Excretory SystemYixuan He

Function• Collect water and filter body fluids.• Maintain homeostasis• Remove and concentrate waste products from body fluids and

return other substances to body fluids as necessary• Eliminate excretory products from the body.

Kidney• Eliminate wastes from the bloodstream by production of

urine.• Function:• Maintain volume of extracellular fluid• Maintain ionic balance in extracellular fluid• Maintain pH and osmotic concentration of the extracellular fluid.• Excrete toxic metabolic by-products

Ureters• Muscular ducts that propel urine from the kidneys to

the urinary bladder.• Urine enters the bladder through the ureters

Bladder• collects urine excreted by the kidneys prior to disposal

by urination. • It is a hollow ,muscular, and elastic organ• Sits on the pelvic floor.

Urethra• A tube which connects the urinary bladder to the outside of

the body• Urine leaves the bladder through the urethra.

Nitrogenous Waste: Ammonia• Very soluble • Can only be tolerated at very low concentrations• Common in aquatic species. • Animals that excrete ammonia need access to lots of water• Ammonia molecules easily pass through membranes and are

readily lost by diffusion to the surrounding water.

Nitrogenous Waste: Urea• Produced in the vertebrate liver by a metabolic cycle that

combines ammonia with carbon dioxide. • Low toxicity. • Permits animals to transport and store urea safety at high

concentrations• Mammals , adult amphibians, sharks, and some marine bony

fishes and turtles• Do not have constant access to sufficient water to excrete

ammonia• Urea-excreting animals requires much less water, because much

less water is lost when a given quantity of nitrogen is excreted

Nitrogenous Waste: Uric Acid• Nontoxic• Largely insoluble in waste• Can be excreted as a semi-solid paste with very little loss• Insects, land snails, and many reptiles, including birds• Little access to water

• However, it is energetically expensive

• Proximal tubule• The portion of a nephron immediately downstream from Bowman’s

capsule • Conveys and helps refine filtrate

• Loop of Henle• The long hairpin turn, with a descending and ascending limb, of the

renal tubule in the vertebrate kidney.• Functions in water and salt reabsorption

• Distal tubule• Helps refine filtrate and empties it into the collecting duct

• Collecting duct• Where filtrate from renal tubules is collected• The filtrate, once in the collecting duct, is called urine.

• Cortical nephrons• Nephrons located almost entirely in the renal cortex.• These have a reduced loop of Henle

• Juxtamedullary nephrons• Nephrons with well-delevoped loops of Henle that extend deeply

into the renal medulla

Filtration• The extraction of water and small solutes, including metabolic

wastes, from the body fluid into the excretory system. • Occurs as blood pressure forces fluid from the blood in the

glomerulus of the nephron into the lumen of the Bowman’s capsule.

Reabsorption • The uptake of solutes from a filtrate of blood, coelomic fluid,

or hemolymph in the excretory organs of animals• The proximal tubules reabsorb about 90% of the important

buffer bicarbonate to maintain the pH. They also reabsorb most of the NaCl and water from the initial filtrate volume.

• Reabsorption of water continues into the descending limb of the loop of Henle.

• The Distal tubule is similar to the proximal tubules in that it reabsorbs buffer bicarbonate and NaCl

Secretion• The discharge of wastes from the body fluid into the filtrate. • Active transport

• The Proximal tubules and the Distal tubules maintains pH by controlling the secretion of H+ and K+

• The Proximal tubule secretes ammonia

Excretion• The disposal of nitrogen-containing waste products of

metabolism• The collecting duct of a nephron, carrying the filtrate through

the medulla to the renal pelvis, becomes permeable to urea in the inner medulla. Along with the salt, the urea contributes to high osmolarity of the interstitial fluid in the medulla, and this high osmolarity enables the kidney to excrete urine, which is hyperosmotic to the general body fluids.

Kidney Stone• A solid piece of material that forms in a kidney when

substances that are normally found in the urine become highly concentrated.

• Symptoms• pain while urinating• blood in the urine• a sharp pain in the back or lower abdomen.

• Kidney stones affect approximately 1 in 11 people in the United States.

• Treatment• Shock wave lithotripsy• Ureteroscopy• Percutaneous nephrolithotomy

Nephritis• inflammation of the nephrons in the kidneys.• Symptoms• Swelling of the tissues• Reduction in urine volume• Dark urine (contains blood which may not be visible)• Increase in blood pressure• Headaches• Drowsiness• Visual disturbances• Nausea

• Treatment:• Restriction of salt• Antibiotics• renal dialysis

• affects 1 in 4,428 Americans

Sources• BBC• http://www.bbc.co.uk/health/physical_health/conditions/nephritis1.shtml

• excretorysystemdiseases• http://excretorysystemdiseases.com/

• Prevalence of Kidney Stones in the U.S.• http://www.ncbi.nlm.nih.gov/pubmed/22498635

• NKUDIC• http://

kidney.niddk.nih.gov/KUDiseases/pubs/stonesadults/index.aspx#symptoms

• http://www.emc.maricopa.edu/faculty/farabee/biobk/biobookexcret.html

• AP Biology Textbook• Campbell, Neil A., Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A.

Wasserman, Peter V. Minorsky, and Robert B. Jackson. AP Edition: Biology. New York: Benjamin/Cummings, 2008.

Sources (Cont.)• Pictures• http://

img.webmd.com/dtmcms/live/webmd/consumer_assets/site_images/articles/image_article_collections/anatomy_pages/Kidney2.jpg

• http://childrenshospital.org/az/Site1318/Images/Kidney.gif• http://

www.urologyhealth.org/urology/articles/images/anatomy_Ectopic_Ureter.jpg

• http://upload.wikimedia.org/wikipedia/commons/thumb/5/57/Illu_bladder.jpg/300px-Illu_bladder.jpg