Acid Base Hemostasis

Question 1

For optimal cellular function, the pH of our extracellular fluid (the fluid outside cells) needs to be maintained at around ____, which corresponds to a hydrogen ion concentration ([H+]) of about ____

Answer 1

7.4
40 nmol/L.

Question 2

What are the sources of H ion

Answer 2

Sources of Hydrogen Ions

Anaerobic Metabolism:

Carbohydrate Metabolism: During anaerobic (without oxygen) metabolism of carbohydrates, lactate is produced. This process releases hydrogen ions, contributing to the overall acid load.

Fatty Acid and Amino Acid Metabolism: Similarly, anaerobic metabolism of fatty acids and ketogenic amino acids (amino acids that can be converted into ketone bodies) produces acetoacetate. This substance also releases hydrogen ions.

2, Amino Acid Conversion:

When the liver converts amino nitrogen (from amino acids) into urea, or when sulphydryl groups (components of certain amino acids) are converted to sulphate, hydrogen ions are released. This further adds to the body’s acid load.

Question 3

If the production of hydrogen ions from these processes exceeds the body’s ability to neutralize or eliminate them, conditions such as _____ or ____ can develop. These are serious medical conditions where the blood becomes too acidic.

Answer 3

lactic acidosis or ketoacidosis

Question 4

How does the body Regulate Acid-Base Balance
The body has several mechanisms to manage and neutralize the constant influx of hydrogen ions which are?

Answer 4

Renal Excretion:

The kidneys play a crucial role in maintaining acid-base homeostasis by secreting hydrogen ions into the urine. This process occurs in the renal tubules, where the kidneys filter blood, removing excess hydrogen ions and thus regulating the pH of body fluids.

Respiratory Compensation:

Aerobic metabolism (metabolism in the presence of oxygen) of organic compounds’ carbon skeletons results in the production of carbon dioxide (CO2) and water (H2O). Carbon dioxide is a critical component of the body’s buffering system, which helps to neutralize excess hydrogen ions.
The lungs help to maintain acid-base balance by expelling carbon dioxide. When CO2 is exhaled, it reduces the amount of acid in the blood, helping to keep the pH within the normal range.

Question 5

For the body to maintain normal acid-base homeostasis, both the kidneys and the lungs must function properly. The kidneys’ ability to excrete hydrogen ions and the lungs’ capacity to eliminate carbon dioxide are essential for keeping the pH of body fluids stable. Any impairment in the function of these organs can lead to acid-base imbalances, which can have significant health consequences.

Question 6

What she the Role of Carbon Dioxide and Hydrogen Ions in Metabolism, when are they produced

Answer 6

Carbon Dioxide (CO₂) in Aerobic Metabolism:

CO₂ is a byproduct of aerobic metabolism, the process by which cells generate energy in the presence of oxygen. Most of this CO₂ is expelled from the body through the lungs during exhalation.

However, some CO₂ is converted into bicarbonate (HCO₃⁻), an important extracellular buffer. This conversion helps in neutralizing acids and thus provides a mechanism to mitigate the potential toxicity of CO₂.

Hydrogen Ions (H⁺) in Anaerobic Metabolism:

H⁺ ions are produced during anaerobic metabolism, which occurs when cells generate energy without oxygen. If not controlled, the accumulation of H⁺ ions can lead to acidosis, a condition where the body fluids become too acidic.

Question 7

For the bicarbonate buffer system, the pKa is ____.

Answer 7

6.1

Question 8

Despite this pKa value being lower than the body’s optimal extracellular fluid (ECF) pH of 7.4, the bicarbonate buffer system remains the most crucial buffer in the body. why?

Answer 8

Blood Buffering Capacity: Bicarbonate accounts for more than 60% of the buffering capacity in the blood. This means it plays a significant role in neutralizing excess acids and maintaining pH balance.

