1.Respiratory Physiology

8/3/2019 1.Respiratory Physiology

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Physiologyof The Respiratory System


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Respiratory System Divisions

U pper tract Nose, pharynx

and associated

structuresLower tract Larynx, trachea,

bronchi, lungs


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Nasal Cavity

N ose:External noseNasal cavity Functions:

Passageway for air Cleans the air Humidifies, warms air Smell

Along with paranasal

sinuses areresonating chambersfor speech


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Nasal Cavity and Pharynx

Pharynx Common opening for

digestive andrespiratory systems

Three regionsNasopharynxOropharynx

Laryngopharynx


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Larynx

Functions Maintain an open passageway for air movement Epiglottis and vestibular folds prevent swallowed material from

moving into larynx Vocal folds are primary source of sound production


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Vocal Folds


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Tracheobronchial Tree

C onducting zone Trachea to terminal

bronchioles which isciliated for removal of debris

Passageway for air

movement Cartilage holds tubesystem open andsmooth musclecontrols tube diameter


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B ronchioles and AlveoliRespiratory zone Respiratory

bronchioles to alveoli Site for gas exchange


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A lveolus and Respiratory Membrane


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Surface area = 100m2

Thickness

= 0.5um


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Types of alveolar cells

Type I cells:

are thin primary liningcells.

Type II cellsthick with manyinclusions bodies (granular pneumocytes). Theysecrete surfactant.Other cells:e.g. pulmonary alveolar

macrophages (P A Ms)lymphocytes, mast cellsand plasma cells.


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Pleura

Pleural fluid produced by pleural membranes Acts as lubricant Helps hold parietal and visceral pleural

membranes together


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Thoracic Walls Muscles of Respiration


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Thoracic Volume


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A ir PassagesB etween the trachea and the

alveoli, the airways divide 23times:

The first 16 divisions (up tothe terminal bronchioles) formthe conducting zone that willtransport gases and perform

air conditioning function.The remaining 7 divisionsform the respiratory zone(from respiratory bronchioles)where gas exchange takesplace with blood and thealveoli.

There are 300 millions of alveoliin human lungs that will have atotal surface area 70 100 m2.


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Pulmonary C irculation1.Pulmonary A rtery :

Contains venous blood and the

pulmonary AB

P equals25/10 mmHg, so:- Upper lung (above the level of heart ) is less perfused.- Middle lung (at the level of heart) is better perfused.- Lower lung (below the level of heart) is well perfused.

2. Pulmonary arterioles:They are l ess muscular and l essinnervated than those of the

systemic circulation.They are co nstri c ted by hypoxia(so the blood is shifted to thebetter ventilated areas), N OR,angiotensin and PG-F2 alpha.They are dilat e d by A ch and

PG- I 2.


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3.Pulmonary veins :They are more distensiblethan those of the systemiccirculation so they act asblood reservoir


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4 .Pulmonary C apillaries :

They are larg e, withmu l tip l e anast o m o ses, sothat each alveolus sets in acapillary b a ske t .

Pulmonary capillaryhydrostatic pressure is only10 mmHg , while colloidosmotic pressure of plasmaproteins is 25 mmHg .This leads to H2Oreabsorption from lung =>lung remains dry which isimportant for its elasticity.


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5 .Physiologic shunt :

Some venous blood (fromthe bronchial and shortcardiac veins) does not passto the pulmonary capillariesto be oxygenated, but

instead, it passes to the leftside of the heart i.e blood inthe left side of heart is not100 % oxygenated, it is only2 % less oxygenated thanblood in the pulmonaryalveoli, i.e arterial Hb is not100 % saturated with O2(about 0.5 1% less).


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V ascularizatia si inervatia plamanului

C irculatia functionala;- a. pulmonara (VD), se capilarizeaza la nivelul alveolelor pulmonare;circulatia de intoarcere asigurata de vv. pulmonare (se varsa in AS).- a. pulmonara contine sange neoxigenat ce se incarca cu O2 la plamani sise intoarce prin vv. pulmonare (sange oxigenat, rosu) in AS.C irculatia nutritiva- face parte din marea circulatie, aduce plamanului sange incarcat cu

substante nutritive si oxigen.- asigurata de aa. bronsice, ramuri ale aortei toracice; ele iriga arborelebronsic.- o parte din sange se intoarce in vv. bronsice care se varsa in vv. azygos siacestea in VCS si AD; o alta parte din sange se intoarce prin vv. pulmonarein AS.

