🫀Anatomy and Physiology II Unit 4 – Respiratory System: Anatomy & Ventilation

Key Structures

• Nose and nasal cavity filter, warm, and humidify inhaled air before it reaches the lungs
• Pharynx (throat) is a passageway for both air and food, connects the nasal and oral cavities to the larynx and esophagus
  • Divided into nasopharynx, oropharynx, and laryngopharynx based on location and function
• Larynx (voice box) contains the vocal cords and serves as a valve to protect the lower respiratory tract during swallowing
• Trachea (windpipe) is a flexible tube that connects the larynx to the bronchi, lined with ciliated pseudostratified columnar epithelium and C-shaped cartilage rings
  • Cilia in the trachea sweep mucus and trapped particles upward toward the pharynx for removal
• Bronchi are the two main branches of the trachea that lead to the left and right lungs, further divide into smaller bronchioles
• Lungs are the primary organs of the respiratory system, responsible for gas exchange between the air and the blood
  • Each lung is divided into lobes (right lung has three lobes, left lung has two) and is surrounded by a double-layered pleural membrane

Respiratory System Overview

• Primary function is to facilitate gas exchange between the air and the blood, allowing oxygen to enter the body and carbon dioxide to be removed
• Consists of the upper respiratory tract (nose, nasal cavity, pharynx, and larynx) and the lower respiratory tract (trachea, bronchi, bronchioles, and lungs)
• Respiratory system works in conjunction with the cardiovascular system to deliver oxygen to tissues and remove carbon dioxide
• Breathing is controlled by the respiratory center in the brainstem, which adjusts the rate and depth of breathing based on blood levels of oxygen, carbon dioxide, and pH
• Respiratory system also plays a role in speech production, olfaction (sense of smell), and protection against inhaled pathogens and irritants
  • Mucus and cilia in the respiratory tract trap and remove particles, while the cough reflex expels foreign material from the airways
• Disorders of the respiratory system include asthma, chronic obstructive pulmonary disease (COPD), pneumonia, and lung cancer

Upper Respiratory Tract

• Consists of the nose, nasal cavity, pharynx, and larynx
• Nose and nasal cavity are responsible for filtering, warming, and humidifying inhaled air
  • Nasal hairs and mucus trap larger particles, while blood vessels in the nasal cavity warm the air to body temperature
  • Conchae (turbinates) increase the surface area of the nasal cavity, enhancing air conditioning and olfaction
• Pharynx is a muscular tube that connects the nasal and oral cavities to the larynx and esophagus
  • Nasopharynx is located behind the nasal cavity and is involved in breathing and speech
  • Oropharynx is located behind the oral cavity and is a common passageway for air and food
  • Laryngopharynx is the lowest part of the pharynx, connecting to the larynx and esophagus
• Larynx (voice box) is a cartilaginous structure that contains the vocal cords and serves as a valve to protect the lower respiratory tract during swallowing
  • Epiglottis is a leaf-shaped cartilage that covers the glottis (opening of the larynx) during swallowing to prevent aspiration of food or liquid into the lungs

Lower Respiratory Tract

• Consists of the trachea, bronchi, bronchioles, and lungs
• Trachea (windpipe) is a flexible tube that connects the larynx to the bronchi
  • Lined with ciliated pseudostratified columnar epithelium and supported by C-shaped cartilage rings to prevent collapse
  • Cilia sweep mucus and trapped particles upward toward the pharynx for removal (mucociliary escalator)
• Bronchi are the two main branches of the trachea that lead to the left and right lungs
  • Further divide into smaller bronchioles, which continue to branch until they reach the alveoli
  • Walls of the bronchi and larger bronchioles contain smooth muscle and cartilage for support and airflow regulation
• Lungs are the primary organs of the respiratory system, responsible for gas exchange between the air and the blood
  • Each lung is divided into lobes (right lung has three lobes, left lung has two) and is surrounded by a double-layered pleural membrane
  • Alveoli are the functional units of the lungs, where gas exchange takes place
    • Alveoli are tiny, thin-walled sacs surrounded by capillaries, allowing for efficient diffusion of gases between the air and the blood
• Pulmonary arteries carry deoxygenated blood from the heart to the lungs, while pulmonary veins carry oxygenated blood from the lungs back to the heart

Mechanics of Breathing

• Breathing involves the movement of air into and out of the lungs, driven by changes in pressure within the thoracic cavity
• Inhalation (inspiration) occurs when the diaphragm and external intercostal muscles contract, increasing the volume of the thoracic cavity and decreasing the pressure inside the lungs
  • As pressure inside the lungs becomes lower than atmospheric pressure, air flows into the lungs until the pressures equalize
• Exhalation (expiration) is typically a passive process, as the diaphragm and external intercostal muscles relax, decreasing the volume of the thoracic cavity and increasing the pressure inside the lungs
  • As pressure inside the lungs becomes higher than atmospheric pressure, air flows out of the lungs until the pressures equalize
  • During forced exhalation, internal intercostal muscles and abdominal muscles contract to further increase the pressure inside the lungs and expel air more rapidly
• Boyle's law describes the inverse relationship between pressure and volume in a closed system, which applies to the mechanics of breathing
  • As volume increases, pressure decreases; as volume decreases, pressure increases
• Lung volumes and capacities can be measured using a spirometer, which helps assess lung function and diagnose respiratory disorders
  • Tidal volume (TV) is the volume of air inhaled or exhaled during normal, quiet breathing
  • Inspiratory reserve volume (IRV) is the additional volume of air that can be inhaled beyond the tidal volume
  • Expiratory reserve volume (ERV) is the additional volume of air that can be exhaled beyond the tidal volume
  • Residual volume (RV) is the volume of air that remains in the lungs after a maximal exhalation

