11.3 The Kidney

1. 11.3 The Kidney Cleaning the blood and water regulation

2. Where are the kidneys? http://www.nlm.nih.gov/medlineplus/ency/images/ency/fullsize/19615.jpg

3. The Urinary system http://image.tutorvista.com/content/excretion/urinary-system-of-man.jpeg

4. The parts of a kidney as seen in dissection. http://femmenoir.net/wp-content/uploads/2009/10/kidney.gif

5. A diagramatic Nephron…. This is the diagram to learn to draw and label! Try to place this in relation to the previous slide. http://www.mrothery.co.uk/module4/webnotes/Image8.gif

6. ….looks more like this though. Look at the blood supply and how it is related to the tubule and the loop of henle. http://www.ratical.org/radiation/vzajic/nephron.jpg

7. Now we know the anatomy…. The Kidney has 2 major functions we need to know about (and a few others we don’t!): • Cleaning the blood. • Regulating the water content of the blood.

8. Cleaning the blood. • Occurs in two main stages: • Ultra-filtration • Selective reabsorbtion.

9. Ultra-filtration • A big blood tube coming in and a little blood tube going out creates pressure that pushes fluid out of the glomerulus. http://click4biology.info/c4b/11/11.3/glomerulus.gif

10. The substances go through 2 membranes • The capillary membrane. • Bowman’s capsule membrane. • Cells and large plasma protein macromolecules cannot pass through this structure • Note the filtrate does not pass through the cells of either the glomerulus or the Bowman's capsule . http://www.colorado.edu/intphys/Class/IPHY3430-200/image/19-4d.jpg

11. Selective reabsorbtion • The process of control and regulation in the kidney begins with a non discriminating filtration (ultrafiltration) that removes just as many useful substances as harmful ones from the blood to make filtrate. • The kidney then takes back from the filtrate to the blood those substances that it still requires in the blood.(Selective Reabsorption) • The beauty of the way the kidney works is that it is able to control how much of a substance it reabsorbs back into the blood (Regulation)

12. The proximal convoluted tubule (PCT) • The PCT has a microvilli cell border to increase the SA for absorption from filtrate. There are also a large number of mitochondria which produce the extra ATP required for active transport. • 1. All glucose, all amino acids and 85% of mineral ions are reabsorbed by active transport from the filtrate to the tissue fluid. They then diffuse into the blood capillaries. • 2. Small proteins are reabsorbed by pinocytosis, digested, and the amino acids diffuse into the blood. • 3. 80% of the water is reabsorbed to the blood by osmosis. • 4. As urea molecules are so small and carry no charge that they diffuse passively through the cell membrane. In part this explains why not all urea is excreted as blood passes through the kidney. http://click4biology.info/c4b/11/hum11.3.htm

13. The descending loop of Henle Function:1. The function of the loop of Henle is to create a salt bath concentration in the surrounding    medullary fluid. 2. Later this results in water reabsorption in the collecting duct 3. There is also a reduction in the filtrate volume. Mechanism:1. There is a concentrated gradient down through the  medullary fluid (a). 2. The descending limb is permeable to water but not to salt.3. Filtrate enters the loop hypotonic to the medullary fluid so water is lost(b).4. The concentration difference between medullary fluid and the filtrate is small.5. The amount of water lost at each stage is small but accumulates on descent. 6. The water is lost but immediately taken up by the blood. 7.. Filtrate volume reduces and filtrate salt concentration increases.8. The base of the loop is impermeable (c) http://click4biology.info/c4b/11/hum11.3.htm

14. The ascending loop of Henle. 1.The filtrate moves up the ascending limb. 2.The ascending limb is permeable to salt. 3.The ascending limb is impermeable to water. 4.The filtrate is slightly more concentrated than the surrounding fluid. 5.There is a small but accumulating loss of salt ( Na+ and Cl-)at each level. 6.The concentration of the filtrate is gradually reduced. 7.The medullary gradient is maintained through exchange with the surrounding blood vessels • Note that this has resulted in: 1.Filtrate entering and leaving the loop of henle are approx isotonic 2.Reduced volume of the filtrate 3.Creation and Maintenance of the medullary salt bath gradient http://click4biology.info/c4b/11/hum11.3.htm

15. The Distal Convoluted Tubule (DCT) and The collecting duct • The concentration gradient of the medullary fluid brings about the removal of water from the collecting duct by osmosis. • The permeability of both Distal Convoluted Tubule (DCT) and the Collecting tube(CT) can be increased by the hormone ADH (Vasopressin). • The cell membranes of these tubules do not allow the movement of water by simple diffusion. Rather pores called Aquaporin can be opened the action of ADH. • The DCT is involved in other homeostatic functions such as the secretion of H+in pH regulation or K+ in salt regulation http://click4biology.info/c4b/11/hum11.3.htm

16. Osmoregulation • Osmoregulation is the control of the water balance of the blood, tissue or cytoplasm of a living cell. • The water content of body fluids has to be controlled such that the movement of water to and from cells can changes be controlled. • The body experiences external and internal changes such as drinking water availability, sweating and the accumulation of salts that require adjustments in the water content of blood, tissues and cytoplasm. • Osmoregulation is under the control of receptors in the hypothalamus. • In responses to changes the hypothalamus controls the sensation of thirst and also the endocrine secretion of anti-diuretic hormone.(ADH). • ADH is secreted from the pituitary and causes the opening of cell membrane pores called aquaporins which allows water reabsorption into the blood.

17. Comparison of glomerular filtrate and urine • The collecting duct is permeable to both water which as the filtrate descends this collecting duct is removed concentrating the filtrate (urine). However the collecting duct also leaks some urea which to the kidney interstitial fluid. Some of this lost urea is reabsorbed by the ascending limb of the loop of henle but not all, hence the 50% reabsorption. This cycling of urea is an important feature of the kidneys ability to produce a concentration gradient through the medulla. • Uric acid is a fairly toxic molecule (main nitrogenous excretion in birds) and is largely removed from blood and tissue fluids. • Glucose is 100% reclaimed by selective reabsorption. The presence of glucose in the urine would be an indication of diabetes. • Amino acids are all selectively reabsorbed in the nephron and then undergo deamination in the liver (urea excretion). • Proteins and other macromolecules should not be filtered in the Bowman's capsule and any presence in urine is usually regarded as an indicator of high blood pressure and damage to the basement membrane (nephritis) of the bowman's capsule.

18. Some animations • A very fast summary….. http://www.youtube.com/watch?v=glu0dzK4dbU • A bit slower but too much detail…. http://www.youtube.com/watch?v=6Wc4f2KnbYo&feature=related