Ch%209

Learning Objectives

  • Explain the role of water in physiological processes.

  • Describe how water is absorbed and excreted in the body.

  • Demonstrate the importance of developing effective communication skills in coaching.

  • Explain the principles of nutrition and analyze how they affect overall health.

Introduction to Water and Hydration

  • Water is a critical aspect of nutrition often overlooked compared to macronutrients (fats, carbohydrates, proteins).

  • The adult human body is approximately 50-60% water and can survive only 3-4 days without water.

Chemical Properties of Water

  • Chemical Formula: H2O (2 hydrogen atoms bound to 1 oxygen atom).

  • Water is polar, with a slight positive charge on hydrogen and a slight negative charge on oxygen.

  • Its polarity enables interaction with various molecules and supports its properties like high specific heat.

Homeostasis and Water

  • Water is vital in maintaining homeostasis, the stable equilibrium of bodily processes.

  • Osmosis: The movement of water through a semi-permeable membrane from high to low concentration.

Total Body Water and Fluid Distribution

  • Total body water divides into:

    • Intracellular Water: About 68% of total; found in cells.

    • Extracellular Water:

      • Interstitial Fluid: 24% of total; found between cells.

      • Plasma Volume: 7% of total; found in blood plasma.

  • Urine production is the primary means of excess fluid excretion, while thirst controls intake.

Hydration Status Definitions

  • Hypohydration: Decreased total body water.

  • Euhydration: Adequate total body water.

  • Hyperhydration: Excess total body water.

  • Dehydration: Process of losing body water.

  • Underhydration: Mild hypohydration with active fluid-regulating hormones but untriggered thirst.

Measuring Hydration

  • Techniques range from body mass measurements (tracking weight changes) to blood/urine tests.

  • Urine Osmolality: Measures urine concentration, with large values indicating concentrated urine.

  • Urine-Specific Gravity: Compares urine density to water density; assessed using a refractometer.

  • Urine Color: Visual self-assessment indicator of hydration status.

Role of Water in Physiological Processes

  • Water is involved in:

    • Cellular metabolism

    • Temperature regulation

    • Solute balance

    • Nutrient transportation

    • Waste elimination

    • Maintaining homeostasis

    • Digestion

    • Balancing pH

    • Oxygen delivery

  • Insufficient hydration linked to chronic diseases.

Physiology of Fluid Balance

  • Blood volume decrease triggers aldosterone release, affecting sodium and water retention.

  • Osmolality: Plasma concentration influenced by sodium.

  • Increased plasma osmolality triggers arginine vasopressin (AVP) to conserve water.

Glucose Regulation and Kidney Health

  • Low water intake affects glucose regulation and is associated with type 2 diabetes.

  • Adequate water intake helps prevent kidney stone formation and chronic kidney disease (CKD).

Digestion and Absorption of Water

  • Water absorbed primarily in the small intestine via osmosis, supported by the structure of microvilli.

  • Gastric emptying rate affects water absorption; highly concentrated liquids delay emptying.

Dietary Sources of Water

  • Main water intake sources: beverages (water, milk, coffee) and food (fruits/vegetables).

  • Recommended Daily Intake:

    • Men: 3.7 L (125 oz)

    • Women: 2.7 L (90 oz)

    • Varies by diet, environment, and individual factors.

Hydration and Athletic Performance

  • Hypohydration impairs performance; athletes often compete dehydrated.

  • Sweat loss reduces blood volume and impairs blood delivery to muscles.

  • Cardiac Drift: Decreases in stroke volume lead to an increased heart rate during hydration loss.

Hydration Strategies for Exercise

  • Goal: Maintain euhydration before, during, and after exercise.

  • Rehydration Formula: 150% of fluid lost during exercise should be replaced immediately.

Safe Hydration Practices

  • Prevent hypohydration and heat illness during exercise.

  • Exercise-Associated Hyponatremia (EAH): Occurs when plasma sodium levels drop dangerously low due to excessive fluid intake without electrolytes.

Performance and Hydration Supplements

  • Caffeine has little effect on hydration if kept below 6 mg/kg.

  • Creatine is generally safe, not significantly affecting hydration status.

This comprehensive overview covers the essential roles of water in the body, hydration needs for athletes, and effective hydration strategies. It highlights the critical physiological processes supported by adequate water intake and the implications of both under- and over-hydration.