Respiratory System

• Respiratory System


  To deliver oxygen to the cells of the body's tissues and remove carbon dioxide

  
• Main structures of the respiratory system

  • Nasal cavity
  • Trachea
  • Lungs

  
• Direct Diffusion


  • Respiratory mechanism present in small multicellular organisms
  • Diffusion of sufficient amount of oxygen takes place across the outer membrane (1 mm in diameter)
  • Cells are kept moist for quick gas diffusion
  • Organisms: cnidarians and flatworms
  • Flat shape increases the surface area for diffusion

  
• Skin and Gills


  • Skin (integument) is used as a respiratory organ
  • Respiratory surface must be kept moist
  • Gills are thin tissue filaments that are highly branched and folded
  • Oxygen diffuses across the gill surfaces into the coelomic fluid
  • Found in mollusks, annelids, and crustaceans
  • Folded surfaces of the gills provide a large surface area
• Tracheal Systems


  • Present in insects
  • Consists of a network of small tubes that carries oxygen to the entire body
  • The most direct and efficient respiratory system in active animals
  • Spiracles allow oxygen to pass into the body and regulate the diffusion of CO2 and water vapor

  
• Parts of the Mammalian Respiratory System

  • Nasal cavity
  • Pharynx
  • Larynx
  • Trachea
  • Lungs

  
• Trachea


  • Funnel the inhaled air to the lungs and the exhaled air back out of the body
  • About 10 to 12 cm long and 2 cm in diameter
  • Divides into the two primary bronchi at the midthorax
  • Made of incomplete rings of hyaline cartilage and smooth muscle
  • Lined with mucus-producing goblet cells and ciliated epithelia

  
• Parts of the Lungs

  • Right lung (larger, 3 lobes)
  • Left lung (smaller, 2 lobes)

  
• Bronchi


  • Passage of air
  • Made of cartilage and smooth muscle except for bronchioles (elastic fibers)
  • Terminal bronchioles rely on inhaled air to support their shape
  • Subdivide into alveolar ducts (at the end is approximately 100 alveolar sacs each containing 20-30 alveoli)

  
• Alveoli


  • Where gas exchange occurs
  • Made of thin-walled parenchymal cells
  • Typically one-cell thick
  • ~300 million per lung
  • 75 m2 - surface area of the lung

  
• Protective Mechanisms


  • Nasal cavity contains hairs and mucus that trap small particles, viruses, bacteria, dust, and dirt
  • Bronchi and bronchioles produce mucus and contain cilia
  • Cigarette smoke destroys or paralyzes the cilia and causes the lungs to produce more mucus
• Gas Exchange


  Occurs primarily through diffusion
• Mechanics of Human Breathing

  1. Intercostal muscles contract

  2. Diaphragm contracts

  3. Lung volume expands

  4. Pressure decreases

  5. Air rushes into respiratory passages

  
• Pleural Layers


  • Parietal pleura - outer layer that attaches to chest wall
  • Visceral pleura - inner layer that covers the lung
  • Intrapleural space contains fluid that reduces friction
• Pleurisy


  Inflammation of pleural layers increases pressure and reduces lung volume
• Surfactant


  • Complex mixture of phospholipids and lipoproteins produced by Type II alveolar cells
  • Reduces surface tension in alveoli to allow easier inflation
• Respiratory Distress Syndrome


  Disorder in premature babies who do not produce enough surfactant, requiring more effort to inflate lungs
• Oxygen Transport in Blood

  Oxygen dissolved in blood and carried by hemoglobin in red blood cells

  
• Hemoglobin


  Protein molecule in red blood cells with four subunits (2 alpha, 2 beta) surrounding a heme group that binds oxygen
• 1 hemoglobin molecule binds 4 oxygen molecules
• Sickle Cell Anemia


  Red blood cells are crescent-shaped, elongated, and stiffened, reducing oxygen delivery
• Thalassemia


  Rare genetic disease causing lower-than-normal hemoglobin levels in red blood cells
• Carbon Monoxide Poisoning


  • Carbon monoxide is a colorless, odorless gas produced by gas-powered vehicles and tools
  • Carbon monoxide has a greater affinity for hemoglobin than oxygen, preferentially binding to it
• Types of Lung Diseases

  • Airway diseases (asthma, COPD, bronchiolitis, bronchiectasis)
  • Lung tissue diseases (pulmonary fibrosis, sarcoidosis)
  • Lung circulation diseases (pulmonary hypertension)