🤾🏻‍♂️Human Physiology Engineering Unit 7 – Respiratory System

Respiratory System Overview

• Consists of organs and tissues that facilitate gas exchange between the environment and the bloodstream
• Primary function is to deliver oxygen to the body's cells and remove carbon dioxide waste
• Includes the upper respiratory tract (nose, pharynx, and larynx) and lower respiratory tract (trachea, bronchi, and lungs)
• Closely interacts with the cardiovascular system to ensure efficient gas transport throughout the body
• Plays a vital role in maintaining the body's acid-base balance by regulating carbon dioxide levels
• Facilitates other functions such as speech production, olfaction (sense of smell), and protection against inhaled particles
• Responds to changes in metabolic demand by adjusting ventilation rate and depth

Anatomy of the Respiratory Tract

• Nose and nasal cavity
  • Serve as the entry point for inhaled air
  • Humidify, filter, and warm the incoming air
  • Contain olfactory receptors for the sense of smell
• Pharynx (throat)
  • Connects the nasal and oral cavities to the larynx and esophagus
  • Plays a role in both the respiratory and digestive systems
• Larynx (voice box)
  • Houses the vocal cords, which vibrate to produce speech sounds
  • Acts as a valve to protect the lower respiratory tract from food and liquid aspiration
• Trachea (windpipe)
  • Tubular structure that connects the larynx to the bronchi
  • Lined with ciliated epithelium and mucus-secreting cells to trap and remove inhaled particles
• Bronchi and bronchioles
  • Branching airways that progressively decrease in size as they extend into the lungs
  • Conduct air to the alveoli, the site of gas exchange
• Lungs
  • Paired, spongy organs located in the thoracic cavity
  • Contain millions of alveoli, which are surrounded by capillaries for efficient gas exchange
  • Right lung is slightly larger than the left lung due to the position of the heart

Mechanics of Breathing

• Breathing involves the coordinated movement of the diaphragm, intercostal muscles, and lungs
• Inhalation (inspiration)
  • Diaphragm contracts and flattens, increasing the vertical dimension of the thoracic cavity
  • External intercostal muscles contract, lifting the ribs and expanding the thoracic cavity
  • Increased thoracic volume decreases intrapulmonary pressure, causing air to flow into the lungs
• Exhalation (expiration)
  • Diaphragm and external intercostal muscles relax, decreasing the size of the thoracic cavity
  • Decreased thoracic volume increases intrapulmonary pressure, forcing air out of the lungs
  • Exhalation is typically passive during quiet breathing but can be active during forceful expiration
• Lung volumes and capacities
  • Tidal volume (TV): volume of air inhaled or exhaled during normal breathing
  • Inspiratory reserve volume (IRV): additional air that can be inhaled beyond tidal volume
  • Expiratory reserve volume (ERV): additional air that can be exhaled beyond tidal volume
  • Residual volume (RV): air remaining in the lungs after maximal exhalation
  • Total lung capacity (TLC): maximum volume of air the lungs can hold, equal to the sum of all lung volumes

Gas Exchange and Transport

• Gas exchange occurs primarily in the alveoli, where the air and blood are separated by a thin, permeable membrane
• Oxygen diffuses from the alveoli into the blood, while carbon dioxide diffuses from the blood into the alveoli
• Factors affecting gas exchange
  • Partial pressure gradients of oxygen and carbon dioxide between the alveoli and blood
  • Surface area of the alveolar-capillary membrane
  • Thickness of the alveolar-capillary membrane
  • Ventilation-perfusion (V/Q) matching, ensuring adequate airflow and blood flow to each alveolus
• Oxygen transport
  • Most oxygen is bound to hemoglobin in red blood cells, forming oxyhemoglobin
  • A small amount of oxygen is dissolved in the blood plasma
• Carbon dioxide transport
  • Dissolved in blood plasma as bicarbonate ions (HCO3-)
  • Bound to hemoglobin as carbaminohemoglobin
  • Dissolved in blood plasma as dissolved carbon dioxide

Respiratory Control and Regulation

• Breathing is controlled by the respiratory center in the brainstem, which consists of the medulla oblongata and pons
• Medullary respiratory center
  • Dorsal respiratory group (DRG) generates the basic rhythm of breathing
  • Ventral respiratory group (VRG) influences the pattern and depth of breathing
• Pontine respiratory centers
  • Pneumotaxic center modulates the duration of inspiration and respiratory rate
  • Apneustic center promotes prolonged inspiration
• Chemoreceptors detect changes in blood gas levels and pH
  • Central chemoreceptors in the medulla respond to changes in cerebrospinal fluid pH
  • Peripheral chemoreceptors (carotid and aortic bodies) respond to changes in arterial blood pH, oxygen, and carbon dioxide levels
• Mechanoreceptors provide feedback on lung volume and airway resistance
  • Stretch receptors in the lung tissue detect lung inflation and prevent overinflation
  • Irritant receptors in the airways respond to noxious stimuli and trigger coughing or bronchospasm
• Voluntary control of breathing
  • Cortical influences can override the automatic control of breathing for short periods (e.g., holding breath, speaking, singing)

