Respiratory System: Structure and Function

Chapter 26: The Respiratory System

Lesson 1: Structure and Function of the Respiratory System

Learning Objectives
  • Define and spell respiratory system terms (26.1).
  • Explain the overall function of the respiratory system (26.2).
  • List the structures of the respiratory system (26.3).
  • Describe respiratory system changes throughout the lifespan (child to older adult) (26.4).
  • Detail how the mechanism of breathing occurs (26.5).
Case Study: Collin McConnley
  • 57-year-old businessman traveling frequently.
  • Presents with severe headache, high fever, fatigue, and diarrhea.
Overview of the Respiratory System
  • Inhalation: Oxygen enters the respiratory system.
  • Exhalation: Carbon dioxide exits the respiratory system.
  • Respiratory tract: mouth, nose, trachea, bronchi, bronchioles, and lungs.
  • Breathing actions are achieved by:
    • Diaphragm contraction and relaxation.
    • Intercostal muscles (attached to ribs) contraction and relaxation.
    • Neck muscles contraction and relaxation.
Structures of the Respiratory System
Upper Respiratory Tract
  • Nose
    • Organ of smell.
    • Air passageway.
    • Warms and moistens inhaled air.
    • Traps dust, pollen, and foreign matter using cilia.
    • Assists in phonation (vocal sound production).
    • External:
      • Bone and cartilage.
      • Lined with mucous membrane.
      • Nostrils (nares).
    • Internal:
      • Septum: Wall of cartilage lined with mucous membrane.
      • Turbinates or conchae (air passageways):
        • Inferior conchae.
        • Middle conchae.
        • Superior conchae.
      • Passageways connect to the middle ear (via the Eustachian tube), paranasal sinuses, and nasolacrimal ducts (tear ducts).
      • Nasal mucosa moistens air and traps foreign matter.
      • Separated from mouth by palatine bones of the skull.
  • Paranasal sinuses
    • Decrease skull weight by creating air pockets.
    • Aid in phonation.
    • Provide protection and insulation.
    • Types:
      • Maxillary sinuses (over medial cheekbones).
      • Frontal sinuses (over eyebrows).
      • Ethmoidal sinuses (between and behind the eyes).
      • Sphenoidal sinuses (behind ethmoidal sinuses).
  • Mouth
    • Passageway for air.
    • Assists in phonation.
    • Does not warm/moisten air or trap foreign matter like the nose.
  • Pharynx (Throat)
    • A 5-inch tube made of muscle and membrane.
    • Connects nose, mouth, and larynx.
    • Passageway for food to esophagus and air to larynx and trachea.
    • Helps form specific phonetic sounds.
    • Contains:
      • Pharyngeal tonsils (adenoids).
      • Palatine tonsils.
      • Lingual tonsils.
      • Tonsils that are part of the immune system, and aid in infection control.
Lower Respiratory Tract
  • Larynx (Voice Box)
    • Muscular, cartilaginous structure lined with mucous membrane.
    • Cartilaginous structures:
      • Thyroid cartilage (Adam's apple; the largest).
      • Epiglottic cartilage (epiglottis; covers larynx during swallowing).
      • Cricoid cartilage (the lowest, allows for expansion when swallowing).
    • Contains false and true vocal folds and glottis.
    • Functions in vocal sound production:
      • Long, relaxed vocal cords produce low sounds.
      • Short, tense vocal cords produce higher-pitched notes.
  • Trachea (Windpipe)
    • A cartilaginous tube, about 1 inch wide and 4.5 inches long.
    • Extends from larynx to bronchi in the chest cavity.
    • C-shaped cartilage rings protect its structure and shape.
    • Serves as an open passageway for air to the lungs.
  • Bronchi
    • Two main branches (right and left bronchus) extending from trachea into lungs.
    • Passageways for air between trachea and lungs.
    • Bronchial tree: subdivisions of bronchi within the lungs, branching into smaller branches.
    • Tertiary bronchi: Branches from secondary bronchi.
  • Bronchioles
    • Smallest components of the bronchial tree.
    • Thin layer of epithelium and smooth muscle.
    • Terminate at alveoli in the lungs.
  • Alveoli
    • Small air sacs supporting a network of capillaries for oxygen and carbon dioxide exchange.
    • Average adult lungs contain about 600 million alveoli.
    • Surfactant reduces surface tension in the air-filled sacs.
  • Lungs
    • Large, cone-shaped organs in the chest.
    • Porous and spongy in texture, highly elastic.
    • Each lung is 10-12 inches in length.
    • Separated by mediastinum (space containing heart, trachea, esophagus, and blood vessels).
    • Hilum: Wedge-shaped area where the primary bronchus, arteries, veins, and nerves enter and exit the lung.
    • Pleura: Thin sheets of epithelium lining the inside of the thorax and the outside of the lungs.
The Respiratory System and the Life Span
  • Child
    • Infants born before 24 weeks gestation may be administered surfactant to decrease surface tension in alveoli.
    • Respiratory rates decrease as a child grows.
    • Maximum lung function occurs between ages 20 and 25.
  • Older Adults
    • After age 35, lung function declines due to anatomical and physiological changes.
    • Respiratory rates may rise due to pollution, smoking, and disease.
    • Breathing becomes diaphragm-based rather than rib-based due to skeletal changes.
    • Lungs lose flexibility and become stiffer, reducing air volume.
    • Reduced ability to remove foreign materials, increasing susceptibility to bronchitis and pneumonia.
Mechanism of Breathing
  • Ventilation: Movement of air to and from the lungs.
    • Two processes: inhalation and exhalation, controlled by the nervous system and respiratory muscles.
  • Major Respiratory Muscles
    • Diaphragm.
    • Internal and external intercostal muscles.
  • Diaphragm
    • Dome-shaped muscle below lungs separating the thoracic cavity from the abdominal cavity.
  • Intercostal Muscles (between ribs)
    • External intercostals: pull ribs upward and outward.
    • Internal intercostals: pull ribs downward and inward.
  • Dyspnea: Difficulty breathing.
  • Apnea: Absence of breathing for more than 19 seconds.
  • Orthopnea: Difficulty breathing unless a certain position is maintained.
Inhalation (Inspiration)
  • Active process involving a precise sequence of events.
  • Nervous system sends impulse to diaphragm and external intercostal muscles.
  • Diaphragm contracts and flattens, elongating the thorax.
  • External intercostals contract, pulling ribs upward and outward, increasing the size of the thorax.
  • Increase in chest cavity size reduces pressure, causing air to flow into lungs.
Exhalation (Expiration)
  • Passive process.
  • Diaphragm and intercostal muscles relax, and thorax returns to resting size and shape.
  • Reduction in thoracic cavity size builds pressure, causing air to flow out of lungs.
  • Elastic recoil of lung tissues aids in quiet expiration.
  • Forceful expiration involves internal intercostals and abdominal muscles.