The Excretory System

Wastes Metabolic wastes from cell metabolism include: Salts Carbon dioxide Urea-toxic compound produced when amino acids are used for energy

Excretion of wastes Skin – excretes water, salts, and a small amount of urea in sweat Lungs – excrete carbon dioxide (produced when sugars are broken down for ATP) Liver – picks up amino acids in blood to make useful compounds producing urea in the process Kidneys – remove urea from blood for excretion from the body

Kidneys Maintain homeostasis by Removing wastes (urea) from the blood Maintaining blood pH Regulating water content of blood Regulating blood volume

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Kidneys Located on either side of the spinal column near the lower back The ureter (tube) carries urine from the kidneys to the urinary bladder (which stores the urine until it leaves the body) Waste-laden blood enters the kidneys through the renal artery Kidneys filter out urea, excess water, and other wastes which pass through the ureter Clean blood leaves the kidneys through the renal vein and returns to circulation

Kidney structure Renal medulla-inner part Renal cortex-outer part Nephrons-functional units of the kidney located in the cortex Loops of Henle-extend from cortex into renal medulla (are extensions of nephrons) Blood supply-arteriole, venule, capillaries Blood enters the nephron through the arteriole, impurities are filtered out and emptied into the collecting duct; purified blood leaves the nephron through the venule

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Filtration Filtering blood takes place in the glomerulus (a small network of capillaries encased at the upper end of the nephron in a Bowman’s capsule) Fluid from blood flows into Bowman’s capsule so the filtrate can be removed Filtrate includes water, urea, glucose, salts, amino acids, some vitamins All blood is filtered every 45 minutes

Reabsorption Some materials removed in Bowman’s capsule will be reabsorbed including amino acids, fats, glucose, and 99% of the water Remaining material (urine) is drained into a collecting duct and runs into the Loop of Henle where urine volume is minimized (by more reabsorption of water) Purified blood returns to circulation Urine is transferred to the urinary bladder and excreted through the urethra

Control of kidney function Controlled mainly by composition of blood and regulatory hormones released due to the composition of blood