Maintaining the Excretory System

1. Maintaining the Excretory System

2. Water Balance • Increased water intake is adjusted for by increasing urine output • The kidneys rely on the nervous and endocrine systems to help maintain a balance of water

3. FYI • DO NOT COPY • Average adult loses 2 L of water a day • Urine • Perspiration • Exhalation • Drop in fluid intake • 1%  thirst • 5%  extreme pain, collapse • 10%  death

4. Regulating ADH • ADH (antidiuretic hormone)regulates the osmotic pressure in the kidneys to increase water absorption • If released, more concentrated urine is produced • ADH is released from the hypothalamus • Shrinking of hypothalamus cells, due to dehydration, also creates a sensation of thirst

5. Osmoreceptors • Nerves in hypothalamus (located in the brain) that detect change in osmotic pressure • High Osmotic Pressure • Water moves into blood stream  hypothalamus shrinks  signals release of ADH from pituitary • ADH causes increased reabsorption of water in kidneys, prevents osmotic pressure from increasing any further

6. Negative Feedback Loop

7. ADH and the Nephron • 85% of the water filtered into the nephron is reabsorbed in the proximal tubule • ADH makes the upper part of the distal tubule and collecting duct permeable to water • This allows NaCl in the intercellular spaces to create an osmotic pressure that draws water from the tubule back into the blood

8. ADH Inhibitors • Alcohol and caffeine are diuretics • Increase the output of urine and decreases the release of ADH • Intensifies thirst and leads to dehydration

9. Kidneys and Blood Pressure • Kidneys regulate blood pressure by regulating blood volume • Aldosteroneacts on nephrons to increase Na+ reabsorption • If there is a decrease in blood pressure, aldosterone is produced, which increases Na+ absorption and therefore brings more water into the blood, increasing its volume (and therefore, pressure)

10. Negative Feedback Loop

11. Kidneys and Blood pH • The blood pH is maintained by acid-base buffer systems • The most important acid-base buffer system is the following equation: H+ + HCO3- H2CO3 H2O + CO2 pH increases pH decreases • Turn to page 317

12. pH continued • The kidneys help to maintain this balance by balancing H+ and HCO3- • If the blood is too acidic, H+ is excreted and HCO3- is reabsorbed and returned to the blood

13. Kidneys are affected when other systems break down Kidney disorders can be detected by urinalysis Important to remember that constituents of urine may change throughout the day due to Dietary intake Physical activity Stress Fatigue Urine is always more concentrated first thing in the morning. (Why?) Kidney Disorders

14. Bacterial or viral infection of the bladder cystitis Infection of the urethra urethritis More common in women than in men Symptoms: Burning sensation during urination Frequent urination Bloody or brown urine Can result in permanent damage to kidneys, possible kidney failure Urinary Tract Infection

15. Kidney Stones • Kidney stones are collections of mineral salts from the blood • These sharp stones become lodged in the pelvis or the ureter, causing severe pain • Ultrasound can be used to break up these stones so that they will be passed in the urine (previously, only surgery could remove the kidney stones)

16. Well Mr. Osborne, it may not be kidney stones after all.

17. Aka: Nephritis Describes many diseases characterized by inflammation of the nephrons Eg.) microbes destroy blood vessels of the glomerulus  affects permeability Proteins pass into nephron, can’t be reabsorbed Creates osmotic gradient Bright's Disease