Mammalian Physiology (BIOL 456): Gas Exchange and Transport in Mammals

Vocabulary flashcards covering key concepts of gas exchange, pulmonary pathologies, oxygen transport, and carbon dioxide transport in blood from the lecture notes.

Hypoventilation

A state of low alveolar ventilation resulting in lower-than-normal volumes of fresh air entering the alveoli, which leads to reduced blood oxygen levels (hypoxia).

Hypoxia

A condition characterized by lower-than-normal levels of oxygen in the blood or body tissues.

Alveolar-Capillary Diffusion Barrier

A $0.1\text{--}1.5\text{ }\frac{1}{\text{m}}$ thick barrier consisting of surfactant, alveolar epithelium, fused basement membranes, and capillary endothelium through which gases diffuse between the alveolar air space and red blood cells.

Fick's Law of Alveolar Diffusion

The physiological principle stating that gas diffusion rate is directly proportional to surface area, concentration gradient, and barrier permeability, and inversely proportional to diffusion distance: $\text{Diffusion Rate} = \frac{\text{SA} \times \text{BP} \times \text{gradient}}{\text{D}}$.

Emphysema

A pathology where smoke chemicals and tar activate alveolar macrophages to release elastase and proteolytic enzymes, destroying the lung's elastic fibers and decreasing alveolar surface area for gas exchange.

Fibrotic Lung Disease

A condition where scar tissue thickens the alveolar membrane, slowing gas exchange by increasing diffusion distance and decreasing lung compliance.

Pulmonary Edema

An accumulation of interstitial fluid filtered from blood capillaries that increases diffusion distance between alveoli and blood, slowing gas exchange.

Asthma

A disease characterized by constricted bronchioles that cause increased airway resistance and decreased alveolar ventilation.

Oxyhemoglobin ($\text{HbO}_2$)

The form of hemoglobin bound reversibly to oxygen molecules.

Heme Group

A structure consisting of a porphyrin ring with an iron atom ($\text{Fe}$) in the center, located within each globin chain of hemoglobin and capable of binding one molecule of $\text{O}_2$.

Solubility Coefficient ($\text{a}$)

A coefficient expressing dissolved gas concentration per unit partial pressure in blood; equal to $0.03\text{ mL O}_2/\text{L blood}/\text{mm Hg } P_{O_2}$ for oxygen and $0.7\text{ mL CO}_2/\text{L blood}/\text{mm Hg } P_{CO_2}$ for carbon dioxide.

Hypercapnia

An abnormally elevated concentration of carbon dioxide in the blood, which can cause acidosis and central nervous system depression.

Carbaminohemoglobin ($\text{HbCO}_2$)

A complex formed when carbon dioxide binds to free amino groups on hemoglobin molecules, accounting for $23$ percent of $\text{CO}_2$ transport in venous blood.

Carbonic Anhydrase (CA)

An enzyme within red blood cells that catalyzes the reversible conversion of carbon dioxide and water into hydrogen ions and bicarbonate: $\text{CO}_2 + \text{H}_2\text{O} \rightleftharpoons \text{H}^+ + \text{HCO}_3^-$.

Chloride Shift

An anion exchange mechanism where bicarbonate ($\text{HCO}_3^-$) leaves the red blood cell in exchange for chloride ($\text{Cl}^-$) via an antiport protein to maintain electrical neutrality.

Respiratory Acidosis

A pH disturbance caused by excess $\text{H}^+$ accumulating in plasma when elevated blood $\text{CO}_2$ levels exceed the buffering capacity of hemoglobin.

Atmospheric and Oxygen Partial Pressure in Denver

At an altitude of $1609\,\text{m}$, Denver has an atmospheric pressure of approximately $628\,\text{mm Hg}$ and a dry air $P_{\text{O}\_2}$ of $132\,\text{mm Hg}$ (compared to $760\,\text{mm Hg}$ atmospheric pressure and $160\,\text{mm Hg}$ $P_{\text{O}\_2}$ at sea level).

Alveolar Water Vapor Pressure ($P_{\text{H}\_2\text{O}}$)

The constant partial pressure exerted by water vapor in fully humidified alveolar air, equal to $47\,\text{mm Hg}$.

Factors Determining Alveolar Ventilation

The rate and depth of breathing, airway resistance, and lung compliance (the stretchability of lung tissue).

Primary Causes of CNS Depression Affecting Ventilation Rate

Alcohol poisoning and drug overdoses, which depress the central nervous system to slow ventilation rate and decrease depth of breathing.

Cause of Hypoxia Outside of Hypoventilation

Impaired gas exchange between alveoli and blood across the diffusion barrier formed by type I alveolar cells and capillary endothelium.

Alveolar Perfusion

The blood flow supplying the pulmonary capillary network surrounding the alveoli, which must be adequate and properly matched with ventilation for optimal gas exchange.

Hemoglobin Oxygen Binding Capacity

Each hemoglobin molecule contains $4$ heme groups, giving a single hemoglobin molecule the potential to reversibly bind up to $4$ oxygen molecules.

Distribution Breakdown of Oxygen Transport in Blood

Approximately $98\%$ of oxygen in blood is transported bound to hemoglobin, while only $\sim 2\%$ is dissolved directly in blood plasma.

Resting Human Oxygen Consumption Requirements

At a resting tissue consumption of $250\,\text{mL O}\_2/\text{min}$ and cardiac output of $5\,\text{L blood}/\text{min}$, blood must deliver a concentration of $50\,\text{mL O}\_2/\text{L blood}$.

Oxygen Delivery Capacity of Plasma Alone

Dissolved oxygen in plasma supplies only $3\,\text{mL O}\_2/\text{L blood}$, resulting in a total delivery of $15\,\text{mL O}\_2/\text{min}$ at resting cardiac output ($5\,\text{L/min}$)—well below the required $250\,\text{mL O}\_2/\text{min}$.

Oxygen Delivery Capacity with Hemoglobin

Hemoglobin increases blood oxygen content to $200\,\text{mL O}\_2/\text{L blood}$, delivering $1000\,\text{mL O}\_2/\text{min}$ at resting cardiac output ($5\,\text{L/min}$), which provides a four-fold safety reserve above resting needs ($250\,\text{mL O}\_2/\text{min}$).

Breakdown of Carbon Dioxide Transport in Venous Blood

$7\%$ is dissolved in plasma, $23\%$ is bound to hemoglobin as carbaminohemoglobin ($\text{HbCO}\_2$), and $70\%$ is converted to bicarbonate ions ($\text{HCO}\_3^-$) that enter plasma.

Physiological Consequences of Hypercapnia

Elevated blood $\text{CO}\_2$ causes acidosis (denaturing cellular proteins) and depresses central nervous system function, leading to confusion, coma, or death.

Primary Extracellular Buffer in the Human Body

Bicarbonate ($\text{HCO}\_3^-$), which enters plasma via the chloride shift to buffer metabolic acids and moderate systemic pH changes.

Role of Hemoglobin in Intracellular pH Buffering

Hemoglobin binds free hydrogen ions ($\text{H}^+$) generated by the carbonic anhydrase reaction to form $\text{HbH}$, preventing excess $\text{H}^+$ from accumulating inside red blood cells.