The Excretory System
9.5
Excretory System
Two main functions:
•concentrates wastes & removes them from the body
•regulates fluids & water within the body
Unicellular Organisms
• water balance is often maintained by contractile vacuoles
• video of Paramecium
Excretion in Earthworms
• hemolymph is taken into metanephridia
• ions and waste are reabsorbed & secreted into bladders
• excess water & wastes exit through pores
Excretion in Grasshoppers
• grasshoppers & other insects use Malphigian tubules to remove uric acid & other wastes
Excretion in Birds
• uric acid is excreted through the cloaca (end of digestive tract), along with feces
Human Excretory System
Renal Blood Flow)
• blood is brought to the kidneys by the renal arteries
• filtered blood leaves the kidneys through the renal veins
The Excretory System
• the kidneys remove wastes, balance blood pH, and maintain water balance
• they filter the blood plasma
• urine (with wastes and toxins) is conducted to the bladder through the ureters
Kidney Structure
Basic structure:• cortex• medulla• renal pelvis
Kidney Kiwi
Kidney Kiwi Dissection
Nephron
• the functional unit of the kidney is the nephron
about 1 million nephrons in each kidney
Review of Structures…
How is urine formed?
Urine Formation
• filtration
• reabsorption
• secretion
Filtration
• higher blood pressure in glomerulus• water, ions, smaller dissolved
molecules (glucose, amino acids, urea) move through the walls of the glomerulus
• your kidneys filter your entire blood plasma 65 times every day!
Reabsorption
• ion pumps reabsorb Na+, K+, Cl- (active)• active transport proteins reabsorb pretty
much all amino acids, glucose & other nutrients
• reabsorption of water is by osmosis (passive) and aided by aquaporins
Proximal Convoluted Tubule
• microvilli increase surface area
• ions, gluose, amino acids reabsorbed by passive & active methods
• water reabsorbed by osmosis
Loop of Henle
• water is reabsorbed in the descending portion
• ions are reabsorbed in ascending portion (“make medulla salty” as Sal Khan says)
Distal Tubule & Collecting Duct
• reabsorption of ions & secretion of H+ and K+ in distal convoluted tubule
• reabsorption of water in collecting duct
• some urea reabsorbed (passive) to allow more reabsorption of water
Secretion
• in the proximal and distal convoluted tubules, and the collecting duct
• Blood pH maintained through secretion of H+ ions and reabsorption of HCO3
-
• detoxified poisons, water-soluble drugs, nitrogen-containing wastes are all secreted
Resources
• This is a nice detailed animation that goes through the structure of the kidney & the formation of urine:
• http://www.sumanasinc.com/webcontent/animations/content/kidney.html
Kidney Disorders
Urinalysis
• can be used to detect many metabolic and kidney disorders as well as urinary tract infections
• urine can be assessed using a dipstick or at a laboratory
Multiple Test Dipstick
Diabetes Mellitus
• Type 1 - body cannot produce insulin
• Type 2 - cells fail to use insulin properly
• gestational - hormones of pregnancy interfere with action of insulin
• urinalysis would show high levels of glucose (and greater volumes of urine)
Kidney Stones
• caused by precipitation of minerals, can be alkaline or acidic
• VERY painful
Kidney Stones - Treatment
• time…• lithotripsy (shock-
wave therapy)• ureteroscopy (and
placement of stent or surgical removal of stone)
Dialysis
• for low-functioning kidneys, dialysis machine can filter blood
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