CH 21: Anatomy of the Respiratory System

CH 21 ~ Quick checks

List the organs of the respiratory system.

• Respiratory tract

• Lungs

• Pulmonary blood vessels

• Rib cage

• Respiratory muscles

Describe the upper and lower respiratory tracts.

• Upper tract: nose, nasal cavity, pharynx, larynx

• Lower tract: trachea, bronchi, bronchioles, alveoli

•  nose → nasal cavity → pharynx → larynx → trachea → bronchi → bronchioles

  • Moves, filters, warms, and humidifies air

Conducting zone

• respiratory bronchioles → alveolar ducts → alveoli

  • Gas exchange occurs here

Respiratory zone

Describe the major functions of the respiratory system.

• Gas exchange (O₂ in, CO₂ out)

• Speech and sound production

• Smell (olfaction)

• Pressure changes for venous/lymph flow

• Acid–base balance

• Produces ACE for blood pressure regulation

air moving in and out of lungs

Pulmonary ventilation

gas exchange between alveoli and blood

Pulmonary gas exchange

movement of gases through the bloodstream

Gas transport

exchange of gases between blood and body tissues

Tissue gas exchange

• Warm, humidify, and filter air

• House olfactory receptors

• Enhance voice resonance

Nose & nasal cavity

Create turbulence to trap dust and debris

Meatuses

• Warm and humidify air

• Lighten the skull

• Enhance voice resonance

Sinuses

• Mucus traps debris

• Cilia move debris toward pharynx

nasal cavity

• Pseudostratified ciliated columnar epithelium

• Warms, humidifies, filters air

• Uvula/soft palate block food during swallowing

Nasopharynx

• Nonkeratinized stratified squamous epithelium

• Passageway for air and food

• Protects against abrasion

Oropharynx

• Nonkeratinized stratified squamous epithelium

• Passageway for air and food

Laryngopharynx

• Keeps food/liquid out of airway

• Houses vocal cords

• Superior region: stratified squamous epithelium

• Inferior region: pseudostratified ciliated columnar epithelium (mucociliary escalator)

• Supported by 9 cartilages

Larynx

• C‑shaped hyaline cartilage rings keep airway open

• Posterior smooth muscle allows esophagus expansion

• Carina triggers cough reflex

• Lined with pseudostratified ciliated columnar epithelium + goblet cells

Trachea

Describe the bronchial tree, including its histology,

• Bronchial tree = branching tubes: primary bronchi → secondary → tertiary → smaller bronchi → bronchioles → terminal bronchioles → respiratory bronchioles → alveolar ducts → alveolar sacs

Histology

• Cartilage decreases (rings → plates → none)

• Smooth muscle increases

• Epithelium goes from pseudostratified → columnar → cuboidal

trace the pathway through which air passes during inspiration.

Nose → nasal cavity → pharynx → larynx → trachea → bronchi → bronchioles → alveoli

thin squamous cells; main site of gas exchange.

Type I cells

produce surfactant to reduce surface tension.

Type II cells

clean debris and pathogens.

Alveolar macrophages

• Right lung = 3 lobes; left lung = 2 lobes + cardiac notch.

• Made of alveoli + elastic connective tissue.

• Hilum = entry for bronchi, blood vessels, nerves.

Lungs

• Two membranes: parietal pleura (outer) and visceral pleura (inner).

• Space between them contains pleural fluid.

• Function: reduces friction, allows smooth lung expansion, and helps lungs stay inflated.

Pleural cavity

List and define the two phases of pulmonary ventilation.

• Inspiration (inhalation): air moves into the lungs.

• Expiration (exhalation): air moves out of the lungs.

State Boyle’s law

Boyle’s law: Pressure and volume are inversely related —

• When volume increases, pressure decreases

• When volume decreases, pressure increases

explain its relationship to pulmonary ventilation.

Changes in thoracic volume create pressure gradients that move air in and out of the lungs.

• Inspiration uses muscle contraction to increase volume and pull air in

• Expiration is mostly passive, relying on relaxation and recoil

• Atmospheric pressure: constant

• Intrapulmonary pressure: drops below atmospheric → air enters

• Intrapleural pressure: becomes more negative as thoracic cavity expands

Inspiration

• Atmospheric pressure: constant

• Intrapulmonary pressure: rises above atmospheric → air exits

• Intrapleural pressure: becomes less negative (but still lower than intrapulmonary)

Expiration

• higher resistance = harder to move air

• bronchodilation = easier airflow

Airway resistance

• High surface tension = alveoli collapse = harder ventilation.

• Surfactant lowers tension = easier ventilation.

Alveolar surface tension

• High compliance = lungs expand easily.

• Low compliance = stiff lungs = difficult ventilation.

Pulmonary compliance

exchange of gases between alveoli and blood (external respiration).

Pulmonary gas exchange

 exchange of gases between blood and tissues (internal respiration).

Tissue gas exchange

is diffusion of gases between alveoli and blood.

external respiration

Explain factors that affect pulmonary gas exchange.

• Surface area: large surface area increases efficiency; reduced area decreases exchange.

• Membrane thickness: thicker membrane slows diffusion and reduces efficiency.

• Ventilation‑perfusion matching: air flow must match blood flow for efficient exchange.

is exchange of oxygen and carbon dioxide between blood and tissues.”

internal respiration.

Explain factors that affect tissue gas exchange.

• Surface area: more capillary surface area = more efficient exchange.

• Diffusion distance: shorter distance = faster diffusion.

• Perfusion: better blood supply = better gas exchange.

Describe the ways in which oxygen is transported in blood.

• Most O₂ is bound to hemoglobin in red blood cells.

• A small amount is dissolved in plasma.

Describe the ways in which carbon dioxide is transported in blood.

• Dissolved in plasma

• Bound to hemoglobin

• As bicarbonate ions (HCO₃⁻) — major form

Describe in more detail how carbon dioxide is converted to bicarbonate.

• CO₂ enters RBC → combines with water → forms carbonic acid (H₂CO₃)

• Carbonic acid quickly breaks into H⁺ + bicarbonate (HCO₃⁻)

• As bicarbonate (HCO₃⁻) leaves the RBC, chloride ions (Cl⁻) enter the RBC.

• This keeps electrical balance inside the cell.

chloride shift

Explain the stimulants for ventilation.

• High CO₂ (primary stimulant)

• High H⁺ (low pH)

• Low O₂

detected by chemoreceptors.

 normal breathing; one of most vital functions body carries out as absence of breathing leads to death

Eupnea

Describe how eupnea is controlled

 respiratory centers in the brainstem, which set the basic rhythm of breathing