Unit 2 Respiratory System Functional Anatomy

Structure of the nose/nasal cavity.

Structure

• External nose:

  • made of hyaline cartilage and maxillary bone

  • covered externally by skin with sebaceous glands and nasal hairs

• Nasal Vestibule:

  • lined with stratified squamous epithelium and big hairs for large particles

• Main Nasal Cavity

  • lined with respiratory epithelium with goblet cells that secrete mucus

  • contains conchae (superior, middle and lower) that project into the cavity like shelves → increase SA and create turbulence in airflow (trappening of particles and moistening of inspired air and heat exchange)

  • has a rich vascular supply

  • Submucosa contains seromucous glands that moisten air and trap particles

• Olfactory Region

  • found in the roof of the nasal cavity near the cribiform plate

  • contains olfactory epithelium with sensory neurons that detect smells

  • secretes mucus that dissolves odor molecules

Function of the nose/nasal cavity

1. Air Conduction:

   • Primary entry point for inhaled air.

   • Channels air to the pharynx and down to the lungs.

2. Air Conditioning:

   • Warming: Through heat exchange with blood vessels.

   • Humidifying: Via moisture from mucus and serous secretions.

   • Filtering: Hairs and mucus trap dust, pathogens, and debris.

3. Olfaction (Smell):

   • Specialized neurons in the roof of the nasal cavity detect odorants.

4. Resonance for Phonation:

   • The nasal cavity contributes to the resonance of the voice (tone quality).

5. Defense:

   • Mucus traps microbes; cilia sweep mucus to the pharynx to be swallowed or expelled.

Location of Nose and Nasal Cavity

• The external nose is located centrally on the face, projecting from the face between the eyes and above the upper lip.

• The nasal cavity is internal, lying posterior to the external nose and extending back to the pharynx.

• It is separated:

  • Superiorly by the cribriform plate of the ethmoid bone (just below the brain).

  • Inferiorly by the hard and soft palate, which separates it from the oral cavity.

  • Medially by the nasal septum, formed by the vomer and perpendicular plate of the ethmoid bone.

  • Laterally by bones that form ridges called conchae (turbinates).

Paranasal Sinuses

• boney chambers surrounding nasal cavity and lined by respiratory epithelium

• air filled cavities in skull bones (frontal, maxillary, sphenoid, ethmoid)

• lighten skin, add resonance to phonation and facilitate air conditioning

• contains canals that drain mucus in the nasal cavity

Pharynx

• connects nasal and oral cavities to the larynx and esophagus

• functions in air conditioning, sound resonance, and food diversion during swallowing

• has 3 regions: nasopharynx, laryngopharynx, and oropharynx

List the protective mechanisms of the respiratory system.

Protective Mechanisms

• mucous and cilia

• goblet cells that secrete mucous with defensins

• nasal hairs

• lysosome and enzymes in mucous

• sneezing and coughing reflexes

• immune surveillance

Conducting Zone

Conducting

• laryngopharynx → terminal bronchioles

• contains structures involved in phonation

• includes larynx (primary organ of phonation), trachea, bronchi and bronchioles

• superior limit is epiglottis

• external structures made of hyaline cartilage linked by ligaments

• mucosa lined by epithelia in regions of high turbulence and respiratory epithelia in other regions

• submucosa contains seromucous glands

Respiratory Zone

• Respiratory Bronchioles to aveoli

• functions in gas exchange

Larynx

• primary organ of phonation

• superior → epiglottis

  • made of elastic cartilage + epithelia with taste buds

  • elevation of larynx allows epiglottis to cover larynx during swallowing

• external structures made of hyaline cartilage linked by ligaments

• internal structures include vocalis muscles and vocal folds

  • superior: vestibular fold (false vocal cord)

  • Inferior: vocal fold (true vocal cord)

    • forms slit like opening → glottis

    • width/stiffness determines pitch (narrow - high)

    • regulated by vocalis muscle

Trachea

• connects the larynx to the bronchi as it goes downward

• in front of esophagus

• mucous lined with resp epithelia

• submucosa contains C-shaped cartilage

  • shorten to decrease diameter during coughing

  • seromucous glands between C’s

• inferior: carina

  • mucosa rich in sensory nerves → coughing

Bronchi/bronchioles

• from trachea to resp bronchioles

• one for each lung

  • primary → secondary → tertiary → bronchioles

  • 3 for right and 2 for left

• branching = small diameter

• mucosal changes from trachea and bronchi → bronchioles

  • fewer mucous glands from bronchi to bronchiole

  • pseudostratified → columnar → cuboidal

  • decrease in goblet cells and cilia

• submucosa → plates of cartilage instead of C shaped in bronchi

• Bronchioles don’t have cartilage

  • major site for air flow/resistance

Respiratory Membrane + its function

• Aveolar membrane (made of type 1 alveolar cells + basement cells)

