Urinary System Lecture 2 2023 - PDF

Chapter 26 The Urinary System Part 2 July 2023 Dr. Kevin Tipper, ND VCMT RENAL PHYSIOLOGY Renal Physiology Urinary system maintains homeostasis by regulating the volume and composition of blood Concentrates urine to 855– 1355 mOsm/L Excrete...

Chapter 26 The Urinary System Part 2 July 2023 Dr. Kevin Tipper, ND VCMT RENAL PHYSIOLOGY Renal Physiology Urinary system maintains homeostasis by regulating the volume and composition of blood Concentrates urine to 855– 1355 mOsm/L Excretes solutes, especially metabolic wastes © 2018 Pearson Education, Inc. Renal Physiology Examples of metabolic wastes Urea Most abundant organic waste By-product of amino acid breakdown Creatinine By-product of creatine phosphate breakdown in muscles Uric acid Formed during recycling of nitrogenous bases of RNA © 2018 Pearson Education, Inc. Renal Physiology There are three processes involved in urine formation 1. Filtration 2. Reabsorption 3. Secretion Glomerular Filtration Filtration: blood hydrostatic pressure forces water and solutes across the membranes of the glomerular capillaries into the capsular space Filtration ONLY happens in the glomerulus The resulting fluid that enters the capsular space is the glomerular filtrate Occurs through the filtration membrane Glomerular Filtration Filtration Membrane 1. fenestrations of glomerular endothelial cells blood cells & proteins too big too cross 2. basement membrane (collagen fibres & proteoglycans) large negatively charged proteins do not fit 3. filtration slit = space between pedicels of podocytes water, glucose, vitamins, amino acids, very small plasma proteins, ammonia, urea, & ions fit Glomerular Filtration Net Filtration Pressure (NFP) Glomerular Blood Hydrostatic Pressure (GBHP) = 55 mmHg blood pressure in glomerular capillaries Pro-filtration Capsular Hydrostatic Pressure (CHP) = 15 mmHg hydrostatic pressure pushing against filtration membrane by fluid already in capsular space Anti-filtration Blood Colloid Osmotic Pressure (BCOP) = 30 mmHg osmotic pressure of large proteins pulling water into capillaries Anti-filtration Glomerular Filtration Net Filtration Pressure (NFP) NFP = (GBHP) – (CHP) – (BCOP) = 55 – 15 – 30 = 10 mmHg (under normal circumstances) NFP dictates how much will move in which direction *** Filtration stops if GBHP drops below 45mmHg b/c opposing pressure = 45mmHg Glomerular Filtration Filtration Fraction (FF) Renal plasma flow (RPF) = volume of plasma that moves through the kidneys per unit time Filtration fraction (FF) is the fraction of RPF that becomes glomerular filtrate Normal FF = 16-20% Daily glomerular filtrate = 150L - 180L 99% of filtrate is returned to bloodstream by tubular reabsorption  1-2L of urine produced daily Glomerular Filtration Glomerular Filtration Rate (GFR) amount of filtrate formed per minute in all the renal corpuscles of both kidneys Normal is 105-120 ml/min GFR is directly related to NFP  NFP =  GFR Kidney function is tested via eGFR (estimated) An eGFR of