Respiratory System

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Chapter 17The Respiratory

System

Functions of the Respiratory System

• Cooperates with the cardiovascular system in supplying oxygen to cells and removing CO2

• Warms, moistens and filters debris and pathogens from inspired air

• Contains receptors for smell• Produces sound• Helps eliminate wastes

RESPIRATORY SYSTEM OVERVIEWOrgans

• The upper respiratory tract includes:• the nose,• the pharynx and• associated structures (tonsils, sinuses,etc.)• The lower respiratory tract includes:• the larynx,• the trachea• the bronchi and • the lungs which contain branches of bronchi that

ultimately end in alveoli.

Functional Divisions• Conducting Structures that conduct air into the

lungs and condition it before it enters the lungs:• the nose,• the pharynx,• the larynx,• the trachea• the bronchi, bronchioles and terminal bronchioles.• Respiratory Structures where gas exchange

occurs:• the respiratory bronchioles, • alveolar ducts, • alveolar sacs • alveoli.

Transition from Conducting to Respiratory Portions of the RT• The cells and tissues of the conducting

portion of the RT gradually change such that there is a decrease in:

• goblet cells• cartilage• ciliated cells• height of cells• and an increase in:• smooth muscle• elastic fibers.

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Air Conditioning• A major function of the conducting portion

of the RT is to condition the inspired air, i.e., to warm, moisten and filter it.

• Structures that carry out these functions are:

• vibrissae (specialized hairs)• The mucous, ciliated respiratory epithelium• highly vascularized underlying CT • nasal conchae (turbinates) within the nasal

fossae

Respiratory Epithelium• PSCCE gradually changes to:• simple columnar ET, then• simple cuboidal ET in terminal

bronchioles • which lacks goblet cells but retains

ciliated cells• simple squamous ET in alveoli

The Respiratory Epithelium

PSCCE lines most of the respiratory tract except the terminal branches of the

bronchioles, the alveoli and inferior portions of the pharynx.

The lamina propria contains serous glands that contribute to moistening inspired air.

SEM of Surface of Respiratory Epithelium

The movement of these cilia propels mucus and trapped particles toward the pharynx.

Five Cell Types in the Respiratory Epithelium(in order of abundance)

• Ciliated columnar cells• Goblet (mucous) cells• Basal (stem) cells• Brush cells• sensory receptors with numerous microvilli• Small granule cells• endocrine - may act on caliber of bv or airwayNote: all cell types sit on the basement membrane

Figure 24-02a

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The Nasal Cavity• Consists of:• the Vestibule• the external portion of the nasal cavity• contains external nares lined with

keratinized stratified squamous ET that gradually changes into respiratory ET before entering

• the Nasal Fossae,• two convoluted openings within the skull• whose lateral walls contain three nasal

conchae.

Paranasal Sinuses and Conchae

Nasal Conchae• Function to increase the surface area of

the respiratory epithelium for filtering, warming and moistening inspired air.

• The lamina propria under the RE contains large venous plexuses called swell bodies

• that alternately become engorged with blood, shifting air flow to allow RE to recover from desiccation

Paranasal Sinuses• Air-filled chambers that occur in the

frontal, maxillary, ethmoid and sphenoidbones of the skull.

• They are lined with a thinner RE that contains few goblet cells.

• They communicate with the nasal cavity through small openings.

• They function to lighten the skull and act as resonating chambers for the voice.

Upper Respiratory Tract

The nasopharynx contains the openings into the Eustachian tubes and pharyngeal tonsil. The oropharynx contains the

lingual and palatine tonsils.

The Larynx

The larynx is a box supported by 9 cartilages.

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Larynx, posterior view Larynx, sagittal section

The lingual surface of the epiglottis is covered with stratified squamous ET which changes to

PSCCE at the base of the laryngeal surface.

Vocal Cords• Below the epiglottis, the mucosa forms

two pairs of folds that extend into the lumen of the larynx:

• The upper pair are the ventricular folds(false vocal cords) covered with RE.

• The lower pair are the true vocal cordscontaining the elastic vocal ligaments and vocalis muscles covered by stratified squamous ET.

The Vocal Cords

The Glottis, closed

Intrinsic laryngeal muscles close the glottis during swallowing.

Laryngoscopic View

Anterior

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VoF VF

VM

GL

LC

Larynx, humanl.s. x14

VM = vocalis muscleVoF = vocal foldVF = vestibular foldGL = mucous and seromucous glands LC = laryngeal cartilage

The Trachea• Extends from the base of the larynx to the

point at which it bifurcates into the two primary bronchi (about 10 cm or 4 in).

• It is lined in RE and contains 16-20 C-shaped rings of hyaline cartilage in the lamina propria.

