Excretion

What is Excretion?

• The removal of metabolic waste products and excess substances from the body.– CO2 is a MWP of Respiration

– CO2 is toxic in large amounts

• Excretion is NOT the same as Egestion– The material in feces is not MWP’s; it was never

digested or absorbed.

3 Main Excretory Products

• Do you remember them all?• Carbon Dioxide

– MWP of cell Respiration

• Urea– MWP of Liver, removed by kidneys

• Water– In excess, removed by kidneys

How do you Produce Urea?

• First, you eat proteins, which get digested into amino acids and absorbed into your blood.

• The AA’s travel to the Liver (thru the hepatic portal vein)

• Extra AA’s get broken down into urea.– This involves deamination; removing the part of

the AA that contains Nitrogen.• The part with N will be excreted as Urea.• So Urea is a “nitrogenous excretory product.”

Urea Production & Excretion

How do you Excrete Urea?

• The urea goes back into the blood and travels to the kidneys.

• Kidneys take urea out of the blood and mix it with water to make urine.

• The urine flows from the kidneys thru 2 ureters to the bladder.

• Then it’s excreted thru the urethra.

Urea Production & Excretion

Human Urinary System

Real Quick Review

• You eat a protein and break it down into AA’s. Where do the AA’s go next?

• To the Liver (thru the HPV)• What happens to extra AA’s in the Liver?• They get deaminated and made into urea• Where does the urea go next?• To the kidneys, then out of the body thru the

ureters bladder urethra.

Put them in order! (pg. 140)# Event

6 AA’s are deaminated in Liver

10 Kidneys remove urea from blood

4 AA’s travel through hepatic portal vein

8 Urea passes into blood

1 Proteins are eaten

14 Urine flows into urethra

2 Proteins are digested into AA’s

13 Urine is stored in the bladder

3 AA’s are absorbed into blood

5 AA’s enter liver cells

7 Urea is produced

9 Urea is carried to kidneys

11 Urine is produced

12 Urine flows through the ureter

More on Kidneys

• Kidneys consist of tiny units of tubules called nephrons.

• The nephron is where urea is filtered out of the blood.

• An intricate network of blood capillaries around the nephron helps urea diffuse down its concentration gradient into the urinary tubules.

• Other substances also diffuse out of the blood in the same way.

Kidney and Nephron

Nephron and Blood Capillaries

Kidney Failure

• When kidneys fail, people still need their blood “cleaned” of urea and other harmful substances.

• They have to undergo dialysis treatment several times a week.

• Dialysis = a mechanical means of filtering blood, using concentration gradients to remove urea and other substances.

• Blood is filtered outside of the body and pumped back in!

Dialysis

Dialysis

Dialysis

Kidneys and Water Regulation

• What if you had too much water in your body?• What if you didn’t have enough?• Kidneys excrete lots of watery urine when you

have too much.• Kidneys excrete only small amounts when

you’re short on water.– So the urine is very concentrated.

Other Excretory Substances (besides the 3 main ones)

• Hormones– Broken down in liver, excreted by kidneys in urine

• Alcohol– Also broken down in liver– Toxic to cells; even liver cells!– Liver damage or failure can result from drinking

too much alcohol.

Question (then we’re done!)

• Why should a person with kidney failure avoid eating salty foods?

• The kidneys will be unable to filter out the extra salt.