Body Water and Electrolytes

Body Water and Osmolality

• The main function of body water is to regulate various bodily functions, including temperature, metabolism, and cellular processes.

Distribution of Body Water

• The average water content of the human body is distributed as follows:
  • 55-60% of body weight is water, with 40% being intracellular fluid and 20% being extracellular fluid.
  • 28% of the total body water is found in blood plasma.

Osmolality

• Osmolality measures the concentration of solutes in a solution, specifically the number of osmoles of solute per kilogram of solvent.

Response to Changes in Blood Osmolality

• When blood osmolality increases, the hypothalamus responds by stimulating thirst and increasing the production of antidiuretic hormone (ADH) to conserve water.
• The response to increased blood osmolality also involves the release of aldosterone, which promotes the retention of sodium and excretion of potassium.

Dehydration

• In dehydration with pure water loss or deficit, the main effect is a decrease in blood volume, leading to a decrease in blood pressure.
• Dehydration can cause intravascular dehydration, where there is a loss of blood volume, leading to decreased blood pressure.

Regulation of Blood Osmolality

• The hypothalamus responds to changes in blood osmolality by regulating the sensation of thirst and the production of ADH.
• The parameter to which the hypothalamus responds is the osmolality of the blood.

Hormonal Regulation

• Aldosterone promotes the retention of sodium and excretion of potassium in response to increased blood osmolality.
• ADH promotes water retention in response to increased blood osmolality.

Plasma Composition

• The normal plasma water content is approximately 92% of the total plasma composition.