The Respiratory System

Chapter 21

Introduction The trillions of cells making up the body

require a continuous supply of oxygen to carry out vita functions

We can survive only a few minutes without oxygen

As cells use oxygen, they give off carbon dioxide a waste product of cellular respiration which the body must eliminate

Introduction The major function of the respiratory system

is to supply the body with oxygen and dispose of carbon dioxide

To achieve this function four distinct processes, collectively called respiration occur– Pulmonary ventilation– External respiration– Transport of respiratory gases– Internal respiration (cellular respiration)

Introduction Pulmonary ventilation

– Air must be moved in and out of the lungs so that the gases in the air sacs (alveoli) of the lungs are continually changed and refreshed

– This air movement is commonly called ventilation or breathing

Introduction External respiration

– Gas exchange (oxygen loading and carbon dioxide unloading) must occur between the blood and the air-filled alveoli of the lungs

Introduction Transport of respiratory gases

– Oxygen and carbon dioxide must be transported between the lungs and tissue cells of the body

– This is accomplished by the cardiovascular system, which uses blood as the transporting fluid

Introduction Internal respiration

– At the systemic capillaries, gas exchanges (oxygen unloading and carbon dioxide loading) must be made between the blood and tissue cells

Respiratory System The organs of the

respiratory system include the nose, nasal cavity, paranasal sinuses pharynx, larynx, trachea, bronchi, and the lungs which contain the terminal air sacs or alveoli

Respiratory System Functionally, the

respiratory structures are divided into respiratory and conducting zones

Visible structures represent the conducting zone

Respiratory zone structures are small and lie deep within the lungs

Respiratory System Functionally, the respiratory system

consists of the respiratory and the conducting zones– The respiratory zone, the actual site of gas

exchange, is composed of the respiratory bronchioles, alveolar ducts, and alveoli

– The conducting zone includes all other respiratory passageways, which provide fairly rigid conduits for air to reach the sites of gas exchange

Respiratory System Organs of the conducting zone clean,

warm and humidify the incoming air Thus, the air reaching the lungs contain

must less dust than what entered the nose and is warm and damp

The Nose The nose is the

only externally visible part of the respiratory system

The external framework of the nose

The Nose The functions of the nose include

– Providing an airway for respiration– Moistening and warming entering air– Filtering inspired air and cleansing it of

foreign matter– Serving as a resonating chamber for speech– Housing the olfactory (smell) receptors

The Nose The structures of

the nose are divided into the– External nose

– Nasal cavity Surface features

– Root (between eyes)

– Bridge

– Dorsum nasi

– Apex

– Philtrum

– External nares

– Alae

The Nose - Nasal Cavity The nasal cavity lies in and posterior to the

external nose During breathing air enters the external

cavity by passing through the external nares or nostrils

The nasal cavity is divided by a midline nasal septum

The nasal cavity is continuous posteriorly with the nasal portion of the pharynx through the internal nares

The Nose - Nasal Cavity The roof of the nasal cavity is formed by

the ethmoid and sphenoid bones of the skull

The floor is formed by the palate which separates it from the oral cavity below

Anteriorly, where the palate is supported by the maxillary processes and the palatine bones is considered the hard palate

The unsupported posterior portion is the muscular soft palate

The Nose - Nasal Cavity

The vestibule is lined with skin containing sebaceous and sweat glands and numerous hair follicles

The hair, or vibrissae, filter coarse particles from inspired air

The Nose - Nasal Cavity The nasal cavity is lined with two types of

mucous membrane– The olfactory mucosa, lining the slitlike

superior region of the nasal cavity, contain the receptors for the sense of smell

– The balance of the nasal cavity is lined with respiratory mucosa

The Nose - Respiratory Mucosa The respiratory mucosa is made up of

pseudostratified columnar epithelium, containing scattered goblet cells, that rests on a lamina propria

This lamina propria is richly supplied with compound tubuloalveolar glands that contain mucous and serous cells

Mucous cells secrete mucus, whereas serous cells in glands secrete a watery fluid containing digestive enzymes

The Nose - Respiratory Mucosa Each day the mucous glands secrete about

a quart of sticky mucous containing lysozyme, an antibacterial enzyme

The mucous traps inspired dust, bacteria and other debris, while lysozyme attacks and destroys bacteria chemically

The epithelial cells of the respiratory mucosa also secrete defensins, natural antibotics that help to get rid of invading microbes

