Respiratory System Anatomy

Gross Anatomy of Upper and Lower Respiratory System

• The respiratory system consists of the nose, nasal cavity, pharynx (throat), larynx (voice box), trachea (wind pipe), bronchi, bronchioles, and alveoli

Components

• Upper: nose, nasal cavities, pharynx
• Lower: larynx, trachea, bronchial trees, alveoli

Structural Division

• Upper respiratory system includes parts outside the chest cavity: nose, nasal cavities, pharynx
• Lower respiratory system includes parts within the chest cavity: larynx, trachea, bronchial trees, alveoli

Functional Division

• Conducting portion: mouth/nose, pharynx, larynx, trachea, bronchus, bronchioles (down to the terminal bronchioles)
  • Functions include transporting gases to and from alveoli
  • It filters, warms, and moistens inspired air
• Respiratory portion: respiratory bronchioles, alveolar ducts, alveolar sacs, alveoli
  • Its the main site of gas exchange between air and blood

The Nose

• Functions include respiration, olfaction, filtration, humidification, reception, and elimination of secretions
• It consists of the external nose and the nasal cavity
• Parts of the external nose include dorsum, root, apex
• The two apertures called anterior nares (nostrils) are separated by the columella

Skeleton of the External Nose - Bony Part

• The bony part of the nose consists of the nasal bones, frontal processes of the maxillae, and the nasal part of the frontal bone and its nasal spine

Skeleton of the External Nose - Cartilaginous Part

• Consists of 5 main cartilages: two lateral, two alar, and one septal cartilage

Nasal Septum

• The nasal septum divides the chamber of the nose into two nasal cavities, and has a bony and cartilaginous part
• The bony part consists of a perpendicular plate of the ethmoid bone, vomer and septal cartilage

Arteries of The Nose

• Alar and septal branches come from the facial artery
• Dorsal nasal branches come from the ophthalmic artery
• Infraorbital branch comes from the maxillary artery

Veins of The Nose

• End in the facial and ophthalmic veins

Lymphatics of The Nose

• Submandibular and superficial parotid lymph nodes

Nerves of The Nose

• Motor: facial nerve innervates the muscles of the nose
• Sensory: infratrochlear and external nasal from ophthalmic, plus infraorbital from maxillary nerve divisions of the trigeminal nerve

Nasal Cavity

• Is a large space in the anterior aspect of the skull that lies inferior to the nasal bone and superior to the oral cavity, lined with muscle and mucous membrane
  • It has several functions:
  • Sense of smell via olfactory nerves
  • Providing airway for respiration
  • Filtering, warming, and moistening inspired air
  • Cleansing itself of foreign matter from the air

Conchae of The Nasal Cavity

• Bony projections in the lateral wall of the nasal cavity
• Middle and superior conchae are processes of the ethmoid bone, while the inferior concha is a separate bone
• They extend medially across the nasal cavity, separating it into four air channels.

Meatus of The Nasal Cavity

• Space between conchae and lateral wall of the nasal cavity
• Superior meatus is below superior concha and contains the opening of the posterior ethmoidal sinus
• Spheno ethmoidal recess - Space between the roof.

Middle Meatus of The Nasal Cavity

• Located under the middle concha
• Elevated via the bulla ethmoidalis
• Produced by the middle ethmoidal air sinus

Inferior Meatus of The Nasal Cavity

• Located below the inferior conchae, the nasolacrimal duct drains here

Regions of The Nasal Cavity

• Olfactory area: contains peripheral organ of smell and olfactory cells, whose axons constitute the olfactory nerve
• Respiratory region: largest part of the nasal cavity with a rich neurovascular supply, lined by respiratory epithelium of mainly ciliated and mucous cells
• Nasal vestibule: a small dilated space just internal to the naris, lined by skin and contains hair

