Respiratory System - Notes

Respiratory System

• Provides the means for gas exchange

• Consists of respiratory passageways in head, neck, and trunk, and the lungs

Respiration

• Gas exchange: O₂ and CO₂

• Occurs between atmosphere and body cells

• Cells need O₂ for aerobic ATP production and need to dispose of CO₂  that process produces

Functions of Respiratory System

• Air passageway

• Site for exchange of oxygen and carbon dioxide

• Detection of odors

• Sound production

Function: Air passageway

Air moves between atmosphere and alveoli as we breathe

Function: Exchanging Gas

• Oxygen diffuses from alveoli into blood

• Carbon dioxide diffuses from blood into alveoli

Function: Detection of Odors

Olfactory receptors in superior nasal cavity

Function: Sound Production

• Air moves across vocal cords of the larynx (voice box)

• Vocal cords vibrate, producing sound

Structural Organization

• Upper respiratory tract: Nose, nasal cavity, pharynx, larynx

• Lower respiratory tract: Trachea, bronchi, bronchioles, alveolar ducts, alveoli

Function Organization

• Structures of the conduction zone transport air

  • Nose to terminal bronchioles

• Structures of the respiratory zone participate in gas exchange

  • Respiratory bronchioles, alveolar ducts, alveoli

Mucosa

• Mucous membrane: respiratory lining

• Epithelium resting on a basement membrane

• Underlying lamina propria made of areolar connective tissue

Respiratory epithelium Structure

• Thinner from the nasal cavity to the alveoli

  • Starts out as pseudostratified ciliated columnar

  • Changes to simple ciliated columnar

  • Changes to simple cuboidal

  • Changes to simple squamous

  • Exceptions: stratified squamous found in high abrasion areas – oropharynx, laryngopharynx, vocal cords, superior portion of larynx

    

Progressively Thinner Epithelium

Respiratory Mucosa: Mucous Secretions

• Produced from secretions of goblet cells of epithelial lining

• Mucous and serous glands of lamina propria

• Contains mucin protein

• Contains defenses against microbes

  • Lysozymes (antibacterial enzyme)

  • Defensins (antibacterial proteins)

  • Immunoglobulin A (antibody)

• Called sputum when coughed up with saliva and trapped substances

Mucin

Increases mucus viscosity and serves to trap dust, dirt, pollen, etc.

Clinical View: Cystic Fibrosis

• Defective chloride channels prevent chloride ion from being pumped from epithelial cells lining respiratory tract into the lumen of respiratory tract

• Without chloride on cell surface, water fails to hydrate the cells’ surface

• Mucus becomes thick and cilia not able to mobilize it, so the mucus blocks the respiratory tract

• Pulmonary infections are common

• Ducts of pancreas and salivary glands can also be blocked

  • Backup of digestive enzyme can destroy pancreas

Which respiratory structure is associated with the exchange of respiratory gases?

Thin barrier between alveoli and pulmonary capillaries

What four structures compose the upper respiratory tract? What three structures compose the respiratory zone?

The nasal cavity (nose), pharynx (throat), larynx (voice box), and mouth

Nose

• First conducting structure for inhaled air

• Formed by bone, hyaline cartilage, dense irregular connective tissue, and skin

• Bridge of nose formed by paired nasal bones

• One pair of lateral cartilages and two pairs of alar cartilages

• Flared part of nostrils (nares) made of dense irregular connective tissue

Nasal Cavity

• From nostrils to choanae

• An oblong-shaped internal shape

• Floor formed by palate

• Roof made of nasal, frontal, ethmoid, and sphenoid bones plus some cartilage

Choanae

• Posterior Nasal Apertures

• Paired openings that lead to pharynx

Nasal Septum

• Divides left and right sides

• Anterior part is septal nasal cartilage

• Posterior part is bony perpendicular plate of ethmoid plate and vomer bone

Nasal Conchae

• Three paired, bony projections on lateral walls of nasal cavity

  • Superior, middle, and inferior nasal conchae

• Also called turbinate bones

  • Produce turbulence in inhaled air

Partition the nasal cavity into separate passages

• Each passage called a nasal meatus

• Each meatus immediately inferior to its corresponding concha

Nasal Cavity Parts: Nasal Vestibule

• Just inside nostrils

• Lined by skin and particle-trapping hairs called vibrissae

Nasal Cavity Parts: Olfactory Region

• Superior part of nasal cavity containing olfactory epithelium

• Airborne molecules stimulate receptors for odor detection

  

