The Respiratory System: Structure and Function (Chapter 22 Study Guide)

The Respiratory System

Overview

The respiratory system is responsible for gas exchange, supplying oxygen to the blood and removing carbon dioxide. It consists of a series of passageways and structures that filter, warm, and humidify air, and facilitate the movement of gases between the external environment and the bloodstream.

Respiratory Passageways: From Nose to Alveoli

The pathway of air through the respiratory system follows a specific order, with each structure playing a distinct role in conditioning and transporting air.

• Nose/Nasal cavity: Entry point for air; filters, warms, and humidifies.

• Pharynx: Passageway shared by respiratory and digestive systems; divided into three regions.

• Larynx: Contains vocal cords; prevents food from entering the trachea.

• Trachea: Windpipe; conducts air to the bronchi.

• Bronchi: Branches into left and right lungs; further divides into bronchioles.

• Bronchioles: Smallest conducting airways; lead to alveolar ducts.

• Alveoli: Site of gas exchange; surrounded by capillaries.

Conducting zone: Nose to terminal bronchioles; transports air but no gas exchange. Respiratory zone: Respiratory bronchioles, alveolar ducts, alveoli; site of gas exchange.

Protective Structures of the Respiratory System

The respiratory system is equipped with multiple mechanisms to protect against dust, bacteria, and other foreign matter.

• Nasal hairs: Trap large particles.

• Mucus: Produced by goblet cells; traps dust and microbes.

• Cilia: Move mucus toward the throat for removal.

• Epiglottis: Prevents food from entering the airway.

• Cough and sneeze reflexes: Expel irritants.

Respiratory Structures in the Skull

Several structures within the skull contribute to respiratory function.

• Nasal cavity: Main air passage; lined with mucosa.

• Paranasal sinuses: Air-filled spaces; lighten skull, warm and moisten air.

• Hard and soft palate: Separate nasal and oral cavities.

Pharynx: Regions and Boundaries

The pharynx is divided into three regions, each with distinct boundaries and functions.

• Nasopharynx: Posterior to nasal cavity; contains pharyngeal tonsil.

• Oropharynx: Posterior to oral cavity; contains palatine and lingual tonsils.

• Laryngopharynx: Posterior to larynx; leads to esophagus and larynx.

Larynx: Structure and Function

The larynx is a cartilaginous structure that houses the vocal cords and acts as a passageway for air.

• Cartilages: Includes thyroid, cricoid, and epiglottis.

• Vocal cords: Produce sound.

• Epiglottis: Prevents food from entering the trachea.

Trachea: Macroscopic and Microscopic Structure

The trachea is a flexible tube supported by C-shaped cartilage rings.

• Macroscopic: 10-12 cm long; extends from larynx to bronchi.

• Microscopic: Lined with pseudostratified ciliated columnar epithelium; contains goblet cells.

Histological Differences: Upper vs. Lower Respiratory Passages

The histology of the respiratory tract changes as air moves deeper into the lungs.

• Upper passages: Ciliated epithelium, goblet cells, cartilage support.

• Lower passages: Simple cuboidal or squamous epithelium; less cartilage, more smooth muscle.

Alveolus and Respiratory Membrane Structure

Alveoli are tiny air sacs where gas exchange occurs. The respiratory membrane is the barrier between air and blood.

• Alveolus: Lined by simple squamous epithelium (type I cells); contains type II cells (produce surfactant).

• Respiratory membrane: Composed of alveolar epithelium, capillary endothelium, and fused basement membranes.

Gross Structure of the Lungs and Pleurae

The lungs are paired organs covered by pleurae, which are serous membranes.

• Lobes: Right lung (3 lobes), left lung (2 lobes).

• Pleurae: Visceral pleura covers lungs; parietal pleura lines thoracic cavity; pleural cavity contains lubricating fluid.

Ventilation: Muscles, Pleural Cavity, and Lung Elasticity

Ventilation is the process of moving air in and out of the lungs, driven by muscle action and lung elasticity.

• Respiratory muscles: Diaphragm and intercostal muscles contract to expand thoracic cavity.

• Pleural cavity: Maintains negative pressure, preventing lung collapse.

• Lung elasticity: Allows lungs to recoil during exhalation.

Surfactant: Definition and Function

Surfactant is a substance produced by type II alveolar cells that reduces surface tension within alveoli.

• Function: Prevents alveolar collapse, facilitates easier inflation during inspiration.

Example: Gas Exchange Equation

The movement of gases across the respiratory membrane is governed by partial pressure gradients.

Equation:

$\Delta P = P_{atm} - P_{alv}$

Where $\Delta P$ is the pressure difference driving airflow, $P_{atm}$ is atmospheric pressure, and $P_{alv}$ is alveolar pressure.

Summary Table: Regions of the Pharynx

Region	Location	Main Structures	Function
Nasopharynx	Posterior to nasal cavity	Pharyngeal tonsil, opening of auditory tube	Air passage only
Oropharynx	Posterior to oral cavity	Palatine tonsils, lingual tonsils	Passage for air and food
Laryngopharynx	Posterior to larynx	None specific	Passage for air and food; leads to esophagus and larynx

Additional info: Academic context was added to expand brief learning objectives into full explanations, including definitions, examples, and a summary table for clarity.