The Nose - Respiratory Mucosa The ciliated cells of the respiratory

mucosa create a gentle current that moves the sheet of contaminated mucus posteriorly toward the throat where it is swallowed and digested by stomach juices

These ciliated cells become sluggish in cold weather allowing mucus to accumulate in the nasal cavity where it “runs” on a cold day when you come inside

The Nose - Respiratory Mucosa The nasal mucosa is richly supplied with

sensory nerve endings A sneeze reflex is stimulated when

irritating particles (dust, pollen) contact this sensitive mucosa

The sneezing propels air outward in a violent burst, expelling the irritant from the nose

The Nose - Respiratory Mucosa A rich plexus of thin walled capillaries

underlies the lamina propria of the nasal mucosa and warms the incoming air as it flows across the mucosal surface

Blood flow increases when the temperature decreases

Because of its superficial location and the extent of vessels, nosebleeds are common and often profuse

The Nose - Nasal Conchae Protruding medially

from each lateral wall of the nasal cavity are three mucosa-covered projections, the superior, middle of the ethmoid bone and inferior conchae which is a separate bone

The Nose - Nasal Conchae The groove inferior

to each concha is a meatus

As inhaled air moves over the concha the turbulance created increases the amount of contact between the nasal mucosa and this inspired air

This acts to trap particulates in mucus

The Nose - Nasal Conchae The conchae and nasal mucosa not only

function during inhalation to filter, heat, and moisten air, but also act during exhalation to reclaim this heat and moisture

This reclamation mechanism minimizes the amount of moisture and heat lost from the body through breathing, helping us to survive in dry and cold climates

The Nose - Paranasal Sinuses The nasal cavity is

surround by sinuses located in the frontal, sphenoid, ethmoid and maxillary bones

They function to– Produce mucus

– Lighten the skull

– Warm the air

– Voice resonance

The Pharynx The pharynx is

the funnel shaped passage way than connects the nasal cavity and mouth superiorly to the larynx and the esophagus inferiorly

Nasopharynx, oropharynx, laryngopharynx

The Pharynx The pharynx serves as a common

pathway for food and air The pharynx extends for about 5 inches

from the base of the skull to the level of the sixth cervical vertebrae

In the context of the digestive tract, the pharynx is commonly called the throat

The Pharynx On the basis of location and function, the

pharynx is divided into nasopharynx, oropharynx, laryngopharynx

The muscular wall of the pharynx consists of skeletal muscle throughout its length, but the nature of the mucosal lining varies among the three pharyngeal regions

The Nasopharynx The nasopharynx lies

above the point of food entry, it serves only as an air passageway

During swallowing the uvula reflects posteriorly to close off the nasopharynx and prevent food from entering the nasal cavity

The Nasopharynx The nasopharynx is

continuous with the nasal cavity through the internal nares

It ciliated pseudo- stratified epithelium produces mucus

Mucosa high on the posterior wall contains masses of lymphatic tissue, the pharyngeal tonsils or adenoids

The Oropharynx The oropharynx lies

posterior to the oral cavity and is continuous with it through an archway called the fauces

Both swallowed food and air pass through

Lined with stratified squamous epithelium for protection from food abrasion and chemical trauma

The Oropharynx Two tonsils lie

embedded in the oropharyngeal mucosa– Paired palatine

tonsils

– Lingual tonsil (posterior surface of the tongue)

The Laryngopharynx The laryngopharynx

serves as a common pathway for food and air and is lined with stratified squamous epithelium

It lies directly posterior to the upright epiglottis and extends to the larynx where the digestive and respiratory pathways diverge

The Laryngopharynx The esophagus

conducts food to the stomach while air enters the larynx anteriorly

During swallowing food has the “right of way” and air passage temporarily stops

The Larynx The larynx attaches

to the hyoid bone superiorly and opens into the laryngopharynx

Inferiorly is is continuous with the trachea

The Larynx The larynx has three important functions

– It provides an airway for respiration– Act as a switching mechanism to route air

and food into the proper channels– Vocal cords housed in larynx are used in

voice production

The Larynx The framework of

the larynx is an arrangement of nine cartilages connected by membranes and ligaments

Except for the epiglottis, all laryngeal cartilages are made of hyaline

The Larynx The large, shield

shaped thyroid cartilage is formed by the fusion of two cartilage plates

The laryngeal prominence marks the midline fusion point

The cricoid cartilage is anchored to the trachea inferiorly

The Larynx Three pairs of

small cartilages, the arytenoid, cuneiform and corniculate form part of the lateral and posterior walls of the larynx