Nasal Cavity Parts: Respiratory Region

• Lined by pseudostratified ciliated columnar epithelium

• Has an extensive vascular network

  

Nosebleeds (epistaxis)

Common due to large numbers of superficial vessels

Nasolacrimal Ducts

Drain lacrimal secretions from eye surfaces to nasal cavity

Nasal Cavity Conditions the Air

• Air is warmed by extensive blood vessels

• Mucus traps dust, microbes, and foreign material

• Cilia sweep mucous toward the pharynx to be swallowed

• Moist environment humidifies

• Air turbulence created by conchae enhances all three processes

Clinical View: Rhinorrhea (runny hose)

• Increased production of mucus (allergies, virus)

• Increased secretions from lacrimal glands draining into the nasal cavity (crying)

• Exposure to cold air (water condensation)

Paranasal Sinuses

• Spaces within skull bones

• Named for specific bone in which they are housed

• All connected by ducts to nasal cavity

• Lined by pseudostratified ciliated columnar epithelium 

• Mucus swept into pharynx and swallowed

  

Paranasal Sinuses: Superior to Inferior

• Frontal sinuses

• Ethmoidal sinuses

  • Sphenoid sinuses posterior to ethmoidal sinuses

• Maxillary sinuses

Clinical View: Sinus Infections and Sinus Headaches

• Respiratory infection or allergy can cause inflammation of the ducts that drain from the paranasal sinuses.

• Drainage of mucus decreases and accumulates in the sinuses.

• Germs can grow in the accumulated mucous, causing a sinus infection.

• Inflamed and blocked sinuses and pressure changes can cause sinus headaches.

Pharynx (throat)

• Funnel-shaped passageway posterior to nasal cavity, oral cavity, and larynx

• Lateral walls composed of skeletal muscles

  • Partitioned into

  • Nasopharynx

  • Oropharynx

  • Laryngopharynx

Nasopharynx

• Most superior part of pharynx, posterior to nasal cavity, superior to soft palate

• Lined by pseudostratified ciliated columnar epithelium

• An air passage-not for food

• Connects to middle ear via auditory (eustachian) tube

• Contains tonsils-infection-fighting lymphatic tissue

Auditory tube

Opening tubes allows equalization of pressure on each side of tympanic membrane

Tubal Tonsils

• Located near auditory tube opening

• Pharyngeal tonsil on posterior nasopharynx wall

  • Called adenoids when enlarged

Oropharynx

• Middle pharyngeal region

• Posterior to oral cavity

  • Extends from soft palate to hyoid bone

• Passageway for both food and air

• Lined by nonkeratinized stratified squamous epithelium

• Contains tonsils

  • Palatine tonsils on the lateral walls

  • Lingual tonsils at base of tongue

Laryngopharynx

• Inferior, narrow region of pharynx, posterior to the larynx

• From level of hyoid down to esophagus

• Passageway for both food and air

• Lined by nonkeratinized stratified squamous epithelium

Larynx (voice box)

Cylindrical airway between laryngopharynx and trachea

Function of Larynx

• Produces sound

• Air passageway

• Prevents ingested materials from entering respiratory tract

  • Epiglottis covers superior opening during swallowing

• Assists in increasing pressure in abdominal cavity

• Participates in sneeze and cough reflexes

Valsalva maneuver

• Vocal folds close off rima glottidis (opening between the folds) and contraction of abdominal muscles

