CB (027) Acid base balance

Acid-Base Balance Lecture Overview

Aims:

• This lecture aims to thoroughly explain the mechanisms by which the body maintains pH levels in blood through the coordinated actions of the kidneys, lungs, and liver. Maintaining pH within narrow limits is vital for various physiological processes, enzyme function, and overall homeostasis, ensuring optimal functioning of bodily systems.

Objectives:

At the end of this lecture, you should be able to:

• Define acids and bases in the context of chemistry and physiology, understanding their roles in biological systems.

• Distinguish between volatile acids (which can change states easily and are excreted as gases) and fixed acids (which do not change states easily and are eliminated through metabolic pathways).

• Define a buffer and explain its role in maintaining pH stability by neutralizing acids and bases.

• Define acidosis (a condition where blood pH falls below the normal range of 7.35) and alkalosis (where blood pH rises above the normal range of 7.45).

• Utilize the Henderson-Hasselbalch equation to explain the effectiveness of the carbonic acid-bicarbonate buffer system, which is essential for regulating blood pH levels.

• Use the Davenport diagram to describe the four main types of acid-base disturbances, helping to visualize changes in pH, bicarbonate, and carbon dioxide levels in various conditions.

• Provide specific examples of causes for acid-base disturbances, including metabolic and respiratory conditions, and their implications for patient care.

Henderson-Hasselbalch Relationship

Key Relationships:

• The equation highlights the conversion between carbon dioxide (CO2), water (H2O), carbonic acid (H2CO3), hydrogen ions (H+), and bicarbonate ions (HCO3 -).

  CO2 + H2O ⇌ H2CO3 ⇌ H+ + HCO3 -

• pH is directly related to bicarbonate concentration (HCO3 -): Higher bicarbonate levels correspond to higher pH values.

• pH is inversely related to the partial pressure of carbon dioxide (PaCO2): This reflects the importance of CO2 removal in regulating acidity.

The formula is:

• pH ≈ HCO3 - / PaCO2

• Also represented as:pH = pK + log ([HCO3 -] / [CO2])

• Normal Value: The ratio of bicarbonate ions to PaCO2 is crucial for maintaining normal pH levels, typically in the range of 7.35 to 7.45.

Compensation Mechanisms

Disturbances:

• The lungs play a vital role in regulating H+ disturbances that have metabolic origins by altering ventilation rates to increase or decrease CO2 excretion.

• The kidneys are responsible for regulating H+ disturbances that stem from respiratory factors by excreting or retaining bicarbonate and hydrogen ions.

Classification Table:

• It is essential to indicate whether conditions are classified as respiratory or metabolic acidosis or alkalosis. This classification is based on provided values for pH, PaCO2, and HCO3 - to determine the underlying cause.

Problem Identification Table**

• Complete the table regarding:

  • Renal failure leading to an inability to produce HCO3 - or excrete H+ efficiently, resulting in acidosis.

  • Conditions causing loss of hydrochloric acid (HCl) due to vomiting, resulting in metabolic alkalosis.

  • Conditions causing loss of bicarbonate (HCO3 -) due to diarrhea, resulting in metabolic acidosis.

Acid Characteristics**

Identification Task:

Strike out the incorrect terms in the following statements:

• Sulphuric acid and phosphoric acid are (strong/weak) acids produced from metabolic processes that are (volatile/non-volatile) and excreted by the (lungs/kidneys). Answer: Strong, Non-volatile, Kidneys.

• Carbonic acid (H2CO3) is produced from CO2 by cells and is a (volatile/non-volatile) acid eliminated by the (lungs/kidneys). Answer: Volatile,