Chapter 23

The Respiratory System

Upper respiratory tract

Lower respiratory tract

Respiratory System AnatomyStructurally, the respiratory system is divided into upper and lower divisions or tracts.

The upper respiratory tract consists of the nose, pharynx and associated structures.The lower respiratory tract consists of the larynx, trachea, bronchi and lungs.

Respiratory System AnatomyFunctionally, the respiratory system is divided into the conducting zone and the respiratory zone.

The conducting zone is involved with bringing air to the site of external respiration and consists of the nose, pharynx, larynx, trachea, bronchi, bronchioles and terminal bronchioles.The respiratory zone is the main site of gas exchange and consists of the respiratory bronchioles, alveolar ducts, alveolar sacs, and alveoli.

Air passing through the respiratory tract traverses the:

Nasal cavityPharynxLarynxTracheaPrimary (1o) bronchiSecondary (2o) bronchiTertiary (3o) bronchiBronchioles Alveoli (150 million/lung)

Respiratory System Anatomy

The external nose is visible on the face.It consists of: a supporting bony framework (frontal bone, nasal bones, and maxillae) and acartilaginous framework of hyaline cartilage

The Nose

The Nasal cavityLies in and posterior to the external noseIs divided by a midline nasal septum

Formed by the perpedicular plate of ethmoid, & the vomer posteriorly and the septal cartilage anteriorly

It opens posteriorly into the nasopharynx

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Three nasal conchae (or turbinates) protrude medially from each lateral wall of nasal cavitySuperior conchaMiddle conchaInferior conchaIncrease mucosal surface area & air turbulence- ensures air contacts mucosaUnder each nasal concha is an opening, or meatus, for a duct that drains secretions of the sinuses and tears into the nose.

Nasal Cavity- lateral wall

The NoseFunctions:Providing an airway for respirationMoistening and warming & filtering inspired airResonation of soundOlfaction

The Paranasal Sinuses• Mucosa-lined, air-filled spaces found in

five skull bones – the frontal, sphenoid, ethmoid, and paired maxillary bones • Sinuses lighten the skull and help to

warm and moisten the air

The Paranasal SinusesMucosal secretions flows from the sinuses into nasal cavity

The PhrynxThe pharynx is a hollow tube that starts posterior to the internal nares and descends to the opening of the larynx in the neck.

It is formed by a complex arrangement of skeletal muscles that assist in deglutition.It functions as: o a passageway for air and foodo a resonating chambero a housing for the tonsils

The Pharynx

Nasopharynx

Oropharynx

Laryngopharynx

The pharynx has 3 regions The nasopharynx is separated

from the oropharynx by the hard and soft palate

Lies posterior to the nasal cavity and superior to the level of the soft palateStrictly an air passageLined with psuedostratified columnar epitheliumCloses during swallowing to prevent food from entering the nasal cavityThe pharyngeal tonsil ( adenoids) lies high on the posterior wall Auditory tubes from middle ears open into the lateral walls

The Nasopharynx

Cilia in the upper respiratory tract move mucous and trapped particles down toward the pharynx.(Cilia in the lower respiratory tract move them up toward the larynx.)

Respiratory Lining

The PharynxThe oropharynx & laryngopharynx are both common passages for food and air & are lined by stratified squamous epitheliumThe oropharynx lies posterior to the oral cavity &

opens into the oral cavity via the fauces The palatine tonsils lie in the lateral walls of the fauces (those usually taken in a tonsillectomy) and small lingual tonsil at the base of the tongueThe laryngopharynx lies posterior to the upright epiglottisLeads into the larynx & the esophagus

The Pharynx

The LarynxThe larynx, composed of 9 pieces of cartilage, forms a short passageway connecting the laryngopharynx with the trachea (the “windpipe”).

The thyroid cartilage (the large “Adam’s apple”) and the one below it (the cricoid cartilage) are landmarks for making an emergency airway (called a cricothyrotomy).

Anterior view of the larynx

The Larynx9 Cartilages of the larynx

Epiglottis – elastic cartilage that covers the glottis during swallowingThyroid cartilage- hyaline cartilage with a midline laryngeal prominence (Adam’s apple)Cricoid cartilage - hyaline cartilage Three pairs of small arytenoid, corniculate, & cuneiform cartilages

The epiglottis is a flap of elastic cartilage covered with a mucus membrane, attached to the root of the tongue.

The epiglottis guards the entrance of the glottis, the opening between the vocal folds.o For breathing, it is held

anteriorly, then pulled back-ward to close off the glottic opening during swallowing.

