Body Fluids and Their Functions

Body Fluids

• About 60% of an adult human body is fluid, primarily a water solution of ions and other substances.
• Most of this fluid is inside cells (intracellular fluid).
• One-third is outside cells (extracellular fluid).
• Extracellular fluid is constantly moving throughout the body.
• This fluid is transported via blood and then mixes with tissue fluids through capillary walls by diffusion.
• Adult females have 50% of total body weight as fluid.
• Adult males have 60% of total body weight as fluid.

Functions of Body Fluid

• Major component of blood plasma.
• Solvent for nutrients and waste products.
• Necessary for the hydrolysis of nutrients.
• Essential for metabolism.
• Lubricant for joints and GI tract.
• Cools the body through perspiration.
• Provides some mineral elements.

Body Fluids Balance Disorders

• Every body part needs water to function.
• A healthy body balances water intake and output.
• Fluid imbalance occurs when water or fluid loss exceeds intake or intake exceeds output.

Causes of Fluid Imbalance

• Water loss through breathing, sweating, and urination.
• Dehydration from insufficient fluid intake.
• Fluid overload from difficulty excreting fluids.
• Edema (excess fluid in skin and tissues) can result from fluid overload.
• Many medical problems can cause fluid imbalance, such as after surgery.

Causes of Body Fluid Imbalance

• Heart failure can cause fluid to collect in lungs, liver, blood vessels, and body tissues, as the heart has a poor job of pumping to the kidneys.
• Kidney disease can cause the body to not function correctly and lose fluids due to difficulty processing fluids.
• Diarrhea, vomiting, or high fever can cause excessive loss of fluids.
• Lack of antidiuretic hormone (ADH) can cause the kidneys to excessively lose fluid and lead to dehydration as a result.
• Medications can affect fluid balance.

Cell Membrane

• Lipids form a barrier in cell membranes to impede water and water-soluble substance movement between cell compartments.
• Proteins in membranes frequently penetrate completely and form pathways or channels for the passage of substances.
• Many membrane proteins are enzymes that catalyze various chemical reactions.

Lipid Layer of Cell Membrane

• The lipid layer of the cell membrane is semipermeable.
• Fat-soluble substances are the only substances that can pass through the lipid layer.

Diffusion

• Passive movement of substances across the membrane due to random molecular movement.

Active Transport

• Requires energy (ATP).
• Involves a protein structure penetrating the membrane to transport substances.

Endocytosis

• Cellular uptake of large particles (e.g., bacteria, whole cells via phagocytosis).
• Pinocytosis is the ingestion of minute particles that form vesicles inside the cell cytoplasm.
• Phagocytosis is the ingestion of larger particles.

Recommended Textbooks

• Bruce Koeppen, Bruce Stanton, Berne & Levy Physiology, 7th Edition, 29th March 2017.

Explore the role of body fluids in human physiology, covering their composition, functions, and importance in maintaining balance. Understand how fluid movement occurs within the body and the consequences of fluid imbalance. This quiz will test your knowledge on these essential concepts.