• Increased pressure facilitates urination, defecation, childbirth

Larynx: Sneezing and Coughing

• Help remove irritants from nasal cavity or lower respiratory tract

• Abdominal muscles contract increasing thoracic pressure

• Vocal cords are forcibly opened by pressure from below

• Explosive blast of exhaled air is a cough or sneeze

Larynx anatomy: Laryngeal Inlet

• Also known as the laryngeal aperture, connects pharynx and larynx

• Formed and supported by nine pieces of cartilage

  • Cartilages held in place by ligaments and muscles

  • Single thyroid, cricoid, and epiglottis cartilages

  • Paired arytenoid, corniculate, and cuneiform cartilages

Larynx anatomy: Thyroid Cartilage

• Large, shield-shaped

• Forms lateral and anterior walls of larynx

  • Attached to lateral surface of cricoid cartilage

• Anterior protrusion = laryngeal prominence (Adam’s apple)

  • Larger in males; enlarge during puberty

Larynx anatomy: Cricoid Cartilage

• Ring-shaped

• Just inferior to thyroid cartilage

Larynx anatomy: Epiglottis

• Spoon-shaped

• Anchored to inner aspect of thyroid cartilage

• Projects postersuperiorly into the pharynx

• Closes over laryngeal inlet during swallowing

Larynx anatomy: Arytenoid, corniculate, and cuneiform

• All laryngeal cartilages are made of hyaline cartilage, except the epiglottis, which is made of elastic cartilage

• Laryngeal ligaments are extrinsic or intrinsic

Extrinsic Ligaments

Attach external surface of larynx to other structures (for example: hyoid bone)

Intrinsic Ligaments

• Are located within the larynx

• Include the vocal ligaments and the vestibular ligaments

Larynx

Larynx anatomy: Vocal Ligaments

• Extend between thyroid and arytenoid cartilages

• Composed primarily of avascular elastic connective tissue

• Covered with mucosa to form the vocal folds (true vocal cords)

• Produce sound when air passes between them

• Opening between ligaments = rima glottidis

• Rima glottidis + vocal folds = glottis

Larynx anatomy: Vestibular Ligaments

• Extend from thyroid cartilage to arytenoid and corniculate cartilages (superior to vocal folds)

• Covered with mucosa to form the vestibular folds (false vocal cords)

• Play no role in sound production; protect vocal cords

• Opening between vestibular folds = rima vestibuli

Larynx anatomy: Extrinsic muscles

• Skeletal muscles that stabilize larynx and help it move during swallowing

• Originate on hyoid bone or sternum; insert on thyroid cartilage

Larynx anatomy: Intrinsic Muscles

• Skeletal muscles located within larynx

• Attach to arytenoid and corniculate cartilages

• Contraction results in change in dimension of rima glottidis

  • Narrowing with adduction; widening with abduction

• Involved in voice production and swallowing

Sound Production

• Vocal cord vibration

• Intrinsic laryngeal muscles narrow opening of rima glottidis

• Air is forced past vocal cords during expiration

Sound Production: Range

• Voice determined by length, thickness of vocal cords

• Males have longer and thicker folds, and so deeper voices

• Folds increase in length with growth, deepening range

Sound Production: Pitch (frequency)

• Determined by tension on vocal cords

• Increased tension = folds vibrate more = higher pitch

• Regulated by intrinsic laryngeal muscles

Sound Production: Loudness

• Depends on force of air passing across vocal cords

• More air = loud sound

Clinical View: Laryngitis

• Inflammation of the larynx

• Symptoms of hoarse voice, sore throat, sometimes fever

• Caused by bacterial or viral infection, or overuse (yelling)

• Serve cases can extend to the epiglottis

  • May lead to sudden airway obstruction, especially in children

Lower Respiratory Tract

• Includes conducting pathways from trachea to terminal bronchioles

• Includes structures involved in gas exchange: respiratory bronchioles, alveolar ducts, and alveoli

Trachea (windpipe)