The arytenoid anchors the vocal cords

The Larynx The ninth cartilage

the flexible, spoon shaped epiglottis is composed of elastic cartilage

It is almost entirely covered by mucosa

The epiglottis extends from the posterior aspect of the tongue to its anchoring point on the thyroid cartilage

The Larynx When only air is

flowing into the larynx, the inlet to the larynx is open wide and the free edge of the epiglottis projects upward

During swallowing the larynx is pulled superiorly and the epiglottis tips to cover the laryngeal inlet

The Vocal Folds The vocal ligaments

attach the arytenoid and thyroid cartilages

These ligaments are composed of elastic fibers

The vocal cords vibrate, producing sound as air rushes up from lungs

The Vocal Folds The opening

through which air passes is the glottis

Superior to the vocal cords are the vestibular cords which play no part in voice production

Vocal Folds Stratified squamous epithelium lines the

superior portion of the larynx, an area subject to food contact

Below the vocal folds the epithelium is pseudostratified ciliated columnar epithelium

Cilia move the mucus away from our lungs

Voice Production Speech involves the intermittent release

of expired air and opening and closing of the glottis

The length of the true vocal cords and the size of the glottis are altered by the action of the intrinsic laryngeal muscles most of which move the arytenoid cartilages

As the length and tension of the vocal folds change, the pitch of the sound is altered

Voice Production The glottis is wide when we produce deep

tones and narrows to a slit for high pitched sounds

Length and thickness of the vocal folds changes for males during puberty

Loudness of the voice depends on the force with which the airstream rushes across the vocal cords

The greater the force, the stronger the vibration and the louder the sound

Sphincter Functions of Larynx The vestibular folds can perform a

sphincter function under certain conditions In abdominal straining associated with

defecation and urination, inhaled air is held temporarily in the lower respiratory tract by closing the epiglottis

The abdominal muscle then contract and the interabdominal pressure rises

The action know as the Valsalva manuever can also stabilize the trunk when one lifts a heavy load

Innervation of the Larynx The larynx receives its sensory and motor

innervation through the superior laryngeal branch of each vagus nerve and from the recurrent laryngeal nerves, which branch off the vagus in the superior thorax and loop superiorly to ascend through the neck

The backtracking course these nerves is unusual

The Trachea The trachea

descends from the larynx through the neck and into the mediastinum

It ends by dividing into the two primary bronchi at midthorax

10 cm long and 2.5 cm in diameter

The trachea is very flexible and mobile

The Tracheal Wall

The tracheal wall consists of several layers that are common in many tubular organs of the body

The Tracheal Wall

From internal to external these layers are the mucosa, submucosa, and adventitia

The Tracheal Wall

The mucosa contains the same goblet cells containing pseudostratifed epithelium that occurs throughout most the of respiratory tract

The Tracheal Wall

Its cilia continually propel mucus, loaded with dust particles and other debris, toward the larynx

The Tracheal Wall Smoking inhibits and ultimately destroys

the cilia in the mucosa layer When their function is lost, coughing is

the only means of preventing mucus from accumulating in the lungs

Smokers with respiratory congestion should avoid medications that inhibit the cough reflex

The Tracheal Wall

The submucosa, a connective tissue layer, contains seromucous glands that help produce the mucus “sheets” within the trachea

The Tracheal Wall

The adventitia is a connective tissue layer that is reinforced by 16 to 20 C-shaped rings of hyaline cartilage

The Tracheal Wall

The cartilage rings prevent the trachea from collapsing and keep the airway open despite the changes in pressure that occur in breathing

The Tracheal Wall

The open posterior parts of the rings, which abut the esophagus are connected by smooth muscle fibers of the trachealis muscle and soft connective tissue

The Tracheal Wall

Since this portion of the tracheal wall is not rigid, the esophagus can expand anteriorly as swallowed food passes through it

The Trachea The last tracheal

cartilage is expanded and a spar of cartilage called the carina projects posteriorly from its inner surface, marking the point where the trachea splits

Contacting this point results in violent coughing

The Trachea Tracheal obstruction is life threatening The Heimlich maneuver was developed

to expel an obstruction using the residual air in the victim’s lungs

The maneuver creates interthoracic pressure that drives the obstruction from its lodging point

The Conducting Zone

The right and left main (primary) bronchi are the largest conduits in the bronchial tree

