🫁Honors Anatomy and Physiology Unit 12 – Respiratory System

Key Structures and Functions

• Nose and nasal cavity filter, warm, and humidify incoming air before it reaches the lungs
• Pharynx (throat) connects the nasal and oral cavities to the larynx and esophagus
• Larynx (voice box) contains the vocal cords and prevents food and liquid from entering the trachea
• Trachea (windpipe) is a tubular structure that connects the larynx to the bronchi
  • Composed of C-shaped cartilage rings that prevent collapse during breathing
• Bronchi are two main branches of the trachea that lead to the left and right lungs
  • Further divide into smaller bronchioles and terminal bronchioles
• Lungs are the primary organs of the respiratory system where gas exchange occurs
  • Right lung has three lobes (upper, middle, and lower) while the left lung has two lobes (upper and lower)
• Alveoli are tiny air sacs at the end of the respiratory tree where gas exchange takes place
  • Surrounded by a network of capillaries for efficient oxygen and carbon dioxide exchange

Mechanics of Breathing

• Breathing involves the movement of air into (inspiration) and out of (expiration) the lungs
• Inspiration is an active process that requires contraction of the diaphragm and external intercostal muscles
  • Diaphragm contracts and flattens, increasing the vertical dimension of the thoracic cavity
  • External intercostal muscles contract, lifting the ribs and increasing the anteroposterior dimension of the thoracic cavity
• Expiration is typically a passive process that occurs due to the elastic recoil of the lungs and thoracic wall
  • Diaphragm and external intercostal muscles relax, decreasing the size of the thoracic cavity
• Boyle's law explains the relationship between pressure and volume in the respiratory system
  • As volume increases, pressure decreases, and vice versa
• Pleural membranes (parietal and visceral) create a fluid-filled space that allows the lungs to expand and contract smoothly

Gas Exchange Process

• Gas exchange occurs between the alveoli and 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 partial pressure gradients of oxygen and carbon dioxide
  • Oxygen moves from an area of high partial pressure (alveoli) to an area of low partial pressure (blood)
  • Carbon dioxide moves from an area of high partial pressure (blood) to an area of low partial pressure (alveoli)
• Hemoglobin in red blood cells binds to oxygen, forming oxyhemoglobin, for transport to the tissues
• In the tissues, oxygen dissociates from hemoglobin and diffuses into the cells, while carbon dioxide diffuses from the cells into the blood
• Carbon dioxide is transported in the blood in three forms: dissolved, bound to hemoglobin (carbaminohemoglobin), and as bicarbonate ions

Respiratory Volumes and Capacities

• Tidal volume (TV) is the volume of air inhaled or exhaled during a normal breath at rest (approximately 500 mL)
• Inspiratory reserve volume (IRV) is the additional volume of air that can be inhaled beyond tidal volume (approximately 3000 mL)
• Expiratory reserve volume (ERV) is the additional volume of air that can be exhaled beyond tidal volume (approximately 1100 mL)
• Residual volume (RV) is the volume of air remaining in the lungs after a maximal expiration (approximately 1200 mL)
• Vital capacity (VC) is the maximum volume of air that can be exhaled after a maximal inhalation (TV + IRV + ERV)
• Inspiratory capacity (IC) is the maximum volume of air that can be inhaled after a normal expiration (TV + IRV)
• Functional residual capacity (FRC) is the volume of air remaining in the lungs after a normal expiration (ERV + RV)
• Total lung capacity (TLC) is the total volume of air in the lungs after a maximal inhalation (TV + IRV + ERV + RV)

Control of Breathing

• Breathing is controlled by the respiratory center in the medulla oblongata and pons of the brainstem
• The medullary rhythmicity area generates the basic rhythm of breathing
  • Dorsal respiratory group (DRG) primarily controls inspiration
  • Ventral respiratory group (VRG) primarily controls expiration
• Pontine respiratory group modulates the activity of the medullary respiratory centers
• Chemoreceptors detect changes in blood pH, carbon dioxide, and oxygen levels
  • Central chemoreceptors in the medulla detect changes in cerebrospinal fluid pH due to carbon dioxide levels
  • Peripheral chemoreceptors (carotid and aortic bodies) detect changes in arterial blood pH, carbon dioxide, and oxygen levels
• Stretch receptors in the lungs (Hering-Breuer reflex) prevent overinflation and help maintain a smooth breathing pattern
• Higher brain centers (cerebral cortex and hypothalamus) can voluntarily override the automatic control of breathing

