ch6 bio310

BODY FLUIDS, WATER-SALT, & ACID-BASE BALANCE

  • Study material for BIO310 focusing on body fluids, water-salt balance, and acid-base mechanisms.

LESSON OUTCOMES

  1. Body Fluids: Describe various fluids in the body.

  2. Water-Salt Balance: Explain ADH systems and the RAAS (Renin-Angiotensin-Aldosterone System).

  3. Acid-Base Balance: Discuss kidney functions in acid-base equilibrium.

INTRODUCTION

  • Maintaining normal extracellular fluid volume and composition is crucial for life.

  • Three types of homeostasis involved:

    • Fluid Balance

    • Electrolyte Balance

    • Acid-Base Balance

  • Exchange happens between Intracellular Fluid (ICF) and Extracellular Fluid (ECF).

FLUID COMPARTMENTS

  • Body fluids consist of water and solutes:

    • Intracellular Fluid (ICF): 2/3 of body fluid, located within cells.

    • Extracellular Fluid (ECF): 1/3 of body fluid, major subdivisions include:

      • Plasma: Fluid portion of blood.

      • Interstitial Fluid (IF): Fluid in spaces between cells.

WATER BALANCE

Major Sources of Body Water

  • Average daily intake: 2,500 mL

    • Water from beverages: 1,500 mL (60%)

    • Water from moist food: 750 mL (30%)

    • Metabolic water: 250 mL (10%)

Water Loss Sources

  • Urine: 1,500 mL (60%)

  • Skin (sweat): 150 mL (6%)

  • Lungs and skin: 700 mL (28%, insensible loss)

  • Intestines: 150 mL (6%)

  • Loss can increase significantly during vomiting or diarrhea.

REGULATION OF WATER & SALT

  • Hormonal regulators play a key role:

    • ADH (Antidiuretic Hormone): Promotes water reabsorption in kidneys.

    • ANP (Atrial Natriuretic Peptide): Causes sodium and water loss when blood pressure is high.

    • Aldosterone: Promotes sodium (and water) reabsorption.

    • Angiotensin II: Triggers thirst and constricts blood vessels to regulate pressure.

Mechanisms for Regulation

  1. ADH Release: Triggered by increased blood osmolarity.

  2. RAAS Activation: Initiated by low blood volume or pressure, leading to Na+ and water reabsorption.

ELECTROLYTES

  • Types of Electrolytes:

    • Cations: Positive ions (e.g., Na+, Ca2+, K+)

    • Anions: Negative ions (e.g., Cl-, HCO3-)

Roles of Sodium (Na+)

  • Most abundant cation in ECF (90-95% of solutes).

  • Regulates plasma volume, blood pressure, and fluid movement between compartments.

Homeostasis of Sodium Concentration

  • Water moves toward compartments with higher electrolyte concentrations due to osmotic gradients.

ACID-BASE BALANCE

pH Regulation

  • Normal blood pH is maintained between 7.35 and 7.45.

  • Acidosis: pH drops below 7.35.

  • Alkalosis: pH rises above 7.45.

Sources of Hydrogen Ions

  • Cellular metabolism, breakdown of food, and respiration contribute to free H+ in the body.

BUFFER SYSTEMS

Types of Buffer Systems

  1. Chemical Buffer Systems

    • Bicarbonate Buffer: Involves carbonic acid and bicarbonate ions, regulating pH changes.

    • Phosphate Buffer: Dominant in ICF and urine, effective for buffering.

    • Protein Buffer: Proteins in plasma provide resistance against pH changes.

  2. Physiological Buffer Systems

    • Respiratory Buffer System: Adjusts blood pH by altering CO2 levels through breathing rate changes.

    • Renal Buffer System: Kidneys manage acid-base balance via bicarbonate reabsorption and H+ secretion.

COMPENSATIONS IN ACID-BASE IMBALANCE

  • Respiratory Compensations: Adjustments in ventilation in response to metabolic changes.

  • Renal Compensations: Control of bicarbonate and hydrogen ion levels over hours to days.

ACIDOSIS AND ALKALOSIS TYPES

  • Respiratory Acidosis: Caused by hypoventilation, CO2 retention; characterized by low pH.

  • Respiratory Alkalosis: Results from hyperventilation; characterized by high pH.

  • Metabolic Acidosis: Decreased bicarbonate; symptoms include headache, vomiting.

  • Metabolic Alkalosis: Increased bicarbonate, often due to vomiting or excessive antacid use.

SUMMARY OF ACID-BASE IMBALANCES

  • Each condition alters plasma pH, necessitating compensatory mechanisms from kidneys and respiratory systems.

  • Effective management of acid-base balance is pivotal for homeostasis and overall health.