The Conducting Zone

The right and left primary bronchi are formed by the division of the trachea at the level of T4 (T7 living)

The Conducting Zone

Each bronchi runs obliquely in the mediastinum before plunging into the medial depression (hilus) of the lung on each side

Conducting Zone: Bronchial Tree

Once inside the lungs, each primary bronchus sub- divides into secondary and then tertiary bronchi which then divide further (23 orders of branching)

The Conducting Zone

Air passages under 1mm in diameter are called bronchioles and the smallest of these are called terminal bronchioles and are less than 0.5mm

The Conducting Zone The tissue composition of the walls of the

primary bronchi mimics that of the trachea but as the conducting tubes become smaller, a number of structural changes occurs– The cartilage supports change

• Rings are replaced by plates and then none at all

– The epithelium type changes• Pseudostratified columnar, to columnar, to cuboidal

• Debris removed by macrophages at bronchiole level

– The amount of smooth muscle increases• A complete layer of circular smooth muscle allows for

vasoconstriction and vasodilation

The Respiratory Zone

The respiratory zone begins as the terminal bronchioles feed into respiratory bronchioles within the lungs

Protruding from these smallest bronchioles are scattered alveoli

The Respiratory Zone The respiratory

bronchioles lead into alveolar ducts

The ducts lead into terminal clusters of alveoli called alveolar sacs

Respiration takes place within the alveoli

The Respiratory Zone About 300 million air-filled alveoli crowd

together within the lungs, accounting for most of the lung volume

All these cells provide for a tremendous surface area for gas exchange

The total area of all alveoli in an average pair of lungs is 140 square meters, or 1500 square feet, which is 40 times greater than the surface of the skin

The Respiratory Zone

The wall of each alveolus consists of a single layer of squamous epithelial cells called Type I cells surrounded by a delicate lamina

The Respiratory Membrane The cell walls are

extremely thin to allow for ease of gas exchange

The wall is 15 times thinner than a piece of paper

The Respiratory Membrane The external surfaces

of the alveoli are densely covered with a web of pulmonary capillaries

Together the alveolar and capillary walls and their fused basal lamina form the respiratory membrane with gas on one side and blood on the other

The Respiratory Membrane Gas exchange occurs

by simple diffusion across the respiratory membrane

Oxygen from the alveoli passes into the blood and carbon dioxide leaves the blood to enter the alveoli

The Respiratory Membrane Scattered amid the

type I squamous cells that form the alveoli walls are cuboidal type II cells

Type II cells secrete a fluid containing a surfactant that coats the alveolar surfaces which prevents the walls from sticking during exhalation

The Respiratory Membrane Lung alveoli have

three other features– Surrounded by fine

elastic fibers

– Open pores connect adjacent alveoli

• Allow for pressure equalization

• Alternative air routes for blocked bronchi

– Alveolar macrophages crawl freely along the internal alveolar surfaces

The Respiratory Membrane Alveolar macrophages (dust cells) which

actually live in the air space and remove the tiniest inhaled particles not trapped by the mucus

Most dust filled macrophages migrate from the alveoli to the broncholes where ciliary action carries them into the pharynx to be swallowed

By this mechanism over 2 million dust cells are cleared each hour!

The Pleurae Around each lung is

a flattened doulbe layered sac whose walls form a serous membrane called the pleurae

There is an outer parietal pleura and an inner visceral pleura

The Pleurae The parietal pleura

covers the internal surface of the thoracic wall, the superior surface of the diaphragm and the lateral surfaces of the mediastinum

It also enclosed the great vessels running to the lung root

The Pleurae In the area of the

lung root the membrane reflects inward forming the visceral pleura which covers the entire external lung surface

The Pleurae The pleural cavity is

the space between the parietal and visceral pleurae

It is actually a slit like space filled with a layer of pleural fluid

The Pleurae Secreted by the pleurae, this lubricating

fluid allows the lungs to glide without friction over the thoracic wall during breathing movements

The fluid also holds the parietal and visceral pleurae together, just as a film of oil or would hold two glass plates together

The Pleurae The two pleurae can easily slide from

side to side across each other, but their separation is strongly resisted by the surface tension of the fluid between the membranes

Consequently, the lungs cling tightly to the thoracic wall and are forced to expand and recoil as the volume of the thoracic cavity increases and decreases during breathing