Common Respiratory Disorders

• Asthma is a chronic inflammatory disorder characterized by airway hyperresponsiveness and reversible airflow obstruction
  • Triggered by allergens, irritants, or exercise
  • Symptoms include wheezing, coughing, chest tightness, and shortness of breath
• Chronic obstructive pulmonary disease (COPD) is a progressive disorder characterized by airflow limitation that is not fully reversible
  • Includes chronic bronchitis and emphysema
  • Risk factors include smoking, air pollution, and genetic factors (alpha-1 antitrypsin deficiency)
• Pneumonia is an infection of the lungs caused by bacteria, viruses, or fungi
  • Symptoms include cough, fever, chills, and difficulty breathing
• Sleep apnea is a disorder characterized by repeated episodes of airway obstruction during sleep
  • Obstructive sleep apnea (OSA) is caused by collapse of the upper airway
  • Central sleep apnea (CSA) is caused by a lack of neural drive to breathe
• Lung cancer is a malignant tumor that originates in the lungs
  • Risk factors include smoking, exposure to radon or asbestos, and family history

Diagnostic Tests and Procedures

• Pulmonary function tests (PFTs) assess lung volumes, capacities, and flow rates
  • Spirometry measures the volume and flow of air during inspiration and expiration
  • Lung volume measurements determine the volume of air in the lungs at different points in the breathing cycle
• Arterial blood gas (ABG) analysis measures the partial pressures of oxygen and carbon dioxide, as well as pH and bicarbonate levels in arterial blood
• Chest X-ray provides a two-dimensional image of the lungs, heart, and surrounding structures
• Computed tomography (CT) scan creates detailed cross-sectional images of the lungs and chest
• Bronchoscopy involves the insertion of a flexible tube with a camera (bronchoscope) into the airways to visualize the lungs and collect samples
• Pulse oximetry is a non-invasive method of measuring the oxygen saturation of arterial blood using a sensor placed on the finger or earlobe

Clinical Applications and Case Studies

• Case study: A 25-year-old male presents with wheezing, coughing, and shortness of breath after exercising. He has a history of allergies and a family history of asthma.
  • Diagnosis: Exercise-induced asthma
  • Treatment: Short-acting bronchodilators (albuterol) before exercise, long-term control medications (inhaled corticosteroids), and avoidance of triggers
• Case study: A 60-year-old female with a 40-pack-year smoking history presents with chronic cough, sputum production, and progressive shortness of breath.
  • Diagnosis: Chronic obstructive pulmonary disease (COPD)
  • Treatment: Smoking cessation, bronchodilators (beta-2 agonists and anticholinergics), inhaled corticosteroids, pulmonary rehabilitation, and oxygen therapy if needed
• Case study: A 45-year-old male presents with fever, cough, and chest pain. He has a history of hypertension and type 2 diabetes.
  • Diagnosis: Community-acquired pneumonia
  • Treatment: Antibiotics (based on local resistance patterns and patient factors), supportive care (rest, hydration, and oxygen if needed), and management of underlying comorbidities
• Clinical application: Mechanical ventilation is used to support patients with respiratory failure or those undergoing surgery
  • Positive pressure ventilation delivers air or a mixture of gases into the lungs
  • Settings include tidal volume, respiratory rate, fraction of inspired oxygen (FiO2), and positive end-expiratory pressure (PEEP)
• Clinical application: Pulmonary rehabilitation is a comprehensive program designed to improve the quality of life for patients with chronic respiratory diseases (COPD, asthma, interstitial lung disease)
  • Components include exercise training, education, nutritional counseling, and psychosocial support
  • Goals include reducing symptoms, increasing exercise tolerance, and improving overall functional status