Download Excretion & Homeostasis

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.