Textbook notes for lecture 8 & 9
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Lecture 8 & 9 – Salt & H2O Balance & N. Excretion
• What Roles Do Excretory Organs Play in Maintaining Homeostasis?
• How Do Animals Excrete Toxic Wastes from Nitrogen Metabolism?
• How Do Invertebrate Excretory Systems Work?
• How Do Vertebrates Maintain Salt and Water Balance?
• How Does the Mammalian Kidney Produce Concentrated Urine?
• What Mechanisms Regulate Kidney Function?
Overview: A Balancing Act
•Life evolved in the oceans (= salt water)
•Physiological systems of animals operate in fluid environment
•Relative concentrations of water and solutes in internal environment must be maintained within
fairly narrow limits
• Simplest marine animals (e.g. protists) still live in seawater
- Directly exposed to external environment
- Easier to maintain water and ionic balance across small cellular distances
•More complex animals have cells isolated from external environment – bathed in tissue
fluids. PROBLEM: relative concentrations of water and solutes in internal fluid environment
must be maintained within narrow limits to avoid cell damage
Water Balance Crucial for Animal Cells
• Animal cells - lack cells walls
- Must remain in osmotic balance with external environment to prevent destructive loss or gain of
water by cells = isotonic or iso-osmotic
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