Lecture Notes: Importance of Water in Human Physiology

Introduction

• Water is crucial for human anatomy and physiology.
• Constitutes 70% of adult body mass.

Functions of Water in the Body

Lubrication

• Water acts as a lubricant in fluid-filled body cavities.
• Reduces friction, allowing organs like the heart and lungs to move without friction.
• Fluid in cavities, such as the pericardial and pleural cavities, is water-based.

Cushioning

• Provides shock absorption and protection.
• Cerebrospinal fluid makes the brain buoyant, preventing damage from movement.

Heat Regulation

• Water acts as a heat sink, absorbing and dissipating heat.
• Sweating is an example of evaporative cooling where hot water molecules evaporate, cooling the body.

Solvent Properties

• Water is a universal solvent due to its polarity.
• Polar molecules and ions dissolve in water (e.g., sugar dissolves in water).
• Terms:
  • Hydrophilic: Water-loving substances that dissolve in water.
  • Hydrophobic: Water-fearing substances that do not dissolve (e.g., oil).

Types of Mixtures Involving Water

Colloids

• Large molecules (usually proteins) suspended in water but do not settle.
• Example: Milk, with proteins and fats suspended.

Suspensions

• Mixtures where particles will settle over time.
• Example: Muddy water, where debris settles over time.

Chemical Reactions Involving Water

Reactive Nature of Water

• Water is involved in crucial biochemical reactions.

Dehydration Synthesis

• "Dehydration" means removing water; "synthesis" means to make.
• A reaction where water is removed to form larger molecules (anabolic reaction).
• Example: Combining molecule AH and BOH to form AB and water.

Hydrolysis

• "Hydrolysis" can be thought of as water splitting (lysis = to break).
• A reaction where water is used to break down molecules (catabolic reaction).
• Example: Breaking AB into AH and BOH using water.
• Key in digestion, where food is broken down into nutrients via hydrolysis.
• Nutrients are transported for cellular dehydration synthesis to build necessary molecules.

Conclusion

• Processes of dehydration synthesis and hydrolysis are continuously occurring in the body.
• Upcoming discussion on salts, acids, and bases.
• Reminder to take care of oneself and others.