The kidneys control water levels in the body and remove waste from the bloodstream. The kidneys filter the blood, reabsorbing useful nutrients while producing urine containing waste products like urea and excess water. This urine travels from the kidneys through the ureters to the urinary bladder for storage before being excreted through the urethra. In this way, the kidneys play a vital role in regulating water balance and removing toxins from the body.

1. The Kidney

2. Controlling water levels
 The control of water levels is carried out by the
KIDNEYS.
 It is closely linked to the excretion of urea.
 Urea is a waste product that is made when the
LIVER breaks down proteins that are not
needed by the body.
 Urea contains the element Nitrogen.

3. Kidneys
 Two reddish organs just above the waist
behind the stomach
 Filter the blood and removes waste

4. The Human Kidney & Nephron

6. Ureter
 Connects the kidneys to the urinary
bladder

7. Urinary Bladder
 Smooth muscle bag
 Stores waste solution - urine

8. Urethra
 Connects bladder to outside of the body
 Allows urine to pass out of the body

9. Nephron
 Filtering unit of the
kidney
 Blood enters full of
waste and leaves
filtered
 Blood enters under
high pressure and
flows into the
capillary beds

11. The kidneys
The kidneys “clean” the blood of waste
products and control how much water
is kept in the body. The waste
products and water make up urine
which is excreted via the ureter.
“Dirty” blood enters the kidney
through the renal artery. Then,
several things happen to clean the
blood...

12. 1. Filtration: Glomerulus and
Renal Capsule
Blood enters the tubule area in
a capillary.
The capillary forms a small
“knot” near the kidney tubule.
The blood is filtered so all the
small particles go into the
tubule.
The capillary then carries on
to run next to the tubule.

13. The kidney tubule now contains
lots of blood components
including:
Glucose:
Ions:
Water:
Urea:

14. 2. Reabsorb sugar: First
Convoluted Tubule
The body needs to have sugar
in the blood for cells to use in
respiration. So all the sugar is
reabsorbed back into the
capillary.
What sort of transport do you
think must be used if all sugar
is reabsorbed?

15. 2. Reabsorb sugar
The body needs to have sugar
in the blood for cells to use in
respiration. So all the sugar is
reabsorbed back into the
capillary.

16. 3. Reabsorb water: Loop of
Henle
Water and ions are the next to
be absorbed. It depends on
how much is needed by the
body.

17. 3. Reabsorb Ions: Second
Convoluted Tubule
Ions are the next to be
absorbed. It depends on how
much is needed by the body.
If a lot of ions need to be
reabsorbed again active
transport is used.

18. Water content of Water content of
the blood LOW the blood HIGH
Too much water drunk
Too much salt
or sweating
Brain
Brain
produces Water content
produces
More ADH of the blood normal
Less ADH
High volume of water Low volume of water
reabsorbed by kidney reabsorbed by kidney
Urine output Urine output
LOW HIGH
(small volume of (large volume of
Concentrated urine) dilute urine)

19. Reabsorbing water
If you have too If you have too
little water in your much water in your
blood, you will blood, you will
produce very produce very dilute
concentrated urine. urine.
(very little water in (lots of water in it)
it)

20. 5. Excrete the waste
Everything that is left in the
kidney tubule is waste:
•All the urea
•Excess water
This waste is called urine. It is
excreted via the ureter and is
stored in the bladder.
Renal vein
The “clean” blood leaves the
kidney in the renal vein.
Ureter

21. Summary of urine production
 Urea is a waste product made in the LIVER
 Water content of the body is controlled in the
KIDNEYS
 Urea, water and other waste makes up URINE.
 Urine travels down the URETER and is stored
in the BLADDER
 Urine is excreted through the URETHRA.

22. Animation
 http://www.kscience.co.uk/animations/kidney.
htm