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Lecture 8

Textbook notes for lecture 8 & 9

Biological Sciences
Course Code
Kamini Persaud

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Lecture 8 & 9 Salt & H2O Balance & N. Excretion
(Chapter 49)
Key Points:
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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