Anatomy and Physiology of the Respiratory System: Structure and Function

The Respiratory System: Overview

Major Processes of Respiration

The respiratory system is responsible for the exchange of gases (oxygen and carbon dioxide) between the body and the environment. This process involves four key steps:

• Pulmonary Ventilation: The movement of air into and out of the lungs, commonly known as breathing.

• External Respiration: The exchange of oxygen (O2) and carbon dioxide (CO2) between the lungs and the blood.

• Transport of Gases: The movement of O2 and CO2 in the blood to and from tissues.

• Internal Respiration: The exchange of O2 and CO2 between systemic blood vessels and body tissues.

Note: Pulmonary ventilation and external respiration are functions of the respiratory system, while transport and internal respiration are closely linked to the circulatory system.

Functional Anatomy of the Respiratory System

Major Organs and Divisions

The respiratory system is divided into upper and lower regions, each with specific structures and functions:

• Upper Respiratory Tract:

  • Nose and nasal cavity

  • Paranasal sinuses

  • Pharynx

• Lower Respiratory Tract:

  • Larynx

  • Trachea

  • Bronchi and branches

  • Lungs and alveoli

Each region plays a role in conducting air, filtering particles, and facilitating gas exchange.

The Upper Respiratory System

Structures and Functions

Structure	Description/Features	Function
Nose	External portion supported by bone and cartilage; divided by midline nasal septum; lined with mucosa.	Produces mucus; filters, warms, and moistens incoming air; resonance chamber for speech.
Paranasal Sinuses	Mucosa-lined, air-filled cavities in cranial bones surrounding the nasal cavity.	Lighten skull; may warm, moisten, and filter incoming air.
Pharynx	Passageway connecting nasal cavity to larynx and oral cavity to esophagus; three subdivisions: nasopharynx, oropharynx, laryngopharynx.	Passageway for air and food; houses tonsils for immune defense.

The Lower Respiratory System

Structures and Functions

Structure	Description/Features	Function
Larynx	Connects pharynx to trachea; framework of cartilage and dense connective tissue; houses vocal folds.	Air passageway; prevents food from entering lower respiratory tract; voice production.
Trachea	Flexible tube running from larynx and dividing into two main bronchi; walls contain C-shaped cartilage rings.	Air passageway; cleans, warms, and moistens incoming air.
Bronchial Tree	Right and left main bronchi subdivide within lungs to form lobar and segmental bronchi and bronchioles.	Air passageways connecting trachea with alveoli; cleans, warms, and moistens incoming air.
Alveoli	Microscopic chambers at termini of bronchial tree; walls of simple squamous epithelium overlie thin basement membrane.	Main sites of gas exchange.
Lungs	Paired composite organs; composed primarily of alveoli and respiratory passageways.	House respiratory passages smaller than main bronchi.
Pleurae	Serous membranes; parietal pleura lines thoracic cavity; visceral pleura covers external lung surfaces.	Produce lubricating fluid and compartmentalize lungs.

Nose and Paranasal Sinuses

Structure and Functions of the Nose

• The nose is the only external portion of the respiratory system.

• Functions of the nose:

  • Provides an airway for respiration

  • Moistens and warms entering air

  • Filters and cleans inspired air

  • Houses olfactory receptors

• The nose is divided into two regions:

  • External nose: Includes the root, bridge, dorsum nasi, and apex. The nostrils (nares) are bounded laterally by the alae.

  • Nasal cavity: Located within and posterior to the external nose, divided by the midline nasal septum (formed by septal cartilage anteriorly and vomer and ethmoid bones posteriorly).

Nasal Cavity Details

• Nasal vestibule: The area superior to the nostrils, lined with vibrissae (hairs) that filter coarse particles from inspired air.

• The rest of the nasal cavity is lined with mucous membranes, which help trap dust, microbes, and other particles.

Paranasal Sinuses

• Air-filled cavities in the frontal, sphenoid, ethmoid, and maxillary bones.

• Functions:

  • Lighten the skull

  • Help warm and moisten air

  • Produce mucus that drains into the nasal cavity

Key Terms

• Vibrissae: Stiff hairs in the nasal vestibule that filter large particles from inspired air.

• Nasal septum: The partition dividing the nasal cavity into right and left sides.

• Mucosa: The mucous membrane lining the respiratory tract, important for trapping particles and humidifying air.

Example: Air Filtration in the Nasal Cavity

As air enters the nasal cavity, it passes over the vibrissae and mucous membranes, which trap dust and microbes, preventing them from reaching the lower respiratory tract. This is a critical first line of defense in respiratory health.