Water and electrolyte balance

Learning outcome 1.Describe the general functions and importance of water and electrolytes in the body

Water and electrolytes are essential components of the human body that perform various important functions.

• Water: Water is the most abundant substance in the body and is involved in many vital processes, including:
  • Regulating body temperature
  • Lubricating joints
  • Transporting nutrients and waste products
  • Maintaining blood volume
  • Supporting digestion and metabolism
  • Aiding in the elimination of waste

• Electrolytes: Electrolytes are minerals that dissociate into ions when dissolved in water, and they play a crucial role in:
  • Regulating fluid balance in the body
  • Maintaining the acid-base balance
  • Transmitting nerve impulses
  • Contracting and relaxing muscles
  • Regulating heart function

The electrolytes commonly found in the body include sodium, potassium, calcium, magnesium, and chloride. An imbalance of electrolytes can lead to various health problems, such as dehydration, muscle cramps, heart palpitations, and more

Learning outcome 2.Identify the fluid compartments and the concentrations of electrolytes within these

The human body has several fluid compartments, each with different electrolyte concentrations:

• Intracellular Fluid (ICF): This fluid compartment is located inside the cells and makes up about two-thirds of the body’s total fluid. The main electrolytes found in the ICF are potassium (K+) and magnesium (Mg2+).

• Extracellular Fluid (ECF): This fluid compartment is located outside the cells and includes plasma (the liquid portion of blood) and interstitial fluid (the fluid between cells). The main electrolytes found in the ECF are sodium (Na+) and chloride (Cl-).

• Plasma: This is the liquid portion of blood and contains dissolved electrolytes, hormones, and waste products. The main electrolytes found in plasma include sodium (Na+), potassium (K+), calcium (Ca2+), and chloride (Cl-).

Learning outcome 3.Explain fluid shifts between these compartments

Fluid shifts between the intracellular fluid (ICF), extracellular fluid (ECF), and plasma compartments can occur due to various physiological and pathological processes. Some of the common causes of fluid shifts include:

• Hormonal changes: Hormones like antidiuretic hormone (ADH) and aldosterone can regulate the balance of water and electrolytes between the ICF, ECF, and plasma compartments. For example, an increase in ADH can lead to increased water reabsorption in the kidneys, leading to an increase in ECF volume and a decrease in ICF volume.

• Pressure changes: Changes in pressure can cause fluid to shift between the ICF and ECF compartments. For example, an increase in interstitial fluid pressure can cause fluid to move from the interstitial fluid into the plasma.

• Electrolyte imbalances: An imbalance of electrolytes, such as an increase in sodium (Na+) or a decrease in potassium (K+), can cause fluid to shift between the ICF and ECF compartments.

• Physical activity: Physical activity can cause fluid to shift between the ICF and ECF compartments. For example, during exercise, fluid can move from the plasma into the interstitial fluid to help regulate body temperature.

• Inflammation: Inflammatory processes can cause fluid to shift from the plasma into the interstitial fluid, leading to edema (swelling).

Learning outcome 4.Explain the principles of water and electrolyte balance

Water and electrolyte balance in the body is maintained by a delicate balance of intake and elimination. The principles of water and electrolyte balance are as follows:

• Intake and elimination: The body must take in an adequate amount of water and electrolytes to meet its needs, and it must eliminate any excess through urine, feces, and sweat. The balance between intake and elimination is important for maintaining fluid balance and preventing dehydration or overhydration.

• Electrolyte concentration: The concentration of electrolytes in the body is tightly regulated to maintain normal cellular function. Electrolytes, such as sodium (Na+), potassium (K+), and chloride (Cl-), play important roles in regulating fluid balance, blood pressure, and cell function.

• Osmosis: The movement of water across a selectively permeable membrane, such as cell membranes, is regulated by the concentration gradient of solutes, such as electrolytes. Osmosis is important for maintaining fluid balance within and between the intracellular fluid (ICF), extracellular fluid (ECF), and plasma compartments.

• Hormonal regulation: Hormones, such as antidiuretic hormone (ADH) and aldosterone, play a critical role in regulating fluid and electrolyte balance by controlling the reabsorption of water and electrolytes in the kidneys.

• Homeostasis: The body’s ability to maintain a stable internal environment, even when faced with changes in the external environment, is called homeostasis. The regulation of fluid and electrolyte balance is an important aspect of maintaining homeostasis.

Learning outcome 5.Discuss the pathophysiology of selected electrolyte imbalance

An electrolyte imbalance can have a significant impact on the body’s normal functions. The following is a discussion of the pathophysiology of selected electrolyte imbalances:

• Sodium imbalances: Sodium (Na+) is the primary electrolyte in the extracellular fluid (ECF) compartment. A decrease in serum sodium levels (hyponatremia) can cause cells to swell, leading to symptoms such as headache, nausea, and confusion. On the other hand, an increase in serum sodium levels (hypernatremia) can cause cells to shrink and become dehydrated, leading to symptoms such as muscle cramps, confusion, and seizures.

• Potassium imbalances: Potassium (K+) is the primary electrolyte in the intracellular fluid (ICF) compartment. A decrease in serum potassium levels (hypokalemia) can cause muscle weakness, fatigue, and heart arrhythmias. An increase in serum potassium levels (hyperkalemia) can cause muscle weakness, paralysis, and cardiac arrest.

• Calcium imbalances: Calcium (Ca2+) is important for normal bone health, muscle function, and blood clotting. A decrease in serum calcium levels (hypocalcemia) can cause muscle cramps, tetany, and seizures. An increase in serum calcium levels (hypercalcemia) can cause nausea, vomiting, confusion, and kidney damage.

• Magnesium imbalances: Magnesium (Mg2+) is important for normal nerve and muscle function. A decrease in serum magnesium levels (hypomagnesemia) can cause muscle weakness, tremors, and cardiac arrhythmias. An increase in serum magnesium levels (hypermagnesemia) can cause muscle weakness, drowsiness, and cardiac arrest.

Learning outcome 6.(Na+ and K+ imbalance)

Refer to above mentioned Na+ and K+ imbalance.

Learning outcome 7.Define acid, base, buffer, acidosis, alkalosis, acidemia, alkalemia

Acid: An acid is a substance that donates hydrogen ions (H+) in a solution, causing it to have a pH less than 7.

Base: A base is a substance that accepts hydrogen ions (H+) in a solution, causing it to have a pH greater than 7.

Buffer: A buffer is a substance that can resist changes in pH by accepting or donating hydrogen ions (H+) as needed to maintain a relatively constant pH.

Acidosis: Acidosis is a condition in which the body fluids have an excess of hydrogen ions (H+), causing the pH to be lower than 7.3.

Alkalosis: Alkalosis is a condition in which the body fluids have a deficiency of hydrogen ions (H+), causing the pH to be higher than 7.45.

Acidemia: Acidemia is a medical condition in which the blood has an excess of hydrogen ions (H+), causing the blood pH to be lower than 7.35.

Alkalemia: Alkalemia is a medical condition in which the blood has a deficiency of hydrogen ions (H+), causing the blood pH to be higher than 7.45.

Learning outcome 8.Outline the concepts of physiological pH regulation

The physiological pH regulation is important for maintaining acid-base balance in the body.

• Blood buffers (bicarbonate, hemoglobin, and proteins) are the first line of defense against pH changes.

• If blood pH deviates, the respiratory and kidney systems work together to correct it.

• The respiratory system regulates carbonic acid levels by excreting or conserving CO2.

• The kidney regulates blood pH by excreting H+ ions, conserving bicarbonate, and generating new bicarbonate.