Common Respiratory Disorders

• Asthma
  • Chronic inflammatory disorder characterized by airway hyperresponsiveness and reversible airflow obstruction
  • Triggers include allergens, irritants, and exercise
  • Symptoms: wheezing, coughing, chest tightness, and shortness of breath
• Chronic obstructive pulmonary disease (COPD)
  • Progressive, irreversible airflow limitation due to chronic bronchitis and/or emphysema
  • Main risk factor is long-term exposure to tobacco smoke
  • Symptoms: dyspnea, chronic cough, and sputum production
• Pneumonia
  • Infection of the lung tissue caused by bacteria, viruses, or fungi
  • Symptoms: fever, chills, cough, chest pain, and difficulty breathing
  • Can lead to consolidation of lung tissue and impaired gas exchange
• Sleep apnea
  • Repeated episodes of partial or complete upper airway obstruction during sleep
  • Types: obstructive sleep apnea (OSA) and central sleep apnea (CSA)
  • Symptoms: loud snoring, gasping during sleep, daytime sleepiness, and morning headaches
• Lung cancer
  • Malignant growth in the lung tissue, often caused by long-term exposure to carcinogens (e.g., tobacco smoke, radon, asbestos)
  • Symptoms: persistent cough, chest pain, weight loss, and hemoptysis (coughing up blood)
  • Treatment options include surgery, chemotherapy, radiation therapy, and targeted therapy

Respiratory System Engineering Applications

• Mechanical ventilation
  • Devices that provide artificial ventilation for patients with respiratory failure
  • Types: invasive (endotracheal or tracheostomy tube) and non-invasive (face mask or nasal interface)
  • Modes: volume-controlled, pressure-controlled, and pressure support ventilation
• Extracorporeal membrane oxygenation (ECMO)
  • Technique that provides prolonged cardiac and respiratory support for patients with severe cardiopulmonary failure
  • Blood is drained from the patient, oxygenated through an artificial lung, and returned to the patient's circulation
• Pulmonary function testing
  • Devices and techniques used to assess lung function and diagnose respiratory disorders
  • Spirometry measures lung volumes and flow rates during forced breathing maneuvers
  • Plethysmography measures total lung capacity and airway resistance
  • Diffusing capacity of the lung for carbon monoxide (DLCO) assesses the efficiency of gas exchange
• Aerosol drug delivery systems
  • Devices that deliver medication directly to the lungs in the form of an aerosol
  • Examples: metered-dose inhalers (MDIs), dry powder inhalers (DPIs), and nebulizers
  • Advantages include targeted delivery, rapid onset of action, and reduced systemic side effects
• Artificial lung development
  • Research aimed at creating functional, bioartificial lungs for long-term respiratory support or transplantation
  • Approaches include decellularized lung scaffolds, 3D bioprinting, and microfluidic devices
  • Challenges include replicating the complex structure and function of the native lung and preventing immune rejection

Key Takeaways and Review

• The respiratory system is responsible for gas exchange between the environment and the bloodstream, delivering oxygen to cells and removing carbon dioxide waste
• The respiratory tract consists of the upper (nose, pharynx, and larynx) and lower (trachea, bronchi, and lungs) portions, each with specific functions
• Breathing mechanics involve the coordinated movement of the diaphragm, intercostal muscles, and lungs, resulting in changes in intrapulmonary pressure and airflow
• Gas exchange occurs in the alveoli, where oxygen and carbon dioxide diffuse across the alveolar-capillary membrane based on partial pressure gradients
• Respiratory control is primarily regulated by the medullary and pontine respiratory centers in the brainstem, with input from chemoreceptors and mechanoreceptors
• Common respiratory disorders include asthma, COPD, pneumonia, sleep apnea, and lung cancer, each with specific pathophysiology and treatment approaches
• Respiratory system engineering applications encompass mechanical ventilation, ECMO, pulmonary function testing, aerosol drug delivery systems, and artificial lung development
• Understanding the structure, function, and regulation of the respiratory system is crucial for diagnosing and treating respiratory disorders and developing innovative engineering solutions