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BIOL 1175

Excretion Several organs eliminate waste and excess essential ions Lungs – heat, water, c02 Skin – heat water, bicarbonate ions, salt Organs of the GI tract - Solid wastes and some metabolic waste Kidney - form urine Amazing Kidney facts ~ 1600 L of blood flow through a pair of human kidneys each day - 300 times normal blood volume - This produce ~180 of initial filtrate 1. Excretion - Mostly of nitrogenous wastes:  Urea made by the breakdown of amino acids in the liver  Main issue is to get rid of amino group (ammonia) very toxic o Ammonia + carbon dioxide = urea and water  Uric acid made by the break down of nucleotides  Creatine - Nephrons are the filters of the kidney Three steps of urine formation Glomerular filtration Tubular reabsorption Tubular secretion Bowman’s capsule Proximal convoluted tubule (Glucose amino acid vitamin water sodium chloride) Loop of Henle – Descending limb and Ascending limb Distal convoluted tubule Step one: Glomerular Filtration - Water and small molecule move from glomerulus to glomerular capsule while large molecules formed elements remain in the glomerular blood Tubular reabsorption and secretion Many molecules and ion are reabsorbed from the nephron and return to the blood eg. NaCl, H20 In descending loop of henle water gets reabsorbed In ascending loop of henle salt gets reabsorbed 2. Maintained of salt balance The water-salt balance (How is blood volume and pressure maintained by the kidneys?) - aka osmoregulation – maintain a constant blood pressure (related to blood volume) and constant blood osmolarity (solute concentration in blood) - eg. Low bp would rigger and reabsorb water and salt - Increase water = increase salt Renin - > angio-tensinogen -> tensin ->adrenal gland ->aldosterone ->increase in Na+ and H210 salt Renin - > a
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