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Why Is Homeostasis of Internal Fluids Important To Animals?

  • Animals expend expend a significant amount of energy in maintaining homeostatic conditions within the body, including salt and water balance.

    • Animal tissues have a high water content; insufficient water intake can cause dehydration.

    • Salts (ions) are essential for many biological functions; they are found in all body fluids.

    • Salt and water balance are maintained in spite of disturbances during routine bodily processes.

  • Excretory systems assist in the regulation of salt and water balance while removing toxic waste products.

    • Most aquatic invertebrates that live in salt water are osmoconformers, but most fish are osmoregulators; marine and freshwater fish face different problems in maintaining a salt/water balance.

    • Animals that live on land must find fresh water to drink and risk water loss by evaporation.

    • Salts are lost in the sweat of mammals which is essential for cooling the body; drinks like Gatorade are recommended to restore salts during heavy exercise.

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What Type of Excretory Systems Do Animals Use?

  • Sponges and Cnidarians do not need an excretory system since metabolic wastes diffuse from cells into the surrounding water, but most other invertebrates use a filtration mechanism to cleanse bodily fluids.

    • Flatworms utilize flame cells that filter interstitial fluid within the mesoderm.

    • Annelids, many molluscs, and crustaceans utilize a filtration system composed of metanephridia.

    • Insects have a different type of excretory organ that utilizes secretion rather than filtration.

  • The kidney of vertebrate animals is a complex and efficient filtration organ.

    • The functional unit of the kidney is the nephron; the mammalian nephron consists of four parts.

    • Filtration of blood occurs through capillaries within the renal corpuscle.

    • Most reabsorption of organic molecules and salts occurs in the proximal convoluted tubule.

    • More water and sodium are removed from the filtrate within the loop of Henle, and final concentration of urine occurs within the collecting ducts of the kidney.

  • Changes in the filtrate within the nephron and collecting ducts of the kidney are illustrated in this summary.

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