1. Excretion

2. Do Now Your Body’s Filter Have you ever seen a water-purification system attached to a faucet? This system removes impurities from the water such as arsenic or other chemicals that can be harmful to people. As water passes through the filters contained in the system, the impurities are trapped on the surface of the filters. Eventually, the water that comes out of this purifier is free of the impurities. Section 38-3 1. Your body has its own system for filtering blood. Why might the blood in your body need to be filtered? 2. What organ(s) do you think filters your blood? 3. How do you think the filtered materials leave your body?

3. Checks and Balances Your body is amazingly maintaining homeostasis through an intricate system of checks and balances to satisfy your body’s needs and remove waste products that are not useful or toxic

4. Excretion Excretion = the process by which wastes are eliminated from the body The excretory system includes: –Lungs: excrete gaseous carbon dioxide from cellular respiration –Rectum: excrete solid undigested remains from food –Skin: excretes excess water, salts, urea –Kidneys and accessory organs

5. The Urinary System The urinary system rids the blood of wastes produced by the metabolism of nutrients and controls blood volume by removing excess water produced by body cells. The urinary system includes: –Kidneys –Urinary bladder –Connecting tubules: Ureter Urethra

6. Kidney (Cross Section) Cortex Medulla Vein Artery Kidney Ureter Urinary bladder Urethra The Urinary System Section 38-3

7. Kidneys Most people have 2 kidneys located on either side of the spinal column on your lower back Ureters = tubes that carry urine from each kidney to the urinary bladder Urinary bladder = saclike organ that stores urine until it can be excreted The kidneys filter blood by removing urea, excess water and other wastes collected as urine and the clean filtered blood returns to circulation

8. Kidney Structure Inner part = renal medulla Outer part = renal cortex Functional units of the kidney = nephrons About 1 million nephrons in each kidney Each nephron has its own arteriole (small artery), venule (small vein), and network of capillaries to filter blood

9. Kidney Nephron Cortex Medulla Renal artery Renal vein Ureter To the bladder Bowman’s capsule Glomerulus Capillaries Collecting duct To the ureter Loop of Henle Artery Vein Figure 38–17 Structure of the Kidneys Section 38-3

10. Filtration Blood enters a nephron through the glomerulus (network of capillaries) in Bowman’s capsule (cup-shaped structure) Blood is under high pressure causing fluid to flow from the blood into Bowman’s capsule = filtration The filtrate contains water, urea, glucose, salts, amino acids, and some vitamins

11. Reabsorption Most of the material removed from the blood at Bowman’s capsule makes its way back into the blood = reabsorption –99% of water is reabsorbed into blood

12. Secretion Some materials, including hydrogen ions (H+) are transferred from the blood into the filtrate = secretion

13. Filtration Most filtration occurs in the glomerulus. Blood pressure forces water, salt, glucose, amino acids, and urea into Bowman’s capsule. Proteins and blood cells are too large to cross the membrane; they remain in the blood. The fluid that enters the renal tubules is called the filtrate. Reabsorption As the filtrate flows through the renal tubule, most of the water and nutrients are reabsorbed into the blood. The concentrated fluid that remains is called urine. Secretion Substances such as hydrogen ions are transferred from the blood to the filtrate. Figure 38–18 The Nephron

14. Urine The material that remains = urine containing urea, salts, water and other substances The loop of Henle conserves water and minimizes the volume of urine Urine is stored in the urinary bladder until it can be released from the body through a tube = urethra

15. Kidney Function The kidneys maintain homeostasis by: –Regulating the water content of the blood (blood volume) –Maintaining blood pH –Removing waste products from the blood

16. Dialysis Although you are born with two kidneys, you can live with only one kidney. If both kidneys malfunction, a kidney dialysis machine can artificially filter blood

17. Vein Artery Shunt Air detector Dialysis machine Blood pump Blood in tubing flows through dialysis fluid Used dialysis fluid Compressed air Fresh dialysis fluid Figure 38–19 Kidney Dialysis Section 38-3