BIOH122 Human Biological Science 2

Transcription

1 BIOH122 Human Biological Science 2 Session 18 Urinary System 3 Tubular Reabsorption and Secretion Bioscience Department Endeavour College of Natural Health endeavour.edu.au

2 Session Plan o Principles of Tubular Reabsorption and Secretion o Reabsorption and secretion in the Proximal Convoluted tubule o Reabsorption in the Loop of Henle o Reabsorption and secretion in the Distal Convoluted tubule and the Collecting Ducts o Hormonal Regulation of Tubular reabsorption and secretion Endeavour College of Natural Health endeavour.edu.au 2

3 Principles of Tubular Reabsorption and Secretion Endeavour College of Natural Health endeavour.edu.au 3

4 Tubular Reabsorption and Secretion o Tubular reabsorption: The process of returning most of the filtered water and many of the filtered solutes to the bloodstream. PCT with their microvilli do most of work with the rest of the nephron doing just the fine-tuning solutes reabsorbed by active and passive processes water follows by osmosis small proteins by pinocytosis Endeavour College of Natural Health endeavour.edu.au 4

5 Tubular Reabsorption and Tubular Secretion o Tubular secretion: The transfer of materials from the blood and tubule cells into glomerular filtrate. helps control blood ph because of secretion of H+ helps eliminate certain substances (NH4+, creatinine, K+) Endeavour College of Natural Health endeavour.edu.au 5

6 Tubular Reabsorption and Secretion Endeavour College of Natural Health endeavour.edu.au 6

7 Reabsorption Routes o Two routes: Paracellular reabsorption - movement between cells Transcellular reabsorption movement through cells Endeavour College of Natural Health endeavour.edu.au 7

8 Reabsorption Routes o Paracellular reabsorption: between adjacent tubule cells Fluid leakage between cells Up to 50% of the reabsorption of certain ions and the water that accompanies them via osmosis o Transcellular reabsorption: through an individual tubule cell a substance passes from the fluid in the tubular lumen through the apical membrane of a tubule cell, across the cytosol, and out into interstitial fluid through the basolateral membrane. by active transport Endeavour College of Natural Health endeavour.edu.au 8

9 Transport Mechanisms o Two main transport mechanisms: Active transport Primary Secondary Passive transport Osmosis Marieb and Hoehn, 2011 Endeavour College of Natural Health endeavour.edu.au 9

10 Transport Mechanisms o Primary active transport: The energy derived from ATP is used to pump a substance across a membrane. Na+/K+ ATPase pumps in the the basolateral membrane o Secondary active transport: The energy stored in an ion s electrochemical gradient drives another substance across the membrane. Symporters: Membrane proteins that move two or more substances in the same direction across a membrane. Na+ glucose symporters in the apical membrane Antiporters: Membrane proteins that move two or more substances in opposite directions across a membrane. Na+/H+ antiporters in the apical membrane Endeavour College of Natural Health endeavour.edu.au 10

11 Transport Mechanisms o Osmosis: Water is only reabsorbed by osmosis. Obligatory water reabsorption: occurs when water is obliged to follow the solutes (Na +, Cl -, and glucose) being reabsorbed ( water follows sodium ) occurs in the proximal convoluted tubule and the descending limb of the loop of Henle Facultative water reabsorption: adapted to specific needs. Occurs in the collecting duct under the control of antidiuretic hormone Endeavour College of Natural Health endeavour.edu.au 11

12 Reabsorption and secretion in the Proximal Convoluted tubule Endeavour College of Natural Health endeavour.edu.au 12

13 Reabsorption and secretion in the Proximal Convoluted Tubule o Reabsorption in PCT: The largest amount of solutes and water 100% of most filtered organic solutes such as glucose and amino acids; 80 90% of the filtered HCO 3-65% of the filtered water, Na + and K + 50% of the filtered Cl - and filtered urea; A variable amount of the filtered Ca +, Mg 2+ and HPO 4 2- o Secretion in PCT: A variable amount of H + ions, ammonium ions (NH4 + ), and urea. Endeavour College of Natural Health endeavour.edu.au 13

14 Reabsorption in the Proximal o Na + reabsorption: Convoluted Tubule o Na + -glucose symporters: Reabsorb Na + with glucose, amino acids, lactic acid, water-soluble vitamins, and other nutrients. Endeavour College of Natural Health endeavour.edu.au 14

