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  • Respiratory tract

    • Upper respiratory tract
    • Nose
    • Pharynx
    • Larynx
    • Lower respiratory tract
    • Trachea
    • Bronchial tree
    • Lungs

  • Respiratory mucosa 

    • Function
    • Cilia on mucosal cells beat in only one direction, moving mucus upward to pharynx for removal

  • Nose

    • Structure
    • Nasal septum separates interior of nose into two cavities
    • Mucous membrane lines nose
    • Frontal, maxillary, sphenoidal, and ethmoidal sinuses drain into nose (Figure 15-3)
    • Function
    • Warms and moistens inhaled air
    • Contains sense organs of smell

  • Pharynx

    • Structure (Figure 15-4)
    • About 12.5 cm (5 inches) long
    • Divided into nasopharynx, oropharynx, and laryngopharynx
    • Two nasal cavities, mouth, esophagus, larynx, and auditory tubes all have openings into pharynx
    • Pharyngeal tonsils and openings of auditory tubes open into nasopharynx; tonsils found in oropharynx
    • Mucous membrane lines pharynx
    • Function
    • Passageway for food and liquids
    • Air distribution; passageway for air

  • Larynx

    • Structure (Figure 15-5)
    • Several pieces of cartilage form framework
      • Thyroid cartilage (Adam’s apple) is largest
      • Epiglottis partially covers opening into larynx
    • Mucous lining
    • Vocal cords stretch across interior of larynx
    • Function
    • Air distribution; passageway for air to move to and from lungs
    • Voice production

  • Trachea

    • Structure (Figure 15-6)
    • Tube about 11 cm (4.5 inches) long that extends from larynx into the thoracic cavity
    • Mucous lining
    • C-shaped rings of cartilage hold trachea open
    • Function
    • Passageway for air to move to and from lungs
    • Obstruction
    • Blockage of trachea occludes the airway, and if blockage is complete, causes death in minutes
    • Tracheal obstruction causes more than 4000 deaths annually in the United States

  • Bronchial tree

    • Structure
    • Trachea branches into right and left bronchi
    • Each bronchus branches into smaller and smaller tubes eventually leading to bronchioles
    • Bronchioles end in clusters of microscopic alveolar sacs, the walls of which are made up of alveoli
    • Function
    • Air distribution
    • Passageway for air to move to and from alveoli

  • Alveoli 

    • Exchange of gases between air and blood

  • Lungs

    • Structure
    • Size: Large enough to fill the chest cavity, except for middle space occupied by heart and large blood vessels
    • Apex: Narrow upper part of each lung, under collarbone
    • Base: Broad lower part of each lung; rests on diaphragm
    • Pleura: Moist, smooth, slippery membrane that lines chest cavity and covers outer surface of lungs; reduces friction between the lungs and chest wall during breathing
    • Function
    • Breathing (pulmonary ventilation)

  • Respiration means exchange of gases between a living organism and its environment

  • External respiration: Pulmonary ventilation (breathing) and pulmonary gas exchange

  • Internal respiration: Systemic gas exchange and cellular respiration

  • Mechanics of breathing

    • Inspiration (movement of air into lungs)
    • Active process: Air moves into lungs
    • Inspiratory muscles include diaphragm and external intercostals
      • Diaphragm flattens during inspiration: Increases \n top-to-bottom length of thorax
      • External intercostals contraction elevates the ribs: Increases the size of the thorax from the front to the back and from side to side
    • Increase in the size of the chest cavity reduces pressure within it; air then enters the lungs

  • Mechanics of breathing

    • Expiration (movement of air out of lungs)
    • Quiet expiration is ordinarily a passive process
    • During expiration, thorax returns to its resting size and shape
    • Elastic recoil of lung tissues aids in expiration
    • Expiratory muscles used in forceful expiration are internal intercostals and abdominal muscles
      • Internal intercostals: Contraction depresses the rib cage and decreases the size of the thorax from the front to back
      • Contraction of abdominal muscles elevates the diaphragm, thus decreasing size of the thoracic cavity from the top to bottom
    • Reduction in the size of the thoracic cavity increases its pressure and air leaves the lungs

  • Pulmonary volumes

    • Spirometer measures amount of air exchanged in breathing
    • Tidal volume
    • We take 500 mL of air into our lungs with each normal inspiration and expel it with expiration
    • Vital capacity
    • The largest amount of air that we can inhale deeply and exhale fully

  • Pulmonary volumes

    • Expiratory reserve volume (ERV)
    • Amount of air that can be forcibly exhaled after expiring the tidal volume
    • Inspiratory reserve volume (IRV)
    • Amount of air that can be forcibly inspired over and above the normal inspiration

  • Regulation of ventilation

    • Homeostasis of blood gases
    • Permits the body to adjust to varying demands for oxygen supply and carbon dioxide removal
    • Brainstem control of respiration
    • Most important central regulatory centers in medulla are called respiratory control centers (inspiratory and expiratory centers)
    • Under resting conditions, nervous activity in the respiratory control centers produces a normal rate and depth of respirations (12 to 18 breaths a minute)
    • Regulation of ventilation
      • Cerebral cortex control of respiration
      • Voluntary (but limited) control of respiratory activity
      • Respiratory reflexes
      • Chemoreceptors respond to changes in carbon dioxide, oxygen, and blood acid levels: Located in carotid and aortic bodies
      • Pulmonary stretch reflexes: Respond to the stretch in lungs

  • Various breathing patterns

    • Eupnea
    • Normal breathing
    • Hyperventilation
    • Rapid and deep respirations
    • Hypoventilation
    • Slow and shallow respirations
    • Dyspnea
    • Labored or difficult respirations
    • Apnea
    • Stopped respiration
    • Respiratory arrest
    • Failure to resume breathing after a period of apnea

  • Carbaminohemoglobin breaks down into carbon dioxide and hemoglobin

  • Pulmonary gas exchange

    • Carbon dioxide moves out of lung capillary blood into alveolar air and out of body in expired air
    • Oxygen moves from alveoli into lung capillaries
    • Hemoglobin combines with oxygen, producing oxyhemoglobin

  • Systemic gas exchange

    • Oxyhemoglobin breaks down into oxygen and hemoglobin
    • Oxygen moves out of tissue capillary blood into tissue cells
    • Carbon dioxide moves from tissue cells into tissue capillary blood
    • Hemoglobin combines with carbon dioxide, forming carbaminohemoglobin

  • Blood transportation of gases

    • Transport of oxygen
    • Transport of carbon dioxide