Excretory System David Moy - Graham Nadel - Sydney Lehman - Andrew Mikula Purple - 11/4/13

1. Excretory System David Moy - Graham Nadel - Sydney Lehman - Andrew Mikula Purple - 11/4/13

2. The Urinary System The urinary system consists of the kidneys, ureters, urinary bladder, and urethra (Augusta tech, “Urinary system”) Main Functions: to eliminate wastes from the body, control blood pressure, control levels of electrolytes, and regulate pH.

3. Kidney Filters water, mineral ions, and organic waste from the blood Both nutrients and waste (not proteins) are drawn into nephrons within the kidney. Water and solutes which are not returned to the blood are excreted through the urinary system. Ex: The kidney will form an acid (H+) urine if the body is too acidic or alkaline (bicarbonate ion) urine if the body is too basic. This maintains the optimal pH of the body. This is the body maintaining homeostasis (Mader, “Body systems and Homeostasis”).

4. The Kidney Nephrons

5. Kidney structures Ureter- tubular channel which carries urine from the kidney Renal artery- tube which carries blood into the kidney Renal vein- tube which carries blood out of the kidney Kidney cortex- surrounds the medulla Kidney medulla- contains nephrons in a cluster Renal pelvis- central cavity of the kidney, where the ureter, renal artery, and renal vein meet the kidney Renal capsule- envelopes the cortex Nephrons- extend down from kidney cortex into the medulla, filter water and solutes (Taggart, 751)

6. Nephron structures Glomerulus- a group of glomerular capillaries, arterioles bring blood to capillaries via blood pressure Bowmans capsule- surrounds the glomerulus Proximal tubule- straight tube linked to the glomerulus Loop of henle- hairpin shaped tube, linked to proximal tube. Distal tubule- linked to the loop of henle Collecting duct- leads to central cavity Lumen- the nephron wall Peritubular capillaries- around the lumen, they reclaim water and solutes for the blood (Taggart, 751)

7. Transport in the Nephron • Blood pressure gathers filtrate in the Bowman’s Capsule • In the proximal convoluted tubule, materials are reabsorbed from the filtrate. This is called tubular reabsorption. • The proximal tubule actively transports salt and nutrients out through microvilli in a series of tight junctions, which allow for osmosis. • In the descending section of the loop of henle water passively diffuses out, then while ascending salt first passively, then actively exits. • The thin segment of the ascending limb is too thin to allow much osmosis, and countercurrent flows restrict osmosis anyway, but some NaCl can still permeate. • In the distal tubule salt and HCO3 are actively transported out and H+ as well as K+ are actively transported in. This creates a hypertonic environment outside the nephron and allows for osmosis. • In the collecting duct salt is actively transported out, and water passively exits.

8. Definitions of Basic Terms Filtration: Process by which bodily fluids (blood, hemolymph, etc.) are brought in contact with a transport epithelium, a selectively permeable membrane found throughout the body (Washington University). Whole cells and large molecules such as proteins cannot cross this membrane, but water, salts, amino acids, and other small molecules can. In the nephrons, this process is as a result of higher blood pressure in the blood vessels compared to the fluid in the Bowman’s capsule. (Campbell, 702-703). Tubular Reabsorption: The process by which water, ions, and valuable organic molecules are re-absorbed by peritubular capillaries from the nephrons into bodily fluids. This occurs in the proximal tubule. This occurs as a result of active transport within the ascending loop of the hene. Also, small outpocketings called malpighian tubules remove salt, water, and nitrogenous wastes in the large intestine. (Campbell, 959-965)

9. Terms, cont. • Secretion in nephron: An auxiliary mechanism that uses active transport to pump excess H+ ions and K+ ions out of the blood. The H+ binds with NH3 to make NH4+. This is then secreted into the collecting ducts. • Examples of homeostasis in the excretory system: • water balance maintained (as some water escapes in urine). • Removes toxins like ammonia - keeps bodily organs healthy. • Maintains concentration of solutes in bodily fluids through secretion/reabsorption.

10. References 1. "Body Systems and Homeostasis." Mader Biology. McGraw College Division, 1997. Web. 3 Nov. 2013. <http://www.mhhe.com/biosci/genbio/maderbiology/supp/ homeo.html>. 2. Campbell, Neil. Biology: AP edition. 8th edition. San Francisco, CA: Pearson Benjamin Cummings, 2007. Text. 3. Washington University. “Epithelial Transport.” University of Washington Courses Web Server, 2013. Web. 3 Nov. 2013. <http://courses.washington.edu/conj/bess/transport/epithelialtransport.htm> 4. "Urinary System." Bio 2114. Augusta Tech, n.d. Web. 3 Nov. 2013. <http://www.augustatech.edu/anatomy/notes%20for%20194/urinary.htm>. 5. Taggart, Ralph, and Cecie Starr. Biology: The Unity and Diversity of Life. Brooks/Cole, 2001. Print. 6. Campbell, Neil. Biology: Exploring Life. Boston, MA: Pearson Prentice Hall, 2006. Print.