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February 26, 2013
The Human Excretory System
­ path of the digestive system
­ the excretory system helps to maintain body homeostasis by removing the waste products of body metabolism (such as water, salt and metabolic concentrations in the blood)
­ organs of the digestive system
­ various organs play a role in the excretory process:
­ role of enzymes
(a) Kidneys: primary organ of excretion in the body
­ digestive disorder
(b) Lungs: remove carbon dioxide from the body
(c) Liver: amino acids are broken down, liver also removes bacteria, certain drugs and hormones. As well, the liver also detoxifies (changes substances into less poisonous forms such as alcohol)
(d) Skin: removes excess heat from the body to maintain a balanced body temperature
May 11­7:32 AM
May 11­7:34 AM
Role of Kidneys in the Excretory System:
primary function is to filter blood and remove cellular waste products from the blood
­ at any time 20% of your blood is in the kidneys
­ if one kidney stops working the other can increase in size to handle the workload
­ other functions include the excretion of cellular waste:
(a) Urea: nitrogenous waste produced in the liver from the breakdown of protein
(b) Uric Acid: produced from the breakdown of DNA and RNA
(c) Creatine: waste product of muscle action
May 11­7:49 AM
May 11­8:07 AM
* kidneys also control water pH, secrete a hormone that stimulates red blood cell production (erythropoiten) and activate vitamin D production in the blood
­ each kidney is composed of three sections:
(a) The outer section is the cortex where the blood is filtered
(b) The middle section is the medulla where there are collecting ducts which carry filtrate to the pelvis
(c) The pelvis is the hollow inner cavity where urine accumulates and drains into the ureter
May 11­7:55 AM
Apr 26­2:46 PM
February 26, 2013
once urine leaves the kidneys (pelvis) they travel through the ureters to the urinary bladder for temporary storage
­ the urethra is the tube that carries urine from the bladder to the outside of the body
­ at the outer end of the urethra is a sphincter
­ see figure 11.17 on page 374
­ see handout provided
­ see figure 11.19 on page 375
May 11­8:06 AM
May 11­7:59 AM
­ text pages 374 ­ 379
­ complete sheets on excretory system
May 11­8:09 AM
May 11­8:03 AM