Acid-Base Balance in Physiology G 31

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Questions and Answers

Which of the following statements is TRUE regarding the regulation of acid-base balance in the body?

The most powerful acid-base regulatory systems operate over a period of minutes.

The pH of urine can vary significantly depending on the acid-base status of the extracellular fluid. (correct)

Hypoxia and poor blood flow can lead to an accumulation of acids in the body. (correct)

The kidneys play a minor role in correcting abnormalities of extracellular fluid H+ concentration.

What is the general form of the buffering reaction in the body fluids?

Buffer - H+ ⇌ H Buffer

Buffer + H+ ⇌ H Buffer (correct)

Buffer + H2O ⇌ H Buffer

Buffer + OH- ⇌ H Buffer

What happens to the buffering reaction when the H+ concentration increases?

The reaction shifts to the right, and less H+ binds to the buffer.

The reaction shifts to the left, and more H+ binds to the buffer.

The reaction shifts to the right, and more H+ binds to the buffer. (correct)

The reaction remains unchanged, as the buffer is already saturated.

What is the role of a buffer in the body fluids?

To temporarily bind H+ ions, minimizing changes in H+ concentration. (B) Signup and view all the answers

What is an example of a situation that could cause acid accumulation and decreased intracellular pH?

Hypoxia or poor blood flow to the tissues (C) Signup and view all the answers

What does the term "acidosis" describe?

A decrease in the pH of the body fluids, below the normal range. (B) Signup and view all the answers

What is the normal pH range of extracellular fluids?

7.35 to 7.45 (C) Signup and view all the answers

What is the primary role of the kidneys in regulating acid-base balance?

To excrete acids or bases at variable rates to maintain the proper pH balance. (D) Signup and view all the answers

What happens to the partial pressure of carbon dioxide (PCO2) in the extracellular fluid when the rate of metabolic formation of CO2 increases?

PCO2 increases. (B) Signup and view all the answers

How does an increased rate of pulmonary ventilation affect the PCO2 in the extracellular fluid?

PCO2 decreases due to CO2 being blown off. (B) Signup and view all the answers

Which buffer system is considered MOST important in managing acid-base balance?

Phosphate buffer (B) Signup and view all the answers

What is the normal range of pH for the extracellular fluid?

7.4 to 7.8 (A) Signup and view all the answers

Under what specific condition does the kidney generate new HCO3−?

When there is excess H+ in the tubular fluid (A) Signup and view all the answers

A decrease in pH from 7.4 to 7.0 causes what change in alveolar ventilation rate?

A four to five-fold increase in ventilation rate. (C) Signup and view all the answers

What happens to the ventilation rate when plasma pH rises above 7.4?

The ventilation rate decreases. (D) Signup and view all the answers

Where in the nephron do the Type A intercalated cells primarily function?

Late distal tubule and collecting tubules (C) Signup and view all the answers

What is the direct consequence of H+ secretion in Type A intercalated cells?

Reabsorption of HCO3− (C) Signup and view all the answers

How does the body's response to changes in pH differ at reduced versus increased levels of pH?

The change in ventilation rate per unit pH change is greater at reduced levels of pH. (D) Signup and view all the answers

What is the primary mechanism responsible for the movement of H+ out of Type A intercalated cells?

Active transport (A) Signup and view all the answers

What is the timeframe for the respiratory system to return the pH to approximately 7.2 to 7.3 after a significant decrease in pH?

Within 3 to 12 minutes. (A) Signup and view all the answers

What role does alveolar ventilation play in regulating the pH of body fluids?

Alveolar ventilation affects pH by influencing CO2 levels, which then impacts H+ concentration. (A) Signup and view all the answers

What is the ratio of HCO3− reabsorbed to H+ secreted in the Type A intercalated cells during normal conditions?

1:1 (D) Signup and view all the answers

In the context of acid-base balance, what is the specific role of the ammonia buffer in the kidney?

Generating new HCO3− for the blood (D) Signup and view all the answers

When looking at the overall process of H+ secretion in the kidney, what is the net effect on the blood pH?

Increase in blood pH (B) Signup and view all the answers

What does the isohydric principle state?