15 Reabsorption in the Proximal o Na + reabsorption: Convoluted Tubule o Na + /H + antiporters: cause Na + reabsorption into blood and H + secretion into tubular fluid. Endeavour College of Natural Health endeavour.edu.au 15

16 Reabsorption in the Proximal Convoluted Tubule o Reabsorption of HCO3 - : Facilitated diffusion through the basolateral membrane For every H+ secreted into the tubular fluid, one filtered bicarbonate eventually returns to the blood Endeavour College of Natural Health endeavour.edu.au 16

17 Reabsorption in the Proximal Convoluted Tubule o Reabsorption of Na +, K +, Ca +2, Mg +2 and urea: Passive diffusion into peritubular capillaries via both paracellular and transcellular routes. In the second half of the PCT Electrochemical gradients Endeavour College of Natural Health endeavour.edu.au 17

18 Reabsorption in the Proximal Convoluted Tubule o Water reabsorption: osmosis followed by solute reabsorption Via both the paracellular and transcellular routes. Aquaporin-1 Endeavour College of Natural Health endeavour.edu.au 18

19 Secretion in the Proximal Convoluted Tubule o Urea and ammonia in blood: Filtered at the glomerulus and secreted by the proximal convoluted tubule cells into the tubules. o deamination of the glutamine by PCT cells: generates both NH 3 and HCO 3-. NH 3 quickly binds to H+ and becomes NH 4+. NH 4+ can substitute for H+ aboard Na + /H + antiporters and be secreted into tubular fluid. o Na + /HCO 3- symporters: provide a route for reabsorbed Na + and newly formed HCO 3- to enter the bloodstream. Endeavour College of Natural Health endeavour.edu.au 19

20 Reabsorption in the Loop of Henle Endeavour College of Natural Health endeavour.edu.au 20

21 Reabsorption in the Loop of Henle o Reabsorption in the Loop of Henle: 15% of the filtered water 20 30% of the filtered Na +, and K + 35% of the filtered Cl -, 10 20% of the filtered HCO - 3 a variable amount of the filtered Ca +2, and Mg +2 o The loop of Henle thus sets the stage for independent regulation of both the volume and osmolarity of body fluids. Endeavour College of Natural Health endeavour.edu.au 21

22 Reabsorption in the Loop of Henle o Na +, Cl -, and K + reabsorption: At the apical membrane: Na + -K + -2Cl - symporters: reclaim one Na +, two Cl -, and one K + from the fluid in the tubular lumen. K + leakage channels: return much of the K + back into tubular fluid. Paracellular route: Na +, K +, Ca 2+, and Mg 2+ Endeavour College of Natural Health endeavour.edu.au 22

23 Reabsorption in the Loop of Henle o Na +, Cl -, and K + reabsorption: At the basolateral membrane: Active transport of Na + : into into the vasa recta. Leakage channels: moves Cl - into the vasa recta. Endeavour College of Natural Health endeavour.edu.au 23

24 Reabsorption in the Loop of Henle o Water reabsorption: o In the descending limb of the loop of Henle: about 15% of the filtered water o In the ascending limb of the loop of Henle: apical membranes are virtually impermeable to water little or no water is reabsorbed Endeavour College of Natural Health endeavour.edu.au 24

25 Reabsorption and secretion in the Distal Convoluted tubule and Collecting Duct Endeavour College of Natural Health endeavour.edu.au 25

26 Reabsorption in the Early Distal Convoluted Tubule o Reabsorption in the Early Distal Convoluted Tubule: 10 15% of the filtered water, 5% of the filtered Na + 5% of the filtered Cl - o Reabsorption of Na + and Cl - : At the apical membranes:.by Na + Cl - symporters At the basolateral membranes: Sodium potassium pumps and Cl - leakage channels permit reabsorption of Na + and Cl - into the peritubular capillaries. Endeavour College of Natural Health endeavour.edu.au 26

27 Reabsorption in the Early Distal Convoluted Tubule o Reabsorption of Ca 2+ : Parathyroid hormone (PTH) stimulates reabsorption depending on the body s needs o Reabsorption of water: DCT is not very permeable to water No/little water reabsorption Endeavour College of Natural Health endeavour.edu.au 27

