14.02 Internal Environment

1. Definition of Internal Environment

• The internal environment refers to all conditions inside the body that influence cellular function.
• Immediate Cellular Environment: For individual cells, this is the tissue fluid surrounding them, providing necessary conditions for cell activities.

2. Four Key Features of Tissue Fluid Influencing Cell Activities

1. Temperature
   • Effect on Cells: Low temperatures reduce the rate of metabolic reactions; high temperatures cause protein denaturation, disrupting enzyme function.
   • Optimal Range: Cellular processes require stable temperatures to maintain enzyme activity.
2. Water Potential
   • Importance: Water balance is crucial for cell function; changes in water potential affect cellular osmotic balance.
   • Decreased Water Potential: Leads to water moving out of cells, slowing or halting metabolic reactions.
   • Increased Water Potential: Can cause water to enter cells excessively, potentially leading to swelling and cell lysis.
3. Blood Glucose Concentration
   • Role in Cellular Function: Glucose is essential for respiration; low levels deprive cells of energy, while high levels disrupt osmotic balance.
   • Regulation: Homeostatic mechanisms maintain glucose within an optimal range.
4. pH
   • Effect on Enzymes: Cellular enzyme activity is highly sensitive to pH, with an optimal range of 6.5 to 7.0 for cytoplasm.
   • Extreme pH: Causes enzyme denaturation and disrupts metabolic processes.

3. Homeostatic Control of Tissue Fluid Composition

• Homeostatic Mechanisms: There are control systems for each of the critical factors—temperature, water potential, glucose concentration, and pH.
• Blood Composition: Homeostasis regulates blood composition, which in turn controls tissue fluid composition surrounding cells.