Chapter 9–15 Key Vocabulary for Respiratory, Cardiovascular, and Acid-Base Physiology

A set of vocabulary flashcards covering key terms from chapters on respiratory development, anatomy, physiology, gas exchange, pulmonary circulations, neural control, thoracic structures, acid-base balance, and related clinical concepts.

Ductus venosus

Fetal shunt that bypasses the liver; blood from the umbilical vein goes to the inferior vena cava and into the right heart.

Foramen ovale

Interatrial opening in the fetal heart allowing right-to-left shunting; normally closes after birth.

Ductus arteriosus

Fetal vessel connecting the pulmonary artery to the aorta; diverts blood away from the nonfunctional fetal lungs; closes after birth.

Chorionic villi

Finger-like projections of the chorion that invade the uterine lining to form the placenta for maternal–fetal exchange.

Intervillous spaces

Maternal blood-filled pockets in the placenta where exchange with fetal villi occurs.

Surfactant

Lipid–protein coating produced by type II pneumocytes that reduces alveolar surface tension and prevents collapse; essential for lung inflation.

Type I pneumocyte

Flat alveolar epithelial cell covering most of the gas-exchange surface.

Type II pneumocyte

Cuboidal alveolar cell that produces surfactant and can differentiate into type I cells.

Alveolar-capillary membrane

Thin barrier where gas diffusion occurs between alveolar air and pulmonary capillary blood.

Acinus (primary lobule)

Functional gas-exchange unit consisting of respiratory bronchioles, alveolar ducts, and alveoli supplied by a terminal bronchiole.

Terminal bronchiole

Conducting airway that does not participate in gas exchange; leads to respiratory bronchioles.

Mucociliary escalator

Cilia move mucus toward the pharynx to clear inhaled particles.

Pseudoglandular stage

Embryonic lung stage (≈6–16 weeks) with tree-like branching but no alveoli yet.

Canalicular stage

Lung stage (≈16–26 weeks) with more bronchioles and developing capillaries; type I/II pneumocytes appear.

Alveolar period

Lung development phase (≈32 weeks–years) with formation of alveoli and maturation of surfactant.

Alveolar period oxygen delivery

Period when surfactant increases and alveolar-capillary interface matures for gas exchange.

Alveolar number at term

About 50 million alveoli at term; increases through early childhood.

Alveolus

Gas-exchange unit consisting of alveolar walls (type I/II cells) and surrounding capillaries.

Alveolar-capillary membrane thickness

Thin barrier (usually <1 μm) facilitating efficient gas diffusion.

L/S ratio

Lecithin (phosphatidylcholine) to Sphingomyelin ratio used to assess fetal lung maturity; ≥2 indicates lower risk of RDS.

Lecithin (PC)

Major phospholipid component of surfactant (dipalmitoylphosphatidylcholine) critical for reducing surface tension.

Phosphatidylglycerol (PG)

Surfactant phospholipid that aids in maturation and function of surfactant.

Canalicular vs pseudoglandular stages

Pseudoglandular stage: branching up to terminal bronchioles; canalicular: respiratory bronchioles and capillary development.

Alveolar period markers

Formation of alveolar ducts and sacs; type I/II pneumocytes proliferate; surfactant increases.

Alveolar air–blood barrier

Diffusion barrier formed by alveolar epithelium, basement membranes, and capillary endothelium.

Acinus (functional unit)

Region containing a terminal bronchiole and its alveolar ducts/sacs; primary site of gas exchange.

Hilum

Pulmonary entry/exit point for bronchi, vessels, and nerves.

Pleural membranes

Parietal pleura lines chest wall; visceral pleura covers the lung; pleural space contains lubricating fluid.

Mediastinum

Central thoracic compartment containing heart, great vessels, trachea, and esophagus.

Angle of Louis (sternal angle)

External marker where the trachea divides into the right and left main bronchi.

Carina

Bifurcation of the trachea into the right and left mainstem bronchi.

Bronchial circulation

Systemic arterial supply to the airways and visceral pleura; ~1–2% of cardiac output.

Pulmonary circulation

Low-pressure, low-resistance circulation delivering blood to alveoli for gas exchange.

Pulmonary capillaries

Extensive network where surface gas exchange occurs; endothelium is thin for diffusion.