• Open tube connecting larynx to main bronchi

• Anterior to esophagus, posterior to part of sternum

• About 13 cm long, 2.5 cm in diameter

Gross anatomy of the trachea: Tracheal Cartilages

• Support anterior and lateral walls

• C-shaped rings of hyaline cartilages

• Ensheathed in perichondrium and dense fibrous membrane

• Rings are connected to each other by anular ligaments

Gross anatomy of the trachea: Trachealis Muscle

• On trachea’s posterior surface

• Connects open ends of C-shaped cartilages

• Allow accommodation for esophagus when bulge of food passes

• Trachealis contracts during coughing

Gross anatomy of the trachea: Carina

• Internal ridge at inferior end of trachea (where it splits) containing many sensory receptors

• Initiates cough reflex when irritants are present

Clinical View: Tracheotomy

Incision into trachea to facilitate breathing when:

• Airway is blocked

• Ventilation compromised by disease or injury

Clinical View: Cricothyrotomy

Incision between cricoid cartilage and thyroid cartilage

• Tube placed in opening to facilitate air exchange

Histology of the Tracheal Wall: Mucosa

• Innermost layer

• Pseudostratified ciliated columnar epithelium and lamina propria

Histology of the Tracheal Wall: Submucosa

• Middle layer

• Areolar connective tissue with blood vessels, nerves, serous, and mucous glands, lymphatic tissue

  

Histology of the Tracheal Wall: Tracheal Cartilage

Adventitia: Elastic connective tissue

Bronchial Tree

System of highly branched air passages

• Originates at main bronchi, branches to more narrow tubes

• Ends in small bronchiole passageways

Gross anatomy of the bronchial tree

• Trachea splits into right and left main bronchi (primary bronchi) at level of sternal angle

• Each main bronchus branches into lobar bronchi (secondary bronchi)

  • Further divide into segmental bronchi (tertiary bronchi)

• Tree continues to divide into smaller passageways

  • Leads to tubes of <1mm, the bronchioles

  • Leads to terminal bronchioles (last part of conducting zone)

Clinical View: Bronchitis

Inflammation of the bronchi caused by bacterial or viral infection or inhaled irritants

Clinical View: Acute Bronchitis

• Occurs during or after an infection

• Coughing, sneezing, pain with inhalation, fever

• Most cases resolving in 10 to 14 days

Clinical View: Chronic Bronchitis

• Occurs after long-term irritant exposure

• Large amounts of mucus, and cough lasting 3 months

• Permanent changes to bronchi occur

• Increases likelihood of future bacterial infections

Histology of Bronchial Tree

• Main bronchi are supported by incompleted rings of hyaline cartilage (keeps them open)

• Wall support (cartilage) lessens as bronchi divide

• Bronchioles have no cartilage (thicker layer of smooth muscles)

  

Bronchoconstriction

• Muscle contraction narrows bronchiole diameter

• Less air through bronchial tree (less entry of potentially harmful substances)

Bronchodilation

• Muscle relaxation increases bronchiole diameter

• More air through the bronchial tree

Clinical View: Asthma

• Episodes of bronchoconstriction, wheezing, coughing, shortness of breath, and excess mucus

• Asthmatic with sensitivity to airborne agent

• Localized immune reaction occurs in bronchi and bronchioles

• Walls of the bronchi becoming permanently thickened

• Primary treatments

  • Inhaled steroids

  • Bronchodilators

• Exercise-induced asthma (bronchoconstriction) leads to excessive constriction of airways during exertion

Respiratory Zones

• Respiratory bronchioles subdivide to alveolar ducts

• Alveolar ducts lead to alveolar sacs, clusters of alveoli

• Alveoli = saccular out pocketing

  

Epithelium

• Respiratory bronchioles lined with simple cuboidal epithelium

• Alveoli and alveolar ducts lined by simple squamous

• Thinness facilitates gas exchange

Alveoli

• Each lung contains 300 to 400 million

• Alveolar pores: openings providing collateral ventilation

• Surrounded by pulmonary capillaries

• Divided by interalveolar septum

  • Contain elastic fibers

    

