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
      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