5. Physiology Chapter on Acid-Base Balance

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

Which of the following best describes the timeframe for renal compensation mechanisms to take effect?

Simultaneously with buffering

Hours to days (correct)

Within seconds

Within minutes

What is the approximate daily production rate range of volatile acid (CO2) in the human body?

1,000-5,000 mmol/day

5,000-10,000 mmol/day

10,000-12,000 mmol/day

13,000-20,000 mmol/day (correct)

In the context of acid-base balance, CO2 is considered a:

Precursor to a weak acid (correct)

Strong acid

Non-acidic compound

Directly acting base

Where does the conversion of CO2 to H+ and HCO3- primarily occur in the blood?

Red blood cells Signup and view all the answers

The volatile acid, CO2, is not directly buffered in the blood, but rather managed by:

Reversed reaction in the lungs and subsequent expiration Signup and view all the answers

Which of the following is a key difference between the handling of CO2 and nonvolatile acids in the context of maintaining blood pH?

CO2 converted back, and removed from body as gas; non-volatile acids are buffered then eliminated in the kidneys Signup and view all the answers

What is the normal, slightly alkaline pH of arterial blood?

7.4 Signup and view all the answers

Why, after all the acid generated daily, does arterial pH remain slightly alkaline?

Result of buffering and compensation mechanisms. Signup and view all the answers

What does the Henderson-Hasselbalch equation help to calculate?

The pH of a buffered solution Signup and view all the answers

What characteristics determine the pK value of a buffer pair?

The ratio of the rate constants K1 and K2 Signup and view all the answers

In the context of buffering, what does a high equilibrium constant (K) indicate?

The acid has low pK values Signup and view all the answers

What effect does a strong acid like HCl have on the equilibrium constant compared to a weak acid like H2CO3?

It results in a higher K value Signup and view all the answers

What ratio is essential for the calculation of pH using the Henderson-Hasselbalch equation?

The ratio of the concentrations of base to acid forms Signup and view all the answers

Which of the following correctly describes the relationship between pK and K?

pK is equal to the logarithmic transformation of K Signup and view all the answers

What does the term [A−] represent in the Henderson-Hasselbalch equation?

The concentration of the base form of the buffer Signup and view all the answers

What condition must be met for a buffered solution to be considered at chemical equilibrium?

The forward and reverse reaction rates must be equal Signup and view all the answers

What is the primary function of the respiratory center in regulating acid-base balance?

To regulate the removal of CO2, which is linked to H2CO3. Signup and view all the answers

Which of the following accurately describes the role of the kidneys in acid-base balance?

The kidneys act as a slower defense mechanism but are the most powerful in regulating acid-base balance. Signup and view all the answers

What is the core principle of the first two lines of defense in acid-base balance?

To buffer the pH of the extracellular fluid quickly. Signup and view all the answers

How does the kidney regulate acid-base balance?

By eliminating excess acid or base through urine, primarily through H+ and HCO3-. Signup and view all the answers

Which of the following correctly describes the relationship between lung function and kidney function in acid-base balance?

The lungs eliminate volatile acid (CO2), while the kidneys eliminate non-volatile acid. Signup and view all the answers

What is the term used to describe the net amount of acid that the body produces?

Net endogenous acid production (NEAP) Signup and view all the answers

What factors contribute to the body's 'net endogenous acid production' (NEAP)?

Dietary intake, cellular metabolism, and loss of acid and alkali from the body. Signup and view all the answers

What is the primary goal of both the respiratory and renal buffer systems?

To balance the pH of the blood within a narrow range. Signup and view all the answers

What is a primary reason for the increased buffering power of the phosphate buffer in the kidneys?

Phosphate concentration is higher in the tubules. Signup and view all the answers

How do plasma proteins affect free calcium ion concentration during acid-base disturbances?

They bind more H+ during acidemia, decreasing free calcium. Signup and view all the answers

Which of the following best describes the buffering role of hemoglobin in red blood cells?

Hemoglobin acts as a buffer by binding H+ and thereby reducing pH. Signup and view all the answers

What is the consequence of alkalemia on plasma protein binding?

Decreased binding of H+ and increased ionized calcium. Signup and view all the answers

Why is the buffering ability of intracellular proteins often delayed during acid-base abnormalities?

H+ and HCO3− move slowly through cell membranes. Signup and view all the answers

In which fluid compartment is phosphate considered a minor buffer?

Extracellular fluid. Signup and view all the answers

What happens to calcium levels during an acid-base disturbance when there is an increase in free H+?

