Acid-Base Balance and Buffer Systems

Flashcards covering the vocabulary and core concepts of acid-base balance, buffer systems, and respiratory regulation from the Chapter 1-8 lecture transcript.

Strong acids and strong bases

Substances that dissociate completely when in a mixture or water and have difficulty reforming into their original state.

Weak acids and weak bases

Substances that dissociate in a fluid mixture reversibly but not completely, allowing the equation to be pushed in either direction.

Carbonic acid ($H_2CO_3$)

A weak, volatile, and unstable acid created in the $CO_2$ hydration reaction when carbon dioxide hits water.

Bicarbonate ($HCO_3^-$)

A weak base that, along with a hydrogen ion, is the product of dissociated carbonic acid used to carry $CO_2$ to the lungs.

Systemic capillary circulation

The level of circulation where $CO_2$ created by tissue metabolism flows into the capillary bed and venous system.

Chemical buffer systems

The first line of defense for regulating acids and bases that responds the fastest; it is subdivided into the carbonic acid-bicarbonate, phosphate, and protein systems.

Carbonic acid-bicarbonate buffer system

The most powerful chemical buffer in the body which operates in the blood plasma to maintain $pH$ balance.

Henderson-Hasselbalch equation

A conceptual mathematical proof used to evaluate the relationship between acids and bases; it shows that under normal conditions, the $pH$ should be 7.4.

Normal ratio of bases to acids

A relationship of $20:1$ that is required to maintain a normal $pH$ of 7.4.

$$pK$$

A specific mathematical constant associated with a particular acid, such as carbonic acid, which never changes.

Phosphate buffer system

A buffer system only about one-sixth as effective as the carbonic acid-bicarbonate system; it is primarily effective in the intracellular fluid and the kidneys (urine).

Glomerular filtrate

The initial product in the kidneys that eventually becomes urine and contains various types of phosphates.

Protein buffer system

A system found in plasma and cells where intracellular proteins provide $75\%$ of the buffering power of body fluids.

Amphoteric molecules

Unique molecules, such as hemoglobin, that can function as either an acid or a base depending on the environment.

Reduced hemoglobin

Hemoglobin that has lost its oxygen at the tissue level, resulting in a negative charge that allows it to bind with free hydrogen ions to decrease plasma acidity.

Respiratory system (buffering)

The second system of acid-base regulation which has twice the buffering power of chemical systems but is slower to respond.

Right shift

A shift in the equilibrium of the $CO_2$ hydration reaction caused by an increase in $CO_2$ produced by tissues or resulting from hypoventilation.

Left shift

A shift in the equilibrium of the $CO_2$ hydration reaction that occurs during hyperventilation when $CO_2$ is blown off too quickly.

Normal Resting $CO_2$ Production

The body produces $200\,mL$ of $CO_2$ per minute under normal resting conditions.

$V_A$ (with dot over V)

The symbol used for Alveolar Ventilation, which is normally about $4\,L\,min^{-1}$ at rest.

Eucapnia

A condition of normal ventilation where the amount of $CO_2$ eliminated in the breath matches the amount created at the tissue level.

Hypoventilation

A clinical condition defined by a decrease in minute ventilation accompanied by an elevated $PaCO_2$ (hypercapnia).

Hypercapnia

A condition characterized by an elevated partial pressure of carbon dioxide in the blood ($PaCO_2$).

Hyperventilation

An increase in ventilation above normal resting levels that results in a reduction of $CO_2$ in the blood (hypocapnia).

Hypocapnia

A condition characterized by a reduction in plasma $CO_2$ due to excessive ventilation.

Fixed acids

Acids that are removed through the kidneys, including phosphoric, uric, lactic, and ketones.

Renal system

The third system for acid-base regulation which rids the body of fixed acids and regulates alkaline substances by retaining bicarbonate.

ABG analysis (Arterial Blood Gas)

An invasive test and the most basic measure of lung function, involving an anaerobic sample of arterial blood.

Normal $pH$ range

The range between 7.35 and 7.45 where body cells are most stable.

Normal $PaCO_2$ range

The normal range for the partial pressure of arterial carbon dioxide is $35$ to $45\,mmHg$ (or torr).

Normal $PaO_2$ range

The normal range for the partial pressure of arterial oxygen at rest is $80$ to $100\,mmHg$ (or torr).

A-a gradient

The difference in oxygen tension between the alveoli and the arterial blood, which is usually less than $20\,mmHg$ in healthy people.

Anatomical shunts

Normal physiological pathways, such as the bronchial circulation and thebesian veins, where venous blood mixes with arterial blood.

Diffusion defect

An impairment in gas exchange that can be caused by a decrease in surface area, a decrease in the pressure gradient, or an increase in membrane thickness (Fick's law).

$CaO_2$ (Arterial oxygen content)

The total content of oxygen in arterial blood, calculated as the sum of oxygen bound to hemoglobin plus the oxygen free-floating in the plasma.

Oxygen delivery ($DO_2$)

The process of getting oxygen to the tissues, which depends on both arterial oxygen content ($CaO_2$) and cardiac output.