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.