7.3: Excreting Wastes

1. 7.3: Excreting Wastes • Waste products must be removed from the body to maintain life processes. • Examples: • Lungs remove CO2. • Large intestine removes toxic wastes. • Liver • Transforms toxins such as alcohol and heavy metals into soluble compounds. • Transforms products of protein metabolism into metabolites. • Kidneys remove waste, balance blood pH and maintain water balance. Control and Regulation of Metabolic Wastes

2. What happens to excess Protein? • Converted into carbohydrates • Amino group must be removed from the body – Deamination

3. Deamination • Occurs in the liver • Byproduct is ammonia, which is water soluble and extremely toxic • Ammonia combines with CO2 to form urea, which is 100 000 times less toxic • Uric Acid is formed by the breakdown of nucleic acids • Ammonia, Urea and Uric Acid are all removed by the Kidneys

4. Excretion in Unicellular Organisms • Waste moves directly out of the cell. • Excess water is regulated by contractile vacuoles that pump out excess water. • Multicelluar organisms need specialized cells and structures to get rid of waste.

5. Removal of Metabolic Wastes

6. Some Key Terms: • Deamination the breaking up of amino acids (removal of an amino group from an organic compound) • (NH3 = toxic and must be further processed) • Urea 2 molecules of highly insoluble, toxic ammonia (NH3) mixed with one molecule of CO2 = soluble (made in liver) • (waste product of amino acid – NH3) • Uric acid waste product formed from the breakdown of nucleic acids • Liver responsible for removing/breaking down waste in the blood which is then sent to the kidneys to be filtered into the bladder • Section 7.3 Questions, pp. 345, # 1-4

7. 7.4: The Urinary System

10. http://www.wisc-online.com/objects/AP2504/AP2504.swf

11. Nephrons http://www.wisc-online.com/objects/AP2204/AP2204.swf

13. Cortex: Bowman’s capsule, efferent and afferent arterioles are located here Medulla: Loop of Henle descends into this portion. *See kidney above. *Concentration of solute in the interstitial fluid increases from the cortex down to the medulla – this facilitates movement of water and solutes during reabsorption. Section 7.4, pp. 348, #1-4 http://www.biologymad.com/resources/kidney.swf

14. 7.5: Formation of Urine • There is a lot going on here! The main point is that the nephron is able to expel unneeded or harmful substances and retain or reabsorb substances useful to the body. You would be rather dysfunctional and have to pee a lot if this didn’t happen! • For every 120 mL of fluid (amount filtered by kidneys each minute), 1 mL of urine is formed, 119 mL of fluid and solutes need to be reabsorbed. • Urine is formed by: 1. filtration of the blood 2. reabsorption into the blood 3. secretion from the blood

15. Filtration • Structures involved – glomerulus and Bowman’s capsule • pressure in capillary bed = 2 kPa, pressure in glomerulus = 8 kPa • Blood moves from the afferent arteriole into the glomerulus (high pressure filter) • Dissolved solutes such as H2O, NaCl & H+ pass into the Bowman’s capsule • Large molecules such as protein, blood cells and platelets cannot pass through the glomerulus.

16. Reabsorption • Structures: convoluted tubules, loop of henle • Selective reabsorption occurs by both active and passive transport • Carrier molecules move Na+ ions across cell membranes, negative ions (Cl-) follow • Reabsorption occurs until the threshold level is reached. • Excess salt remains in the nephron and is excreted with the urine.

17. Reabsorption • On average, 600 mL of fluid in kidney/minute • ~ 120 mL of that fluid is filtered into the nephrons • 1 mL of urine is formed and 119 mL of fluid is reabsorbed by active and passive transport into the blood stream • reabsorption occurs until the threshold level is reached (maximum amount of material that can be moved across the nephron)

20. Reabsorption Continued • Glucose and amino acids attach to carrier molecules, which drives them out of the nephron and into the blood. • Solutes actively transported out of the nephron create an osmotic gradient that draws water from it. • A second osmotic force is created by proteins helps reabsorption. • Proteins remain in the blood stream and draws water from interstitial fluid into the blood.

21. Reabsorption Continued • As water is reabsorbed from the nephron, remaining solutes become more concentrated. • Urea and uric acid diffuse from the nephron back into the blood but less is reabsorbed than was originally filtered. • On average 600 ml of fluid flows through the kidneys every minute • Approx. 120 ml of that fluid is filtered into the nephrons. • 1 ml of urine is formed and 119ml of fluid is reabsorbed by active and passive transport into the blood stream.

22. Secretion • Occurs in distal/proximal tubule • Wastes from the blood move into the nephron • Nitrogen-containing wastes, excess H+ and K+ secreted • Cells loaded with mitochondria line the distal tubule • Tubular secretion occurs by active transport therefore require mitochondria.

23. Summary of Urine Formation

26. 6. collecting duct What is a kidney stone? = hard mass developed from crystals that separate from the urine within the urinary tract. Do not normally form due to inhibitors in urine. Common type of stone contains calcium in combination with either oxalate or phosphate. http://msjensen.cehd.umn.edu/1135/Links/Animations/Flash/0041-swf_micturition_re.swf

27. Target Practice Quiz: Kidney Section 7.5, pp. 352, # 2-6