Kidney Function: The kidneys use the bicarbonate system to secrete H+. This process involves the reabsorption of bicarbonate and the excretion of hydrogen ions in the urine, helping to regulate blood pH.

Hemoglobin (Hb) Buffering: Hemoglobin, the protein in red blood cells that carries oxygen, also contributes to blood buffering. However, its efficiency relies on the presence of bicarbonate. Hemoglobin provides most of the remaining blood buffering capacity

Question 9

A buffer pair consists of a weak acid and its conjugate base (or a weak base and its conjugate acid). The effectiveness of a buffer pair in maintaining pH is highest when the ratio of the base to the acid is close to 1, which typically occurs when the pH is near the buffer pair’s pKa.

Answer 9

For the bicarbonate buffer system, the pKa is 6.1, but the body maintains the ECF at a pH of about 7.4. Despite this mismatch, the bicarbonate buffer system remains crucial due to its substantial presence and interaction with other buffering systems, such as hemoglobin.

Question 10

Explain howone Buffer Systems interacts with another

Answer 10

The conversion of CO2 to bicarbonate illustrates how one buffering system can support another. When CO2 is converted to HCO3–, it helps neutralize H+ ions. This dual role—expelling CO2 through the lungs and using it to form bicarbonate for buffering—demonstrates the body’s efficient strategy for managing potentially toxic byproducts.

Question 11

The control of carbon dioxide (CO2) levels in the body is primarily managed by the ____. CO2 is a byproduct of metabolism, and its concentration in the blood needs to be regulated to maintain acid-base balance. The pCO2 is maintained at ____

Answer 11

lungs

5.3 kPa (40 mmHg).

Question 12

Explain the Sequence of Events in CO2 Regulation

Answer 12

Oxygen Transport:

Oxygen (O2) is inhaled into the lungs and binds to hemoglobin (Hb) in red blood cells. This oxygen-rich blood is then transported to the tissues.

Cellular Respiration:

In the tissues, cells use the inhaled oxygen for aerobic metabolism, which is the process of generating energy. During this process, some of the carbon from organic compounds is converted into carbon dioxide (CO2).

CO2 Diffusion and Transport:

The newly produced CO2 diffuses from the cells into the extracellular fluid (ECF) and is carried back to the lungs via the bloodstream. This diffusion occurs along a concentration gradient, meaning CO2 moves from areas of higher concentration (inside cells) to areas of lower concentration (the blood).

CO2 Elimination:

Once the CO2-rich blood reaches the lungs, CO2 is expelled from the body during exhalation.

Question 13

Respiratory Control Mechanisms

Answer 13

The rate at which CO2 is eliminated from the body is regulated by chemoreceptors located in the respiratory center of the brainstem (specifically, the medulla oblongata) and in the carotid and aortic bodies:

Chemoreceptors: These receptors are sensitive to changes in the levels of CO2 and hydrogen ions (H+) in the blood and cerebrospinal fluid. An increase in PCO2 or a decrease in pH (indicating higher acidity) triggers these chemoreceptors to increase the rate of respiration.

Medulla Oblongata: This area of the brainstem directly controls the rate and depth of breathing.

Carotid and Aortic Bodies: These are peripheral chemoreceptors located in the carotid arteries and the aorta, which also monitor blood chemistry and send signals to the respiratory center to adjust breathing.

Question 14

The Henderson-Hasselbalch equation is essential for understanding how CO2 affects blood pH:
pH = 6.1 + log
⁡
(
[
HCO3
−
]
0.03
×
PCO2
)
pH=6.1+log(
0.03×PCO2
[HCO3
−
]
​
)

Question 15

The Henderson-Hasselbalch equation is essential for understanding how CO2 affects blood
pH:pH= 6.1+ log([HCO3−]/0.03×PCO2)

Question 16

Respiratory Reserve Capacity

The lungs have a substantial reserve capacity for eliminating CO2, meaning they can handle increases in CO2 production without difficulty. This capacity allows the respiratory system to maintain CO2 levels within tight limits, even during periods of increased metabolic activity or in response to acid-base disturbances.

