Respiratory System

Functions of Respiratory System

1. Provides for gas exchange

2. Regulates blood pH

3. Contains receptors for smell

4. Filters inspired air

5. Produces vocal sounds

6. Excretes small amounts of water and heat

Classification of Respiratory System Components

according to:

Structure:

• Upper Respiratory System

  • Nose

  • Nasal Cavity

  • Pharynx

• Lower Respiratory System

  • Larynx

  • Trachea

  • Bronchi

  • Lungs

Function:

• Conducting Zone

  • Nose

  • Nasal Cavity

  • Pharynx

  • Trachea

  • Bronchi

  • Bronchioles

  • Terminal Bronchioles (end point)

• Respiratory Zone

  • Respiratory Bronchioles

  • Alveolar Ducts

  • Alveolar Saccules (Sacs)

  • Pulmonary Alveoli

Note: Conducting zone filters, warms, moistens, passes air into respiratory zone; Respiratory zone is where gas exchange occurs

Related Branches of Medicine

Otorhinolaryngology:

• diagnosis and treatment of ear, nose, throat disease

• ENT

Pulmonology:

• specializes in diagnosis and treatment of lung diseases 

Nose

External Nose:

visible section of the nose

• Bony Framework

  • nasal bones + frontal bone + maxillae (upper jaw)

• Cartilaginous Framework

  • hyaline cartilage + fibrous connective tissue

• External Nares/Nostrils

Internal Nose:

nasal cavity inside skull

• Lateral Walls

  • walls formed from bone

• Nasal Cavity

  • space in skull above oral cavity

• Internal Nares

  • two openings from internal nose into pharynx

  • also called choanae

• Olfactory Epithelium

External Nose

Functions of Interior Structures:

• Warming of Air

• Moistening of Air

• Filtering Incoming Air

• Detecting olfactory stimuli

• Modifying speech vibrations

  • as they pass through large, hollow, resonating chambers

Internal Nose

• a large cavity in anterior aspect of skull

• lies inferior to nasal bone

• lies superior to oral cavity

Lateral Walls:

• formed by:

  • Maxilla bone (upper jaw)

  • Ethmoid bone (at root of nose)

  • Lacrimal bone (eye socket)

  • Palatine bone (part of hard palate)

  • Inferior nasal conchae bones

Nasal Cavity:

• Vestibule

  • entrance of nasal cavity; just after nostrils

  • lined with skin w/ hair follicles, sweat glands, sebaceous glands

  • filters out large dust particles

• Nasal Septum

  • vertical partition

  • divides nose equally into left and right

  • anterior: hyaline cartilage

  • posterior: bone

• Conchae

  • different from choanae

  • also called nasal turbinates

  • three pairs of bony projections

  • superior, middle, and inferior conchae

  • increases surface area

Internal Nares:

• choanae

• posterior to nasal cavity; opens into nasopharynx

Olfactory Epithelium:

• also called olfactory receptors

• superior portion of nasal cavity

Airflow Process in Nose

1. Air enters nostrils/external nares → 

2. air passes through vestibule →

3. air is warmed by blood in capillaries as it whirls around conchae and meatuses →

4. mucus moistens air and traps dust →

5. cilia move mucus/trapped dust towards pharynx (where it can then be swallowed/spit)

Pharynx

• muscular tube-like structure

• connects nasal cavity + mouth to esophagus + larynx (voice box)

• begins at internal nares

• reaches until cricoid cartilage

Location:

• posterior to nasal + oral cavity

• superior to larynx

• anterior to cervical vertebrae

Regions:

• Nasopharynx:

  • immediately after nasal cavity; upper part

• Oropharynx

  • led into from oral cavity; middle part

  • below nasopharynx

• Laryngopharynx/Hypopharynx

  • bottom part

  • below both cavities

Pharynx Functions

• conducts air from nasal cavity + mouth to larynx and trachea (breathing)

• conducts food + liquid from oral cavity to esophagus (swallowing)

