Chapter_31[1][1] - Chapter 31- U rina ry System Digestive...

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Chapter 31- Urinary System Digestive system is unselective (random), while the Excretory system is selective. The excretory system (plays a role in homeostasis) restores and maintains the proper internal amounts of minerals, water, sugar, protein, fat, etc. in the body despite differences in diet. ( Excretion- the elimination of substances from the body ) Functions of excretory systems : all performed simultaneously as blood is selectively filtered by kidneys; water and nutrients are selectively reabsorbed into blood 1. Excretion of cellular waste products : (in cells) (in liver) (in kidneys) a. Ammonia + CO 2 Urea + wastes Urine (predominate waste, toxins, excessive water and nutrients collected by the kidneys and eliminated from body as urine) Liver helps convert ammonia to urea and then kidneys filter out urea and other wastes as urine Figure 31-3: know the different steps: 1. In cells, amino acids are broken into simpler molecules, releasing ammonia (NH 3 ). 2. In the liver, ammonia (very toxic) is combined with CO 2 to produce urea (less toxic) 3. In the kidneys, urea and other water soluble wastes are converted into urine 2. Regulation of fluid composition (blood level of ions, water content, retains nutrients such as glucose) 3. Secretion of hormones Simple Excretory Systems (found in invertebrates): 1. Flame cells - (ex: in flatworms) Simple excretory system; major function is to regulate water balance. Network of tubes that branch throughout the body and end in bulbs, called flame cells. H
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Chapter_31[1][1] - Chapter 31- U rina ry System Digestive...

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