28 Reabsorption and Secretion in the Late DCT and Collecting Duct o Late DCT and Collecting Duct: water and solute reabsorption and solute secretion vary depending on the body s needs. o Consist of two different types of cells Principal cells: Reabsorb Na + and secrete K + ; Intercalated cells: reabsorb K + and HCO 3- and secrete H +. Endeavour College of Natural Health endeavour.edu.au 28

29 Reabsorption and Secretion in the Late DCT and Collecting Duct o Principal cells: Na + reabsorption: At the apical membrane: Na + leakage channels At the basolateral membrane: active transport by sodium potassium pump Secretion of K + : In apical and basolateral membranes: K+ leakage channels Major source of K+ that is excreted in urine. Endeavour College of Natural Health endeavour.edu.au 29

30 Reabsorption and Secretion in the Late DCT and Collecting Duct Reabsorption of Na + and secretion of K + by principal cells Endeavour College of Natural Health endeavour.edu.au 30

31 Reabsorption and Secretion in the Collecting Duct o Intercalated cells: reabsorb K+ and bicarbonate ions and secrete H+ HCO 3- reabsorption: Cl - /HCO 3- antiporters Regulate ph of body fluids H + secretion: Proton pumps (H + ATPases) Against a concentration gradient so urine can be 1000 times more acidic than blood o Urine is buffered by HPO4 2- and ammonia, both of which combine irreversibly with H + and are excreted. Allows the body to excrete more H + in the urine. Endeavour College of Natural Health endeavour.edu.au 31

32 Reabsorption and Secretion in the Collecting Duct Secretion of H + and reabsorption of HCO 3 - by intercalated cells in the collecting duct. Endeavour College of Natural Health endeavour.edu.au 32

33 o buffered by HPO4 2- and ammonia Buffering of Urine by HPO4 2- and ammonia Endeavour College of Natural Health endeavour.edu.au 33

34 Hormonal Regulation of Tubular Reabsorption and Secretion Endeavour College of Natural Health endeavour.edu.au 34

35 Hormonal Regulation o Five hormones: affect the tubular reabsorption and secretion in the renal tubules. Angiotensin II Aldosterone Antidiuretic hormone Atrial natriuretic peptide Parathyroid hormone Endeavour College of Natural Health endeavour.edu.au 35

36 Hormonal Regulation o Angiotensin II: Increases reabsorption of Na +, other solutes, and water, which increases blood volume and blood pressure. Works at the Proximal Convoluted Tubule o Aldosterone: Increases secretion of K + and reabsorption of Na+, Cl - Increases reabsorption of water, which increases blood volume and blood pressure. Works at Distal convolulted Tubule/ Collecting Duct Endeavour College of Natural Health endeavour.edu.au 36

37 Hormonal Regulation o Atrial natriuretic peptide: Increases excretion of Na + in urine Increases urine output and thus decreases blood volume and blood pressure. o Parathyroid hormone: Increases reabsorption of Ca 2+. o Antidiuretic hormone (ADH)/ Vasopressin: Increases facultative reabsorption of water, which decreases osmolarity of body fluids. Works at the Collecting Duct Endeavour College of Natural Health endeavour.edu.au 37

38 Hormonal Regulation Negative feedback regulation of facultative water reabsorption by ADH: o ADH stimulates the insertion of aquaporin-2 channels into the membrane water molecules move more rapidly o When osmolarity of plasma and interstitial fluid increases, more ADH is secreted and facultative water reabsorption increases. Endeavour College of Natural Health endeavour.edu.au 38

39 Readings and Resources o Tortora, GJ & Derrickson, B Principles of Anatomy and Physiology, 14th edn, Wiley. o Harris, P, Nagy, S & Vardaxis, N 2010, Mosby s Dictionary of Medicine, Nursing and Health Professions, 2nd edn, Mosby Elsevier. o Guyton, AC & Hall, JE 2011, Textbook of Medical Physiology, 12th edn, Saunders Elsevier. o Marieb, EN & Hoehn, K 2011, Human Anatomy and Physiology, 9th edn, Benjamin Cummings Pearson. o Moore, KL, Dalley, AF & Agur, AMR 2010, Clinically Orientated Anatomy, 6th edn, Lippincott, Williams & Wilkins. Endeavour College of Natural Health endeavour.edu.au 39

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