005_Ventilation, Gas Exchange & pH Homeostasis – Core Vocabulary

Eighty key vocabulary flashcards covering lung volumes, gas laws, oxygen and carbon dioxide transport, and acid–base regulation from the HYMS lecture on ventilation, gas exchange and pH homeostasis.

Ventilation

The cyclical movement of air into and out of the lungs.

Minute Volume (MV)

Total volume of air entering or leaving the lungs each minute; MV = RR × VT.

Tidal Volume (VT)

Volume of air inspired or expired with each normal breath (~500 mL in adults).

Respiratory Rate (RR)

Number of breaths taken per minute (adult normal ≈ 12–20 breaths/min).

Pulmonary Ventilation

Bulk movement of gases into and out of the lungs, synonymous with minute volume.

Alveolar Ventilation (VA)

Portion of inspired air that reaches alveoli and participates in gas exchange; VA = RR × (VT – VD).

Dead Space

Inspired air that does not take part in gas exchange.

Anatomical Dead Space

Conducting airway volume from nose/mouth to terminal bronchioles (~150 mL).

Physiological Dead Space

Anatomical dead space plus any poorly perfused/alveolar dead space.

Spirometry

Technique that records lung volumes and airflow using a calibrated volume displacement device.

Inspiratory Reserve Volume (IRV)

Extra volume that can be inspired above a normal tidal inspiration (~2 L).

Expiratory Reserve Volume (ERV)

Extra volume that can be expired beyond a normal tidal expiration (~1–1.5 L).

Residual Volume (RV)

Gas remaining in lungs after maximal expiration (~1.5–1.9 L).

Vital Capacity (VC)

Maximum volume change possible; VC = VT + IRV + ERV.

Total Lung Capacity (TLC)

Air in lungs after maximal inspiration; TLC = VC + RV.

Inspiratory Capacity (IC)

Maximum air that can be inspired after a normal expiration; IC = VT + IRV.

Functional Residual Capacity (FRC)

Volume remaining in lungs after a normal expiration; FRC = ERV + RV.

Forced Expiratory Volume in 1 s (FEV1)

Volume forcibly expired in the first second of a maximal expiration.

Forced Vital Capacity (FVC)

Total volume forcibly expired after a full inspiration.

FEV1/FVC Ratio

Percentage of FVC exhaled in the first second; normal ≈ 75–80 %.

Peak Expiratory Flow Rate (PEFR)

Highest airflow achieved during forced expiration, used to monitor airway obstruction.

Plethysmography

Body-box method measuring lung volumes (including RV/FRC) via pressure–volume changes.

Helium Dilution Method

Closed-circuit technique to determine FRC or RV using changes in a known He concentration.

Conducting Zone

Airways (nose to terminal bronchioles) that transport, warm and humidify air but do not exchange gases.

Respiratory Zone

Region from respiratory bronchioles to alveolar sacs where gas exchange occurs.

Boyle’s Law

At constant temperature, gas volume is inversely proportional to pressure (P × V = constant).

Charles’ Law

At constant pressure, gas volume is directly proportional to absolute temperature (V ∝ T).

Avogadro’s Law

Equal volumes of gas at the same T and P contain equal numbers of molecules (V ∝ n).

Ideal Gas Law

Relationship combining gas laws: PV = nRT.

Graham’s Law

Rate of diffusion of a gas is inversely proportional to the square root of its molecular weight.

Henry’s Law

Amount of gas dissolved in a liquid is proportional to its partial pressure and solubility coefficient.

Dalton’s Law of Partial Pressure

Total pressure of a gas mixture equals the sum of individual gas partial pressures.

Partial Pressure

Pressure exerted by a single gas in a mixture; drives diffusion across membranes.

Alveolar Air

Mixture of gases within alveoli; composition differs from atmospheric air (e.g., lower O2, higher CO2, water-saturated).

Diffusing Capacity (DL)

Measure of gas transfer ability across alveolar-capillary membrane (e.g., DLCO for CO).

Hemoglobin (Hb)

Tetrameric protein in red cells that reversibly binds O2 and CO2 for transport.

Heme Group

Porphyrin ring with central Fe2+ that binds one O2 molecule.

Oxygen Dissociation Curve

Sigmoid plot showing relationship between PaO2 and Hb saturation (SaO2).

Bohr Effect

Right shift of O2 curve due to ↑CO2 or ↓pH, lowering Hb affinity for O2 at tissues.

Haldane Effect

Deoxygenation of Hb enhances CO2 and H+ binding, aiding CO2 transport from tissues.

2,3-Bisphosphoglycerate (2,3-BPG)

RBC metabolite that decreases Hb affinity for O2, promoting unloading.