All buffer systems in a common solution are in equilibrium with the same H+ concentration. (B) Signup and view all the answers

What happens to all buffer systems in the body when there is a change in H+ concentration in the extracellular fluid?

The balance of all buffer systems changes simultaneously. (C) Signup and view all the answers

Given the formula for the isohydric principle: H+ = K1 × A1/HA1 = K2 × A2/HA2 = K3 × A3/HA3, what do K1, K2, and K3 represent?

The dissociation constants of the acids. (D) Signup and view all the answers

What happens to the extracellular fluid pH when the rate of alveolar ventilation increases?

The pH increases due to a decrease in CO2. (D) Signup and view all the answers

What is the primary factor that affects PCO2 in the extracellular fluid, assuming metabolic CO2 formation remains constant?

The rate of alveolar ventilation (D) Signup and view all the answers

How does an increase in alveolar ventilation affect the balance of the buffer systems in the body?

It shifts the equilibrium of all buffer systems towards the alkaline side. (B) Signup and view all the answers

Why is the isohydric principle important for maintaining acid-base balance in the body?

It allows for rapid and efficient adjustments to changes in H+ concentration. (C) Signup and view all the answers

Which of the following factors can influence the balance of the buffer systems in the body?

All of the above. (D) Signup and view all the answers

What is the primary role of bicarbonate (HCO3-) in the renal tubular lumen?

To neutralize excess hydrogen ions (H+) secreted into the lumen. (B) Signup and view all the answers

What is the role of the enzyme carbonic anhydrase in the process of acid-base regulation by the kidney?

It converts carbon dioxide (CO2) into bicarbonate (HCO3-) and hydrogen ions (H+). (B) Signup and view all the answers

Which of the following is TRUE about the process of ammonium ion (NH4+) production and secretion by proximal tubular cells?

For each glutamine molecule metabolized, two NH4+ are produced and secreted, and one HCO3- is returned to the blood. (B) Signup and view all the answers

How does filtered phosphate (NaHPO4) contribute to buffering secreted H+ in the renal tubular lumen?

By directly combining with H+ and being eliminated in urine as NaH2PO4. (C) Signup and view all the answers

Which of the following statements correctly describes the role of sodium ions (Na+) in the renal tubular lumen during H+ secretion?

Na+ is secreted into the lumen in exchange for H+ to maintain electroneutrality. (C) Signup and view all the answers

What is the primary mechanism by which the kidney eliminates excess H+?

By directly excreting it in urine. (C) Signup and view all the answers

How does the kidney regulate blood pH?

By producing and secreting bicarbonate (HCO3-) and ammonium ion (NH4+). (A), By regulating the reabsorption of sodium ions (Na+) and potassium ions (K+). (D) Signup and view all the answers

What happens to the bicarbonate (HCO3-) produced during glutamine metabolism in proximal tubular cells?

It is reabsorbed into the blood, contributing to the body's overall acid-base balance. (B) Signup and view all the answers

What is the primary source of glutamine used in the renal ammonium-ammonia buffer system?

Metabolism of amino acids in the liver (B) Signup and view all the answers

What happens to the NH4+ that is generated in the proximal tubules?

It is secreted into the tubular lumen in exchange for sodium. (C) Signup and view all the answers

How does an increase in extracellular fluid H+ concentration impact the renal ammonium-ammonia buffer system?

It stimulates glutamine metabolism, increasing NH4+ production. (A) Signup and view all the answers

What is the mechanism by which NH4+ is excreted in the collecting tubules?

Reaction with NH3, resulting in trapping within the lumen. (B) Signup and view all the answers

What is the net effect on the body fluids for every molecule of glutamine metabolized in the proximal tubules?

Two HCO3− are added to the blood. (A) Signup and view all the answers

Which of the following is NOT a direct consequence of chronic acidosis?

Decreased renal excretion of HCO3−. (A) Signup and view all the answers

What is the primary role of the renal ammonium-ammonia buffer system in maintaining acid-base balance?

To generate new HCO3− to neutralize H+ in the blood. (C) Signup and view all the answers

Why is the loss of HCO3− considered the same as the addition of H+ to the blood?