Lymphatics of lung

Extensive lymphatic network draining interstitium and pleural space; helps maintain fluid balance and immune defense.

Autonomic innervation of lungs

Parasympathetic and sympathetic nerves regulate bronchomotor tone, secretion, and vascular tone via vagus and thoracic sympathetic trunks.

Somatic innervation

Phrenic and intercostal nerves control diaphragm and intercostal muscles.

Diaphragm

Primary inspiratory muscle; dome-shaped, innervated by phrenic nerves (C3–C5).

Tripod position

Posture used by COPD patients to improve breathing by elevating the chest and using accessory muscles.

Ribs and chest wall mechanics

Pump-handle and bucket-handle rib movements; chest wall compliance affects ventilation effort.

Pleural space pressure

Negatively pressured under normal inspiration (sub-atmospheric); drives lung expansion.

Transpulmonary pressure (PTP)

Pressure difference between airway opening and pleural space; PTP = PAO − Ppl; drives lung inflation.

Transairway pressure (PTAW)

Pressure difference across the airways from airway opening to alveoli (PAO − PA).

Transalveolar pressure (PTA)

Pressure difference across the alveolar wall (PA − Ppl).

Trans-chest wall pressure (PTCW)

Pressure difference between pleural space and body surface (Ppl − Pbs).

Ventilation–perfusion (V/Q) ratio

Relationship between alveolar ventilation and pulmonary blood flow; ideal value is about 1; imbalances cause hypoxemia.

Alveolar dead space

Ventilated alveoli with little or no perfusion; contributes to wasted ventilation.

Anatomic dead space

Conducting airways where no gas exchange occurs; volume ≈ 1 mL per lb ideal body weight.

Physiologic dead space

Sum of anatomic and alveolar dead space; represents wasted ventilation.

Bohr effect

Shift of the HbO2 dissociation curve to the right with high CO2 or low pH, promoting O2 unloading at tissues.

Haldane effect

Shift of CO2 dissociation curve with oxygenation state of Hb; deoxygenated Hb carries more CO2.

Oxyhemoglobin dissociation curve

S-shaped relationship between Hb saturation and PaO2; illustrates loading/unloading of O2.

CaO2

Total arterial O2 content: CaO2 = 0.003 × PaO2 + 1.34 × Hb × SaO2.

Do2 (O2 delivery)

DO2 = Cardiac output × arterial O2 content (CaO2).

Anion gap

Difference between measured cations and anions (Na+ − [Cl− + HCO3−]); normal ~9–14 mEq/L; indicates metabolic acidosis with unmeasured anions.

Base excess (BE)

Amount of base above or below normal in blood after standardized PCO2; +BE indicates metabolic alkalosis or base gain; −BE indicates metabolic acidosis.

Henderson–Hasselbalch equation

pH = 6.1 + log([HCO3−] / (0.03 × PaCO2)); relates pH to bicarbonate and CO2.

Bicarbonate open system

Bicarbonate buffering system open to CO2 removal; HCO3− buffers H+ with CO2 exhaled.

Nonbicarbonate buffers (closed system)

Buffers such as Hb, organic phosphates, and plasma proteins; buffer H+ but are not replenished by ventilation.

Kussmaul respiration

Very deep, labored breathing seen in severe metabolic acidosis (e.g., ketoacidosis).

Respiratory acidosis

Elevated PaCO2 with acidemia; primary respiratory problem with renal compensation.

Respiratory alkalosis

Low PaCO2 with alkalemia; primary respiratory problem with renal compensation.

Metabolic acidosis

Low HCO3− or fixed acid gain; compensated by hyperventilation (lower PaCO2).

Metabolic alkalosis

High HCO3− or base gain; compensated by hypoventilation (increased PaCO2).

Acid-base regulation centers

Medullary respiratory centers (DRG/VRG) with pontine influence (pneumotaxic and apneustic centers) regulate breathing.

Central chemoreceptors

Respond to changes in H+ in CSF, driven by PaCO2 through the blood–brain barrier; primary minutes-to-hours ventilatory drive.

Peripheral chemoreceptors

Carotid and aortic bodies respond to arterial hypoxemia and acidosis; carotid bodies have major influence.