The Pleurae The pleurae also

help divide the thoracic cavity into three separate compartments– Central

mediastinum with the heart

– Two lateral pleurae each containing a lung

The Pleurae The compartments

prevent the moving lungs or heart from interfering with one another

The compartments also limit the spread of local infections and the extent of traumatic injury

The Lungs

The lungs occupy all of the thoracic cavity except the mediastinum

Each cone shaped lung is suspended in its own pleural cavity and connected to the mediastinum

The Lungs

The anterior, lateral and posterior lung surfaces lie in close contact with the ribs and forms a curving surface called the costal surface

The apex is the superior tip of the lung

The Lungs

The concave inferior surface that rests on the diaphragm is called the base

The hilus is the location where the pulmonary and systemic circulation and the primary bronchi enter

The Lungs The left lung is divided

into two lobes (upper and lower) while the right has three lobes (upper, middle, lower)

Each of the lobes contains a number of bronchopulmonary segments separated by connective tissue

Each lung has 10 similar segments

The Lungs The bronchopulmonary segments have

clinical significance in that they limit the spread of some diseases within the lung, because infections do not easily cross the connective tissue partitions between them

The Lungs Furthermore,

because only small veins span these partitions, surgeons can neatly remove segments without cutting any major blood vessel

The Lungs The smallest sub division of the lung is

the lobule Appearing on the lung surface as

hexagons ranging in size from the size of a pencil eraser to the size of a penny each lobule is served by a large bronchiole

In most city dwellers and in smokers the connective tissue that separates individual lobules is blackened with carbon

The Lungs

The lungs consist largely of air tubes and spaces

The balance of the tissue, its stroma, is a framework of connective tissue containing many elastic fibers

As a result the lungs are light, soft, spongy, elastic organs that weigh only 1.25 pounds

The elasticity helps to reduce the effort required for breathing

Blood Supply / Nerves of the Lungs

The pulmonary arteries deliver oxygen poor blood to the lungs for oxygenation

In the lung, these arteries branch along the bronchial tree

Blood Supply / Nerves of the Lungs Generally, the arteries lie posterior to the

corresponding bronchi The smallest arteries feed into the

pulmonary capillary network around the alveoli

Oxygenated blood is carried from the alveoli of the lungs back to the heart by the pulmonary veins, whose tributaries generally lie anterior to the corresponding bronchi within the lungs

Blood Supply / Nerves of the Lungs The lungs are innervated by sympathetic,

parasympathetic, and visceral sensory fibers that enter each lung through the pulmonary plexus on the lung root

Parasympathetic fibers constrict the air tubules whereas the sympathetic fibers dilate them

Ventilation Breathing or pulmonary ventilation

consists of two phases– Inspiration is the period when air flows into

the lungs– Expiration is the period when gases exit the

lungs

Inspiration During inspiration the lungs increase in

volume by enlarging in all dimensions Inspiration lowers the air pressure within

the lungs Air flows from areas of high pressure to

areas of low pressure to equalize the pressure within the lung to that outside the lung

Inspiration During normal quiet inspiration, the

diaphragm and external intercostal muscles produce the muscle movement

Inspiration When the dome

shaped diaphragm contracts, it moves inferiorly and flattens

As a result the vertical dimension of the thoracic cavity increases

Inspiration The external inter-

costal muscles contract to raise the ribs

Because the ribs normally extend anterioinferiorly from the vertebral column, lifting them enlarges both the lateral and anterior dimensions

Inspiration Although these

actions expand the thoracic dimensions by only a few millimeters along each plane, this movement is sufficient to increase thoracic cavity volume by almost a pint which is equal to normal resting inspiration

Inspiration During deep or

forced inspiration, additional muscles contract and further increase thoracic volume

The rib cage is elevated by the scalenes and sterno-cleidomastoid in the neck and the pectoralis minor

Expiration Quiet expiration in

healthy people is a passive process

As the respiratory muscles relax, the rib cage drops under the force of gravity and the relaxing diaphragm moves superiorly

Expiration At the same time,

the many elastic fibers with the lungs recoil

The result is that the volume of the thorax and lungs decrease simultaneously, which pushes air from the lungs

Expiration Forced expiration is an active process

produced by the contraction of muscles in the abdominal wall, primarily the oblique and transverse abdominis muscles

These contractions– Increase the interabdominal pressure which

forces the diaphragm superiorly– Sharply depresses the rib cage and thus

decreases thoracic volume

Expiration The internal intercostal muscles,

quadratus lumborum, and the latissimus dorsi also help to depress the rib cage

End of Material

Chapter 21