1. Excretion

2. Do Now Your Body’s Filter
Section 38-3
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.
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. Human Excretion
Excretion = the process by which wastes are eliminated from the body
The excretory system includes:
Lungs: excrete gaseous carbon dioxide and water from cellular (aerobic) respiration
Rectum: excrete solid undigested remains from food
Skin: excretes excess water, salts, urea
Kidneys and accessory organs

5. Protozoa and Cnidarians
Since all cells are in contact with the external, aqueous environment, they excrete using simple diffusion through the cell membrane.
Contractile vacuole = organelle specialized for water excretion by active transport in freshwater organisms

6. Annelida (Earthworm)
Nephridia tubules = excrete water, mineral salts and nitrogenous wastes (urea) from each body segment
Fluid from the circulatory system is also filtered out of the blood into fluid that fills the central body cavity.

7. Arthropods (Grasshopper)
Malpighian tubules = accumulate mineral salts and uric acid forming solid uric acid crystals (conserving water)
Crystals are excreted with solid waste in the intestines.

8. The Human 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

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

10. 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

11. 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

12. Figure 38–17 Structure of the Kidneys
Section 38-3
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

13. 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

14. 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

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

16. Figure 38–18 The Nephron
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.
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.
Secretion
Substances such as hydrogen ions are transferred from the blood to the filtrate.

17. Urine
The material that remains = urine containing urea, salts, water and other substances (ammonia and uric acid)
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

18. 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

19. 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