The human body is a complex and dynamic system that requires a stable internal environment to function optimally. One of the critical aspects of this stability is the maintenance of pH balance, which is essential for various biochemical processes. Physiological buffers play a crucial role in maintaining this balance, ensuring that the body’s pH remains within a narrow range despite the constant production of acids and bases.
The normal hydrogen ion concentration of body fluids is about 40 nmol/liter (pH 7.4); during the course of one day, some 60 mmol/liter of hydrogen ion is added to it, which, if not buffered, would raise the concentration of the extracellular fluid (12 liters, say) to 5 mmol/liter.
This would change the hydrogen-ion concentration by over 10,000 times (to a pH of 2.3) if not buffered in any way.
This does not happen because most of these extra hydrogen ions are taken up by the various physiological buffers found in body fluids.
Ultimately, of course, these excess hydrogen ions and associated bases need to be excreted by the kidneys (making it acid), but initially, they combine with buffers to minimize the change in pH.
This article delves into the concept of physiological buffers, their types, mechanisms, and their importance in human health.
Table of Contents
Understanding pH and Homeostasis
What is pH?
pH is a measure of the acidity or alkalinity of a solution, ranging from 0 to 14. A pH of 7 is considered neutral, below 7 is acidic, and above 7 is alkaline. The human body maintains a slightly alkaline pH of around 7.4 in the blood and extracellular fluid, which is crucial for the proper functioning of enzymes, proteins, and other cellular processes.
The Concept of Homeostasis
Homeostasis refers to the body’s ability to maintain a stable internal environment despite external changes. This stability is vital for the optimal functioning of cells, tissues, and organs. pH homeostasis, in particular, is critical because even slight deviations from the normal pH range can disrupt cellular functions and lead to severe health consequences.
What are Physiological Buffers?
Physiological buffers are substances that help maintain the pH of body fluids within a narrow range by neutralizing excess acids or bases. They do this by either releasing or absorbing hydrogen ions (H⁺) to counteract changes in pH. Buffers are essential because the body continuously produces acids and bases through metabolic processes, which can alter the pH if not regulated.
Importance of Buffers in the Body
Buffers are crucial for:
- Enzyme Activity: Enzymes, which catalyze biochemical reactions, are highly sensitive to pH changes. Buffers ensure that enzymes function optimally by maintaining the appropriate pH.
- Protein Structure: The structure and function of proteins, including hormones and antibodies, are pH-dependent. Buffers help preserve protein integrity.
- Cellular Function: Proper pH is essential for cellular processes such as nutrient transport, signal transduction, and energy production.
- Oxygen Transport: The affinity of hemoglobin for oxygen is pH-dependent. Buffers ensure efficient oxygen delivery to tissues.
Types of Physiological Buffers
The human body employs several buffer systems to maintain pH balance. These include the bicarbonate buffer system, phosphate buffer system, and protein buffer system. Each system operates in different parts of the body and has unique mechanisms for regulating pH.
1. Mammalian body fluids
Fluids contains much-dissolved CO2 for they are in equilibrium with alveolar gas which contains 5% CO2 rather than with air which contains practically none. As a buffer, it, therefore, behaves as
H+ + Buffer (HCO3–) ⇔ H-buffer (H2CO3) ⇔ dissolved CO2
The acceptor of hydrogen ions in the buffer base (HCO–) ) as usual: the 3 donor is the weak acid (H2CO3) which is in equilibrium with the dissolved CO2: as the amount of CO2 dissolved far exceeds the amount of carbonic acid present and the dissolved CO2 can be considered as the proton donor.
The equation then becomes
H+ + HCO3– ⇔ dissolved CO2
Proton acceptor Proton donor
(25 m mol/1) (1.34m mol/1)
From the concentrations given, the pH is 7.4. i.e., that of the body.
2. Bicarbonate Buffer System
The bicarbonate buffer system is the primary buffer system in the extracellular fluid, including blood plasma. It consists of carbonic acid (H₂CO₃) and bicarbonate ions (HCO₃⁻).
Mechanism
The bicarbonate buffer system operates through the following reversible reaction:
CO2 + H2O ↔ H2CO3 ↔ H++ HCO3−
- When pH Decreases (Acidosis): Excess H⁺ ions combine with HCO₃⁻ to form H₂CO₃, which then dissociates into CO₂ and H₂O. The CO₂ is exhaled by the lungs, reducing acidity.