Blood Supply of The Nasal Cavity-Medial & Lateral Walls

• Anterior ethmoidal artery, posterior ethmoidal artery (from the ophthalmic artery)
• Sphenopalatine artery and greater palatine artery (from the maxillary artery)
• Septal branch of the superior labial artery (from the facial artery)

Kiesselbach area

• The anterior part of the nasal septum
• Is the site of the anastomotic arterial plexus
• Involves all five arteries supplying the septum

Applied Anatomy - Nasal Cavity

• Nose bleeds (epistaxis) resulting from rupture of arteries particularly at site of anastomoses can occur.
• The region of the vestibule is a site of anastomosis and a frequent area of hemorrhage.
• Infections of nasal cavities can spread to: anterior cranial fossa through cribriform plate, nasopharynx, and retropharyngeal soft tissues, middle ear through auditory tube, paranasal sinuses, and lacrimal apparatus and conjunctiva

Veins of The Nasal Cavity

• Venous drainage of the nasal cavity is into the submucosal plexus overlying inferior and middle concha
• Nasal septum is drained: plexus to facial drain anterior and pterygoid plexus drain posterior
• Lateral wall: plexus to facial (anterior), pharyngeal plexus (posterior)

Nerves of The Nasal Cavity

• Maxillary, ophthalmic, facial, and olfactory nerves are the main nerves of the nasal cavity

Paranasal Sinuses

• Air-filled cavities in the bones around the nasal cavity, lined by the respiratory epithelium
• Includes: frontal, ethmoidal, sphenoid, and maxillary
• Are rudimentary or absent at birth, enlarging to full size due to enlargement in respiratory use.

Functions of Paranasal Sinuses

• Reduce the weight of the skull
• Increase the resonance of sound; the voice deepens at puberty because there is an increase in the size of the sinus.

Frontal Sinuses

• Usually detectable in children by 7 years of age
• Located in the frontal bone above the nasal cavity and orbit, two in number
• Drain into the middle meatus of the nasal cavity

Ethmoidal Sinuses

• They are located within the lateral mass of ethmoidal bone between the orbit laterally and nasal cavity medially
• There are three sinuses: anterior, middle, and posterior.
• Anterior and middle ethmoidal sinuses (cells) drain into the middle meatus, while the posterior drains into the superior meatus

Clinical significance-Ethmoidal Sinuses

• If nasal drainage is blocked, infections of the ethmoidal cells may break through medial wall of the orbit
• Severe infections from this source may cause blindness (posterior ethmoidal cells lie close to the optic canal) and also affect the dural nerve sheath of the optic nerve, causing optic neuritis.

Sphenoidal Sinuses

• Body of the sphenoid is fragile, due to extensive pneumatization
• Two in number and are found in the body of the sphenoid drain into the sphenoethmoidal recess.

Maxillary Sinuses

• Two, largest in body of maxilla
• Located above the upper teeth and lateral to the nasal cavity
• Drain into the middle meatus of the nasal cavity.

Applied Anatomy- Paranasal Sinuses

• Infection may spread from nasal cavity to sinuses and produce sinusitis, swelling of mucosa may block opening to nasal cavity.
• Maxillary sinus is commonly involved because its aperture is located superior to floor of sinus thus drainage is poor, primarily viral.

The Pharynx

• Funnel-shaped fibro-muscular tube serves as common pathway for air and food
• It is continuous with the esophagus at C6 vertebral level
• Superior part of the alimentary system expanded posterior to nasal, oral, and laryngeal cavities.

Features of the Pharynx

• Extends inferiorly from cranial base to inferior border of cricoid cartilage anteriorly
• Inferior border of C6 vertebra posteriorly
• The cavity above the inlet of the larynx is wide and always open
• The cavity below the inlet of the larynx is narrow, the anterior and posterior parts are in contact except when food passes

Division of the Pharynx

• Nasopharynx: posterior to the nose and superior to the soft palate
• Oropharynx: posterior to the mouth Laryngopharynx: posterior to the larynx

Openings in the Pharynx

• Anterior: Two posterior nasal openings, oropharyngeal isthmus, inlet of larynx
• Lateral: openings of the auditory tube
• Inferior: into esophagus

Walls of the Pharynx

• Composed of (inside to out): mucus membrane, submucosa, pharyngobasilar fascia

Pharyngeal Muscles

• The wall of the pharynx has a muscular layer composed entirely of voluntary muscle arranged into external circular and internal longitudinal layers.

