Chapter 22: The Respiratory System

Learning Objectives

This chapter covers the structure and function of the respiratory system, the mechanics of breathing, partial pressure changes, and the interaction between the respiratory and circulatory systems.

• Identify the location and role of major respiratory structures.

• Explain the mechanics of breathing and the musculature involved.

• Describe partial pressure changes within the respiratory system.

• Discuss the interaction of the circulatory system with the respiratory system.

Anatomy of the Respiratory System

Nose

The nose forms the external portion of the respiratory system and serves several key functions in respiration and olfaction.

• Passageway for respiration: Air enters the respiratory tract through the nose.

• Moistens and warms air: The nasal cavity conditions incoming air for the lungs.

• Filters and cleans inspired air: Vibrissae (nasal hairs) and mucous membranes trap particles.

• Resonating chamber for speech: The nose contributes to sound amplification and resonance.

• Houses olfactory receptors: Responsible for the sense of smell.

• Regions: External nose and nasal cavity.

Nasal Cavity

• Lined with vibrissae: These hairs filter large particles from inspired air.

• Mucous membranes: The rest of the nasal cavity is lined with mucosa that traps smaller particles and humidifies air.

• Nasal conchae: Scroll-like, mucosa-covered projections that increase surface area and turbulence, enhancing air filtration, heating, and moistening.

Homeostatic Imbalance 22.1: Inflammation of Nasal Mucosa

Inflammation of the nasal mucosa can lead to the spread of infection throughout the respiratory tract and associated structures.

• Sinusitis: Blockage of sinus passageways due to infection or inflammation, resulting in pressure and overproduction of mucus.

• Spread of infection: The continuity of mucosa allows infections to move from the nose to the throat, chest, tear ducts, and paranasal sinuses.

Paranasal Sinuses

Paranasal sinuses are air-filled spaces located in the frontal, sphenoid, ethmoid, and maxillary bones.

• Lighten the skull: Reduce the weight of the skull.

• Secrete mucus: Help trap pathogens and particles.

• Warm and moisten air: Assist in conditioning inspired air.

• House nerves: Contribute to sensation and pain in sinus infections.

Major Structures of the Respiratory System

Pharynx

The pharynx is a muscular tube that serves as a passageway for air and food, connecting the nasal cavity to the larynx and esophagus.

• Nasopharynx: Posterior to the nasal cavity.

• Oropharynx: Posterior to the oral cavity.

• Laryngopharynx: Posterior to the larynx (windpipe).

Larynx

The larynx is continuous with the trachea and functions in air passage, voice production, and protection of the lower airways.

• Epiglottis: Elastic cartilage that covers the laryngeal inlet during swallowing.

Trachea

The trachea, or "windpipe," extends from the larynx into the mediastinum and divides into the primary bronchi.

• Layers:

  • Mucosa: Ciliated pseudostratified epithelium with goblet cells.

  • Submucosa: Connective tissue with seromucous glands.

  • Cartilage rings: C-shaped rings provide structural support.

  • Adventitia: Outermost connective tissue layer.

Bronchi and Subdivisions

The trachea divides into right and left main (primary) bronchi, which branch into smaller bronchi and bronchioles.

• Main bronchi: Enter the hilum of each lung.

• Lobar (secondary) bronchi: Three on the right, two on the left.

• Bronchioles: Less than 1 mm in diameter.

• Terminal bronchioles: Smallest branches leading to alveoli.

Alveoli

Alveoli are the primary sites of gas exchange in the lungs.

• Type I alveolar cells: Single layer of squamous epithelium for gas diffusion.

• Type II alveolar cells: Secrete surfactant and antimicrobial proteins.

• Alveolar macrophages: Remove debris and pathogens.

• Pulmonary capillaries: Surround alveoli for gas exchange.

Pleurae

The pleurae are serous membranes that divide the thoracic cavity and cover the lungs.

• Parietal pleura: Lines the thoracic wall and diaphragm.

• Visceral pleura: Covers the external lung surface.

• Pleural fluid: Fills the pleural cavity, providing lubrication and surface tension for lung expansion.

Functional Zones of the Respiratory System

Conducting Zone

The conducting zone consists of all respiratory passageways that transport air to the respiratory zone.

• Functions: Cleanses, warms, and humidifies air.

• Structures: Nasal cavity to terminal bronchioles.

Respiratory Zone

The respiratory zone is the site of gas exchange.

• Structures: Respiratory bronchioles, alveolar ducts, alveolar sacs, and alveoli.

Mechanics of Breathing

Pulmonary Ventilation

Pulmonary ventilation consists of inspiration and expiration, driven by changes in thoracic cavity volume and pressure.

