Anatomy and Physiology of the Respiratory System

The Respiratory System

• Consists of tubes that filter incoming air and transport it into the microscopic alveoli where gases are exchanged.
• Includes:
  • Nose
  • Pharynx (throat)
  • Larynx (voicebox)
  • Trachea (windpipe)
  • Bronchi (airways)
  • Lungs

Organs of the Respiratory System

• Divided into two groups:
  • Upper respiratory tract (nose, nasal cavity, sinuses, and pharynx)
  • Lower respiratory tract (larynx, trachea, bronchial tree, and lungs)
• Locations of infections:
  • Upper respiratory tract: above vocal cords
  • Lower respiratory tract: below vocal cords

Tracheostomy and Intubation

• Re-establishing airflow past an airway obstruction:
  • Crushing injury to larynx or chest
  • Swelling that closes airway
  • Vomit or foreign object
• Tracheostomy: incision in trachea below cricoid cartilage if larynx is obstructed
• Intubation: passing a tube from mouth or nose through larynx and trachea

Bronchi and Bronchioles

• Primary bronchi: supply each lung
• Secondary bronchi: supply each lobe of the lungs (3 right + 2 left)
• Tertiary bronchi: supply each bronchopulmonary segment
• Repeated branchings form a bronchial tree

Histology of Bronchial Tree

• Epithelium changes from pseudostratified ciliated columnar to non-ciliated simple cuboidal as pass deeper into lungs
• Incomplete rings of cartilage replaced by rings of smooth muscle and then connective tissue
• Sympathetic nervous system and adrenal gland release epinephrine that relaxes smooth muscle and dilates airways
• Asthma attack or allergic reactions constrict distal bronchiole smooth muscle

Lungs: Gross Anatomy

• Lungs occupy all of the thoracic cavity except the mediastinum
• Root: site of vascular and bronchial attachments
• Costal surface: anterior, lateral, and posterior surfaces in contact with the ribs
• Apex: narrow superior tip
• Base: inferior surface that rests on the diaphragm
• Hilus: indentation that contains pulmonary and systemic blood vessels

Gross Anatomy of Lungs

• Cardiac notch: cavity that accommodates the heart
• Left lung: separated into upper and lower lobes by the oblique fissure
• Right lung: separated into three lobes by the oblique and horizontal fissures
• Each lung has 10 bronchopulmonary segments

Pleurae

• Thin, double-layered serosa
• Parietal pleura: covers the thoracic wall and superior face of the diaphragm
• Visceral, or pulmonary, pleura: covers the external lung surface and divides the thoracic cavity into three chambers

Pleural Membranes and Pleural Cavity

• Visceral pleura covers lungs; parietal pleura lines ribcage and covers upper surface of diaphragm
• Pleural cavity: potential space between ribs and lungs contains a lubricating fluid

Mechanics of Breathing

• Pulmonary ventilation (breathing): process by which gases are exchanged between the atmosphere and lung alveoli
• Consists of two phases:
  • Inspiration: air flows into the lungs
  • Expiration: gases exit the lungs
• Breathing is an active process requiring the contraction of skeletal muscles
• Primary muscles of respiration:
  • External intercostal muscles (located between the ribs)
  • Diaphragm (a sheet of muscle located between the thoracic and abdominal cavities)

Pressure Relationships in the Thoracic Cavity

• Respiratory pressure is always described relative to atmospheric pressure
• Atmospheric pressure (Patm): pressure exerted by the air surrounding the body
• Intrapulmonary pressure (Palv): pressure within the alveoli
• Intrapleural pressure (Pip): pressure within the pleural cavity
• Intrapulmonary pressure and intrapleural pressure fluctuate with the phases of breathing

Pulmonary Ventilation

• A mechanical process that depends on volume changes in the thoracic cavity
• Volume changes lead to pressure changes, which lead to the flow of gases to equalize pressure

Inspiration

• The movement of air into and out of the lungs depends on pressure changes governed in part by Boyle's law
• Pleural cavities are sealed cavities not open to the outside

Compliance of the Lungs

• Ease with which lungs and chest wall expand
• Determined by two main factors:
  • Distensibility (elasticity) of the lung tissue and surrounding thoracic cage
  • Surface tension of the alveoli

Factors That Diminish Lung Compliance

• Scar tissue or fibrosis that reduces the natural resilience of the lungs
• Blockage of the smaller respiratory passages with mucus or fluid
• Reduced production of surfactant
• Decreased flexibility of the thoracic cage or its decreased ability to expand

Compliance Changes in Disease

• Lungs become somewhat more compliant with natural aging and become markedly more compliant with emphysema
• Lungs become less compliant (stiffer) with pulmonary fibrosis or during edema caused by rheumatic heart disease
• Chest wall becomes less compliant (stiffer) in conditions where the chest wall is deformed (e.g. kyphoscoliosis)

Breathing Patterns

• Eupnea: normal quiet breathing
• Apnea: temporary cessation of breathing
• Dyspnea: difficult or labored breathing
• Tachypnea: rapid breathing
• Diaphragmatic breathing: descent of diaphragm causes stomach to bulge during inspiration
• Costal breathing: just rib activity involved

Modified Respiratory Movements (MRM)

• Coughing: deep inspiration, closure of rima glottidis, and strong expiration blasts air out to clear respiratory passages
• Hiccupping: spasmodic contraction of diaphragm and quick closure of rima glottidis produce sharp inspiratory sound

Lung Volume and Capacities

• Air volumes exchanged during breathing and rate of ventilation are measured with a spirometer, or respirometer, and the record is called a spirogram
• One inspiration followed by expiration is called a respiratory cycle
• Tidal Volume (TV): amount of air that enters or leaves the lungs during one respiratory cycle (Normal: about 500 ml)
• Inspiratory Reserve Volume (IRV): amount of air that can be forcibly inhaled over and above normal (approx. 2100-3200 ml)
• Expiratory Reserve Volume (ERV): additional amount of air forcibly expired after tidal expiration (1000-1200 ml)
• Residual Volume (RV): amount of air that stays trapped in the alveoli (about 1.2 liters)
• Total Lung Capacity (TLC): volume of air contained in the lungs at the end of a maximal inspiration (approximately 6000 ml in males)
• Vital Capacity (VC): maximum volume of air that can be forcefully expelled from the lungs following a maximal inspiration