- When pH Increases (Alkalosis): The reaction shifts to the left, with H₂CO₃ dissociating to release H⁺ ions, which combine with OH⁻ to form water, reducing alkalinity.
Regulation
The bicarbonate buffer system is tightly regulated by the respiratory and renal systems:
- Respiratory Regulation: The lungs control the levels of CO₂, which directly affects the concentration of H₂CO₃.
- Renal Regulation: The kidneys regulate the reabsorption and excretion of HCO₃⁻, adjusting the body’s buffer capacity.
3. Phosphate Buffer System
The phosphate buffer system is primarily active in the intracellular fluid and the renal tubules. It consists of dihydrogen phosphate (H₂PO₄⁻) and monohydrogen phosphate (HPO₄²⁻).
Mechanism
The phosphate buffer system operates through the following reaction:
H2PO4− ↔ H++ HPO42−
- When pH Decreases (Acidosis): H⁺ ions combine with HPO₄²⁻ to form H₂PO₄⁻, reducing acidity.
- When pH Increases (Alkalosis): H₂PO₄⁻ releases H⁺ ions, which combine with OH⁻ to form water, reducing alkalinity.
Importance in the Kidneys
The phosphate buffer system is particularly important in the kidneys, where it helps maintain pH balance by excreting excess H⁺ ions in the urine. This system is crucial for long-term pH regulation.
4. Protein Buffer System
Proteins, particularly hemoglobin in red blood cells and intracellular proteins, act as buffers due to their ability to bind and release H⁺ ions.
Mechanism
Proteins contain amino acids with side chains that can act as weak acids or bases. For example:
- Histidine Residues: The imidazole group of histidine can bind or release H⁺ ions, making it an effective buffer.
- Hemoglobin: Hemoglobin can bind H⁺ ions, which helps stabilize blood pH during the transport of CO₂ from tissues to the lungs.
Role in Intracellular Buffering
Intracellular proteins play a significant role in buffering pH within cells, where metabolic processes generate acids and bases. Proteins help maintain the pH of the cytoplasm, ensuring proper cellular function.
Acid-Base Disorders
Despite the efficiency of physiological buffers, acid-base disorders can occur when the body’s pH regulation mechanisms are overwhelmed or impaired. These disorders are classified as acidosis (pH < 7.35) or alkalosis (pH > 7.45) and can be further categorized based on their cause.
1. Respiratory Acidosis
Causes
Respiratory acidosis occurs when the lungs cannot remove enough CO₂, leading to an accumulation of H₂CO₃ and a decrease in pH. Common causes include:
- Chronic obstructive pulmonary disease (COPD)
- Asthma
- Respiratory depression due to drug overdose
Symptoms
- Shortness of breath
- Confusion
- Fatigue
- Headaches
Treatment
Treatment focuses on improving ventilation, often through mechanical ventilation or medications that open the airways.
2. Respiratory Alkalosis
Causes
Respiratory alkalosis results from excessive removal of CO₂, leading to a decrease in H₂CO₃ and an increase in pH. Common causes include:
- Hyperventilation due to anxiety or panic attacks
- High altitude
- Fever
Symptoms
- Lightheadedness
- Numbness or tingling in extremities
- Muscle spasms
Treatment
Treatment involves addressing the underlying cause, such as calming the patient during a panic attack or providing oxygen at high altitudes.
3. Metabolic Acidosis
Causes
Metabolic acidosis occurs when there is an excess of acids or a loss of bicarbonate, leading to a decrease in pH. Common causes include:
- Diabetic ketoacidosis
- Lactic acidosis
- Renal failure
Symptoms
- Rapid breathing
- Confusion
- Fatigue
- Nausea
Treatment
Treatment involves correcting the underlying cause, such as administering insulin for diabetic ketoacidosis or dialysis for renal failure.
4. Metabolic Alkalosis
Causes
Metabolic alkalosis results from an excess of bicarbonate or a loss of acids, leading to an increase in pH. Common causes include:
- Prolonged vomiting
- Excessive use of antacids
- Diuretic use
Symptoms
- Muscle twitching
- Nausea
- Confusion
- Hand tremors
Treatment
Treatment focuses on correcting the underlying cause, such as rehydrating the patient after vomiting or adjusting medication use.