Free calcium levels decrease due to increased H+ binding. Signup and view all the answers

Which statement accurately describes the relationship between plasma proteins, H+, and calcium during acidemia?

More H+ binding leads to decreased free calcium concentration. Signup and view all the answers

What characterizes metabolic acidosis?

Decrease in pH due to gain of fixed H+ Signup and view all the answers

What happens during respiratory alkalosis?

Decreased pH caused by hyperventilation Signup and view all the answers

In a case of metabolic acid-base disturbance, what compensatory mechanism is primarily activated?

Respiratory compensation to adjust Pco2 Signup and view all the answers

Which of the following is true regarding respiratory acidosis?

Hypoventilation leads to increased Pco2 Signup and view all the answers

What primary disorder is associated with changes in bicarbonate (HCO3−)?

Metabolic alkalosis Signup and view all the answers

How does the body respond to a respiratory acid-base disturbance?

Through renal compensation that alters HCO3− Signup and view all the answers

Which of the following statements best describes metabolic alkalosis?

Involves loss of fixed H+ leading to a high pH. Signup and view all the answers

What is the initial defense mechanism when an acid-base disturbance occurs?

Buffering in ECF and ICF Signup and view all the answers

What is the primary reason why the HCO3−/CO2 buffer system is so effective in extracellular fluid?

The HCO3−/CO2 system is aided by the enzyme carbonic anhydrase, which accelerates the formation of H2CO3, increasing the buffer's effectiveness. Signup and view all the answers

If a large amount of HCl is introduced into the extracellular fluid (ECF), how does the HCO3−/CO2 buffer system respond? Select the most accurate sequence of events.

HCl combines with HCO3− to form H2CO3; H2CO3 dissociates into CO2 and H2O, both of which are expired by the lungs; the pH of the blood decreases slightly. Signup and view all the answers

How does the enzyme carbonic anhydrase contribute to the regulation of pH in the extracellular fluid?

Carbonic anhydrase accelerates the formation of H2CO3 from CO2 and H2O, which then dissociates into H+ and HCO3−, aiding in the buffering of excess H+ in the ECF. Signup and view all the answers

In the context of regulating pH in the body, where is carbonic anhydrase particularly abundant?

The walls of the lung alveoli and the epithelial cells of the renal tubules, where it assists in CO2 transport and H2CO3 formation. Signup and view all the answers

How does the respiratory system contribute to the regulation of pH in the blood?

Respiration regulates the amount of CO2 in the blood, which in turn influences the concentration of HCO3− and therefore pH. Signup and view all the answers

What is the relationship between the pK of the HCO3−/CO2 buffer system and the pH of the extracellular fluid?

The pK of the HCO3−/CO2 buffer system is very close to the pH of the extracellular fluid, making it particularly effective at buffering changes within the physiological range. Signup and view all the answers

If the rate of respiration increases significantly, what is the likely impact on the pH of the blood?

The blood will become more alkaline due to the removal of excess CO2 and a decrease in H+ ions. Signup and view all the answers

Study Notes

Lecture 4: Acid-Base Balance

Acid-base balance maintains a normal hydrogen ion concentration in body fluids.
A balance between intake/production of H+ and removal from the body is critical for homeostasis.
This balance is achieved through buffers (extracellular and intracellular fluid), respiratory mechanisms (removing CO₂), and renal mechanisms (reabsorbing bicarbonate and secreting hydrogen ions).

Introduction to Acids and Bases

A hydrogen ion (H+) is a single proton released from a hydrogen atom.
Molecules releasing hydrogen ions in solution are called acids.
Strong acids rapidly dissociate, releasing significant amounts of H+. HCl is an example.
Weak acids dissociate less readily, releasing H+ less vigorously. H₂CO₃ is an example.
A base (or alkali) is an ion or molecule accepting H+. OH⁻ is a strong base, reacting rapidly with H+ to form water. HCO₃⁻ is a typical weak base.
Body proteins also function as bases due to some amino acids with negative charges readily accepting H+. Hemoglobin in red blood cells is an example.