• Inspiration: Diaphragm and external intercostal muscles contract, increasing thoracic volume and decreasing pressure, allowing air to flow in.

• Expiration: Normally passive; muscles relax, thoracic volume decreases, and air flows out.

• Forced expiration: Active process using abdominal and internal intercostal muscles.

Pressure Relationships

Respiratory pressures are measured relative to atmospheric pressure ().

• Atmospheric pressure (): Pressure exerted by air surrounding the body (~760 mm Hg at sea level).

• Intrapulmonary pressure (): Pressure in alveoli; fluctuates with breathing.

• Intrapleural pressure (): Pressure in pleural cavity; always negative relative to and .

Equations

• Gas flow:

• Boyle's Law:

Factors Influencing Pulmonary Ventilation

• Airway resistance: Inversely related to gas flow; minimized by large airway diameters and branching.

• Alveolar surface tension: Surfactant reduces surface tension, preventing alveolar collapse.

• Lung compliance: Measure of lung stretchability; high compliance makes breathing easier.

Gas Exchange

External Respiration

Exchange of gases between alveoli and blood, influenced by partial pressure gradients, membrane thickness, and surface area.

• Partial pressure gradients: Oxygen diffuses from alveoli ( mm Hg) to blood ( mm Hg); carbon dioxide diffuses from blood ( mm Hg) to alveoli ( mm Hg).

• Ventilation-perfusion coupling: Matching of alveolar ventilation with pulmonary blood flow for efficient gas exchange.

Internal Respiration

Exchange of gases between blood and tissues, driven by partial pressure differences.

Transport of Respiratory Gases by Blood

Oxygen Transport

Oxygen is primarily transported bound to hemoglobin in red blood cells.

• Oxyhemoglobin (): Hemoglobin bound to oxygen.

• Deoxyhemoglobin (): Hemoglobin after releasing oxygen.

• Equation:

• Hemoglobin saturation: Influenced by , temperature, pH, and (Bohr effect).

Carbon Dioxide Transport

• Dissolved in plasma (7-10%)

• Bound to hemoglobin as carbaminohemoglobin (20-30%)

• As bicarbonate ions in plasma (60-70%)

• Equation:

Regulation of Breathing

Neural and Chemical Control

• Respiratory centers: Located in the brainstem; regulate rate and depth of breathing.

• Chemoreceptors: Central (brainstem) and peripheral (aortic arch, carotid arteries) detect changes in , , and pH.

• Hypercapnia: Increased stimulates increased ventilation.

• Hypocapnia: Decreased leads to reduced ventilation.

Homeostatic Imbalances and Diseases

Hypoxia

• Anemic hypoxia: Low RBCs or abnormal hemoglobin.

• Ischemic hypoxia: Impaired blood circulation.

• Histotoxic hypoxia: Cells unable to use oxygen (e.g., cyanide poisoning).

• Hypoxemic hypoxia: Abnormal ventilation or pulmonary disease.

• Carbon monoxide poisoning: CO binds hemoglobin with much higher affinity than oxygen.

Chronic Obstructive Pulmonary Disease (COPD)

• Emphysema: Permanent enlargement and destruction of alveoli; reduced lung elasticity and ventilation efficiency.

• Chronic bronchitis: Chronic inflammation and excessive mucus production in lower respiratory passages.

• Asthma: Acute episodes of airway inflammation and bronchospasm.

Sleep Apnea

• Obstructive sleep apnea: Collapse of upper airway during sleep, leading to repeated breathing interruptions.

• Treatment: CPAP (continuous positive airway pressure) devices.

Cystic Fibrosis

• Genetic disease: Abnormal, thick mucus clogs airways, leading to infections.

• Treatments: Mucus-dissolving drugs, antibiotics, airway clearance techniques.

Summary Table: Major Structures and Functions of the Respiratory System

Key Equations and Concepts

• Boyle's Law: (Pressure and volume are inversely related in a closed system)

• Gas Flow: (Flow is proportional to pressure difference and inversely proportional to resistance)

• Oxygen-Hemoglobin Dissociation:

• CO2 Transport:

Clinical Applications

• Sinusitis: Inflammation of paranasal sinuses; causes pain and pressure.

• Pneumothorax: Air in pleural cavity causing lung collapse; treated with chest tubes.

• Surfactant deficiency: Common in premature infants; leads to alveolar collapse and respiratory distress.

Additional info: These notes expand on the provided slides and images, adding definitions, examples, and equations for a comprehensive review suitable for college-level Anatomy & Physiology students.