The Role of the Kidneys in pH Regulation
The kidneys play a crucial role in long-term pH regulation by excreting excess acids or bases and reabsorbing bicarbonate. This process involves several mechanisms:
- Reabsorption of Bicarbonate: The kidneys filter bicarbonate from the blood, but most of it is reabsorbed in the proximal tubule to maintain the body’s buffer capacity.
- Excretion of Hydrogen Ions: The kidneys excrete excess H⁺ ions in the urine, which helps reduce acidity. This process is facilitated by the secretion of H⁺ ions into the renal tubules.
- Production of Ammonium Ions: The kidneys produce ammonium ions (NH₄⁺) from glutamine, which can be excreted in the urine, further aiding in the removal of excess acids.
The Role of the Lungs in pH Regulation
The lungs regulate pH by controlling the levels of CO₂ in the blood. This is achieved through the process of ventilation:
- Increased Ventilation: When the blood becomes too acidic, the respiratory center in the brainstem increases the rate and depth of breathing, leading to the expulsion of more CO₂ and a reduction in H₂CO₃.
- Decreased Ventilation: When the blood becomes too alkaline, the respiratory center decreases the rate and depth of breathing, allowing CO₂ to accumulate and increase H₂CO₃.
These are the basic roles of the lungs in pH regulation.
Conclusion
Physiological buffers are essential for maintaining pH homeostasis in the human body, ensuring that biochemical processes can occur optimally. The bicarbonate, phosphate, and protein buffer systems work together to neutralize excess acids and bases, while the kidneys and lungs provide additional regulation. Understanding these mechanisms is crucial for diagnosing and treating acid-base disorders, which can have severe consequences if left unmanaged. By maintaining a stable internal environment, physiological buffers play a vital role in promoting overall health and well-being.
FAQs: Physiological Buffers in Humans
What are physiological buffers, and why are they important?
Physiological buffers are substances in the body that help maintain a stable pH by neutralizing excess acids or bases. They are crucial because even small changes in pH can disrupt enzyme activity, protein function, and overall cellular processes, leading to health issues.
How does the bicarbonate buffer system work?
The bicarbonate buffer system uses carbonic acid (H₂CO₃) and bicarbonate ions (HCO₃⁻) to regulate pH. When there’s too much acid, bicarbonate binds to H⁺ ions to form carbonic acid, which breaks down into CO₂ and water. The CO₂ is then exhaled by the lungs, reducing acidity.
Can the body function without buffers?
No, without buffers, the body would struggle to maintain its pH balance. Metabolic processes constantly produce acids and bases, and without buffers, these would cause dangerous pH fluctuations, disrupting cellular functions and potentially leading to life-threatening conditions.
What role do the kidneys play in pH regulation?
The kidneys help regulate pH by excreting excess acids or bases in urine and reabsorbing bicarbonate. They also produce ammonium ions to remove excess acids, ensuring long-term pH balance.
How do the lungs help maintain pH balance?
The lungs control pH by regulating CO₂ levels in the blood. When CO₂ levels rise (making blood more acidic), breathing increases to expel CO₂. When CO₂ levels drop (making blood more alkaline), breathing slows to retain CO₂.
What happens if the body’s pH balance is disrupted?
Disruptions in pH balance can lead to acid-base disorders like acidosis (too acidic) or alkalosis (too alkaline). Symptoms may include fatigue, confusion, shortness of breath, and muscle weakness. Severe cases can be life-threatening if not treated promptly.
Can diet affect the body’s pH balance?
Yes, diet can influence pH balance. Foods like fruits and vegetables tend to be alkaline-forming, while processed foods, meat, and dairy can be acid-forming. However, the body’s buffer systems usually compensate for dietary changes, so extreme diets are needed to significantly alter pH.
References
- Hall, J. E. (2020). Guyton and Hall Textbook of Medical Physiology. Elsevier.
- Sherwood, L. (2015). Human Physiology: From Cells to Systems. Cengage Learning.
- Rhoades, R. A., & Bell, D. R. (2012). Medical Physiology: Principles for Clinical Medicine. Lippincott Williams & Wilkins.
- Boron, W. F., & Boulpaep, E. L. (2016). Medical Physiology. Elsevier.
- Levitzky, M. G. (2013). Pulmonary Physiology. McGraw-Hill Education.
