Mammalian Physiology (BIOL 456): Respiratory System Physiology and Ventilation

A collection of vocabulary flashcards covering key terms, pulmonary volumes, capacities, mechanics of breathing, gas laws, and ventilation patterns from the lecture notes.

Tidal volume ($V_T$)

The volume of air that moves during a single inspiration or expiration, averaging about $500\,m L$ during normal quiet breathing.

Inspiratory reserve volume (IRV)

The additional volume of air inspired above the tidal volume during maximal inhalation, averaging about $3000\,m L$ in a $70\text{-kg}$ man.

Expiratory reserve volume (ERV)

The amount of air forcefully exhaled after the end of a normal expiration, averaging about $1100\,m L$ in males.

Residual volume (RV)

The volume of air remaining in the lungs and airways after maximal exhalation, averaging about $1200\,m L$ in males.

Inspiratory capacity (IC)

The total volume of air that can be inspired after a normal exhalation, calculated as the sum of tidal volume and inspiratory reserve volume ($V_T + IRV$).

Vital capacity (VC)

The total amount of air that can be moved into and out of the lungs during a maximal respiratory cycle, calculated as $V_T + IRV + ERV$ (averaging about $4600\,m L$).

Total lung capacity (TLC)

The total volume of air in the lungs after a maximum inhalation, calculated as $V_T + IRV + ERV + RV$ ($5800\,m L$ in males and $4200\,m L$ in females).

Functional residual capacity (FRC)

The volume of air remaining in the lungs at the end of a normal passive expiration, calculated as the sum of expiratory reserve volume and residual volume ($ERV + RV$).

Passive expiration

Expiration during quiet breathing that does not require active muscle contraction, relying on the elastic recoil of the lungs and thoracic cage.

Active expiration

Forced exhalation that recruits internal intercostal and abdominal muscles to pull the rib cage inward and displace abdominal contents upward, decreasing thoracic cavity volume.

Pneumothorax

A medical condition occurring when air enters the pleural cavity, breaking the fluid bond holding the lung to the chest wall and causing the lung to collapse.

Compliance

The ability of the lung to stretch, expressed mathematically as $C = \frac{\Delta P}{\Delta V}$; high compliance indicates a lung that stretches easily.

Elastance

The ability of the lung to resist being deformed and to return to its resting volume when a stretching force is released; it is the reciprocal of compliance.

Emphysema

A pulmonary pathology characterized by low elastic recoil (elastance) in the lungs, forcing patients to actively contract expiratory muscles to force out air.

Law of LaPlace

A physical law stating that pressure inside a fluid-film bubble is $P = \frac{2T}{r}$, meaning smaller bubbles experience higher inward pressure than larger bubbles when surface tension ($T$) is equal.

Surfactant

A mixture of proteins and phospholipids (such as dipalmitoyl-phosphatidylcholine) secreted by type II alveolar cells that decreases surface tension in alveolar fluid and reduces lung resistance to stretch.

Newborn respiratory distress syndrome (NRDS)

A condition in premature infants caused by a lack of surfactant, leading to stiff, low-compliance lungs and impaired oxygen and carbon dioxide exchange.

Poiseuille's law (in airway resistance)

A relationship establishing that airway resistance ($R$) is directly proportional to length ($L$) and viscosity ($\eta$), and inversely proportional to the fourth power of radius ($r^4$), expressed as $R \propto \frac{L\eta}{r^4}$.

Bronchoconstriction

The narrowing of bronchiolar diameter that increases airway resistance and decreases fresh air reaching the alveoli, often triggered by histamine from mast cells, tissue damage, or allergies.

Bronchodilation

The relaxation of bronchiolar smooth muscle that decreases airway resistance, mediated by $\beta\text{-receptors}$ responding to circulating epinephrine.

Total pulmonary ventilation

The total volume of air moved into and out of the lungs each minute (also called minute volume), calculated as $\text{ventilation rate} \times V_T$ (e.g., $12\,\text{breaths/min} \times 500\,m L/\text{breath} = 6000\,m L/\text{min}$).

Anatomic dead space

The volume of air occupying conducting airways (such as the trachea and bronchi) that does not reach the alveoli, averaging about $150\,m L$.

Alveolar ventilation

The volume of fresh air that reaches the alveoli each minute, calculated as $\text{ventilation rate} \times (V_T - V_D)$ (e.g., $12\,\text{breaths/min} \times (500 - 150\,m L) = 4200\,m L/\text{min}$).

Maximum voluntary ventilation

The maximum volume of air moved into and out of the lungs when breathing as deeply and quickly as possible, typically $125\text{--}170\,L/\text{min}$.

Eupnea

Normal quiet breathing.

Hyperpnea

An increase in respiratory rate and/or volume in response to increased metabolic activity, such as during exercise.

Hyperventilation

An increase in respiratory rate and/or volume without an increase in metabolism, such as during emotional hyperventilation or blowing up a balloon.

Hypoventilation

A decrease in alveolar ventilation, such as during shallow breathing, asthma, or restrictive lung disease.

Tachypnea

Rapid breathing, usually characterized by an increased respiratory rate with decreased breathing depth, such as panting.

Dyspnea

A subjective feeling of difficulty breathing, often described as 'air hunger', occurring in various pathologies or intense exercise.

Apnea

The complete cessation of breathing, caused by voluntary breath-holding or depression of CNS control centers.

Airflow equation (pulmonary ventilation)

A formula stating that airflow is directly proportional to the pressure gradient ($\Delta P$) between the atmosphere and alveoli, and inversely proportional to airway resistance ($R$), expressed as $\text{Air Flow} \propto \frac{\Delta P}{R}$.

Diaphragm contribution to quiet inspiration

Moves downward approximately $1.5\,cm$ upon contraction, driving $60\text{--}75\%$ of the total thoracic volume change during normal resting inhalation.

Scalenes (in respiratory mechanics)

Inspiratory muscles that contract during inhalation to lift the sternum and upper ribs; their dysfunction or paralysis prevents normal up-and-out rib cage movement.

Alveolar pressure during quiet inspiration

Drops to a minimum of $-1\,mm\,Hg$ relative to atmospheric pressure roughly halfway through inspiration, causing ambient air to move down its pressure gradient into the alveoli.

Alveolar pressure during quiet expiration

Rises to a maximum of $+1\,mm\,Hg$ relative to atmospheric pressure due to elastic recoil, pushing air out of the lungs until alveolar and atmospheric pressures equalize.

Primary site of airway resistance

The rigid trachea and bronchi, which account for approximately $90\%$ of total normal airway resistance because of their smaller total cross-sectional area compared to smaller airways.

Energy expenditure of quiet breathing

Accounts for approximately $3\text{--}5\%$ of the body's total energy budget under normal resting conditions.

Normal resting respiration rate

A baseline breathing frequency averaging $12\text{--}20\,\text{breaths/min}$ in healthy adults.

Female pulmonary reference values (50-kg woman, 28 years old)

Standard respiratory metrics consisting of Tidal Volume ($V\_T$) = $500\,mL$, Inspiratory Reserve Volume ($IRV$) = $1900\,mL$, Expiratory Reserve Volume ($ERV$) = $700\,mL$, Residual Volume ($RV$) = $1100\,mL$, Vital Capacity ($VC$) = $3100\,mL$, and Total Lung Capacity ($TLC$) = $4200\,mL$.