Pharynx-Muscular Layer

• Inner longitudinal and outer circular skeletal muscles
• Three pairs of circular muscles (external muscle), superior, middle and inferior constrictor muscles.
• Three pairs of longitudinal (internal muscles): palatopharyngeus, salpingopharyngeus, and stylopharyngeus

Innervation of Constrictor Muscles

• Superior and middle constrictor muscles - pharyngeal branch of vagus and pharyngeal plexus
• Inferior constrictor muscle - Pharyngeal, recurrent, and external branches of the vagus nerve

Internal Muscles of Pharynx

• Stylopharyngeus: Nerve supply - CN IX
• Palatopharyngeus: Nerve - Pharyngeal branch of vagus (CN X) and pharyngeal plexus
• Salpingophayngeus: Nerve - Pharyngeal branch of vagus (CN X) and pharyngeal plexus

Vessels of The Pharynx

• Arteries that supply upper parts of pharynx include ascending pharyngeal artery

  • Ascending palatine and tonsillar branches of facial artery
  • Numerous branches of maxillary and lingual arteries

• Arteries that supply lower parts of pharynx include: Pharyngeal branches from inferior thyroid artery, which originates from thyrocervical trunk

Venous and Lymphatic Drainage of The Pharynx

• Veins of the pharynx form a plexus

• Superiorly into the pterygoid plexus

• Inferiorly into the facial and internal jugular veins

• Lymphatic vessels drain into the deep cervical nodes: retropharyngeal, paratracheal, and infrahyoid nodes

Nerves of The Pharynx

• Motor and most sensory innervation of the pharynx is mainly through branches of the vagus [X] and glossopharynge [IX] nerves, which form a plexus.
• Pharyngeal plexus is formed by:
• Pharyngeal branch of the vagus nerve
• Pharyngeal branches of the glossopharyngeal nerve
• Branches from external laryngeal nerve
• Motor fibers in the plexus are derived from vagus nerve and supply all muscles of the pharynx and soft palate
• Except stylopharyngeus (supplied by CN IX) and tensor veli palatini (supplied by CN V₃).
• Sensory fibers in the plexus are derived from glossopharyngeal nerve

Tonsils

• The tonsillar bed is between the palatoglossal and palatopharyngeal arches where tonsil lies

Tonsillar Ring

• Formed by pharyngeal, tubal, palatine and lingual tonsils

Applied Anatomy-Tonsillar

• Tonsillitis is an inflammation of tonsills
  • Adenoids is an enlargement of pharyngeal tonsils that obstruct nasal respiration and infection may spread to middle ear through auditory tube
• Tonsillectomy - Bleeding may arise from tonsilar artery and external palatine vein.

Function of Pharynx

• Passageway for air and food
• Provides resonating chamber for speech sounds
• Houses the tonsils

The Larynx

• The larynx (voice box) is the complex organ of voice production
• Lies in the midline of the neck, anterior to the 3rd or 4th to 6th cervical vertebrae
  • It is a short passageway that connects the laryngopharynx and the trachea

Larynx - Cartilages

• It walls is composed of nine pieces of cartilages:
• Three single: thyroid, epiglottis, cricoid
• Three paired: arytenoid, cuneiform, corniculate
• The arytenoid cartilages control changes in position and tension of the vocal folds.
• The thyroid cartilage consists of two fused plates of hyaline cartilage, larger in males
• Epiglottis: leaf-shaped elastic cartilage, prevents aspiration

