A-Level Biology: Homeostasis

Definition and Importance

• Homeostasis: The body's process of maintaining a stable internal environment.
• Essential for cells' health and optimal function.
• Maintains optimal conditions for enzyme activity and metabolic reactions.

Key Parameters Controlled

• Temperature
  • Optimal: 37°C.
  • High temperature (>40°C): Causes enzyme denaturation, inefficient metabolism, cell collapse.
  • Low temperature: Reduces enzyme activity, slows metabolism.
• pH Levels
  • Optimal pH: 7.
  • Extreme pH values lead to enzyme denaturation.
• Blood Glucose Concentration
  • Too high: Reduces blood water potential, causes cells to lose water.
  • Too low: Insufficient energy for cellular functions.

Mechanisms of Homeostasis

• Negative Feedback Loops
  • Components: Receptors, Communication System, Effectors.
  • Receptors sense change.
  • Communication through nervous or hormonal systems.
  • Effectors counteract changes.

Example: Blood Glucose Regulation

1. Sensors: Pancreatic cells monitor blood glucose.
2. Communication: Hormones insulin and glucagon are released.
   • Insulin: Secreted by beta cells, lowers blood glucose.
   • Glucagon: Secreted by alpha cells, raises blood glucose.
3. Effectors: Liver and muscle cells
   • High glucose: Insulin promotes glucose uptake and storage as glycogen.
   • Low glucose: Glucagon promotes glycogen breakdown to glucose.

Diabetes Mellitus

• Type 1 Diabetes: Autoimmune destruction of beta cells, treated with insulin therapy.
• Type 2 Diabetes: Insufficient insulin production, managed with lifestyle changes and medication.

Water Potential Regulation

• Sensors: Osmoreceptors in the hypothalamus.
• Communication and Effectors: Hormone ADH controls kidney's water reabsorption.
  • Dehydration: High blood concentration, more ADH, increased water reabsorption.
  • Hydration: Low blood concentration, less ADH, decreased water reabsorption.

Kidney Function

• Structure: Nephrons filter blood, control water and electrolyte balance.
• Processes:
  • Ultrafiltration: High-pressure filtration in Bowman's capsule.
  • Selective Reabsorption: Reabsorption of glucose, water, ions.

Temperature Regulation

• Sensors: Detected in the hypothalamus.
• Responses to High Temperature
  • Vasodilation, increased sweating, reduced metabolic rate.
• Responses to Low Temperature
  • Vasoconstriction, reduced sweating, goosebumps, shivering.

Conclusion

• Homeostasis is vital for maintaining stable internal conditions necessary for survival.
• The body uses a combination of hormones, nervous signals, and physiological changes to maintain homeostasis.

Next Topic: Control and Coordination (upcoming video)