The Excretory System By: Madeline Frazer, Mark Sibold, Catherine Peta, Catie Ward and Delaney Secrest

Function of the Urinary System To rid the body of water and solutes that are in excess of the amounts required to maintain extracellular fluid, reclaim certain solutes (potassium, sodium) and water that the body needs. (1, pg 751) Also, the urinary system works with the digestive system to maintain the balance of chemicals and water in the body. (2) Urine under a microscope :)

Filtration ●In the Urinary System, blood is filtered through kidneys so that big molecules such as cells and proteins, which are important to the body, can be retained and used by the body, yet unneeded waste can be exported from the body. ●Structure: the filtrate, which is in the nephron, is composed of water, ions (sodium, potassium, chloride), glucose and small proteins. ●The filtrate (known as glomerular capillaries) are 10 to 100 times more permeable to water and small solutes than other capillaries are. Therefore there is a high filtration rate. ●Rate: Filtration rates depend on flow volume to the kidneys. For example, when you run a race the nervous system diverts an above normal volume of blood away from kidneys, towards the heart and skeletal muscles. ●Fun Fact: The rate of filtration is approximately 125 ml/min or 45 gallons (180 liters) each day. Humans have about 7 to 8 liters of blood in their bodies, meaning that your entire blood volume gets filtered approximately 20 to 25 times each day. (3)

Filtration of blood in the Urinary System

Kidneys ●pair of bean shaped organs ●kidneys filter water and other substances from blood ●after filtration- return to blood ●anything unclaimed becomes urine (1)

Nephrons ●(1) millions throughout kidney ●where filtration takes place ●blood enters glomerulus and moves through proximal tube ●loop of henle where water and solute’s volume are reduced to create a hypertonic medulla ●loop of henle dilutes the filtrate by drawing out water and sodium chloride ●collection tube draws out water. Anything left over flows through kidney and into urinary tract

Tubular Reabsorption -Nutrients are absorbed in 6 different places throughout the Nephron -Luminal Membrane -active and passive transport of filtrate from tubule lumen-->peritubular capillary -concentration gradient created by Na+ -channel proteins move Glucose+Amino Acids -water-->osmosis -Proximal Convoluted Tubule -65% of reabsorption occurs here -Loop of Henle -Descending - Ascending -becomes increasingly concentrated as H20 leaves -filtrate becomes increas. dilute as Na+ is reabsorbed -Renal Tubules and Collecting Duct -reabsorption is regulated by hormones (PTH, ADH, aldosterone, and ANP) -Distal Convoluted Tubule -Collecting Duct -Hormone controlled reabsorption -water reabsorbed through Aquaporins -

Tubular Reabsorption Active+Passive Transport through the Luminal Membrane-->peritubular capillary Overview of tubular reabsorption/where it takes place in nephron

Tubular Secretion Tubular secretion is the opposite of tubular reabsorption. Cells along the walls of the nephron secrete solutes, mostly H+ and K+, after absorbing water and solutes from the fluid. (1) After the hairpin turn, sodium and chloride ions are pumped in, making the fluid saltier, while water is absorbed from the fluid. (1) ●Secretion prevents certain metabolites (like uric acid) and foreign substances (like any drugs) from collecting in the bloodstream. (1)

Homeostasis urine formation is a fluid that rids the body of excess and waste products o we can lose water through urine, evaporation (sweat), elimination in feces o we gain solutes from absorption (eating), secretion from cells, respiration and metabolism the kidney is responsible for filtering out as much or as little solute as necessary to maintain a balance in the body o the bloods system’s preferred pH is 7.4 Before the “hairpin” turn, water moves out of filtrate by osmosis. After the turn, only salt is able to permeate the walls of the nephron ADH is the hormone responsible for monitoring the levels of water in the body o it is able to constrict/expand the ducts in the nephron to ensure homeostasis by water retention

References: ❏ (1) Starr, Cecie, Ralph Taggart, and Lisa Starr. Biology: The Unity and Diversity of Life. 9th ed. Australia: Brooks/Cole, Print. ❏ (2) Zimmermann, Kim Ann. "Urinary System: Facts, functions and diseases." Livescience.com. Tech Media Network, 11 Feb Web. 31 Oct urinary-system.html ❏ (3) Freudenrich, Craig. "How Your Kidneys Work."howstuffworks.com. HowStuffWorks.inc, n.d. Web. 31 Oct ) ❏ (4) U of New Mexico. "Homeostasis." UNM Biology Undergraduate Labs. U of New Mexico, n.d. Web. 3 Nov ❏ (5) McGraw-Hill College Division. "Body Systems and Homeostasis." Body Systems and Homeostasis. N.p., n.d. Web. 3 Nov