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7 reabsorpon of the 180 l uid ltered each day only 15

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Unformatted text preview: and chemicals of that organism are in consistent balance b.  Involves the removal and gain of equal amounts of material Remember in answering any ques*ons •  Osmoregula*on is always a con*nuum, therefore, –  Regula*ng and conforming are two extremes of a con*nuum. –  No animal is a perfect regulator or conformer. –  Some animals regulate some internal condi*ons and allow others to conform. Balance of NaCl and Water Filtra*on (Glomerulus) •  Fluid is pushed out of the plasma passing through the glomerular capillaries –  Plasma proteins and cells are retained in the blood –  Small par*cles pushed out into glomerular capsule and nephron tubules (rela*vely non ­selec*ve) Fig 13.7 Reabsorp*on •  Of the 180 L fluid filtered each day, only ~1.5 L of urine is excreted –  Can be as low as 400 ml •  Most of the material in the filtrate is reabsorbed •  Selec*ve movement of substances from fluid in tubules to blood in the peritubular capillaries •  Ac*ve or passive transport mechanisms used to drive reabsorp*on Secre*on •  Also occurs in tubules •  Addi*onal materials transported from plasma in peritubular capillaries into tubule –  excess K+, Ca2+ and H+, uric acid –  foreign compounds (e.g., penicillin) •  Typically driven by ac*ve carrier transport Reabsorp*on in the Proximal Tubule •  Most (65%) of the filtrate is reabsorbed in the proximal tubule 1.  Na+ •  Na+ pumped from the tubule wall cells into the blood of the peritubular capillaries by Na+/K+ pumps •  Creates gradient for Na+ to flow into the cells from the filtrate 2.  Cl ­ •  Moves passively out of filtrate, through cells, and into blood by the electrical gradient created by pumping Na+ 3.  Water •  Flows from filtrate to blood because of osmo*c gradient created by moving Na+ and Cl...
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