Respiratory Physiology: Functional Anatomy and Lung Mechanics

These flashcards cover the fundamental anatomy, respiratory muscles, lung volumes, capacities, and ventilation equations as discussed in the Respiratory Physiology lecture.

Chest Wall

The ribcage along with the muscles of respiration.

Pulmonary Ventilation

The inflow and outflow of air between the atmosphere and the lung alveoli.

Normal Inspiratory Muscles

The diaphragm and external intercostals, which flatten and lift the ribs upward and outward respectively.

Accessory Inspiratory Muscles

Muscles such as the sternocleidomastoid and scalenes that are recruited during exercise or respiratory distress.

Quiet Expiration

A passive process driven by the relaxation of inspiratory muscles and the elastic recoil of the lungs and chest wall.

Active Expiratory Muscles

The internal intercostals and abdominal muscles used during forced breathing, such as coughing or exercise.

Pump handle movement

Movement where ribs move upwards and forwards, increasing the anteroposterior diameter of the rib cage.

Bucket handle movement

Movement where ribs move upwards and outwards (laterally), increasing the transverse diameter of the rib cage.

Pleura

A thin, double-walled serosa surrounding the lungs consisting of the parietal pleura and visceral pleura.

Pleural Effusion

The accumulation of excessive amounts of fluid in the pleural cavity; normal fluid volume is typically $10\text{--}15\,ml$.

Phrenic Nerve

The nerve arising from spinal cord segments $C3$, $C4$, and $C5$ that supplies the central diaphragmatic pleura.

Pneumothorax

A condition occurring when air leaks into the pleural cavity, commonly caused by chest trauma or diseases like COPD and Asthma, resulting in lung collapse.

Bronchial Arteries

Arteries that carry oxygenated blood to supply the conducting airways.

Parasympathetic Lung Innervation

Causes bronchoconstriction via $M3$ muscarinic receptors.

Sympathetic Lung Innervation

Causes bronchodilatation via $\beta 2$ receptors.

Conducting Zone

The portion of the respiratory system extending from the top of the trachea to the beginning of the respiratory bronchioles.

Respiratory Zone

The region where gas exchange takes place, extending from the respiratory bronchioles down to the alveolar sacs.

Weibel’s 23-generation Model

A model of airway branching where generation 0 is the trachea and generation 23 represents the alveolar sacs.

Bronchioles

Cartilage-free airways with diameters less than $1\,mm$.

Airway Resistance Distribution

Maximum resistance is found in large central airways like the trachea and medium-sized bronchi rather than peripheral airways.

Type I Pneumocytes

Large flat cells that form a part of the thin gas diffusion barrier in the alveoli.

Type II Pneumocytes

Cells that produce surfactant, proliferate in injury, and act as progenitor cells for Type I pneumocytes.

Respiratory Membrane

The blood gas interface with an average thickness of $0.6\,\mu m$ and a total surface area of $70\,m^2$.

Pulmonary Alveolar Macrophages (PAMs)

Cells responsible for clearing particles smaller than $2\,\mu m$ from the respiratory tract.

Mucociliary Escalator

A defense mechanism involving the coordinated beating of cilia to clear particles between $2\text{--}10\,\mu m$ trapped in the trachea and bronchi.

Angiotensin Converting Enzyme (ACE)

Produced by pulmonary capillary endothelial cells, it activates Angiotensin I to Angiotensin II.

Spirometer

A device that measures the volume of air inspired and expired to track changes in lung volume.

Tidal Volume ($VT$)

The volume of air that moves into the lung with each quiet inspiration, typically $\sim 500\,mL$ or $6\text{--}8\,mL/kg$.

Inspiratory Reserve Volume ($IRV$)

The volume of air that can still be breathed in after a normal inspiration.

Expiratory Reserve Volume ($ERV$)

The volume of air that can still be breathed out after a normal expiration.

Residual Volume ($RV$)

The volume of air remaining in the lung after maximal expiration; it cannot be measured by direct spirometry.

Inspiratory Capacity ($IC$)

The air that can be breathed in after a normal exhalation, calculated as $IRV + VT$.

Functional Residual Capacity ($FRC$)

The volume of gas in the lungs after a normal expiration ($RV + ERV$); the equilibrium point where outward chest wall recoil balances inward lung recoil.

Vital Capacity ($VC$)

The maximum volume of gas that can be expired after a maximal inspiration ($IRV + VT + ERV$).

Total Lung Capacity ($TLC$)

The total volume of gas present in the lungs after a maximal inspiration, calculated as $VC + RV$.

Helium Dilution Technique

An indirect measurement method based on the law of conservation of mass used to determine $RV$, $FRC$, and $TLC$.

Anatomic Dead Space

The volume of the conducting airways (ending at terminal bronchioles) where no gas exchange occurs; approximately proportional to body weight in pounds.

Physiological Dead Space

The total dead space in the lungs, calculated as Anatomic Dead Space + Alveolar Dead Space.

Bohr’s Equation

$VD = VT \times \frac{Paco_2 - P\epsilon co_2}{Paco_2}$, used for the calculation of physiologic dead space.

Minute Ventilation

The total volume of air moving in or out of the respiratory system per minute, calculated as $Tidal \, volume \times Respiratory \, rate$.

Alveolar Ventilation ($VA$)

The volume of air delivered to the respiratory zone per minute, calculated as $(Tidal \, Volume - Dead \, Space \, Volume) \times breaths/min$.

Alveolar Ventilation Equation

The formula $VA = \frac{VCO_2 \times K}{PaCO_2}$, which describes the inverse relationship between alveolar ventilation and arterial $PCO_2$.