Download Maintaining Water Balance

Maintaining Water Balance
The Kidneys
Homeostasis
• Regulation of a stable internal environment no
matter where we are or what we do…
• We put our bodies through A LOT on a daily
basis
– Adding food, liquid, chemicals
– Changing temperature & activity levels
• BUT…. Our bodies roll with it!
• How (examples)???
Excretory System
• Star QB of maintaining homeostasis in our bodies
– Responsible for maintaining the right amount of water
and dissolved substances in your body
(osmoregulation)
• Includes:
–
–
–
–
Kidneys
Bladder
Ureter
Urethra
Osmoregulation
• How our bodies get rid of the “stuff” we don’t
need such as…
– Byproducts of metabolized food
• Makes sure we don’t get dehydrated
• Your body’s GREATEST balancing act
The Excretory System
• Not all animals excrete waste in the same
way…
• Main byproduct of metabolizing food (mainly
protein) is ammonia (NH3)  TOXIC
– Converted into either urea or uric acid depending
on the amount of water available to the animal
Urea:
Compound made from
combining ammonia
with carbon dioxide (in
the liver)
Low toxicity: can hang
out in circulatory system
for a while with no ill
effects
BUT….
You have to have extra
water around to dissolve
it and get rid of it (you
pee)
Uric Acid:
Have to be light enough
to fly and don’t have a
lot of spare water
Excreted as paste (not a
lot of water is needed)
Have you ever seen bird
poop?
** The white part of
it is actually the uric acid
How do humans excrete urea?
• Starts with the kidney
– Maintains levels of water and dissolved materials
– Controls blood pressure
• Very Inefficient Process
– Filter the water and dissolved material out of
blood
• 99% is reabsorbed back
• 1% is sent on to make urine
• Avg day: kidneys filter out 180L of fluid from your
blood, BUT only 1.5L gets peed out
How do your kidney’s do this?
• Use nephrons
– Fun Fact: If you were to unravel all of your nephrons, they
would stretch ~180 km
• Must follow blood flow to understand how they work…
–
–
–
–
–
–
–
–
Heart
Kidney (enters via renal arteries)
Glomerulus
Bowman’s Capsule
Proximal Convoluted Tubule
Loop of Henle
Distal Tubule
Collecting Duct
Glomerulus & Bowmans Capsule
• Start point for single nephron
• Pressure is high enough that 20% of the fluid is squeezed out
and enters the Bowmans Capsule
– Cup like sac (fluid is no longer blood, but filtrate: water, urea,
small ions)
Promimal Convoluted Tubule
• Site of osmoregulation
– Reabsorb water and other materials to create
whatever balance your body needs
– Mainly reabsorbs organic solutes (ie: glucose);
recaptures Na, K and water
Loop of Henle
• Site where most of the reabsorption happens
– Extracts most of the water that we need
– Pumps salts
– Creates a concentration gradient to cause more
water to be extracted
***By the time the filtrate gets to the bottom of the
loop it is HIGHLY concentrated
Distal Tubule
• Regulates Na, K, Ca levels
– Controlled by pumps and hormones that control
the reabsorption process
• By the time its done, we have taken
everything we want OUT of the filtrate
– Filtrate is now mainly excess water, urea and
excess waste
Collecting Duct

reabsorbed
 H2O

excretion
 urea passed through to bladder
Descending
limb
Ascending
limb