The Larynx

The LarynxThe mucous membrane of the larynx forms two pairs of folds:The superior pair are the Ventricular folds ( false vocal cords) -also called vestibular folds

The space between the ventricular folds is the rima vestibuli

The inferior pair are the vocal folds ( true vocal cords)

The space between the vocal folds ( true vocal cords) is the rima glottidis

True vocal cords & the opening between them form the glottis

The LarynxThe functions of the larynx are:To provide an airwayTo route air and food into the proper channelsTo function in voice production- True vocal cords vibrate to produce sound as air passesFalse vocal cords have no part in sound production; help close glottis during swallowing

Valsalva’s maneuver- by closing the glottis the larynx is closed during certain abdominal straining conditions to prevent exhalation

Upper respiratory tract

Lower respiratory tract

Lower Respiratory TractAs air passes from the laryngopharynx into the larynx, it leaves the upper respiratory tract and enters the lower respiratory tract.

Air passing through the respiratory tract

Nasal cavityPharynxLarynxTracheaPrimary bronchiSecondary bronchiTertiary bronchiBronchioles Alveoli (150 million/lung)

The TracheaThe trachea is a semi-rigid pipe made of semi-circular cartilaginous rings, and located anterior to the esophagus.It is about 12 cm long and extends inferior to larynx into the mediastinum At the level of carina ( an internal ridge of last tracheal cartiage) it divides into right and left primary (1o, “mainstem”) bronchi.It is composed of 4 layers: the mucosa ( lined by ciliated respiratory epithelium), submucosa, hyaline cartilage, and adventitia

The tracheal cartilage rings are incomplete posteriorly, facing the esophagus.

Esophageal masses can press into this soft part of the trachea and make it difficult to breath, or even totally obstruct the airway.

The Trachea

The BronchiThe right and left primary (1o or “mainstem”) bronchi emerge from the inferior trachea to go to the lungsRight primary bronchus is more vertical compared to left primary bronchus

The BronchiPrimary bronchi- subdivide into:Secondary bronchi (lobar bronchi), each supplying a lobe of the lungs –two on the left side and three on the rightSubdivide into tertiary bronchi (segmental bronchi)- each supplies one bronchopulmonary segmentThere are upto 10 bronchopulmonary segments in each lung

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Air passages undergo 23 orders of branchingsBronchioles- smaller than 1mm in diameter- lack cartilageBronchioles divide into terminal bronchioles

A branch of the terminal bronchioles supplies air to a lobule

Terminal bronchioles branch into respiratory bronchioles which now have alveoliRespiratory bronchioles lead to the alveolar ducts which have alveoli

The respiratory bronchioles, alveolar ducts and alveoli form the 'respiratory zone'

Bronchioles

Pulmonary lobule:

Wrapped in elastic C.T., each pulmonary lobule contains a lymphatic vessel, an arteriole, a venule and a branch of terminal bronchiole.

Lung lobule

The bronchi and bronchioles go through structural changes as they branch and become smaller.

The mucous membrane changesThe cartilaginous rings become more sparse, and eventually disappear altogether.As cartilage decreases, smooth muscle (under the control of the Autonomic Nervous System) increases.o Sympathetic stimulation causes airway

dilation, while parasympathetic stimulation causes airway constriction.

All the branches from the trachea to the terminal bronchioles are conducting airways – they do not participate in gas exchange.

AlveoliAlveoli are the cup-shaped outpouchings which participate in gas exchangeAlveoli make up a large

surface area (750 ft2).They are lined chiefly by type I alveolar cells, simple squamous epithelium)which allow for exchange of gases with the pulmonary capillaries.

AlveoliType II cells in the alveoli secrete a substance called surfactant that prevents collapse of the alveoliAlveoli macrophages (also called “dust cells”) engulf and remove pathogens & debris

Respiratory MembraneThe Respiratory membrane across which diffusion of gases occurs is composed of:

Alveolar lining epitheliumCapillary endotheliumTheir fused basement membranes

Blood Supply to the Lungs

The lungs receive blood via two sets of arteries

Pulmonary arteries carry deoxygenated blood from the right heart to the lungs for oxygenationBronchial arteries branch from the aorta and deliver oxygenated blood to the lungs primarily perfusing the muscular walls of the bronchi and bronchioles ( not the alveoli)

The lungs are divided into lobes by fissures.The right lung is divided by the oblique fissure and the horizontal fissure into 3 lobes .The left lung is divided into 2 lobes by the oblique fissure.

Each lobe receives it own 2o bronchus that branches into 3o segmental bronchi (whichcontinue to further divide).

The Lungs

The apex of the lung is superior, and extends slightly above the clavicles. The base of the lungs rests on the diaphragm.The cardiac notch – in the left lung (the indentation for the heart)

• The medial mediastinal surfacehas the hilus – an indentation

The lungs are separated from each other by the heart and other structures in the mediastinum.Each lung is enclosed by a double-layered pleural membrane.

The parietal pleura line the walls of the thoracic cavity.The visceral pleura adhere tightly to the surface of the lungs themselves.

Respiratory System AnatomyOn each side of the thorax, a pleural cavity is formed.The pleural cavity contains pleural fluid -reduces friction The pleura, adherent to the chest wall and to the lung, produces a mechanical coupling for the two layers to move together.

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