• 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

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