood

Production of sound

Regulation of acid base balance.

Infection prevention.

1.the mucus used to stick & remove

any pathogens & particles.2. cilia propel mucus & debris to the

exterior.


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Process of respiration composed of

4 sequential phases.

1. Pulmonary ventilation air movement in &out of the lung.

2. External respiration exchange of gases

between air in the alveoli & blood in pulcap.

3. Transport of gases.

4. Internal respiration exchange of gasesbetween blood in systemic cap.& tissue.

5. Cellular respiration.


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Minute ventilation.

MV = TV x RR.

AV = (TV DV) x RR


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The lung natural tendency is to collapse;

thus expiration at rest is normally passive

because gas flows out of the lungs when

they elastically recoil.

The thoracic cage exerts an outward-

directed force, & the lungs exert an

inward-directed force.

Together these forces result in a sub

atmospheric intra pleural pressure.

Lung mechanics.


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The inward force of the lung ( elastic recoil)

consists of-

-the elastic fibers of lung tissue.-the contractile forces of airway smooth

muscles.

- the surface tension of alveoli.

The outward force of the chest wall is exerted

by - the ribs, joints & muscles.


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Contd

Because the outward force of the thoracic

cage exceeds the inward force of the lung

, the overall tendency of the lung is to

remain inflated when it resides within thethoracic cage.

When the outward & the inward forces on

the lung are equal ?


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Contd

Atmospheric pressure the pressure of the air surrounding the bodyat see level (760mmhg).

Intra alveolar pressure( intrapulmonary pressure) the pressure withinthe alveoli.

1.I AP must be lower than ATMP during inspiration.

2.IAP > ATMP during expiration.3.IAP= ATMP when ?.

Intra pleural pressure( intra thoracic pressure ) the pressure with inthe pleura sac.( 756mmhg)

1. the pressure exerted outside the lung within the thoraciccavity.

2.IPP < ATMP.3. IPP does not equilibrate with the ATMP or IAP because

there is no communication b/n them.


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Negativity of intra pleural pressure.

Both the lungs & thoracic wall are elasticstructures i.e. if they are stretched or

compressed by some force they will recoil

(return to their original size & positionwhen the force is removed.)

At rest the lungs are partially stretched(

inflated) & are attempting to recoil.

At rest the chest wall is compressed &

attempting to move out ward.


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Trance pulmonary pressure.

IAP IPP is known as trance pulmonary pressure.

760 756 = 4mmhg. This pressure is known asthe distending pressure of the alveoli.

Pneumothorax1. intra pleural & intra alveolar pressure are

equilibrated with the atmospheric pressure.

2.trance pulmonary pressure gradient no

longer exist.3. no force present to stretch the lung or

chest wall as a result the lung collapse.


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compliance.

Elastic recoil is usually measured in terms of

compliance ( C ) it is defined as the

change in volume divided by the change in

distending pressure.

C = change in lung volume/change in

transpulmonary pressure.


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alveolar-capillary membrane ( respiratory

membrane) has the following layers.

1.fluid & surfactant layer.2.the alveolar epithelium.

3. an epithelial basement membrane.

4. interstitial space b/n the alveolar

epithelium & the capillary membrane.

5.capillary basement membrane.

6. the capillary endothelial membrane.

diffusion across alveolar capillary membrane is


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diffusion across alveolar capillary membrane isdepending upon-

-surface area the smaller the lung, the less theoverall diffusion.

-membrane thickness, the longer the diffusiondistance & the lower the diffusion capacity.

-pressure gradient across the respiratorymembrane is the difference b/n the partial pressure ofthe gas in the alveoli & in the pulmonary capillaryblood.

-molecular weight the larger the molecule, the moredifficult it will be to pass through the membranes.

-solubility CO2 is almost 30x more soluble in waterthan oxygen is & diffuses more than 20x faster.

9. the respiratory system

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