Water and Waste
How the kidneys remove excess water, salts and nitrogen from the body
Water balance – Gaining water
• We take in water from DRINKING IT! We don’t just drink water, but tea, coffee and Irn Bru.
• Food contains a lot of water too. Some foods, especially vegetables and fruit have a high water content.
• Chemical reactions in the body produce water as a waste product. REMEMBER RESPIRATION!!
Water balance - Loss
• We lose water in SWEAT.• We lose water in BREATH, which can be
seen when we breathe onto a glass surface.
• Excess water is removed by the kidneys in URINE!!
• Although FAECES still contain water. The water absorbed from food goes into the bloodstream, and then into the urine.
Maintenance of internal water balance
Why this is essential, and why water gain must equal water loss.
The KIDNEYS are the main organs of water regulation
Water gain
2150 cm3 from food and drink
350 cm3 from chemical reactions
Total gain = 2500 cm3
Water loss
500 cm3 in sweat400 cm3 in breath1500 cm3 in urine100 cm3 in faeces
Total loss = 2500 cm3
Only the KIDNEYS can REGULATE the volume of
water lost from the body, by producing a LARGE or
SMALL volume of
URINE.
The role of ADHADH = Anti-diuretic hormone.
It is produced by the pituitary gland in the brain, and controls the volume of
water reabsorbed by the kidneys.
Waste disposal by the Kidneys
Harmful waste products such as UREA are removed from the blood.
UREA which is dissolved in excess water -forms URINE. Urea is formed by the breakdown of surplus amino acids
(remember protein?)
So! Where are the
kidneys?
Filtration and Reabsorption
Blood enters the kidney through theRENAL ARTERY!
Blood leaves the kidney through theRENAL VEIN!
So!The blood isfiltered in the
Bowman’s capsule
AND! Useful substances are
reabsorbed in the kidney tubule
Nephrons are the working part
of the kidney
There are about a million
nephrons in each kidney
A nephron looks like this!
You must be able to….Label all
these parts!
AND where glucose, excess
water and salts are REABSORBED into
the blood
Reabsorption• 99% of water in the glomerular filtrate is
reabsorbed from the tubule, especially in the Loop of Henle.
• Glucose is reabsorbed in the tubule just after it leaves the Bowman’s capsule.
• Salts are reabsorbed at the end of thetubule just before it reaches the collecting duct.
But! What happens if you get
kidney failure?
You have to go on to a dialysis system
whilst you wait for a kidney transplant
If you didn’t have dialysis..
• Urea would poison you.• Salts would build up in your blood and
you would dehydrate.• Excess water would give you high blood
pressure and maybe a stroke.