Respiratory System I

Respiratory System Overview

Introduction

The respiratory system is responsible for the exchange of gases between the body and the environment. It consists of a series of organs and structures that conduct air to the lungs, where oxygen is absorbed and carbon dioxide is expelled.

• Respiratory tract (before entering lung): Includes the nose, nasal cavity, paranasal sinuses, pharynx, larynx, and trachea.

• Lungs and pleurae: Bronchial tree and alveoli are the main sites for gas exchange.

• Ventilation: The process of moving air into and out of the lungs.

Upper Respiratory Tract

Nose and Nasal Cavity

The nose and nasal cavity serve as the primary entryway for air into the respiratory system, performing several important functions.

• Provides an airway for respiration

• Moistens and warms air

• Filters inhaled air

• Resonating chamber for speech

• Houses olfactory receptors

External Nose

The external nose is composed of skin, bone, and cartilage, and contains several anatomical landmarks.

• Skin: Extends into the vestibule; thin at the root, thicker over cartilages; contains many sebaceous glands.

• Bone: Frontal bone, nasal bones, maxillary bone (frontal process).

• Cartilage (hyaline): Alar cartilages, septal cartilage.

• Landmarks: Root and bridge, apex, ala, nostrils (nares).

• Size variation: Due to differences in nasal cartilages.

Skeleton of External Nose

• Bones: Frontal, nasal, maxillary (frontal process).

• Cartilages: Alar and septal cartilages.

Nasal Cavity

The nasal cavity is divided by the nasal septum and is continuous with the nasopharynx. It is lined with a mucous membrane and contains structures that help filter, warm, and moisten air.

• External nares: Nostrils

• Nasal septum: Divides cavity; composed of ethmoid, vomer, and septal cartilage.

• Continuous with nasopharynx: Via posterior nasal apertures (choanae).

• Nasal conchae and meatus: Superior, middle, and inferior conchae increase surface area and turbulence.

• Lined with mucous membrane

Nasal Vestibule

The nasal vestibule is the entryway to the nasal cavity, lined with skin and specialized structures for filtering air.

• Lined with skin: Contains hair, sebaceous glands, and sweat glands.

• Function: Filters large particles from inspired air.

Nasal Mucosa

The nasal mucosa lines most of the nasal cavity and paranasal sinuses, playing a key role in air filtration and humidification.

• Respiratory epithelium: Pseudostratified ciliated columnar epithelium with goblet cells.

• Cilia: Whiplike, highly motile extensions that move mucus.

• Goblet cells: Unicellular exocrine glands that produce slimy mucus.

Respiratory Mucosa

Consists of respiratory epithelium and lamina propria, which contains loose connective tissue and mucous/serous cells.

• Mucous and serous cells: Produce ~1L mucus/day.

• Cilia: Move contaminated mucus posteriorly to the pharynx.

• Blood vessels: Rich plexus warms cold air.

Skeleton of the Nasal Cavity

• Roof: Ethmoid and sphenoid bones.

• Nasal concha: Superior and middle (ethmoid), inferior (own bone).

• Floor: Hard palate (palatine process of maxillary bone, palatine bone), soft palate (muscles).

Nasal Septum

• Components: Ethmoid, vomer, septal cartilage.

Nasal Concha and Meatus

• Superior, middle, inferior conchae: Increase surface area, create turbulence.

• Meatus: Passageways beneath each concha.

Nasal Concha, Meatus, and Mucosa Functions

• Particulate matter: Deflected to mucus-coated surfaces.

• Inhalation: Filter, heat, and moisten incoming air.

• Exhalation: Moisture and heat are reclaimed.

• Kiesselbach area: Anterior nasal septum, site of arterial anastomoses; common site for nosebleeds (epistaxis).

Paranasal Sinuses

Structure and Function

Paranasal sinuses are air-filled spaces within the bones surrounding the nasal cavity. They are lined with mucous membrane and have several functions.

• Sinuses: Frontal, ethmoid, sphenoid, maxillary.

• Functions: Produce mucus to moisturize nasal cavity, lighten the skull, improve voice resonance.

• Most sinuses open into the middle nasal meatus.

Clinical Conditions

• Rhinitis: Mucosa swollen and inflamed in the nasal cavity.

• Sinusitis: Mucosa swollen and inflamed in paranasal sinus.

• Pansinusitis: Multiple sinuses are inflamed.

Pharynx

Structure and Function

The pharynx is a funnel-shaped passageway for both air and food, connecting the nasal cavity and mouth to the larynx and esophagus. It is divided into three sections by location and function.

• Nasopharynx

• Oropharynx

• Laryngopharynx

Nasopharynx

• Continuous with nasal cavity: Via posterior nasal aperture (choanae).

• Superior: Base of the skull.

• Inferior: Level of soft palate; closed off during swallowing.

• Uvula: Reflects superiorly during swallowing.

• Only an air passageway.

• Respiratory epithelium: Propels mucus from nasal cavity downward.

• Pharyngeal tonsil (adenoids): Located on posterior wall, destroys pathogens in inhaled air.

• Opening of pharyngotympanic tube (auditory tube): Tubal tonsil provides some protection from infection.

Oropharynx

• Passageway for both food and air.

• Superior: Soft palate.

• Inferior: Epiglottis.

• Archlike entranceway: Fauces.

• Epithelium: Stratified squamous epithelium.

• Tonsils: Palatine tonsils (lateral walls of fauces), lingual tonsils (posterior surface of tongue).

Laryngopharynx

• Passageway for both food and air.

• Epithelium: Stratified squamous epithelium.

• Continuous with esophagus and larynx.

• Extends to inferior boundary of cricoid cartilage.

Table: Major Structures of the Upper Respiratory Tract

Structure	Main Components	Epithelium Type	Function
Nose & Nasal Cavity	External nose, nasal septum, conchae, vestibule	Pseudostratified ciliated columnar (except vestibule: skin)	Airway, filter, moisten, warm air, olfaction
Paranasal Sinuses	Frontal, ethmoid, sphenoid, maxillary	Pseudostratified ciliated columnar	Moisten air, lighten skull, resonance
Pharynx	Nasopharynx, oropharynx, laryngopharynx	Nasopharynx: pseudostratified ciliated columnar; others: stratified squamous	Air/food passage, immune defense (tonsils)

Key Terms and Definitions

• Pseudostratified ciliated columnar epithelium: A type of tissue with cells appearing layered but all attached to the basement membrane, with cilia for moving mucus.

• Goblet cells: Mucus-producing cells found in respiratory epithelium.

• Lamina propria: Loose connective tissue underlying epithelium, containing blood vessels and glands.

• Concha: Curved bony structures in the nasal cavity that increase surface area.

• Meatus: Air passageways beneath each concha.

• Choanae: Posterior nasal apertures connecting nasal cavity to nasopharynx.

• Fauces: Archlike entranceway from oral cavity to oropharynx.

• Tonsils: Lymphoid tissue involved in immune defense.

Example: Airflow Pathway in the Upper Respiratory Tract

1. Air enters through the external nares (nostrils).

2. Passes through the nasal vestibule (lined with skin and hair).

3. Moves into the nasal cavity (lined with respiratory mucosa).

4. Flows past the nasal conchae and meatuses, where it is filtered, warmed, and moistened.

5. Exits via the choanae into the nasopharynx.

6. Continues through the oropharynx and laryngopharynx toward the larynx and trachea.

Additional info:

• The notes are based on a college-level anatomy lecture and reference standard textbooks (Marieb, Moore, Grant's Atlas).

• Clinical relevance includes common conditions such as rhinitis, sinusitis, and epistaxis (nosebleeds).