Urine Formation PDF

12/17/2019 Urine Formation The formation of urine occurs in three processes: 1 Step 1: FILTRATION The movement of fluids and solutes from the blood into the Bowman's capsule of the nephron. About 1400 L of blood pass through th...

12/17/2019 Urine Formation The formation of urine occurs in three processes: 1 Step 1: FILTRATION The movement of fluids and solutes from the blood into the Bowman's capsule of the nephron. About 1400 L of blood pass through the kidneys/day  From this, Bowman’s capsules filter 180 L of fluid Body contains 2.75 L of blood plasma, and is filtered 65 times/day Only 1.5 L of daily filtrate is excreted as urine (rest is reabsorbed) 2 1  12/17/2019 Not all solutes make it through.  DO: H2O, NaCl, Glucose, Amino Acids, H+, urea, uric acid  DON'T (too large): plasma proteins, red blood cells, platelets 3 Step 2: REABSORPTION The transfer of essential solutes and most water back into the interstitial fluid  For every 120 mL of fluid (amount filtered each minute), 1 mL of urine is formed, 119 mL of fluid and solutes is reabsorbed. Occurs mainly in the proximal tubule, loop of Henle and distal tubule. Occurs by active and passive transport. 4 2  12/17/2019 Specialized ion pumps, transport K+, Na+ and Cl- from filtrate (in proximal tubule) to the interstitial fluid Inner walls of the tubule have microscopic extensions called microvilli that increase surface area for reabsorption Movement of water is facilitated by membrane proteins called aquaporins (water channels) 5 Hypoosmotic Gradient Reabsorption processes make the filtrate hypoosmotic to the interstitial fluid in the tubules  Thiscauses water to flow out of the tubule via osmosis  Aquaporins help additional water flow out 6 3  12/17/2019 Proximal tubule reabsorbs: 67% of the Na+, K+, and Cl- 65% of the water 50% of the urea into interstitial fluid nearly all of the other nutrients  These enter the peritubular capillaries Remaining fluid in tubule is highly concentrated with urea and wastes  Goes to loop of Henle, where Na+, Cl- are reabsorbed via passive diffusion and active transport  Then to distal tubule, more salt and water removed 7 Concentrated urea and wastes goes to collecting ducts  Further concentrates urine as more water is removed Salt concentration is higher in the medulla (due to passive urea transporters in the ducts; urea and uric acid diffuse out) This draws water out via osmosis Material left in nephron = filtrate 8 4  12/17/2019 9 STEP 3: SECRETION The movement of wastes from the blood and interstitial fluid Purpose:  to release any toxins/drugs that were not filtered  Maintain the electrolyte balance of the body (ions)  Acid-base balance (usually it is an acid (H+ ions) being secreted). 10 5  12/17/2019 Urine formation Wastes are secreted at several points in the nephron from the interstitial fluid  Proximal tubule (H+, detoxified poisons from liver, water-soluble drugs, small amounts of NH3)  Distal tubule in response to hormones (K+, H+)  Collecting ducts (excess H+, in response to pH levels in blood and body fluid) 11 Bottom of collecting ducts – urine is 4X as concentrated with waste as the interstitial fluid Urine flows from: ducts  renal pelvis  ureters  bladder  urethra 12 6  12/17/2019 13 Kidney Disease Many kidney disorders can be diagnosed through urinalysis.  Kidneys are in constant contact with blood  Any damage to the body can affect the kidneys (vice-versa)  Any metabolite from a disease will show up in the urine 14 7  12/17/2019 Diabetes Mellitus – insufficient insulin secretion, causes blood sugar to rise  Excess sugar remains in the nephron, causing water retention  Urinate more frequently Diabetes Insipidus – inadequate production/secretion of ADH, leads to frequent urination  Urine is often watery and the patient is always thirsty 15 Bright’s Disease (acute or chronic nephritis) – inflammation of the kidneys, usually caused by infection or autoimmune disorders  inadequate filtration at the glomerulus leading to the presence of protein (albumin) in urine 16 8  12/17/2019 Kidney stones – buildup of mineral solutes that can combine with calcium to produce crystals that accumulate and forms stones.  Sharp edges cause pain & bleeding when lodged in renal pelvis or as they pass through the ureter and urethra  Removed by sound wave therapy (extracorporeal shock wave lithotripsy, ESWL), uteroscope, or surgery 17 18 9  12/17/2019 19 20 10  12/17/2019 Loss of kidney function requires the use of dialysis (filtering machine)  Blood is passed through an “external kidney” machine  Total loss requires a transplant 21 22 11  12/17/2019 Homework Finish Pg. 454 # 2 – 6, 9, 10 (refer to pg. 423) Copy/peruse Table 1 on page 452 into your notes (would go nicely on the reverse of the colouring handout) Colouring Worksheet, Flow chart 23 24 12