• These incomplete rings keep the tracheal lumen open and allow changes in its diameter.

• A fibroelastic ligament (annular ligament) and the trachealis muscle (smooth muscle) bridge the open ends.

Trachea and Esophagus, cs

The incomplete rings of cartilage permit expansion of the esophagus into the trachea during swallowing.

Trachea and Esophagus, cs

Trachea, monkeyl.s. x270

Identify:Goblet cell Lamina propriaSubmucosaMucous and glandsPerichondriumC-shaped hyaline cartilage

The Thoracic Cavity

The Right lung is thicker, broader and shorter and has 3 lobes separated by 2 fissures.

The L lung has 2 lobes separated by a single oblique fissure.

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Trachea and Bronchi, anterior view

The right primary bronchus is shorter, wider and more vertical than the left. Implications?

The Bronchial Tree• After entering the lungs, the primary bronchi give

rise to 3 bronchi in the R lung and 2 in the L.• These are the secondary (lobar) bronchi which

are characterized by 5-6 cartilagenous plates around their circumference.

• The lobar bronchi divide repeatedly (about 12 times) giving rise to smaller bronchi with fewer and smaller plates of cartilage in their walls.

• Tertiary (segmental) bronchi have 3 plates of cartilage.

The Bronchial Tree

Each lobe receives its own secondary (lobar) bronchus which branches multiple times. As long as

cartilage is present, these branches are bronchi.

This is a plastic cast of an adult bronchial tree.

Bronchi and Bronchioles Bronchus, x.s.x132

LSM

HC

LT

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A Large Bronchus Photomicrograph of a section of Lung

Bronchi have cartilage in their walls, bronchioles do not.

Bronchioles• The terminal branches of bronchi are

bronchioles.• Bronchioles lack cartilage and glands but

retain PSCCE that gradually changes to simple ciliated columnar with few goblet cells and finally to simple cuboidal epithelium.

• They are 1 mm or less in diameter and have scalloped lumens.

• Their lamina propria is composed largely of smooth muscle and elastic fibers.

• Vagal (parasympathetic) stimulation causes constriction and sympathetic stimulation causes dilatation of the bronchioles.

Bronchiole, x.s.x270

Sm LT

Terminal Bronchioles• Lack cartilage,• Lined in ciliated simple columnar

epithelium without goblet cells,• Accompanied by branches of the

pulmonary artery,• Branch to form 2 or more respiratory

bronchioles.• The epithelium of terminal

bronchioles contains nonciliated,secretory Clara cells.

Terminal Bronchioles, x.s.

x132

TB

TB

TB

RB

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Clara CellsA Lung Lobule

Pulmonary lobules are pyramid-shaped with the apex (containing a bronchiole) pointed toward the

hilum of the lung. Each bronchiole divides to form 5-7 terminal bronchioles within the lobule.

Organization of a Lung Lobule Respiratory Bronchioles

• Lined with ciliated cuboidal epithelial and Clara cells,

• With underlying smooth muscle and elastic CT.

• Walls are interrupted by numerous alveoli where gas exchange occurs.

• At the distal portions, alveoli become more numerous and the cuboidalepithelial cells lose their cilia.

Alveolar Ducts

• The walls of alveolar ducts consist of alveoli with smooth muscle bundles in the lamina propria,

• Smooth muscle disappears at the distal ends of alveolar ducts,

• Elastic and collagen fibers provide the only support for the duct and its alveoli.

Alveolar Sacs• Common areas for openings of a

cluster of alveoli,• Supported by elastic and reticular

fibers.

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Diagram of Lung Tissue

Note:Smooth muscle bundles in the

walls of alveolar ducts appear as knobs between

adjacent alveoli.

SEM of Alveoli

Alveoli• Sac-like evaginations of the respiratory

bronchioles, alveolar ducts and alveolar sacs;• The terminal portions of the bronchial tree;• Covered by the richest capillary network in the

body.• Walls contain:• Type I (squamous alveolar) cells, • Type II (great alveolar or septal) cells and• macrophages (dust cells).• A few brush cells may be present to serve as

receptors monitoring air quality.

Cell Types in Alveoli

Type I (squamous alveolar) cells make up 97% of the alveolar surface and

Type II (septal or “great alveolar”) cells are most of the remaining 3%.

The alveolar

septum has thin and

thick portions.

The squamous Type I cells provide a barrier of minimal thickness that is readily permeable to

gases. The Type II cells secrete surfactant which lowers alveolar surface tension preventing

collapse of alveoli.

Respiratory Membrane The Respiratory Membrane (Blood-air Barrier or Alveolar-capillary Barrier)

The thinnest

membrane in the

body is found

where the alveolar

air space meets a

capillary.

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Lungx14

RB

TBLN

HC

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