• provides resonating chamber for speech production

• houses tonsils

  • part of immune system, fight infections

Nasopharynx

• uppermost part of pharynx

• situated behind nasal cavity

• passageway for air only

• posterior wall contains pharyngeal tonsil

  • also called adenoid tonsil

• lined with ciliated pseudostratified columnar epithelium

  • traps and removes dust + foreign matter

• has 5 openings

  • 2 internal nares

  • 2 openings that lead into the auditory tubes

  • 1 opening into oropharynx

Functions:

• accepts air from nasal cavity

• gathers clusters of mucus with dust particles

  • cilia proper mucus downwards towards laryngopharynx

• shares some air with Eustachian Tubes (auditory tube)

  • balances air pressure between pharynx and middle ear

Oropharynx

• located behind oral cavity

• has only one opening, the fauces (opening from the mouth)

• contains palatine and lingual tonsils

• common passageway for food and air

• lined with nonkeratinized stratified squamous epithelium

  • same as GI tract because also part of GI tract

Laryngopharynx

• also called hypopharynx

• lowest part of pharynx

• situated behind the larynx (voice box)

• common pathway for food and air

• leads to esophagus, involved in swallowing process/deglutition

• lined with stratified squamous epithelium

  • protects against mechanical/chemical irritation

• begins at level of hyoid bone

• opens into esophagus (inferiorly) and larynx (anteriorly)

Larynx

• also called voice box

• short passageway, connects laryngopharynx to trachea

• pathway for air to travel when breathing

• in the middle of the neck

  • anterior to esophagus

  • anterior to C4-C6 cervical vertebrae 

• Wall is composed of 9 cartilages

  • Epiglottis

  • Thyroid

  • Cricoid

  • Arytenoid (2)

  • Cuneiform (2)

  • Corniculate (2)

Epiglottis

• primarily composed of elastic cartilage

• large, leaf-shaped

• closes the glottis

  • glottis = vocal cords + rima glottidis (the space between the cords)

• when swallowing, larynx rises which pushes the leaf portion closed

  • prevents entry of food into larynx

  • “leaf” portion is superior, broad, unattached, and free to move up and down (like flap or trap door)

Thyroid Cartilage

• also called the Adam’s Apple

• largest cartilage in larynx

• anterior region of neck, just below thyroid gland

• shield-shaped, consists of two plate-like structures (laminae)

  • meet in the midline to form front portion of larynx

• provide structural support and protection

• house and protect the vocal cords

  • role in controlling tension of vocal cords

  • crucial for speech production

Cricoid Cartilage

• ring of hyaline cartilage

• forms inferior wall of larynx 

• serves as a landmark for making an emergency airway (cricothyrotomy)

Arytenoid Cartilage

• small, triangle shaped segments of hyaline cartilage

• situated at the upper, back edge of the cricoid cartilage

• influence changes in tension and position of vocal cords

  • important for production of vocal sounds

Corniculate Cartilage

• horn-shaped pieces of elastic cartilage

• located at the apex of each arytenoid cartilage

• supporting structure for the epiglottis

Cuneiform Cartilage

• anterior to corniculate cartilage

• club-shaped elastic cartilage

• support the vocal folds

• support the lateral aspects of the epiglottis

Structures of Vocal Production

• Ventricular Folds

  • false vocal cords

  • superior to vocal folds

  • have protective function; cover the true vocal cords

  • hold breath against pressure when brought together

• Vocal Folds

  • true vocal cords

  • inferior to ventricular folds

  • thicker and longer in males (due to androgens)

  • vibrate slowly

  • bands of elastic ligament stretch within

    • when air passes through them, sound is made

• Rima Glottidis

  • space between vocal folds

• Rima Vestibuli

  • space between ventricular folds

• Laryngeal Sinus

  • lateral expansion of middle portion of laryngeal cavity

Laryngitis

• inflammation of the larynx

Common Causes:

• respiratory infection

• irritants

Hoarseness or Loss of Voice:

• potential consequence of laryngitis

• caused by inflammation of vocal cords

• can be permanent due to chronic inflammation (ex: due to smoking)

Laryngeal Cancer

• almost exclusively found in smokers

• Symptoms:

  • hoarseness

  • pain on swallowing

  • pain radiating to ear

• Treatment:

  • radiation therapy

  • surgery

  • laryngectomy

    • surgical removal of larynx

    • leaves a hole in the throat

    • patient unable to speak without device afterwards

    • patients can no longer breathe normally (epiglottis removed)

    • must breathe through stoma (hole in neck)

Trachea

• also called windpipe

• tubular passageway for air

• anterior to esophagus

• extends from larynx to superior border of fifth thoracic vertebra (T5)

• composed of 16-20 incomplete hyaline rings (C-Shaped)

C-Shaped Rings:

• incomplete ring allows for slight expansion of esophagus into trachea when swallowing

• semi-rigid support; prevents trachea from collapsing inwards

Tracheal Wall Layers:

from deep to superficial

• mucosa

  • ciliated pseudostratified columnar epithelium

  • lamina propria of elastic and reticular fibers

• submucosa

  • areolar connective tissue

  • seromucous glands and ducts

• cartilaginous layer (hyaline)

• adventitia (areolar connective tissue)

Tracheal Obstruction

Causes:

• collapse of cartilage rings due to crushing injury to chest

• inflammation of mucus membrane

• accidental inhalation of foreign objects (ex: small toys, food particles, etc.)

• cancerous tumors that protrude into airway

Management:

Tracheostomy:

• operation, creates opening in trachea

• short, longitudinal, incision inferior to cricoid cartilage

• metal/plastic tracheal tube inserted into hole

Intubation:

• tube inserted through mouth or nose; guided downwards through larynx & trachea

• tube displaces blockages; also allows air to pass through

• mucus causing obstruction may be suctioned out using tube

Bronchi

• consists of right primary and left primary bronchi

• right bronchi is more vertical, shorter, and wider

  • as such, an inhaled object is more likely to enter and lodge in the right primary bronchus

• left and right primary bronchus enter left and right lung respectively

• also contain incomplete hyaline cartilage rings

Carina:

• also called tracheal carina

• ridge/cartilaginous projection

• point where trachea bifurcates into left and right primary bronchi

• widening/distortion of carina is indicative of carcinoma

Path from Trachea to Bronchi

Note:

• approaching bronchi (downwards), cartilage decreases, smooth muscle increases

  • cartilage plates also tend to replace incomplete cartilage rings going downwards

• approaching trachea (upwards), cartilage increases, smooth muscle decreases

Pathway:

Trachea → Primary Bronchi → Secondary Bronchi → Tertiary Bronchi → Bronchioles → Terminal Bronchioles

Pathway Histology:

• From Trachea to Tertiary: ciliated pseudostratified columnar epithelium

• Large Bronchioles: ciliated simple columnar epithelium with some goblet cells

• Small Bronchioles: ciliated simple cuboidal epithelium with no goblet cells

• Terminal Bronchioles: non-ciliated simple cuboidal epithelium

Bronchi Branches

• left primary bronchi → left lung; right primary bronchi → right lung

• upon entering lungs; divide into secondary (lobar) bronchi (one for each lobe)

  • right lung = 3 lobes

  • left lung = 2 lobes

• Lobar bronchi further branch into tertiary (segmental) bronchi

  • supply specific segments within the lobes

  • 10 in each lung, despite different lobe count

• which then branch into bronchioles, which branch further repeatedly

• eventually branch into terminal bronchioles

Lungs

• paired, cone-shaped organs

• located in thoracic cavity; protected by ribcage

• pair is separated by heart and other structures in mediastinum

Right Lung:

• consists of three lobes

  • Upper/Superior

  • Middle

  • Lower/Inferior

• thicker, broader, but shorter than left lung

Left Lung:

• consists of two lobes

  • Upper/Superior

  • Lower/Inferior

  • 10% smaller than right lung

Note: if one lung collapses, the other may still function

Pleural Membrane

• a double layer of serous membrane that encloses and protects each lung

Parietal Pleura:

• superficial

• lines the walls of the thoracic cavity

Visceral Pleura:

• deep

• covers the lungs

Pleural Cavity:

• small space between the pleurae

• contains a small amount of lubricating fluid that is secreted by the membranes

Related Conditions:

Pleuritis:

• also called pleurisy

• inflammation of pleura

Pleural Effusion:

• abnormal accumulation of fluid in the pleural cavity

• may be caused by persisting inflammation

Pneumothorax:

• presence of air or gas in pleural cavity

• Causes:

  • surgical opening of chest

  • stab or gunshot wounds

• air accumulation can cause partial/complete collapse of lung

  • air takes space; presses down on lung causing collapse

Hemothorax:

• presence of blood in pleural cavity

• treatment: evacuation of blood from pleural space

Thoracentesis:

• treatment method used to remove excess fluid/air from thoracic cavity

• needle is inserted anteriorly through 7th intercostal space (space between ribs)

  • if inserted anywhere inferior to 7th, risk of accidentally hitting diaphragm 

Lungs: Surface Anatomy

Base:

• broad, concave surface

• rests on diaphragm

• extends downwards to level of the rib cage

• can be felt just above costal margin

Apex:

• rounded, superior portion

• extends above clavicle into root of neck

• can be palpated (examined by touch) just above medial third of clavicle

Cardiac Notch:

• notch on the left lung

• where the heart rests along the lung

• anterior and inferior; can be palpated along left border of the sternum

Costal Surface:

• surface of lungs that lays against the ribs

• matches round curvature of the ribs

Mediastinal (Medial) Surface:

• contains hilum

  • structure where bronchi, blood and lymph vessels, and nerves enter and exit

Fissures:

• divide the lobes

• Right Lung:

  • Oblique: separates upper and middle

  • Horizontal: separates middle and lower

• Left Lung:

  • Oblique: separates upper and lower

Lungs: Lobes

Right Lung = 3 Lobes

Left Lung = 2 Lobes

• each lobe gets its own secondary bronchus

• Right Lobe gets superior, middle, and inferior secondary bronchi

• Left Lobe gets superior and inferior secondary bronchus

Secondary Bronchi give rise to tertiary bronchi

• there are 10 in each lung, irrespective of how many lobes they have

• each tertiary bronchus supplies a bronchopulmonary segment

• branch into bronchioles

Bronchopulmonary Segments:

• also called pulmonary segments

• both a functional and anatomical unit of the lung

• supplied by a tertiary bronchus

• surrounded by connective tissue septa

• have own segmental veins that drain into the pulmonary veins

• contain small compartments called lobules

Lungs: Lobules

• small, discrete, pyramid shaped unit

• surrounded by elastic connective tissue

• contains:

  • 1 lymphatic vessel

  • 1 arteriole 

  • 1 venule

  • 1 terminal bronchiole branch

• terminal bronchioles then branch into smaller respiratory bronchioles

  • which then subdivide into several alveolar ducts

Lungs: Alveoli

Alveoli:

• tiny, ballon-like structures

• where gas exchange takes place

• around 300 million in the lungs

• provides surface area of 70 m²

Alveolar Sac:

• clusters of alveoli in the lungs

• 2 or more alveoli that share an opening

• terminal ends of the respiratory tree

• responsible for majority of gas exchange

Alveolar Ducts:

• connect respiratory bronchioles to alveolar sacs

Alveolar Wall:

• consists of two types of alveolar epithelial cells

  • Type I: 

    • extremely flat, thin

    • predominant; form most of wall

    • main site of gas exchange

  • Type II:

    • interspersed among Type I cells

    • secrete alveolar fluid

      • keeps surface between air and cells moist

    • produce surfactant

      • reduce alveolar fluid surface tension

      • reduces tendency of alveoli to collapse

      • also called septal cells

• also contain alveolar macrophages (dust cells)

  • wandering phagocytes

  • remove fine dust, particles, other debri

Alveolar Fluid:

• thin layer of fluid; lines inner surface of alveoli

• maintains proper function; facilitates gas exchange

• Composition:

  • water

  • surfactant

  • electrolytes

  • proteins

  • immune cells

Respiratory Membrane

• the membrane through which gas must diffuse in gas exchange

• allows rapid diffusion of gasses between lungs and blood

• includes alveolar and capillary walls

Consists of four layers:

• Alveolar Wall (with Type I and II cells)

• Epithelial Basement Membrane

• Capillary Basement Membrane

• Endothelial Cells of Capillaries