Voice production

• Mucous membrane of the larynx forms two pairs of folds
  • Superior pair is called false vocal folds (ventricular folds) and supports the true vocal cords but does not produce sound
  • Inferior pair is called the true vocal cords
• The space between the true vocal cords is known as rima glottidis

Vocal Folds

• Used to produce sound via vocal ligament and vocalis muscle and a mucous membrane
• Wedge-shaped; apex pointed medially and base lies against thyroid lamina
• Shape of rima glottidis vary according to position of vocal folds as it relates to breathing

Blood Supply of The Larynx

• Superior laryngeal artery (branch of superior thyroid); runs with internal laryngeal nerve and pierce thyrohyoid membrane and supply interior of larynx up to vocal folds
• Inferior laryngeal artery (branch of inferior thyroid); supply mucosa and muscles below vocal folds
• Cricothyroid artery is a small branch of the superior thyroid artery
• It supplies the cricothyroid muscle

Vieins of The Larynx

• Superior laryngeal vein usually joins the superior thyroid vein and through it drains into the internal jugular vein

• Inferior laryngeal vein joins the inferior thyroid vein or the venous plexus on the anterior aspect of the trachea. and empties into the left brachiocephalic vein

Innervation of Larynx

• All intrinsic muscles are supplied by recurrent laryngeal nerve except cricothyroid (by external laryngeal)
• Internal laryngeal is located above vocal folds
• Recurrent laryngeal located below vocal folds

Applied Anatomy - Laryngeal

• Recurrent laryngeal nerve is vulnerable to injury during thyroidectomy
• Damage to laryngeal nerve produces anesthesia of mucosa superior to vocal folds which break the reflex arc causing explosive coughing
• Damage to external structures causes phonation weakness

Trachea (Windpipe)

• Non collapsible fibrocartilagenous tube, extends from larynx to lung roots.
• Kept patent by c-shaped cartilaginous rings; the posterior deficient part is covered by trachealis muscle and fibrous tissue = allows for expansion of esophagus
• Whole length =12 cm, lower level of cricoid cartilage (C6) to level of T4/T5 and 2.5 cm in diameter.
• Bifurcates at the level of T4/5 (sternal angle)

Section of The Trachea

• Consists of connective tissue with submucosal glands.

Neurovasculature of The Trachea

• The branches from inferior thyroid & bronchial arteries provide blood supply
• The drainage is by left brachiocephalic through the inferior thyroid vein
• The Lymphatics drained are pretracheal and paratracheal lymph nodes. -Nerve innervation provided by the vagus via the recurrent laryngeal

Applied Anatomy to the Trachea

• Tracheotomy is the process in which surgical incision through anterior wall of trachea in case of laryngeal obstruction
• It’s done in 2nd and 3rd rings covered by isthmus because supra isthmus is liable to stricture, and infra isthmus is dangerous due to thyroid vessels

Bronchi

• The trachea divides at T5 vertebra into the right primary bronchus (to the right lung) and the left primary bronchus (to the left lung)
• At the point of tracheal division an internal ridge called carina is formed, which becomes sensitive for any irritants.
• Like the trachea, primary bronchi contain incomplete rings of cartilage.

Primary Bronchi

• Incomplete rings of hyaline cartilage ensure that they remain open

Right Primary Bronchus

• It is shorter, wider, and more vertically oriented than the left primary bronchus
• Foreign particles are more likely to lodge in the right primary bronchus

Secondary Bronchi

• The right lung has 3 lobes, with three secondary bronchi
  • The left lung has 2 lobes, and two secondary bronchi
• The secondary bronchi continue to branch through tertiary and quaternary

Alveolar Ducts

• Proceeding distally along the respiratory bronchioles and the tube is now called an alveolar duct
• Both the alveolar ducts and the alveoli are lined with extremely attenuated squamous alveolar cells.
• A rich matrix of elastic and reticular fibers provides the only support of the duct and its alveoli.
• Gas exchange can take place in respiratory bronchioles