Gas Exchange Process

• Gas exchange occurs between the air in the alveoli and the blood in the pulmonary capillaries
• Oxygen diffuses from the alveoli into the blood, while carbon dioxide diffuses from the blood into the alveoli
  • Diffusion is driven by concentration gradients, with gases moving from areas of high concentration to areas of low concentration
• Hemoglobin in red blood cells binds to oxygen, forming oxyhemoglobin and facilitating the transport of oxygen throughout the body
  • Each hemoglobin molecule can bind up to four oxygen molecules
  • Oxygen-hemoglobin dissociation curve describes the relationship between the partial pressure of oxygen and the percentage of hemoglobin saturated with oxygen
• Carbon dioxide is transported in the blood in three main forms: dissolved in plasma, bound to hemoglobin (carbaminohemoglobin), and as bicarbonate ions
  • Carbonic anhydrase enzyme catalyzes the conversion of carbon dioxide and water into carbonic acid, which dissociates into bicarbonate and hydrogen ions
• Ventilation-perfusion (V/Q) ratio is the relationship between the amount of air reaching the alveoli (ventilation) and the amount of blood flowing through the pulmonary capillaries (perfusion)
  • Optimal gas exchange occurs when the V/Q ratio is close to 1, meaning that ventilation and perfusion are well-matched
  • V/Q mismatches can lead to hypoxemia (low blood oxygen levels) and impaired gas exchange

Ventilation Regulation

• Breathing is controlled by the respiratory center in the brainstem, which consists of the medulla oblongata and the pons
• Medullary rhythmicity area in the medulla oblongata generates the basic rhythm of breathing
  • Dorsal respiratory group (DRG) primarily controls inspiration
  • Ventral respiratory group (VRG) primarily controls expiration
• Pontine respiratory group in the pons modulates the activity of the medullary respiratory centers, smoothing the transition between inspiration and expiration
• Chemoreceptors detect changes in blood levels of oxygen, carbon dioxide, and pH, and send signals to the respiratory center to adjust ventilation accordingly
  • Central chemoreceptors in the medulla oblongata detect changes in cerebrospinal fluid pH, which reflects changes in blood carbon dioxide levels
  • Peripheral chemoreceptors in the carotid and aortic bodies detect changes in blood oxygen levels and pH
• Stretch receptors in the lungs and chest wall provide feedback to the respiratory center about lung inflation and deflation, helping to control the depth and rate of breathing (Hering-Breuer reflex)
• Higher brain centers, such as the cerebral cortex and hypothalamus, can also influence breathing in response to emotions, pain, temperature changes, and voluntary control

Clinical Applications

• Spirometry is a common pulmonary function test that measures lung volumes and capacities, helping to diagnose and monitor respiratory disorders
  • Forced vital capacity (FVC) is the total volume of air that can be exhaled after a maximal inhalation
  • Forced expiratory volume in one second (FEV1) is the volume of air exhaled during the first second of a forced exhalation
  • FEV1/FVC ratio is used to differentiate between obstructive and restrictive lung disorders
• Obstructive lung diseases, such as asthma and chronic obstructive pulmonary disease (COPD), are characterized by airflow limitation due to narrowing of the airways
  • Symptoms include wheezing, coughing, and shortness of breath
  • Treatment may include bronchodilators, corticosteroids, and lifestyle modifications (e.g., smoking cessation)
• Restrictive lung diseases, such as interstitial lung disease and kyphoscoliosis, are characterized by reduced lung volumes due to decreased lung compliance or chest wall expansion
  • Symptoms include shortness of breath, rapid shallow breathing, and fatigue
  • Treatment depends on the underlying cause and may include medications, oxygen therapy, and pulmonary rehabilitation
• Ventilator-associated pneumonia (VAP) is a common complication in patients receiving mechanical ventilation
  • Risk factors include prolonged intubation, supine positioning, and inadequate oral hygiene
  • Prevention strategies include elevating the head of the bed, using subglottic secretion drainage, and implementing oral care protocols
• Pulmonary embolism (PE) is a potentially life-threatening condition caused by a blood clot that travels to the lungs
  • Risk factors include deep vein thrombosis, immobility, surgery, and certain medications (e.g., oral contraceptives)
  • Symptoms include sudden shortness of breath, chest pain, and cough
  • Diagnosis may involve CT pulmonary angiography or ventilation-perfusion (V/Q) scanning
  • Treatment typically involves anticoagulation therapy to prevent further clot formation and promote clot dissolution