1. THE KIDNEY - HOW IT WORKS
By the end, you will know about…
Nephrons
Ultrafiltration
Selective Reabsorption
Control of Water Balance
Kidney Damage and possible treatments….

2. Excretion
We need to excrete certain things that may otherwise build up and be poisonous to us, eg:
Carbon dioxide (lungs)
Urea (kidney)
Excess salts or water

3. The Kidney You have two kidneys in your body.
They are located towards your back, near your waist.
They filter the blood, and
remove any harmful or
excessive substances, eg.
Urea, water, salts, hormones.

4. Inside the Kidney The kidney has an outer CORTEX.
The middle section is the MEDULLA.
There are pyramid-like structures in the medulla.
The centre part is known
as the PELVIS.
The tube that carries urine
to the bladder is the URETER.

5. The Nephron Nephrons are small subunits that make up the kidney.
They do the filtering!
There are millions of
these tiny structures
inside the kidney, and all
eventually drain into the
ureter.

6. Ultrafiltration Blood had to be filtered to stay “clean”.
It has to be filtered under high pressure. ULTRAfiltration!
The blood enters
the kidney through
the RENAL ARTERY.
It enters the
GLOMERULUS – a tiny
knot of capillaries.

7. Bowman’s Capsule
As the blood goes from artery to glomerulus, it creates extremely high pressure.
This forces everything
small enough to leave
the blood and enter
the first part of the
nephron; Bowman’s
Capsule.
Proteins and cells are
too big, so stay in the
blood.

8. First Coiled Tubule
After the filtrate trickles down from Bowman’s Capsule, it contains water, salts, urea, glucose, any hormones and drugs.
However, the body needs to reabsorb the useful products back into the blood.
The first coiled tubule is
the first section of the
nephron, near the Bowman’s
capsule. It is long and coiled.
In the first coiled tubule,
glucose is reabsorbed into
the capillaries surrounding the
nephron.

9. The Loop of Henlé
The next section of nephron is the Loop of Henlé. It is a long loop, that goes into the medulla of the kidney.
It is here that water and some useful salts are reabsorbed.

10. Second Coiled Tubule
This is the third section of the nephron. It is another coiled tubule.
Anything else that needs reabsorbing will be reabsorbed here (eg. water and more salt if necessary).

11. Collecting Duct
All the leftover substances end up in the collecting duct.
This includes urea, excess water and salts, any drugs and other waste products from the body’s chemical reactions.
If the body gets dehydrated,
water gets absorbed from the
collecting duct.
This leftover waste liquid is
known as URINE.

12. Urine Urine can be important in diagnosis of certain diseases.
If there are certain substances in the urine that should have been filtered out by the kidneys,
then it can be an
indication of kidney
damage.
Glucose in the urine is an
indication of diabetes.

13. Water Balance
The levels of water in the body need to be properly controlled to avoid death by dehydration.
This is an example of
HOMEOSTASIS – keeping
the environment inside
you at a constant.
Think of it like a driver
trying to stick to the speed
limit!

14. ADH
Anti-diuretic hormone is produced by the pituitary gland in the brain.
Changes in water
levels in the blood
are detected by the
HYPOTHALAMUS in
the brain. It controls
release of ADH by
the pituitary.

15. Water Balance cont…
When you drink a lot, there is a lot of water in your blood.
Your hypothalamus detects this, and stimulates the pituitary to release LESS ADH.
This means the collecting ducts become LESS permeable to water.
LESS water is reabsorbed into the blood.
Therefore you produce a greater amount of weak, pale urine.

16. Water Balance cont…
When you don’t drink enough, the hypothalamus stimulates the pituitary to release MORE ADH.
The collecting ducts become MORE permeable to water.
MORE water is reabsorbed into the blood.
Therefore you produce a small amount of very yellow, concentrated urine.

17. Kidney Damage
The kidneys can be damaged due to diabetes, high blood pressure, developing kidney stones, etc.
You can survive with one working kidney, as the blood can still be filtered by the remaining kidney.
If both kidneys fail, there are only two possible treatments to stop the toxins and salts building up to fatal levels in the body.

18. Treatments – Dialysis
The patient is hooked up to a dialysis machine – this is like an artificial kidney.
The patient’s blood
runs out of the body,
through tubes into
machine where excess
fluids and toxins are
drawn off. Tubes take
blood back into the body.

19. Treatments - Transplants
A donor kidney must be found
that matches the patient’s
own tissue type.
The donor kidney must be
removed from the donor less
than an hour after death.
The kidney is put in the groin,
and attached to a vein and an
artery.
The patient will have to take anti-rejection drugs for the rest of their life.