Cantitatea de sange ce trece prin anastomozele bronsice este1% din totalul sangelui care iriga plamanul.In conditii patologice (insuficienta cardiaca, bronsiectazii)debitul anastomotic poate ajunge la 80% din totalul sangeluicare iriga plamanul.


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Respiratory System Functions

Gas exchange: Oxygen enters blood andcarbon dioxide leavesRegulation of blood pH: Altered bychanging blood carbon dioxide levelsV oice production: Movement of air pastvocal folds makes sound and speechOlfaction: Smell occurs when airborne

molecules drawn into nasal cavityProtection: Against microorganisms bypreventing entry and removing them


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N on-respiratory functionSmell sensation (nose)Sound production (vocalization) via larynxHeat regulationAct as circulatory filter (preventing clots fromentering the circulation) and secretion of heparin andfibrinolytic agentAcid base balance (regulation of blood pH) viachange the rate of CO2 removal from bloodRelease of prostaglandins.Removal of some chemical substances (serotoninand norepinephrine)

Produce Angiotensin Converting Enzyme (ACE).


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RespirationV entilation: Movement of air into and out of lungs

Air moves from area of higher pressure to areaof lower pressurePressure is inversely related to volumeExternal respiration: Gas exchange betweenair in lungs and blood

Transport of oxygen and carbon dioxide inthe bloodInternal respiration: Gas exchange betweenthe blood and tissues


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I. InspirationIt is due to contraction of:1. Diaphragm:

2. External intercostal muscles: (likea handle of a bucket). This willincrease both the antero-posterior and the transverse diameters of thechest.

3. The pressure inside the thoraciccavity decreases only 1 mmHg belowthe atmospheric pressure, so, air rushes inside the lungs.


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On DEEP inspiration there will be:

1. More contraction of thediaphragm (7 cm descent) andthe external intercostal .

2. Contraction of the accessorymuscles of inspiration :- S tern ocl eid o m ast o id - elevates the sternum .- S errat u s anteri o r - elevatesmany ribs more.- S c a l eni mu s cl es - elevates firstrib.Lungs follow passively themovements of the chest wall dueto presence of a thin layer of fluidbetween the parietal and the

visceral pleurae.The diaphragm is responsible for 75 % of inspiration, yet , when it isparalyzed the external intercostalalone can produce inspirationneeded for moderate activity .


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II. Expiration

During normal breathing (eupnea) ,

it does not need muscle contractionbut it is due to elastic recoil of the lungand the chest wall, so the volume of the thoracic cavity decreases and thepressure inside the thorax increasesonly by 1 mmHg more than the

atmospheric causing air to rush outthe lungs.Expiration becomes active (i.e. needsmuscle contraction) during :

1. Forced expiration.2. B ronchial obstruction e.g.

bronchial asthma.3. Decreased lung elasticity e.g.

emphysema.


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Now expiration will be caused bycontraction of:

1- A b d om i n al musc l es : that willincrease the pressure inside theabdominal cavity pushing thediaphragm upward.

2- In t e r n al i n t e r cos tal muscles : thatcauses lowering of the ribs leadingto decreased transverse and APchest diameters.

Respiratory Rate : normally it isabout 12- 16 cycles /min.Respiratory cycle : is composed of :

1-Short inspiration (I)2-Longer expiration (E)3-Expiratory pause (during which theglottis is closed).


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The alveolo-capillary membrane(The respiratory membrane)It consists of the fluid film lining the alveolus,alveolar epithelium , interstitial space , andcapillary endothelium .The thickness of the membrane is about 0.5 umand the total surface area is about 70 m2.In the alveolar wall and the pulmonary interstitialtissue, there are elastin and collagen fibers.These elastic fibers allow alveolar and lungdistention, but at the same time, present a recoilforce in the distended lung.


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Surface area = 100m 2

Thickness

= 0.5um


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Sneeze reflex

Stimulus: : Irritation of nasal mucosaReceptor: in the nasal

cavityA fferent: Trigeminal N.Response: deep inspiration Forced expiration against open glottisA ction: get rid of irritant


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Cough reflexStimulus: Irritation of respiratory mucosaReceptor: trachea &bronchiA fferent: Vagus N.Response: deep inspiration forced expiration against closed glottis

which open suddenlyA ction: get rid of irritant

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1.Respiratory Physiology

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