THE KIDNEY - HOW IT WORKS

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.

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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.

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Bowmans 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 Bowmans
• Capsule.
• Proteins and cells are
• too big, so stay in the
• blood.

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First Coiled Tubule

• After the filtrate trickles down from Bowmans
  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 Bowmans
• capsule. It is long and coiled.
• In the first coiled tubule,
• glucose is reabsorbed into
• the capillaries surrounding the
• nephron.

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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.

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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).

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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 bodys
  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.

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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!

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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.

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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.

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Water Balance cont

• When you dont 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.

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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.

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Treatments Dialysis

• The patient is hooked up to a dialysis machine
  this is like an artificial kidney.
• The patients 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.

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Treatments - Transplants

• A donor kidney must be found
• that matches the patients
• 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.