Question 17

The bicarbonate buffer system is essential for maintaining acid-base homeostasis in the body. It involves intricate interactions between the _____&____ , both of which play crucial roles in generating and regulating bicarbonate (HCO3–), the primary buffer base in this system

Answer 17

kidneys and erythrocytes

Question 18

What’s the Role of Carbonic Anhydrase?

Answer 18

High Concentrations: Carbonic anhydrase is present in high concentrations in both erythrocytes and renal tubular cells. This enzyme accelerates the conversion of CO2 and H2O into carbonic acid, which quickly dissociates into H+ and HCO3–.

Removal of Products: Erythrocytes and renal tubular cells not only have high levels of carbonic anhydrase but also mechanisms to remove H+ ions. This removal drives the reaction towards the production of more bicarbonate (to the right of the equation), enhancing the generation of HCO3–.

Question 19

What are the Conditions Affecting Bicarbonate Production in
Increase CO2
Decrease HCO3
Decrease H+

Answer 19

Increased CO2: When the concentration of CO2 rises, more carbonic acid is formed, which dissociates into more H+ and HCO3–.

Decreased HCO3–: A fall in bicarbonate concentration signals the need for more bicarbonate production.

Decreased H+: When H+ is buffered by erythrocytes or excreted by the kidneys, the reaction is driven towards producing more bicarbonate.

Question 20

Regulation and Homeostasis

Intracellular Adjustments: Increases in intracellular PCO2 or decreases in intracellular [HCO3–] within erythrocytes and renal tubular cells prompt the production of more bicarbonate. This process helps maintain extracellular [HCO3–] levels and minimizes fluctuations in the [HCO3–] to PCO2 ratio, thus stabilizing pH.

Question 21

Regulation and Homeostasis

Normal Conditions: Under normal physiological conditions, at a plasma PCO2 of 5.3 kPa (approximately 1.2 mmol/L CO2), erythrocytes and renal tubular cells maintain extracellular bicarbonate levels at around 25 mmol/L. This results in an extracellular [HCO3–] to [CO2] ratio of just over 20:1, which corresponds to a pH close to 7.4, as calculated using the Henderson-Hasselbalch equation

Question 22

Regulation and Homeostasis

Normal Conditions: Under normal physiological conditions, at a plasma PCO2 of 5.3 kPa (approximately 1.2 mmol/L CO2), erythrocytes and renal tubular cells maintain extracellular bicarbonate levels at around 25 mmol/L. This results in an extracellular [HCO3–] to [CO2] ratio of just over 20:1, which corresponds to a pH close to 7.4, as calculated using the Henderson-Hasselbalch equation

Question 23

Regulation and Homeostasis

Normal Conditions: Under normal physiological conditions, at a plasma PCO2 of 5.3 kPa (approximately 1.2 mmol/L CO2), erythrocytes and renal tubular cells maintain extracellular bicarbonate levels at around 25 mmol/L. This results in an extracellular [HCO3–] to [CO2] ratio of just over 20:1, which corresponds to a pH close to 7.4, as calculated using the Henderson-Hasselbalch equation

Question 24

By maintaining the [HCO3–] to [CO2] ratio near 20:1, the body ensures a pH close to 7.4. If intracellular PCO2 increases or intracellular [HCO3–] decreases, bicarbonate production accelerates to restore this balance, thus minimizing pH changes.

Question 25

By maintaining the [HCO3–] to [CO2] ratio near 20:1, the body ensures a pH close to 7.4. If intracellular PCO2 increases or intracellular [HCO3–] decreases, bicarbonate production accelerates to restore this balance, thus minimizing pH changes.

Question 26

Hemoglobin is an essential blood buffer, but it operates effectively only in cooperation with the bicarbonate system.

