The Excretory System

1. The Excretory System

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

3. 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

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

5. Kidneys & Urinary Tract To return to the chapter summary click escape or close this document.

6. 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

7. 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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9. Nephron To return to the chapter summary click escape or close this document.

10. 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

11. 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

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