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