Lecture 6-1notes

Lecture 6-1notes - Role of excretory systems Kidney...

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10/1/10 1 Kidney function 10/4 Role of excretory systems • Clean blood of wastes – Especially nitrogenous wastes: urea • Major homeostatic organ – Water balance – Salt balance – pH balance • Hormonal control Types of excretory systems • Different mechanisms for initial urine formation – Secretion • Malpighian tubule in insects* – Filtration *Cf. book p. 528; Malpighian tubules are not filtration organs! Malpighian tubule KCl secreted from blood into tubule Concentration gradient generates osmotic gradient Water moves into tubule by osmosis – Water follows salt – Leaky secretory epithelium osmosis Fig. 12-35b Sherwood Klandorf Yancey Cricket
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10/1/10 2 Malpighian tubule • Water moves into tubule by osmosis • Water moves along tubule by bulk flow • Wastes secreted into lumen • Contents emptied into rectum bulk flow Fig. 12-35b Sherwood Klandorf Yancey Cricket Malpighian tubule Empties into rectum Moves through rectum by bulk flow Contents can be further modified Water removed, returned to hemolymph by osmosis Results in circular flow of water bulk flow nitrogenous wastes bulk flow Fig. 12-35b Sherwood Klandorf Yancey Cricket Malpighian tubule Fluid in tubule and and rectum move in opposite directions. What is this phenomenon called? bulk flow nitrogenous wastes bulk flow Fig. 12-35b Sherwood Klandorf Yancey Cricket Initial urine formation • Secretion – Urine formed by secretory epithelium – Advantages • Nothing goes into urine except what is specifically transported there • Can minimize use of water – Disadvantages • Nothing goes into urine except what is specifically transported there
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10/1/10 3 Filtration excretion • Initial urine formation by filtration of blood – Water and all solutes below a certain size move into urine – Cells and large proteins retained in blood • Need blood pressure – Less effective in organisms with open circulatory system (low blood pressure) – Insects, earthworms Filtration excretion • Initial urine formation by filtration of blood • Urine subsequently modified – Secretion of unwanted solutes (wastes, hormones, etc.) – Re-absorption of water and wanted solutes (NaCl, glucose, etc.) – pH regulation Initial urine formation • Filtration – Advantages • Low energy cost to make high filtrate volume • Everything small enough in blood gets into urine – Can excrete foreign chemicals easily – Disadvantages • Everything small enough in blood gets into urine – Must individually retrieve substances to be conserved – Transport systems can be overwhelmed: diabetes • High blood pressure can damage filtration, blood and proteins excreted in urine Filtration-based excretion • Characteristics: – Rate of urine formation depends on blood pressure – Foreign compounds injected into blood stream show up in urine
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This note was uploaded on 09/16/2011 for the course BIO 203 taught by Professor Loretz during the Fall '09 term at SUNY Buffalo.

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Lecture 6-1notes - Role of excretory systems Kidney...

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