The Excretory System

9.5

Unicellular Organisms

• water balance is often maintained by contractile vacuoles

• video of Paramecium:

http://www.youtube.com/watch?v=mTXRcbjuYGU

Excretion in Earthworms

Excretion in Grasshoppers

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 Urinary System

• kidneys can hold up to 25% of the body’s blood at a time

• kidneys filter the blood

• 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

• there are about 1 million nephrons in each kidney

Review Kidney Structure…

How is urine formed?

Urine Formation

• filtration

• reabsorption

• secretion

Filtration

• higher blood pressure in glomerulus• water, ions, smaller dissolved molecules

(glucose, amino acids, urea) can 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

• filtrate becomes hypoosmotic to interstitial fluid, so water is reabsorbed by osmosis and through aquaporins

Where?

• a lot of reabsorption occurs in the proximal convoluted tubule

• filtrate with high concentration of urea and other wastes enters loop of Henle and then distal convoluted tubule:– more water and ions (Na+& Cl-)are

reabsorbed

Where (cont’d)?

• collecting ducts are permeable to water but not salt ions, so more water is reabsorbed

• at bottom of medulla, urea is reabsorbed through passive urea transporters (increasing concentration gradient…more water reabsorbed)

Secretion

• H+ ions (active) to adjust blood pH (HCO3

- is also reabsorbed to balance)• products of detoxified poisons (passive)• water-soluble drugs (passive)• nitrogen-containing wastes (such as

small amounts of NH3)• in the proximal and distal convoluted

tubules

Animations

• I like this narrated animation; diagram is easy to follow:

• http://bcs.whfreeman.com/thelifewire/content/chp51/51020.html

• Narrated animation on urine formation; good amount of detail:

• http://davisplus.fadavis.com/scanlon6e/Animations/animations.cfm?exercise=NephronFiltration&title=Nephron%20Filtration

• Slideshow with animation; shows detail on what substances are reabsorbed, secreted & where:

• http://www.aboutkidshealth.ca/En/HowTheBodyWorks/KidneysandBladderOverview/TheKidneysOverview/Pages/UrineFormation.aspx

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