Strong and Weak Acids and Bases

Most acids and bases involved in acid-base regulation in extracellular fluid are weak.
Carbonic acid (H₂CO₃) and bicarbonate (HCO₃⁻) are crucial examples.

pH of Body Fluids

The hydrogen ion (H+) concentration in body fluids is extremely low.
In arterial blood, H⁺ concentration is 40 × 10⁻⁹ equivalents/liter, significantly lower than sodium (Na⁺) concentration.
pH is a logarithmic scale used for expressing H⁺ concentration. pH = -log₁₀[H⁺]
pH in arterial blood is ~7.4.
Equal changes in pH do not reflect equal changes in H⁺ concentration, especially in the acidic range (pH < 7.4).

pH of Body Fluids: Cautionary Points

A reversal in mental understanding is critical. Increased H⁺ concentration decreases pH values. Decreasing H⁺ concentration increases the pH.
The relationship between H⁺ concentration and pH is logarithmic, not linear.
Small changes in pH can reflect big changes in H⁺ concentration. The range 7.0-7.6 (0.2 pH units) reflects a smaller change in H⁺ concentration compared to a 0.2 pH unit change in the alkaline range.

pH of Body Fluids: Normal Range

The normal range of arterial pH is 7.35-7.45.
Values outside 6.8–8.0 are life-threatening.

Intracellular pH

Intracellular pH is approximately 7.2, slightly lower than extracellular fluid (ECF) pH.
Transporters in cell membranes regulate intracellular pH, particularly by action of sodium/hydrogen exchangers (Na⁺/H⁺).

Acid Production in the Body

Arterial pH is slightly alkaline despite substantial daily acid production due to metabolic processes producing volatile (CO₂) and nonvolatile acids.
CO₂ is the end product of aerobic cellular metabolism and forms carbonic acid (H₂CO₃) when it interacts with body water.
H₂CO₃ dissociates to form H⁺ and HCO₃⁻ (also called bicarbonate), which must be buffered. The lungs exhale the CO₂ in the body, preventing accumulation of acid.
Other fixed acids, such as sulfuric acid, phosphoric acid and various organic acids, arise from protein and phospholipid metabolism and are excreted by the kidneys.

Regulation of Acid-Base Balance (Buffer systems, respiratory and renal)

Three primary physiological systems control H⁺ concentration. These systems are:
- Buffer systems (rapid response)
- Respiratory system (moderate response)
- Renal system (slowest response, but most powerful)

Fluid Buffers

A buffer solution resists changes in pH. It does this by combining with added acid or base compounds, keeping pH fairly stable.
A buffer is a mixture of a weak acid and its conjugate base (or a weak base and its conjugate acid).
Strong acids (e.g., HCl) yield large changes in pH in the absence of buffering, while weak acids (e.g., H₂CO₃) yield smaller changes partly because of their buffering action.
The concentration of H⁺ is adjusted to maintain homeostasis in body fluids.

Extracellular Fluid Buffers

The major extracellular fluid (ECF) buffers are bicarbonate (HCO₃⁻) and phosphate (H₂PO₄⁻/HPO₄²⁻).
- Bicarbonate is a crucial buffer: elevated concentration and regulated volatile nature of CO₂ as acid form enhances its buffering power.
- Phosphate acts as a significant buffer specifically within the kidney tubules
Plasma proteins are also important ECF buffers: they can bind H⁺ and Ca²⁺, impacting blood Ca²⁺ levels under acid/base disorders.

Intracellular Fluid Buffers

There are substantial organic phosphate buffers within the ICF, including ATP(adenosine triphosphate), ADP (adenosine diphosphate), AMP (adenosine monophosphate), and other phosphate-containing compounds such as 2,3-diphosphoglycerate (2,3-DPG).

Renal Mechanisms in Acid-Base Balance

The kidneys control acid/base by either excreting acidic or basic urine.
They play two fundamental roles: removing fixed H⁺ and regulating reabsorption or excretion of bicarbonate (HCO₃⁻).
Secretion of H⁺ and reabsorption of HCO₃⁻ are major renal functions during acid–base regulation.
The kidneys are crucial in regulating acid-base balance when dealing with nonvolatile and/or fixed acids.

Acid-Base Disorders

Acidemia: excess H⁺ in the blood; caused by acidosis (excess H+ levels affecting bodily functions).
Alkalemia: deficiency of H⁺ / excess HCO₃⁻ in blood. Results from alkalosis (low H⁺ levels affecting bodily functions).
Metabolic disorders involve HCO₃⁻ imbalances.
Respiratory disorders include CO₂ imbalances affecting pH.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

This quiz delves into the mechanisms of renal compensation and the role of carbon dioxide in acid-base balance within the human body. Questions cover key concepts regarding the production rates of volatile acids and the physiological processes that help maintain blood pH. Test your knowledge on these crucial physiological functions and their importance in homeostasis.