Physiologic pH and buffers - acid-base physiology

Summary

This script explains the concept of physiologic pH, which is crucial for maintaining the optimal functioning of cells and enzymes. It details how the body uses logarithmic pH to manage hydrogen ion concentrations, with a balanced pH of around 7.4 being essential. The video discusses the role of buffers, such as the bicarbonate system, phosphate buffers, and plasma proteins, in stabilizing pH levels against fluctuations caused by acids and bases. It also touches on the importance of intracellular buffers like hemoglobin and organic phosphates in maintaining cellular pH balance.

Takeaways

• 🔍 Physiologic pH is a measure of the balance between acids and bases in the body, determined by the concentration of hydrogen ions.
• ⚗️ The pH scale is logarithmic, with a pH of 7.4 representing an optimal hydrogen ion concentration of 40 nanoequivalents per liter.
• 📉 As hydrogen ion concentration increases, pH decreases due to the negative sign in the pH formula.
• 🔄 The relationship between pH and hydrogen ion concentration is not linear, with changes in pH reflecting exponential changes in ion concentration.
• 🌡️ The body maintains a narrow pH range between 7.37 and 7.42, which is crucial for cellular function.
• 🛡️ Buffers act as protective mechanisms to prevent rapid changes in pH, using a weak acid and its conjugate base or a weak base and its conjugate acid.
• 💧 The bicarbonate buffering system, involving carbonic acid (H2CO3) and bicarbonate ions (HCO3-), is the most important in the body.
• 🌬️ Excess carbon dioxide can be eliminated through the lungs, helping to regulate the bicarbonate buffer system.
• 🧬 Proteins, such as hemoglobin in red blood cells, serve as intracellular buffers, binding or releasing hydrogen ions based on the pH environment.
• 🧪 The phosphate buffer system involves dihydrogen phosphate (H2PO4-) and monohydrogen phosphate (HPO4^2-), contributing to pH balance.
• 🏗️ Organic phosphates like ATP and glucose 6-phosphate also act as intracellular buffers, managing excess hydrogen ions within cells.

Q & A

What is the definition of physiologic pH?

Physiologic pH is a measure of the balance between acids and bases in the body, defined by the concentration of hydrogen ions and expressed with the equation pH = -log base 10 of the hydrogen ion concentration.

What is the optimal hydrogen ion concentration for cells and enzymes in our tissues and organs?

The optimal hydrogen ion concentration for cells and enzymes is 40 times 10 to the minus 9 equivalents per liter, or 40 nanoequivalents per liter.

Why is it important to express the hydrogen ion concentration as pH rather than using the actual concentration?

Expressing the hydrogen ion concentration as pH is important because the actual concentrations are very small and difficult to work with. The pH scale is a logarithmic function that simplifies these tiny numbers into a more manageable scale.

How does the pH scale relate to the concentration of hydrogen ions?

The pH scale is a logarithmic inverse relationship to the hydrogen ion concentration. As hydrogen ion concentrations increase, the pH decreases, and vice versa, due to the negative sign in the pH equation.

What is the normal pH range for the human body?

The normal pH range for the human body is between 7.37 and 7.42.

What happens when the body's pH drops below 7.4?

When the body's pH drops below 7.4, it is considered acidemia, indicating a more acidic state.

What is the role of buffers in maintaining the body's pH?

Buffers act like a protective cushion or shield to prevent the pH from rising or falling too quickly. They handle excess hydrogen ions without causing a major shift in the overall pH.

What is the most important buffer in the body and how does it work?

The most important buffer in the body is the bicarbonate buffer system, consisting of the weak acid carbonic acid (H2CO3) and its conjugate base bicarbonate ion (HCO3-). It works by taking on extra hydrogen ions to form carbonic acid, which can then be converted to carbon dioxide and water, helping to maintain pH balance.

How does the body handle excess carbon dioxide or bicarbonate ions?

Excess carbon dioxide is eliminated through the lungs by breathing, while excess bicarbonate ions are removed by the kidneys in the urine.

What are the other buffering systems in the body besides the bicarbonate buffer system?

Besides the bicarbonate buffer system, the body also has the phosphate buffer system and plasma proteins, which serve as important buffering systems to maintain pH balance.

How do intracellular buffers, such as hemoglobin, help maintain the pH inside cells?

Intracellular buffers like hemoglobin can reversibly bind to hydrogen ions or oxygen. When there is a buildup of hydrogen ions, deoxygenated hemoglobin binds to them, preventing the pH from falling too quickly. This process also involves the chloride shift, which helps maintain charge balance.

What is the significance of organic phosphates like ATP in intracellular buffering?

Organic phosphates like ATP are significant intracellular buffers because their phosphate groups can serve as a source or sink for excess hydrogen ions, helping to maintain the pH balance inside cells.