Acid-base Balance1

Question 1

What acids are produced by metabolic processes?

Answer 1

1. Carbonic acid
2. Sulfuric acid

Question 2

How are the produced acids transported to the kidneys and lungs

Answer 2

1. through the extracellular fluid
2. by the blood

Question 3

How is excess base excreted from the body?

Answer 3

In feces

Question 4

Why must excess acid be neutralized or excreted

Answer 4

To maintain the near normal pH of the blood

Question 5

Define a buffer

Answer 5

A buffer is a combination of a weak acid or weak base and its salt that resists changes in pH.

Question 6

Describe the different physiological buffer systems in mammals

Answer 6

1. Bicarbonate/Carbonic Acid Buffer System: This system involves the reversible reaction between carbonic acid (H2​CO3​) and bicarbonate ions (HCO3−​). It helps regulate blood pH by adjusting the concentration of bicarbonate ions in response to changes in acidity.
2. Phosphate Buffer System: Phosphates (HPO42−​
   and H2​PO4−​) act as buffers in both intracellular and extracellular fluids. They play a role in maintaining pH stability.
3. Plasma Protein and Hemoglobin Buffer System: Proteins, especially hemoglobin, can bind to hydrogen ions (H+) and act as buffers. Hemoglobin, found in red blood cells, helps transport carbon dioxide and maintains blood pH.

Question 7

How does the bicarbonate/carbonic acid buffer system function

Answer 7

In this system, carbon dioxide (CO2​) from tissues combines with water (H2​O) to form carbonic acid (H2​CO3​). Carbonic acid then dissociates into bicarbonate ions (HCO3−​) and hydrogen ions (H+). When blood becomes too acidic (due to an increase in H+ ions), the reaction shifts to the left, producing more carbonic acid. Conversely, when blood becomes too alkaline, the reaction shifts to the right, releasing H+ ions.

Question 8

What role do phosphate buffers play in maintaining pH balance?

Answer 8

Phosphate buffers consist of dihydrogen phosphate ions (H2​PO4−​) and monohydrogen phosphate ions (HPO42−​). They help regulate pH in intracellular fluids, such as within cells. When excess H+ ions are present, the system shifts toward the formation of H2​PO4−​, thus buffering the acidity.

Question 9

Explain how plasma proteins and hemoglobin act as buffers

Answer 9

Plasma proteins (such as albumin) and hemoglobin (in red blood cells) can bind to H+ ions. Hemoglobin, specifically, has histidine residues that can accept or release H+ ions. By binding or releasing H+ ions, these proteins help maintain blood pH within a narrow range.

Question 10

Discuss respiratory compensation and its relation to acid-base balance

Answer 10

Respiratory compensation involves adjusting the rate of breathing to regulate blood pH. When blood becomes acidic (due to increased H+ ions), the respiratory system increases ventilation (breathing rate) to expel excess carbon dioxide (which forms carbonic acid). This reduces the H+ concentration. Conversely, when blood becomes too alkaline, ventilation decreases to retain more carbon dioxide.

Question 11

How do the lungs regulate carbon dioxide levels in response to changes in pH?

Answer 11

The lungs control blood pH indirectly by regulating carbon dioxide (CO2​) levels. When blood is too acidic, the lungs increase ventilation, allowing more CO2​
to be exhaled. This reduces carbonic acid formation. Conversely, when blood is too alkaline, ventilation decreases, retaining more CO2​ and increasing carbonic acid.

Question 12

Describe how the kidneys contribute to acid-base homeostasis

Answer 12

The kidneys play a crucial role in maintaining acid-base balance. They can:

1. Reabsorb or excrete bicarbonate ions (HCO3−​) based on blood pH.
2. Excrete excess H+ ions in urine.
3. Regulate the production of new bicarbonate ions.
4. Synthesize ammonia (NH3​) to buffer excess H+
   ions.

Question 13

What is the normal concentration range of H+ in the extracellular body fluid

Answer 13

7.34 - 7.44

Question 14

How does the bicarbonate buffer system regulate pH levels in the body?

Answer 14

The bicarbonate buffer system involves the reversible reaction: H2CO3 =HCO3^- + H+

~When blood becomes too acidic (increased H+ ions), the reaction shifts to the left, producing more carbonic acid (H2CO3).
~ Conversely, when blood becomes too alkaline, the reaction shifts to the right, releasing H+ ions.

Question 15

What happens when a strong acid is added to a solution containing bicarbonate (HCO3-) and carbonic acid (H2CO3)?

Answer 15

When a strong acid is added, H+ ions react with bicarbonate (HCO3-) to form carbonic acid (H2CO3) and subsequently CO2 and H2O.

Question 16

Explain how CO2 disposal or retention by the lungs affects blood pH levels

Answer 16

The effectiveness of the bicarbonate buffer system relies on the fact that the lungs can readily dispose of or retain CO2. By adjusting ventilation, the lungs regulate blood pH by controlling the concentration of carbonic acid (H2CO3) and bicarbonate ions (HCO3^-)

Question 17

What does the effectiveness of bicarbonate buffer based upon

Answer 17

Is based on the fact that the lungs can readily dispose of or retain CO2

Question 18

What are the three reasons why Bicarbonate-carbonic buffer system is important

Answer 18

1. H2CO3 dissociates into CO2 and H2O, allowing CO2 to be eliminated by the lungs and H+ as water
2. Changes in CO2 modify the ventikation (respiratory) rate
3. HCO3^- concentration can be altered by the lungs

Question 19

What percentage of the non-bicarbonate buffer value of plasma is accounted for by the phosphate buffer system?

