rs notes

Boyle’s Law

Pressure and volume are inversely related (P↑ = V↓, P↓ = V↑); drives airflow during breathing

Alveolar Pressure (Palv)

Pressure inside lungs

Atmospheric Pressure (Patm)

Pressure outside body (~760 mmHg)

Intrapleural Pressure (Pip)

Pressure in pleural cavity (always negative relative to Palv)

Inspiration (breathing in)

Palv < Patm → air flows in

Expiration (breathing out)

Palv > Patm → air flows out

Eupnea Inspiration

Muscles: Diaphragm & external intercostals contract

Eupnea Expiration

Passive; muscles relax

Forceful Inspiration

Muscles: + accessory muscles (sternocleidomastoid, scalenes)

Forceful Expiration

Muscles: + internal intercostals & abdominal muscles

Dorsal Respiratory Group (DRG)

Controls basic rhythm (inspiration during eupnea)

Ventral Respiratory Group (VRG)

Active during forceful breathing (inspiration and expiration)

Pontine Respiratory Group (PRG)

Modifies DRG/VRG signals to smooth transitions between inspiration & expiration

Proprioceptors in breathing

Signal muscle/joint movement → ↑ ventilation during activity

Central Chemoreceptors

Sense CO₂ and pH in cerebrospinal fluid (CSF)

Peripheral Chemoreceptors

Sense O₂, CO₂, and pH in blood

Higher Brain Centers

Enable conscious control of breathing (e.g. speech, breath-holding)

Tidal Volume (TV)

Volume of air in a normal breath (~500 mL)

Inspiratory Reserve Volume (IRV)

Extra volume inhaled after tidal inspiration

Expiratory Reserve Volume (ERV)

Extra volume exhaled after tidal expiration

Residual Volume (RV)

Air remaining after maximum exhalation

Vital Capacity (VC)

VC = TV + IRV + ERV

Total Lung Capacity (TLC)

TLC = VC + RV

Ventilation at Rest

Steady tidal volume and rate

Ventilation during Exercise

Increased TV and rate → ↑ minute ventilation

Forced Vital Capacity (FVC)

Max exhale after max inhale; used in spirometry

Minute Ventilation (VE)

VE = Tidal Volume × Breathing Rate

Anatomical Dead Space

Air in conducting zone (no gas exchange)

Alveolar Dead Space

Non-functional alveoli (poor exchange)

Physiological Dead Space

= Anatomical + Alveolar dead space

Alveolar Ventilation

(TV – dead space) × respiratory rate

Dalton’s Law

Total pressure = sum of partial pressures of individual gases

External Respiration

O₂ moves from alveoli to blood; CO₂ from blood to alveoli (based on gradients)

Ventilation-Perfusion (V/Q) Matching

Ensures airflow matches blood flow; mismatches trigger local adjustments

Internal Respiration

O₂: Blood → Tissue; CO₂: Tissue → Blood

Arteriovenous (a-v) O₂ Difference

Difference between arterial and venous O₂; increases with exercise

Fick’s Law of Diffusion

Diffusion rate depends on surface area, membrane thickness, and gradient

Henry’s Law

Gas dissolved = solubility × partial pressure

High O₂ Affinity (Hb)

Enhances O₂ binding

Low O₂ Affinity (Hb)

Promotes O₂ unloading at tissues (triggered by CO₂, heat, acidity)

Oxygen Transport in Blood

98.5% bound to hemoglobin, 1.5% dissolved in plasma

Oxyhemoglobin Dissociation Curve

Shows % Hb saturation at different PO₂ levels

Oxyhemoglobin Curve Shift (Exercise)

Shifts right → more O₂ released to tissues

Bohr Effect

↑CO₂ or ↓pH → ↓Hb-O₂ affinity → ↑O₂ release

Carbon Dioxide Transport in Blood

70% as bicarbonate (HCO₃⁻), 20% bound to Hb, 10% dissolved

Carbon Monoxide (CO) Danger

Binds Hb with 200× O₂’s affinity → prevents O₂ transport → causes hypoxia