Respiratory System Disorders: Structure, Function, and Pathology

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Respiratory System Anatomy and Physiology

Overview of Respiratory Structures

The respiratory system is responsible for gas exchange, supplying oxygen to the blood and removing carbon dioxide. It consists of upper and lower respiratory tracts, including the nasal cavity, pharynx, larynx, trachea, bronchi, bronchioles, and alveoli.

Upper respiratory tract: Nasal cavity, pharynx, larynx
Lower respiratory tract: Trachea, bronchi, bronchioles, alveoli
Alveoli: Primary site of gas exchange
Pleura: Double-layered membrane surrounding the lungs

Anatomy of the respiratory system, including upper and lower tracts, alveoli, and pleura

Mechanics of Ventilation

Ventilation is the process of moving air into and out of the lungs, driven by pressure changes created by the diaphragm and intercostal muscles.

Inspiration: Diaphragm contracts, thoracic cavity expands, intrapulmonary pressure drops, air flows in.
Expiration: Diaphragm relaxes, thoracic cavity volume decreases, intrapulmonary pressure rises, air flows out.
Atmospheric pressure: The pressure exerted by the air surrounding the body, typically 760 mm Hg at sea level.

Mechanics of ventilation: inspiration and expiration

Pulmonary Volumes

Pulmonary volumes are measurements of air movement during different phases of the respiratory cycle. These values are important for assessing lung function.

Name	Volume	Meaning
Tidal volume (TV)	500 mL	Amount of air entering lungs with each normal breath
Residual volume (RV)	1200 mL	Amount of air remaining in the lungs after forced expiration
Inspiratory reserve (IRV)	3000 mL	Maximal amount of air that can be inhaled in excess of normal quiet inspiration
Expiratory reserve (ERV)	1100 mL	Maximal volume of air expired following a passive expiration
Vital capacity (VC)	4600 mL	Maximal amount of air expired following a maximal inspiration
Total lung capacity (TLC)	5800 mL	Total volume of air in the lungs after maximal inspiration

Table of pulmonary volumes

Pulmonary Capillaries and Alveoli

Gas exchange occurs in the alveoli, which are surrounded by a dense network of pulmonary capillaries. Oxygen diffuses from alveoli into blood, while carbon dioxide diffuses from blood into alveoli.

Pulmonary arteriole: Brings deoxygenated blood from the right ventricle to the alveolus.
Pulmonary venule: Returns oxygenated blood to the left ventricle.

Pulmonary capillaries around alveolus

Alveolar Structure

Alveoli are lined with squamous epithelial cells and contain surfactant-producing cells to reduce surface tension, preventing collapse. Alveolar macrophages provide immune defense.

Surfactant: Lipoprotein that reduces surface tension in alveoli.
Alveolar-capillary membrane: Thin barrier for efficient gas exchange.

Cross-section of an alveolus

Diffusion of Gases

Gas exchange is driven by differences in partial pressures of oxygen (O2) and carbon dioxide (CO2) between alveolar air and blood.

Oxygen: Diffuses from alveoli (high PO2) to blood (low PO2).
Carbon dioxide: Diffuses from blood (high PCO2) to alveoli (low PCO2).

Diffusion of gases in the alveolus

Oxyhemoglobin Dissociation Curve

The oxyhemoglobin dissociation curve describes the relationship between the partial pressure of oxygen (PO2) and hemoglobin saturation. Factors such as pH, temperature, and CO2 levels shift the curve, affecting oxygen release to tissues.

Left shift: Increased affinity (alkalosis, low temperature, low CO2).
Right shift: Decreased affinity (acidosis, high temperature, high CO2).

Oxyhemoglobin dissociation curve

Control of Respiration

Respiratory control centers in the medulla and pons regulate the rate and depth of breathing in response to CO2, O2, and pH levels in the blood.

Central chemoreceptors: Respond to increased CO2 (hypercapnia) and decreased pH.
Peripheral chemoreceptors: Respond to low O2 (hypoxemia).

Normal cycle of respiratory control

Hypoxic Drive

In chronic respiratory disorders (e.g., emphysema), the body may rely on low O2 levels (hypoxic drive) rather than high CO2 to stimulate breathing.

Chronic CO2 retention: Central chemoreceptors become less sensitive.
Peripheral chemoreceptors: Stimulated by low O2, increasing respiratory rate.

Hypoxic drive with chronic elevated CO2 levels

Respiratory Patterns and Diagnostic Tests

Respiratory Patterns

Various breathing patterns can indicate underlying respiratory pathology.

Pattern	Description
Eupnea	Normal, smooth, even rhythm
Tachypnea	Rapid, superficial breathing
Bradypnea	Slow, deeper than usual breathing
Apnea	Cessation of breathing
Hyperpnea	Increased depth of respiration
Kussmaul's respiration	Deep, rapid breathing (acidosis)
Cheyne-Stokes respiration	Alternating periods of apnea and deep, rapid breathing
Obstructed breathing	Long, gasping inspiratory phase, short expiratory phase

Table of respiratory patterns

Diagnostic Tests

Several tests are used to diagnose and monitor respiratory diseases:

Spirometry: Measures pulmonary volumes and airflow times.
Arterial blood gas (ABG): Assesses O2, CO2, bicarbonate, and pH.
Oximetry: Measures O2 saturation.
Radiography: Detects tumors, infections, and other abnormalities.
Bronchoscopy: Visualizes airways, allows biopsy.
Culture and sensitivity: Identifies pathogens in sputum.

