chapter42WaterandElectrolyteBalanceinAnimals[1]

chapter42WaterandElectrolyteBalanceinAnimals[1] - BLY122...

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Chapter 42 Water and Electrolyte Balance in Animals 1 BLY122 A. Hunter from C. S. Major Chapter 42 Water and Electrolyte Balance in Animals I. Challenges to Water and Electrolyte Balance in Different Environments A. Osmotic stress—cells can undergo osmotic stress with changes in their environment. If unopposed, osmotic stress will impair cell function and may lead to death. 1. Water moves to the area of highest solute concentration via osmosis. 2. If an animal’s body is hypertonic (has a higher solute concentration) to its environment, the animal will take on water. 3. If an animal’s body is hypotonic (has a lower solute concentration) to its environment, the animal will lose water. B. Osmotic stress may occur with either an imbalance in the water and/or electrolyte content of body fluids. C. Freshwater, marine, and terrestrial habitats impose different forms of osmotic stress on the animals inhabiting them; those animals have adaptations allowing them to achieve homeostasis. 1. Marine invertebrates . . . a. Are isotonic relative to seawater b. Are considered osmoconformers because they do not osmoregulate 2. Marine fish . . . a. Are hypotonic to their environment and tend to lose water and gain excess ions b. Must osmoregulate by drinking water and excreting excess electrolytes 3. Freshwater animals… a. Are hypertonic to their environment and tend to gain excess water and lose electrolytes b. Must osmoregulate by excreting excess water and obtaining electrolytes from their environment and food 4. Terrestrial animals . . . a. Run the risk of dehydration due to evaporation of water from their body surfaces, including respiratory organs b. Must osmoregulate by drinking and excreting excess electrolytes. II. Osmoregulation is the ability to counteract osmotic stress and maintain homeostasis with respect to water and electrolyte balance. A. All organs of osmoregulation possess transport epithelium for exchange of water and electrolytes with the environment. 1. Shark rectal gland—specialized for NaCl secretion 2. Chloride cells—found in abundance in the gill epithelia of marine fish 3. Nasal salt glands of marine birds and reptiles 4. Mammalian kidney B. All such organs use a common molecular mechanism for salt transport.
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This note was uploaded on 11/11/2009 for the course BLY 459 taught by Professor Obrien,j during the Spring '08 term at S. Alabama.

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chapter42WaterandElectrolyteBalanceinAnimals[1] - BLY122...

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