Because they react to form water and CO2. (A) Signup and view all the answers

Study Notes

Acid-Base Regulation

Hydrogen ion (H+) balance regulation is similar to other ion regulation in the body. Precise H+ regulation is crucial due to its impact on nearly all enzyme systems in the body. Extracellular fluid (ECF) H+ concentration is typically low, with a normal level of 0.00004 mEq/L. Variations are minimal compared to other ions.

Acids and Bases

A hydrogen ion is a single proton.
Acids release H+ in solution (e.g., HCl, ionizing into H+ and Cl-). Carbonic acid (H2CO3) forms H+ and bicarbonate (HCO3-).
Bases accept H+. Bicarbonate (HCO3-), and proteins (e.g., hemoglobin) are key body bases. Alkalosis is excess H+ removal; acidosis is excess H+ addition.

Strong and Weak Acids/Bases

Strong acids (e.g., HCl) fully dissociate, releasing large amounts of H+ quickly. Weak acids (e.g., H2CO3) dissociate less readily. Strong bases (e.g., OH-) strongly bind H+ effectively, while weak bases (e.g., HCO3-) bind H+ less powerfully. Most acids/bases in ECF are weak.

Normal H+ Concentration and pH

Blood H+ concentration is tightly controlled near a normal value of 0.00004 mEq/L or pH 7.4.
Acidemia is a blood pH below 7.4, while alkalemia is above 7.4.

Buffering Systems

Buffers resist H+ changes by reversibly binding H+. The most important ECF buffer is the bicarbonate buffer system.
This system comprises carbonic acid (H2CO3) and bicarbonate (HCO3-).
An increase in H+ leads to more H2CO3 formation and CO2 release, and the reverse happens when H+ is reduced.

Acid-Base Regulation Defense Mechanisms

The main systems defending against H+ changes are: buffers (react within seconds), the respiratory center (regulates CO2 elimination within minutes), and the kidneys (adjust acid/base excretion over hours/days).
Buffer systems minimize H+ changes while the respiratory center eliminates CO2 (and thereby H2CO3), delaying the need for renal compensation.

Bicarbonate Buffer System

CO2+H2O ↔ H2CO3 ↔ H+ + HCO3- maintains balance.
If strong acid (e.g., HCl) is added, the increased H+ combines with HCO3-, forming more H2CO3, and leading to higher CO2 production and increased respiratory rate. The opposite occurs when a strong base is added.

Phosphate Buffer System

H2PO4- ↔ H+ + HPO42- acts as an intracellular and renal tubule buffer.
It is less important relative to bicarbonate for ECF.

Protein Buffers

Proteins are important intracellular buffers due to their high concentrations. Hemoglobin in red blood cells is influential. Intracellular pH changes usually reflect ECF changes; however, exchanges take time.

Pulmonary Ventilation and Acid-Base Balance.

CO2 production is continuously balanced by its expulsion via respiration.
Increased ventilation reduces PCO2 lowering H+ concentration; vice versa.

Renal Acid-Base Balance

Kidneys regulate acid-base balance by excreting acidic or basic urine altering H+ concentration in extracellular fluid (ECF)
H+ secretion and HCO3- reabsorption occur in tubules, not the descending or ascending thin limbs of the Loop of Henle.

H+ Secretion and HCO3- Reabsorption: (Renal System)

80-90% of HCO3- reabsorption occurs in proximal tubules, supporting H+ secretion.
Na+-H+ exchange in proximal tubules, thick ascending loop of Henle, and early distal tubule supports H+ secretion with energy from Na+ gradient, derived from Na+-K+ ATPase pumps.
Late distal and collecting tubules employ primary active transport of H+ (using H+-ATPase or H+-K+-ATPase).
This process allows for greater urine acidity.

Excess H+ and Ammonia Buffer System

Excess H+ is buffered via ammonia, in the form of NH4+. The ammonia buffer system is important in generating new HCO3-, aiding ECF HCO3- replenishment during acidosis.

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Description

Test your knowledge on the regulation of acid-base balance in the body. This quiz covers topics such as buffering reactions, the role of kidneys, and conditions that affect pH levels. Understand the principles of acidosis and the importance of pH in bodily fluids.

Acid-Base Balance in Physiology G 31 - 1.7

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