Therapies for Respiratory Disorders

Basic Therapies

Treatment strategies for respiratory disorders include both general and specific interventions.

Treatment	Effect	Example
Avoid irritants	Reduce inflammation and infection	Cigarette smoke
Immunizations	Prevent infection	Influenza, pneumonia vaccines
Humidified air	Moistens mucosa, reduces damage	Humidifier
Chest physiotherapy	Removes thick secretions	Chest percussion
Oxygen therapy	Improves oxygen supply	Nasal cannula, mask
Bronchodilators	Dilate bronchioles	Albuterol
Glucocorticoids	Reduce inflammation	Prednisone
Antibiotics	Treat infections	Amoxicillin

Table of basic therapies for respiratory disorders

Infectious Diseases of the Respiratory System

Pathogenesis of Viral Respiratory Infections

Viral infections such as the common cold and influenza can damage respiratory mucosa, leading to secondary bacterial infections.

Primary infection: Virus invades mucosa, causing necrosis and inflammation.
Secondary infection: Bacteria invade damaged tissue, producing purulent exudate.

Pathogenesis of viral respiratory infection and secondary bacterial infection

Comparison of Respiratory Infections in Children

Respiratory infections in children vary by age group, causative agent, and clinical presentation.

	Laryngotracheobronchitis	Epiglottitis	Bronchiolitis
Age group	3 months to 3 years	3-7 years	2-12 months
Cause	Virus	Haemophilus influenzae	RSV
Pathology	Inflammation of mucosa of larynx and trachea	Supraglottic inflammation and swelling	Inflammation of bronchioles
Onset	Gradual	Rapid	Gradual
Signs	Barking cough, inspiratory stridor	Drooling, dysphagia, tripod position	Wheezing, chest retractions

Table comparing respiratory infections in children

Scarlet Fever

Scarlet fever is caused by group A β-hemolytic Streptococcus (S. pyogenes) and is characterized by a 'strawberry' tongue, fever, and sore throat.

Symptoms: Strawberry tongue, fever, chills, vomiting, abdominal pain, malaise
Treatment: Antibiotics

Strawberry tongue in scarlet fever

Pneumonia and Tuberculosis

Types of Pneumonia

Pneumonia is classified by causative agent, anatomical location, and pathophysiology.

Lobar pneumonia: Involves one or more lobes, usually caused by Streptococcus pneumoniae.
Bronchopneumonia: Scattered patches, multiple bacteria.
Interstitial (atypical) pneumonia: Scattered small patches, often viral or mycoplasma.

Types and locations of pneumonia in the lung

	Lobar Pneumonia	Bronchopneumonia	Interstitial Pneumonia
Distribution	All or one/two lobes	Scattered small patches	Scattered small patches
Cause	Streptococcus pneumoniae	Multiple bacteria	Virus, Mycoplasma
Onset	Sudden, acute	Insidious	Variable
Signs	High fever, chills, productive cough	Mild fever, productive cough	Variable fever, headache, nonproductive cough

Table of types of pneumonia

Tuberculosis Pathogenesis

Tuberculosis is caused by Mycobacterium tuberculosis and can result in primary infection (tubercle formation) or secondary/reactivation disease (cavitation and dissemination).

Primary infection: Formation of granulomas (tubercles) in the lung.
Secondary infection: Reactivation leads to cavitation and spread.

Pathogenesis of tuberculosis: primary and secondary infection Gross and schematic view of tuberculosis cavitation and spread

Obstructive Lung Diseases

Cystic Fibrosis

Cystic fibrosis is an autosomal recessive disorder causing thick, sticky mucus in the lungs, pancreas, and other organs, leading to chronic infections and malabsorption.

Respiratory: Mucus obstructs bronchioles, frequent infections, chronic cough.
Digestive: Pancreatic duct obstruction, malabsorption, steatorrhea.
Reproductive: Infertility due to mucus obstruction.
Diagnosis: Genetic testing, sweat test, pulmonary function tests.

Pathophysiology of cystic fibrosis

Lung Cancer

Lung cancer, most commonly bronchogenic carcinoma, is strongly associated with smoking. Tumors can obstruct airways, cause hemoptysis, and metastasize.

Types: Squamous cell carcinoma, adenocarcinoma, small cell carcinoma.
Symptoms: Persistent cough, chest pain, weight loss, hemoptysis.
Diagnosis: Imaging, bronchoscopy, biopsy.
Treatment: Surgery, chemotherapy, radiation.

Gross pathology of lung cancer

Asthma Pathophysiology

Asthma is a chronic inflammatory disease characterized by bronchial hyperresponsiveness, airway inflammation, and reversible airflow obstruction.

Triggers: Allergens, infections, exercise, cold air, irritants.
Pathology: Mucosal edema, bronchospasm, mucus plugging.

Pathophysiology of asthma: airway inflammation and obstruction

Additional info: This guide covers the structure, function, and common disorders of the respiratory system, integrating clinical and diagnostic perspectives essential for ANP college-level study.