Answer 19

The phosphate buffer system contributes about 5% of the non-bicarbonate buffer value of plasma.

Question 20

How does the phosphate buffer system contribute to the non-bicarbonate buffer value of erythrocytes?

Answer 20

It accounts for approximately 16% of the non-bicarbonate buffer value in erythrocytes.

Question 21

Write down the chemical reaction that shows how the phosphate buffer reacts with acids.

Answer 21

H3PO4⇌H+ + H2PO^-4

Question 22

Write down the chemical reaction that shows how the phosphate buffer reacts with bases

Answer 22

H2PO4- ⇌ H+ + HPO4^2-

Question 23

Explain how a buffer system works, using the phosphate buffer as an example

Answer 23

A buffer system maintains a stable pH by resisting changes when acids or bases are added. In the phosphate buffer system, H₂PO₄⁻ and HPO₄²⁻ ions act as conjugate acid-base pairs, helping to neutralize excess H⁺ or OH⁻ ions

Question 24

Why is it important for buffers to be present in biological systems like blood plasma and erythrocytes?

Answer 24

Buffers prevent drastic pH changes, which are essential for maintaining proper enzyme function and overall cellular homeostasis.

Question 25

Calculate what happens to pH when there is an increase in H⁺ concentration within this buffering system.

Answer 25

An increase in H⁺ concentration leads to a decrease in pH (more acidic).

Question 26

Discuss how changes in respiratory or renal function can affect this buffering system

Answer 26

Respiratory changes (e.g., altered CO₂ levels) impact the bicarbonate buffer, while renal changes (e.g., altered excretion of H⁺ or HCO₃⁻) affect the phosphate buffer system.

Question 27

Write the reaction chain of phosphate buffer reacting with acid and base

Answer 27

H3PO4⇌ H⁺ + H2PO4⁻ ⇌ H⁺ + HPO42- + H⁺ + PO4^3-

Question 28

What percentage do proteins contribute to the non-bicarbonate buffer value of plasma?

Answer 28

Proteins contribute more than 90% to the non-bicarbonate buffer value of plasma.

Question 29

Which protein accounts for the greatest portion of this value

Answer 29

Albumin accounts for the greatest portion

Question 30

How many imidazole groups are present in each albumin molecule

Answer 30

There are 16 imidazole groups present in each albumin molecule

Question 31

What role do these imidazole groups play in the buffer system?

Answer 31

Imidazole groups are responsible for the buffering properties of proteins

Question 32

Which component is responsible for most of the non-bicarbonate buffering capacity in erythrocytes

Answer 32

Hemoglobin is responsible for most of the non-bicarbonate buffering capacity in erythrocyte

Question 33

How does the respiratory system contribute to the bicarbonate buffer system?

Answer 33

The respiratory system plays a crucial role in the bicarbonate buffer system by facilitating the exchange of carbon dioxide (CO₂). CO₂ produced during cellular metabolism diffuses into the bloodstream, combines with water (H₂O) to form carbonic acid (H₂CO₃), which then dissociates into bicarbonate ions (HCO₃⁻) and hydrogen ions (H⁺). During exhalation, CO₂ is removed from the body, helping regulate blood pH.

Question 34

What is the significance of hemoglobin in blood pH regulation

Answer 34

Hemoglobin acts as a buffer by binding and releasing hydrogen ions (H⁺). It helps maintain blood pH by adjusting its affinity for H⁺ based on oxygen (O₂) levels. In the lungs, hemoglobin binds O₂, and in the tissues, it releases O₂ and binds CO₂, contributing to pH balance.

Question 35

Describe the chemical reactions involved in the bicarbonate buffer system

Answer 35

CO₂ + H₂O ⇌ H₂CO₃ ⇌ H⁺ + HCO₃⁻:
Carbon dioxide combines with water to form carbonic acid, which dissociates into bicarbonate ions and hydrogen ions. This reversible reaction helps regulate pH.

Question 36

Explain gas exchange in the human body

Answer 36

1. Lungs:
   Oxygenated blood (bright red) enters the lungs.
   Hemoglobin (Hb) in red blood cells binds O₂ to form oxyhemoglobin (O₂Hb arterial).
2. Venous/Arterial System:
   Deoxygenated blood (dark red) carries CO₂ from tissues to the lungs.
   CO₂ combines with water (H₂O) to form carbonic acid (H₂CO₃).
   Carbonic acid dissociates into bicarbonate ions (HCO₃⁻) and hydrogen ions (H⁺).
3. Peripheral Tissues:
   In tissues, O₂ is released from O₂Hb.
   Metabolism produces CO₂.
   CO₂ combines with water to form H₂CO₃.
4. Transport:
   Bicarbonate (HCO₃⁻) is transported back to the lungs.
   In the lungs, HCO₃⁻ is converted back to CO₂ and exhaled.
5. Role of Hemoglobin:
   Hemoglobin acts as a buffer, binding and releasing H⁺ ions.
   It helps regulate blood pH during gas exchange.