Fetal Hemoglobin (HbF)

α2γ2 form with higher O2 affinity than adult Hb, facilitating maternal-fetal O2 transfer.

Carboxyhemoglobin (COHb)

Complex of CO with Hb; formed when CO binds ~200× more tightly than O2.

Carbaminohemoglobin

Hemoglobin bound to CO2 at amino groups (≈ 23 % of CO2 transport).

Bicarbonate Ion (HCO3−)

Primary form (≈ 70 %) in which CO2 is transported in blood plasma.

Carbonic Anhydrase

Enzyme catalyzing reversible conversion of CO2 + H2O ↔ H2CO3 ↔ HCO3− + H+.

Chloride Shift

Exchange of Cl− for HCO3− across RBC membrane to maintain electroneutrality during CO2 transport.

Oxygen Content (CaO2)

Total O2 in arterial blood (bound + dissolved), expressed in mL O2 per 100 mL blood.

Hemoglobin Saturation (SaO2)

Percentage of Hb binding sites occupied by oxygen.

Partial Pressure of Oxygen (PaO2)

Pressure exerted by dissolved O2 in arterial blood (normal ≈ 100 mmHg).

Partial Pressure of Carbon Dioxide (PaCO2)

Pressure exerted by dissolved CO2 in arterial blood (normal ≈ 40 mmHg).

Hypoventilation

Inadequate alveolar ventilation leading to ↑PaCO2 and respiratory acidosis.

Hyperventilation

Excessive alveolar ventilation causing ↓PaCO2 and respiratory alkalosis.

Hypercapnia

Elevated arterial CO2 tension (> 45 mmHg).

Hypocapnia

Reduced arterial CO2 tension (< 35 mmHg).

Respiratory Acidosis

pH < 7.35 due to CO2 retention from hypoventilation.

Respiratory Alkalosis

pH > 7.45 caused by CO2 loss from hyperventilation.

Metabolic Acidosis

Acid–base disorder from excess non-volatile acid or bicarb loss (e.g., diabetic ketoacidosis).

Metabolic Alkalosis

Disorder from excess base or acid loss (e.g., vomiting, diuretic use).

Henderson–Hasselbalch Equation

pH = 6.1 + log([HCO3−]/0.03 × PaCO2); links bicarb, CO2 and pH.

Davenport Diagram

Graphical tool plotting pH vs. HCO3− to visualize acid–base disturbances.

Acid–Base Balance

Homeostatic maintenance of blood pH (7.35–7.45) via buffers, lungs, and kidneys.

Bicarbonate Buffer System

Primary extracellular buffer involving HCO3−/CO2 equilibrium.

Partial Pressure of Inspired Oxygen (PIO2)

O2 pressure in humidified tracheal air (~150 mmHg at sea level).

Partial Pressure of Alveolar Oxygen (PAO2)

O2 pressure within alveoli (≈ 100 mmHg under normal conditions).

Alveolar–Capillary Membrane

0.2 µm thin barrier across which pulmonary gas exchange occurs.

Peak Inspiratory Flow (PIF)

Maximum airflow achieved during a forceful inspiration.

Mixed Venous Blood

Systemic venous blood entering pulmonary artery with PvO2 ≈ 40 mmHg, PvCO2 ≈ 46 mmHg.

Arterial Blood

Oxygenated blood leaving lungs (PaO2 ≈ 100 mmHg, SaO2 ≈ 98 %).

Oxygen Transport

Combined processes of O2 ventilation, diffusion, and carriage by Hb to tissues.

Carbon Dioxide Transport

Removal of CO2 from tissues via dissolution, carbamino formation, and bicarbonate conversion.

Minute Ventilation Equation

Formula MV = RR × VT describing total air moved per minute.

Peak Flow Meter

Portable device that measures PEFR for self-monitoring asthma/COPD.

Obstructive Lung Disease

Condition (e.g., COPD, asthma) featuring increased airway resistance and low FEV1/FVC.

Restrictive Lung Disease

Disorder (e.g., pulmonary fibrosis, obesity) with reduced lung compliance and low TLC.

Functional Volume (Lung)

Collective term for measurable subdivisions of lung capacity used in physiology.

Increased Residual Volume

Rise in RV seen in emphysema/COPD due to loss of elastic recoil and air trapping.

Oxygen Diffusion Gradient

Difference in PO2 between alveolar gas and blood that drives O2 movement.

Fraction of Inspired Oxygen (FiO2)

Percentage of O2 in the inhaled gas mixture (room air ≈ 0.21).

Carbon Monoxide Poisoning

Toxic state arising from CO binding Hb, impairing O2 delivery and causing hypoxia.