Question 27

Buffering and the Chloride Shift
From CO2 + H2O……

Answer 27

Buffering by Hemoglobin: Much of the H+ produced in the dissociation of carbonic acid is buffered by hemoglobin. Hemoglobin binds these hydrogen ions, preventing significant changes in blood pH.

Bicarbonate Diffusion: The bicarbonate ions (HCO3–) produced in the reaction diffuse out of the erythrocytes into the extracellular fluid (ECF) along a concentration gradient.

Chloride Shift: To maintain electrochemical neutrality, chloride ions (Cl–) move into the erythrocytes in the opposite direction of bicarbonate diffusion. This movement of ions is known as the chloride shift.

Question 28

The production of bicarbonate by erythrocytes is stimulated by higher PCO2 levels in the blood leaving the tissues. As a result, the ratio of bicarbonate to CO2 and, consequently, the pH, remain relatively constant between arterial and venous blood.

Question 29

What are the Other Buffer systems?

Answer 29

While hemoglobin and bicarbonate are the primary buffers in the blood, there are other, less significant buffers:

Phosphate Buffer: Although its plasma concentration is about 1 mmol/L, phosphate plays a more substantial role in buffering within bone and intracellularly, where its concentration is higher.

Protein Buffer: Proteins have some buffering capacity, but due to their low concentrations in plasma, their contribution to blood buffering is minimal.

Question 30

The kidneys play a critical role in maintaining acid-base balance in the body, primarily through the actions of ______ This enzyme is central to the mechanisms involved in hydrogen ion (H+) secretion and in sustaining the bicarbonate (HCO3–) buffering capacity of the blood.

Answer 30

carbonate dehydratase (CD), also known as carbonic anhydrase.

Question 31

Hemoglobin Buffering in Erythrocytes
Hemoglobin (Hb):
Role: Hemoglobin in red blood cells acts as a buffer by binding to hydrogen ions (H+), which helps to prevent significant changes in blood pH.
Saturation: Hemoglobin has a limited capacity to bind H+. Once all the binding sites on hemoglobin are occupied by H+ ions, it becomes saturated. At this point, hemoglobin can no longer effectively buffer additional H+.
Urinary Buffers in the Kidneys
Urinary Buffers:
Role: The kidneys help maintain acid-base balance by secreting H+ ions into the urine. These H+ ions need to be buffered (neutralized) to be effectively excreted from the body.
Replenishment: Unlike hemoglobin in the blood, the buffers in the urine are continuously replenished. This happens because the kidneys constantly filter the blood, producing new urine that contains fresh buffer molecules.

Answer 31

Why This Matters

Saturation vs. Replenishment:

Hemoglobin Saturation: Once hemoglobin in red blood cells is saturated with H+, it can’t bind more H+. This limits its buffering capacity.

Urinary Buffer Replenishment: The continuous filtration process in the kidneys ensures that there is always a fresh supply of buffer molecules in the urine. This means the urine can continually neutralize and excrete H+, without the limitations that hemoglobin faces.

Question 32

What’s the Mechanisms of Bicarbonate Control in the kidney

Answer 32

The kidneys regulate the bicarbonate concentration in the extracellular fluid (ECF) through two main mechanisms:

1. Bicarbonate Reclamation (Reabsorption)

Steady State Maintenance: This is the predominant mechanism for maintaining a steady state of bicarbonate in the blood.

Process: The CO2 driving the CD mechanism in renal tubular cells is derived from filtered bicarbonate (HCO3–). This process involves no net loss of H+.

Bicarbonate Generation

Correction of Acidosis: This mechanism is crucial for correcting acidosis (a condition where the blood is too acidic).

Influencing Factors: The levels of CO2 or HCO3– in the extracellular fluid influence the CD reaction in renal tubular cells.

Net Loss of H+: Unlike bicarbonate reclamation, this process involves a net loss of H+, which is essential for reducing acidity in the body.