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Understanding Excretion: The Role of Wastes and the Mammalian Kidney

Chapter 10 delves into the process of excretion, which involves the removal of toxic nitrogenous wastes produced from protein metabolism, such as ammonia, urea, and uric acid. It explains how different animals manage these wastes based on their environment, highlighting the significant role of the mammalian kidney in this process. The nephron is identified as the kidney's functioning unit, working through ultrafiltration, selective reabsorption, and secretion. The chapter also discusses the influence of alcohol on urine production and hydration.

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Understanding Excretion: The Role of Wastes and the Mammalian Kidney

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  1. Removing Wastes Chapter 10 Excretion is the removal of substances that once formed part of the body of the organism.

  2. Nature of wastes

  3. Nitrogenous wastes – urine • Produced from metabolic processes • nitrogenous waste products are toxic and may cause damage if allowed to accumulate • formed in liver from the breakdown of excess protein through deamination • type of nitrogenous compound produced related to • availability of water in animals environment • toxicity • energy cost in production

  4. Ammonia • highly toxic • small molecule – can diffuse easily across membranes • very soluble in water • limited to aquatic animals as water is plentiful for dilution Urea • low toxicity, high energy cost • very soluble in water – less soluable • mammals are able to regulate water balance Uric acid • low toxicity, highest energy cost • insoluble in water, precipitates out of solution • birds, land reptiles, insects

  5. The mammalian kidney

  6. The mammalian kidney • The kidneys maintain the body fluid composition at a steady rate. • The functioning unit of the kidney is the nephron. • There are three basic principles of kidney function: • 1. Ultrafiltration - the blood is filtered at high pressure across the glomerulus into the Bowman’s capsule • 2. Selective reabsorption – the useful parts of the filtrate are returned to the blood (~99% of primary filtrate) • 3. Secretion – further substances not required by the body are secreted into the filtrate e.g. ammonium, potassium hydrogen ions • View animation: http://www.biologymad.com/resources/kidney.swf

  7. Alcohol • ADH (anti diuretic hormone which is produced in the pituitary gland) regulates reabsorption of water. • Alcohol decreases ADH production • this causes an increase in dilute urine • this can lead to dehydration

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