Head paradoxical reflex

Increased inspiratory drive when Hering-Breuer reflex is inhibited; involves rapidly adapting receptors.

J-receptors (juxtacapillary)

C-fiber receptors near alveoli; stimulate rapid, shallow breathing and dyspnea.

C-fiber afferents

Vagal afferents that respond to chemical and mechanical stimuli, contributing to reflexes.

Pneumotaxic center

Pontine center that terminates inspiration; controls inspiratory time and rate.

Apneustic center

Pontine center that can prolong inspiratory gasps when disconnected from pneumotaxic influence.

Hering–Breuer inflation reflex

Vagal reflex from airway stretch receptors inhibiting inspiration to prevent overinflation.

Scholarly basics: Fick’s law of diffusion

Gas diffusion rate is proportional to area and concentration gradient and inversely proportional to barrier thickness.

Alveolar gas equation (PAO2)

PAO2 = FiO2(PB − PH2O) − PACO2/RQ; estimates alveolar O2 partial pressure.

P/F ratio

PaO2/FiO2; used to assess oxygenation and diagnose ARDS; lower values indicate worse oxygenation.

Pulmonary edema (anatomic shunt context)

Excess fluid in alveoli impairing gas exchange; often increases anatomic shunt fraction.

Carbohydrates in gas exchange: Hb and HbO2

Hemoglobin transports most O2; HbO2 saturation determines arterial oxygen content.

Oxygen delivery equation (DO2)

DO2 = CO × CaO2; combines cardiac output and arterial O2 content.

Oxygen content of blood (CaO2)

CaO2 = 0.003 × PaO2 + 1.34 × Hb × SaO2.

Alveolar ventilation (V̇A)

Ventilation rate into alveoli; V̇A = V̇E × (Alveolar gas contribution) minus dead space.

Ventilation vs perfusion mismatch concepts

Discrepancies between ventilation and blood flow cause V/Q imbalances and hypoxemia.

Anion gap metabolic acidosis

Elevated anion gap indicates accumulation of unmeasured anions (e.g., lactate, ketoacids) in metabolic acidosis.

Base excess (BE) interpretation

BE indicates nonvolatile balance; positive BE = base surplus; negative BE = base deficit.

Buffer systems open vs closed

Open bicarbonate system (CO2 is exhaled) vs closed nonbicarbonate buffers (Hb, proteins) that buffer H+ without CO2 removal.

Isohydric buffering

Maintenance of pH by buffering H+ with CO2/HCO3− without major pH change.

K+ in acid-base balance

Potassium shifts with pH changes; hypokalemia/hyperkalemia affect buffering and acid-base status.

Sputum induction (clinical method)

Inhalation of hypertonic saline to evoke coughing and produce sputum for analysis.

Ciliary ultrastructure (axoneme)

9+2 microtubule arrangement enabling ciliary beating and mucociliary clearance.

Mediastinal compartments

Anterior, middle, and posterior mediastinum; contain thymus, heart, great vessels, esophagus, etc.

Pulmonary vascular resistance (PVR)

Pressure difference across the pulmonary vasculature divided by flow; normally low.

Systemic vascular resistance (SVR)

Pressure difference across the systemic vasculature divided by flow; normally higher than PVR.

Pulmonary lymph flow relevance

Lymphatics help remove interstitial fluid and pathogens; drain via hilar/mediastinal nodes.

Oxygen–hemoglobin dissociation curve shifts

Bohr effect: right shift with low pH/ high CO2; Haldane effect: CO2 carriage altered by Hb oxygenation.

Perfusion zones (Z1–Z3)

Zones of the lung describing relative PA, PAO2, and Pv pressures and blood flow distribution.

Functional residual capacity (FRC)

Volume of air remaining in the lungs after passive expiration; balance of lung and chest wall forces.

Total thoracic compliance

Combined compliance of lungs and chest wall; lower than either alone; affected by disease.

Time constant (RC) in ventilation

Product of resistance and compliance; time to reach ~63% of new volume after a pressure change.

Static vs dynamic mechanics

Static: no flow (pause); dynamic: ongoing flow; different resistance/compliance readings.

Dead space ratio in ventilation

VD/VT; proportion of each breath not participating in gas exchange.