  • inner lining of the air sacs in the lungs

  • consists of Type 1: thin, flattened cells that allow for easy diffusion + the majority of the alveolar surface

  • basement membrane: thin layer of connective tissue that provides support + structure for alveolar cells

• thin interstitial space

  • small gap between aveolar membrane + capillary endothelium that contains fluid + CT fibers

• capillary endothelium

  • lines capillaries that surrounds the alveoli + composed of a thin layer of cells + its own basement membrane

Function

• designed for efficient gas exchange of oxygen in blood and CO2 out of blood

• vast surface area

• Surfactant → reduces surface tension in alveoli → preventing them from collasping

Respiratory Passageway Order

• Nose → nasal cavity → pharynx → larynx → trachea → bronchi (primary, secondary, tertiary) → bronchioles → terminal bronchioles → respiratory bronchioles → alveolar ducts → alveolar sacs → alveoli

Lungs and Pleurae

Lungs

• paired asymmetric organ within thoracic cavity

• apex of lungs inferior clavicle and base rests upon diaphragm

• bronchi,vessels and nerves penetrate lung at hilum forming lung root proximal to heart

• right lung larger and with three lobes separated by fissures

• left lung has two lobes with a fissure and cardiac notch

• divided into connective tissue with bronchopulmonary segments

• divided into lobules → main bronchiole → pulmonary artery/arteriole → branches → alveoli

• thin connective tissue that forms capsule of organ and subdivides lobes, segments and lobules

Pleura

• parietal → thoracic walls → simple squamous

• visceral → lungs surface → simple squamous

• thin layer of serous fluid between parietal and visceral

  • maintain capillary tension to adhere lungs to thoracic walls

  • allows frictionless movement of lung within thoracic cavity

• inflammation of pleural → pleurisy

• too much serous fluid via leaky capillaries → pleural effusion

Partial vacuum + importance

• acts like a suction, preventing lung collapse and ensuring lungs expand during inhalation

• negative pressure relative to aveolar pressure

• during inhalation → the chest wall expands → increasing volume of thoracic cavity

• creates a greater negative pressure + sucks lungs open → increases their volume and draws air in for gas exchange

• Involves balance of forces → elastic recol of stroma and surface tension in aveoli + surface tension at pleura

Boyle’s Law and inspiration/expiration

• PV = P2V2

• pressure inversely changes to volume

• during inspiration → thoracic cavity volume increases → pressure drops → air flows in

• During expiration → volume decreases → pressure increases → air flows out

Inspiration

Inspiration

• increase in lung volume mediated by changes in thoracic cavity volume

• shortening of diaphragm → flattens out and moves inferiorly

• shortening of external intercostal muscle → lifts rib cage + sternum to increase the diameter of thoracic cavity → thoracic volume increase

• decrease Ppul to -1 mm Hg

• involves other muscles that can raise the ribs to expand the thoracic cavity

Expiration

• mostly passive relaxation of the inspiratory muscles and elastic recoil of lungs

• inspiratory muscle relax → diaphragm rises, rib cage descend due to recoil of costal cartilage

• thoracic cavity volume decreases

• elastic lungs recoil passively → intrapulmon volume decreases

  • pressure rises

  • air flows out of the lungs and down the pressure gradient until intrapulmon pressure is 0

Lung Volumes

• Tidal volume → normal relaxed breathing (500 mL)

• Inspiratory Reserve → forced inhalation to maximum above TV (3100 ml)

• Expiratory Reserve → forced exhalation to minimum below TV (1200 ml)

• Residual Volume → volume remaining after forced exhalation → dead space of aveoli and conducting portion (1200 ml)

Capacity

• total lung capacity: TLC = TV + IVR +EVR + RV (6000 ml)

• Vital lung capacity: VC = TV + IVR + EVR = TLC - RV (4800 ml)

• Inspiratory capacity: IC = TV + IVR (3600 ml)

• Functional Residual capacity: FVR = EVR + RC (2400 ml)

Pulmonary Function Tests

• type/effect of respiratory disease

• classification of resp disease

• easily measured with windmill type spirometer

  • FVC = vital capacity measured with volume spirometer

  • FEV = volume forcibly expired over a set time interval

• diagnose obstructive and restrictive disease

Physical Factors Affecting Ventilation

• friction, aveolar surface tension and lung compliance

• Flow rate = pressure diff (boyle’ law) + friction (resistance via conducting zone)

  • Resistance varies (low in trachea, max in med-sized bronchi and min at terminal bronchi)

  • bronchi + bronchioles can modified by smooth muscle + inflammation

  • local effectors and autonomic system can modulate

    • para → bronchoconstriction, sym → bronchodilation

• Surface tension of aveoli

  • wetted surface that sticks together via capillary action

• Lung Compliance

  • stretchiness

  • change in volume by a change in pressure

  • determined by elastin and surface tension of alveoli

  • stretchibility of lungs and thoracic cage