The Respiratory System

Introduction

  • The respiratory system includes the following structures:

    • Nose

    • Nasal cavity

    • Sinuses

    • Pharynx

    • Larynx

    • Trachea

    • Bronchi

    • Bronchioles

    • Alveoli

Overview of the Respiratory System and Respiratory Tract

Upper and Lower Respiratory System

  • Upper Respiratory System:

    • Consists of:

    • Nose

    • Nasal cavity

    • Sinuses

    • Pharynx

  • Lower Respiratory System:

    • Consists of:

    • Larynx

    • Trachea

    • Bronchi

    • Bronchioles

    • Alveoli

Functions of the Respiratory System

  • Provides an area for gas exchange between air and blood

  • Protects respiratory surfaces from dehydration

  • Protects against invading pathogens

  • Produces sound for verbal communication

  • Assists in regulation of blood volume, blood pressure, and body fluid pH

Respiratory Epithelium

  • Composition:

    • Pseudostratified, ciliated, columnar cells (except in pharynx, smaller bronchi, and alveoli)

    • Stratified squamous cells (found in the pharynx)

    • Mucus-producing cells (found in nasal cavity and lower respiratory tract)

  • Functions:

    • Ciliated columnar cells: Move mucus upward (mucus escalator) so debris can be coughed out

    • Stratified squamous cells: Provide protection against abrasion

    • Mucous cells: Produce mucus to trap inhaled debris, preventing entry into the lungs

Protection of the Respiratory System

  • Hairs in the nose (vibrissae) block some inhaled debris

  • Mucus production in the nasal cavity traps debris, which is expelled by sneezing

  • Mucus in the respiratory epithelium traps debris, later removed by coughing

The Upper Respiratory System

Pathway of Air

  1. Air enters external nares

  2. Passes through nasal vestibule, surrounded by two pairs of alar cartilage

  3. Enters nasal cavity

  4. Flows through nasal conchae (inferior, middle, superior)

    • Air swirls, warming and trapping debris in mucus

  5. Air enters internal nares and the nasopharynx area

Anatomy of the Nose and Nasal Cavity

  • The nose consists of:

    • Nasal bones

    • Nasal septum (vomer and perpendicular plate of the ethmoid)

    • Cartilage (including alar cartilage)

Anatomy of the Pharynx

  • The pharynx connects the nose to the mouth, leading to the throat. It is subdivided into:

    • Nasopharynx: Back of the nose area

    • Oropharynx: Back of the mouth area, includes pharyngeal arch and uvula

    • Laryngopharynx: Area with entrance to trachea and esophagus

The Lower Respiratory System

Larynx

  • The larynx is a cylinder of cartilage, stabilized by ligaments/skeletal muscles, located from C3/C4 to C7

Cartilages of the Larynx

  • Unpaired Cartilages:

    • Thyroid cartilage: Contains laryngeal prominence

    • Cricoid cartilage: Unpaired

    • Epiglottis: Closes over the glottis during swallowing

  • Paired Cartilages:

    • Include arytenoid, corniculate, and cuneiform cartilages; play roles in glottis opening/closing

Laryngeal Ligaments

  • Intrinsic ligaments: Bind laryngeal cartilages

  • Extrinsic ligaments: Bind thyroid cartilage to hyoid bone and cricoid cartilage

Sound Production

  • Air passing between vocal cords creates sound

  • Pitch: Influenced by vocal cord diameter, length, and tension

  • Children have shorter vocal folds, producing higher pitches; males develop thicker vocal cords during puberty, resulting in deeper voices

  • Amplification occurs in the sinus cavities; shaping of sounds involves lips, tongue, and cheeks

Laryngeal Musculature

  • Intrinsic muscles: Adjust tension of vocal cords and regulate glottis

  • Extrinsic muscles: Position and stabilize the larynx

Trachea

  • Characteristics:

    • Length: 11 cm; Diameter: 2.5 cm

    • Bifurcates at carina into right and left bronchi at T5

    • Contains 15-20 C-shaped tracheal cartilages, with annular ligaments connecting them

  • Lining includes: Respiratory epithelium, lamina propria, submucosa

  • Trachealis muscle: Allows constriction/dilation

The Primary Bronchi

  • Branching: Trachea branches into right and left primary bronchi

  • Right primary bronchus is steeper and larger, making aspiration of foreign objects into the right lung easier

Lung Anatomy

  • Right lung has three lobes (superior, middle, inferior) with horizontal and oblique fissures

  • Left lung has two lobes (superior and inferior) with an oblique fissure and cardiac notch

The Pulmonary Bronchi

  • Primary bronchi branch into secondary bronchi once inside the lungs

  • Each secondary bronchus further divides into tertiary bronchi:

    • Right lung has 10 tertiary bronchi (10 bronchopulmonary segments)

    • Left lung has 9 tertiary bronchi (9 bronchopulmonary segments)

The Bronchioles

  • Tertiary bronchi give rise to bronchioles, with diameters of 0.3-0.5 mm

  • Self-supporting, with smooth muscle for bronchodilation and bronchoconstriction

Alveolar Ducts and Alveoli

  • Lungs contain approximately 150 million alveoli surrounded by capillaries for gas exchange

  • Elastic tissue surrounds each alveolus, maintaining its shape during breathing

Alveolar Cells

  • Alveoli have:

    • Type I pneumocytes: Squamous cells forming the alveolar lining

    • Type II pneumocytes: Secrete surfactant to prevent collapse

    • Alveolar macrophages: Remove particulate matter

Gas Exchange

  • Mechanism:

    • Carbon dioxide is transferred from pulmonary arteries to capillaries

    • Oxygen moves from alveolar sacs into capillaries and returns via pulmonary veins to the heart

The Pleural Cavities and Membranes

  • Each lung is enveloped in a serous membrane with a visceral layer covering the lungs and a parietal layer lining the thoracic wall

  • Pleural fluid: Reduces friction during lung movement

  • Pleurisy: Painful condition arising from excess fluid or membrane adherence

Respiratory Muscles and Pulmonary Ventilation

Muscles Involved in Pulmonary Ventilation

  • Diaphragm: Contracts and relaxes to facilitate breathing

  • External intercostals: Elevate ribs during inhalation

  • Internal intercostals: Depress ribs during exhalation

Respiratory Movements

  • Eupnea: Quiet breathing involving diaphragmatic and costal breathing

  • Hyperpnea: Forced breathing, utilizing accessory muscles

Respiratory Changes at Birth

  • Before birth, pulmonary arterial resistance is high; lungs contain fluid and are collapsed

  • At birth, air enters and forces fluid out; closure of foramen ovale and ductus arteriosus occurs

Respiratory Centers of the Brain

  • Controlled by nuclei in pons and medulla oblongata, including:

    • Respiratory rhythmicity center

    • Apneustic center

    • Pneumotaxic center

Reflexes Involved in Respiration

  • Mechanoreceptor reflexes: Respond to lung volume or blood pressure changes

  • Chemoreceptor reflexes: Respond to carbon dioxide and oxygen levels as well as pH

  • Protective reflexes: Address physical injury or irritation

Aging and the Respiratory System

  • The respiratory system's efficiency declines with age:

    • Elastic tissue deteriorates

    • Lung expansion/contraction capabilities diminish

    • Rib movement is restricted due to arthritis

    • Approximately 1 square foot of respiratory membrane is lost annually post-age 30