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