Alveolar type I cells

• Squamous alveolar cells

• Most common of the two cell types making up alveolar wall

• 95% of alveolar surface area

• Form the alveolar epithelium for the respiratory membrane

Alveolar type II cells

• Septal cells

• Secrete oil pulmonary surfactant

  • Coats inside of alveolus and opposes collapse during expiration

Alveolar macrophage

• Dust cells

• Leukocytes that engulf microorganisms

• Either fixed in alveolar wall or free to migrate

Respiratory Membrane Anatomy

• Thin barrier (0.5 microns) separating air in alveoli and blood in pulmonary capillaries

• Consists of:

  • Alveolar epithelium and Capillary epithelium and its basement membrane

  • Basement membranes are fused

Respiratory Membrane Function

• Oxygen diffuses from alveolus into capillaries

  • Erythrocytes become oxygenated

• Carbon dioxide diffuses from blood to alveolus

  • Expired to external environment

Clinical View: Pneumonia

• Infection of the lung, resulting in alveoli filling with fluid exudate, or pus

• Usually caused by bacterial or viral infection

• Cough, fever, difficulty breathing, weakness, chills, increased heart rate, and chest pain while inhaling

• Pneumonia with milder symptoms = walking pneumonia

• Older or immunocompromised individuals have a longer illness than younger adults

Gross Anatomy of the Lung

• Lungs are in the thorax

• House bronchial tree and all respiratory portions of respiratory system

• Each lung has a conical shape

  • Wide concave base atop diaphragm

  • Apex (cupula) points superiorly just behind clavicle

Lung Surfaces

• Costal surface adjacent to ribs

• Mediastinal surface adjacent to mediastinum

• Diaphragmatic surface adjacent to diaphragm

Hilum

• Indented region on lung’s mediastinal side

• Bronchi, pulmonary vessels, autonomic nerves, lymph vessels pass through here

  • These structures collectively termed the root of the lung

Right Lung

• Larger and wider than left lung

• Has three lobes divided by two fissures

  • Horizontal fissure separates superior (upper) lobe from middle lobe

  • Oblique fissure separates middle lobe from inferior (lower) lobe

Left Lung

• Smaller than right due to heart’s position

• Has two lobes divided by one fissure

  • Oblique fissure separates superior and inferior lobes

  • Lingula: projection from superior lobe that is homologous to right lung’s middle lobe

    

Three surface indentations accommodate heart and aorta

• Cardiac impression on medial surface

• Cardiac notch on anterior surface

• Groovelike impression for aorta on medial surface

Bronchopulmonary Segments

• 10 segments in right lung; 8-10 in left lung

• Autonomous units encapsulated with connective tissues

• Each supplied with its own segmental bronchus

• Supplied with its own pulmonary artery and vein and lymph vessels

• Can be removed individually in cases of disease

• Each segment organized into lobules

  • Each supplied by terminal bronchiole, arteriole, venule, and lymph vessel

Clinical View: Smoking

• Respiratory infections

• Cellular or genetic changes to the lungs

• Emphysema

• Cancer of the lungs, esophagus, stomach, and pancreas

• Stomach ulcers

• Atherosclerosis

• Lower birth weight babies in pregnant women

• Poor delivery of oxygen and nutrients to all systemic tissues

• Bronchitis, asthma, ear infections from secondhand smoke

Clinical View: Lung Cancer

• Highly aggressive and frequently fatal malignancy originating in respiratory epithelium

• Smoking causes about 85% of all lung cancer

• Symptoms include chronic cough, coughing up blood, excess pulmonary mucus, and increased pulmonary

Blood Supply

Two types of circulation in the lungs

• Pulmonary circulation

• Bronchial circulation

Pulmonary Circulation

• Replenishes O₂ and eliminates CO₂

• Pulmonary arteries carry deoxygenated blood to pulmonary capillaries

• Blood is reoxygenated

• Blood enters pulmonary venules and veins,

Bronch8ial Circulation

• Transports oxygenated blood to tissues of lungs

  • Bronchial arteries (3 to 4) branch off descending aorta

  • Bronchial veins collect venous blood

    • Some drains into the pulmonary veins