Human Physiology Engineering

🤾🏻‍♂️Human Physiology Engineering Unit 7 – Respiratory System

The respiratory system is a complex network of organs and tissues that enable gas exchange between our bodies and the environment. It delivers oxygen to cells and removes carbon dioxide waste, working closely with the cardiovascular system to maintain vital functions. From the nose to the lungs, each part of the respiratory tract plays a crucial role in breathing mechanics and gas exchange. Understanding this system is essential for diagnosing and treating respiratory disorders, as well as developing innovative medical technologies.

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


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© 2024 Fiveable Inc. All rights reserved.
AP® and SAT® are trademarks registered by the College Board, which is not affiliated with, and does not endorse this website.