Preface

1. Preface The following is a slide presentation of the mechanism of urine formation. This presentation should be used in a classroom lecture, while the class is studying the urinary system. The presentation includes embedded video that helps to explain the process.

2. Mechanism of Urine Formation Group 2: Ashley Cotter, Jeremy Kurck, Neco Sullivan, Cheryl Wells, and Casey Wooldridge

3. Learning Objectives • Learn the three steps in the process of urine formation and where does this process begins. • Learn how the nephron filter substances in the process of urine formation. • Learn what is filtered out of the blood during the process of filtration and what remains in the blood and what is not filtered out of the blood by the kidneys. • Learn what is reabsorbed in the process of reabsorption and in what part of the nephron this occurs. • Learn what regulates urine formation in order to maintain homeostasis. • Learn how many milliliters of blood are filtered each minute by the kidneys. • Learn how many nephrons are in each kidney. • Learn what happens during secretion. • Learn the name of the tube that carries urine from the kidneys to the bladder and from the bladder outside the body. Learn the name of the tube that carries urine from the kidneys to the bladder. • Learn what three substances normally compose urine.

4. Where Does Urine Formation Occur • Urine formation occurs in the nephrons of the kidneys. • Each kidney consists of about 1 million nephrons.

5. Each nephron is composed of 10 parts: • Afferent arteriole • Glomerulus • Bowman’s capsule • Vasa rectae • Efferent arteriole • Proximal convoluted tubule • Descending limb of Loop of Henle • Loop of Henle • Ascending limb of Loop of Henle • Distal convoluted tubule

6. Urine formation occurs in three stages:

7. Video on Urine Formation

8. Video on Nephron Function

9. Filtration • Urine formation begins with the process of filtration, which goes on continually in the renal corpuscles. Glomeruli are located in the renal corpuscles. • Glomeruli - filters approx. 180 L/day • Renal corpuscles • Bowman’s capsule • Filtrate – Contains no proteins and no RBCs, too large. Filters water and dissolved substances out of the blood and into Bowman’s capsule

10. Reabsorption • The movement of substances out of the renal tubules back into the blood capillaries located around the tubules (called the peritubular capillaries). Substances reabsorbed are water, glucose and other nutrients, and sodium (Na+) and other ions. • Peritubular capillaries • Proximal convoluted tubules • Loop of Henle • Distal convoluted tubules • Collecting tubules

11. Secretion • The process by which substances move into the distal and collecting tubules from blood in the capillaries around these tubules. • Secretion moves substances out of the blood and into the tubules where they mix with the water and other wastes and are converted into urine. • These substances are secreted through either an active transport mechanism or as a result of diffusion across the membrane. • Substances secreted are hydrogen ions (H+), potassium ions (K+), ammonia (NH3-), and certain drugs. • Kidney tubule secretion plays a crucial role in maintaining the body's acid-base balance, another example of an important body function that the kidney participates in.

12. References • http://www.handwrittentutorials.com/videos.php?id=75 – video 2 link • http://www.youtube.com/watch?v=oCQ-5iwTQvM – video 1 link • http://www.biologycorner.com/anatomy/urinary/urinary_labeling_key.html • http://www.nsbri.org/humanphysspace/focus4/ep-urine.html