Summary BIO 3200 HUMAN PHYSIOLOGY THE KIDNEYS CHAPTER 17

Chronic Kidney Disease GFR (ml/min) Stage 1 Normal function 90 or higher Stage 2 Mild loss of function 60-89 Stage 3a Mild to moderate 45-59 Stage 3b Moderate to severe 30-44 Stage 4 Severe loss of function 15-29 Stage 5 Kidney failure less than 15 Dialysis is required when Glomerular Filtration Rate (GFR) is less than 15 37 million American adults have chronic kidney disease From the National Kidney Foundation End of Lecture 17, Part 1 Part 1. Blood Flow Through the Kidneys Part 2. The Nephron Part 3. Filtration Part 4. Glomerular Filtration Rate Chapter 19 BIO 3200 Human Physiology The Kidneys Lecture 17 Part 2: The Nephron The Urinary System • The kidneys are located on the back wall of the abdomen • Note the prominent renal arteries and renal veins providing substantial circulation through the kidneys • The kidneys regulate the volume and composition of the blood and remove waste products The Kidney The blood supply circulates up and around the nephrons. The nephron is the functional unit of the kidney The Nephron • The strategy of the kidney is to transfer everything to the urine and then take back what is needed • Chemicals in the blood will show up in the urine unless they are very effectively reabsorbed The Nephron • The blood supply of the nephron breaks up into capillaries in the glomerulus and surrounding the tubules • The efferent arteriole connects the two capillary beds • Blood is filtered into the nephron from the glomerulus and reabsorption occurs in the tubules HUMAN PHYSIOLOGY, LECTURE 17, PART 2 12 Structure of the Nephron The ascending and descending limbs of the loop of Henle are untwisted in this drawing The Nephron Most nephrons (80%) are contained in the cortex Juxtamedullary nephrons (longer nephrons, 20%) descend into the medulla End of Lecture 17, Part 2 Part 1. Blood Flow Through the Kidneys Part 2. The Nephron Part 3. Filtration Part 4. Glomerular Filtration Rate Chapter 19 BIO 3200 Human Physiology The Kidneys Lecture 17 Part 3: Filtration Filtration, Reabsorption, Secretion, Excretion Filtration, Reabsorption, Secretion, Excretion Filtration Blood except for blood cells and proteins is filtered into the lumen of the nephron in Bowman’s capsule Reabsorption occurs as the urine travels through the proximal tubule, loop of Henle, distal tubule and collecting duct About 20% of the plasma volume is filtered into the lumen of the nephron More than 99% of that filtrate volume is reabsorbed Filtration Filtration occurs from the glomerular capillary into the lumen of Bowman’s capsule. The filter is formed by the endothelial cells of the capillaries and the podocytes forming the boundary of Bowman’s capsule. Note the foot processes on the podocytes. Filtration Plasma is filtered through the capillary endothelium, the basal lamina and the podocytes lining Bowman’s capsule. Filtration does not allow blood cells or most blood proteins to enter the lumen of the nephron Filtration Pressure • Filtration is driven by pressure • Net filtration pressure is the difference between the blood pressure, the hydrostatic pressure in the lumen of Bowman’s capsule and the colloid osmotic pressure HUMAN PHYSIOLOGY, LECTURE 17, PART 3 23 The colloid osmotic