Water Balance & Homeostasis III (4/23)

Homeostasis and Water Regulation

• Definition of Homeostasis: The body's method of maintaining a stable internal environment despite external changes.
• Water Regulation in Fish:
  • Freshwater Fish:
  • Absorb excess water due to lower osmolarity in their body compared to their environment.
  • Solution: Produce dilute urine to excrete excess water.
  • Saltwater Fish:
  • Face the opposite issue; their body has lower osmolarity than the surrounding seawater, leading to water loss.
  • Solution: They must drink water and excrete salts through specialized gills to maintain internal balance.

Role of Carbon Dioxide in Homeostasis

• Aerobic Metabolism: During exercise, the body produces carbon dioxide (CO₂) which affects blood chemistry.
• Link Between CO₂ and pH:
  • Increased CO₂ leads to higher proton (H⁺) concentration, lowering pH (making blood more acidic).
  • Sensors located in the heart and brain stem detect changes in pH and CO₂ levels.

Respiratory Regulation

• Control Mechanism:
  • Sensors that detect pH changes communicate with the control center in the brain stem.
  • If pH drops (indicating increased acidity), the body responds by increasing respiratory rate via contraction of diaphragm components.
• Respiratory Response:
  • Deeper, more forceful breaths enhance oxygen intake and CO₂ removal, thus stabilizing pH levels.

Gas Exchange and Hemoglobin Affinity

• Oxygen Transport: Hemoglobin's affinity for oxygen varies based on environmental concentrations.
  • In the lungs, high oxygen (O₂) concentration enhances hemoglobin's affinity, leading to effective oxygen loading.
  • In tissues, lower O₂ concentration and factors like pH and CO₂ levels reduce affinity, facilitating oxygen unloading where needed.
• Physiological Responsiveness:
  • Hemoglobin’s ability to adjust its affinity according to local conditions, such as pH and CO₂ concentration, ensures efficient oxygen delivery to active tissues.

Metabolism and Activity Levels

• The overall activity level of the organism (active vs. inactive) significantly affects metabolic rate and thus respiratory and excretory outputs.