Kidneys

Urea is produced as a waste product of the reaction that turns excess amino acids into fats and carbohydrates. This reaction happens in the liver.

Urea is poisonous so it needs to be removed. 

Urea is the key ingredient of urine.

None is reabsorbed into the blood.

Ions are taken into the body through food. 

The wrong balance of ions could mean too much or little water is drawn into cells by osmosis.

This can damage cells or make them less effective.

Excess ions are removed by the kidneys as well as being lost in sweat.

The balance is ALWAYS maintained by the kidneys.

Water is lost from the body in 3 main ways:

• Urine
• Sweat
• Breathing out

There needs to be a constant balance of water.

This means a balance between liquids consumed, amount of sweat and amount excreted in kidneys.

On a cold day, masses of pale, dilute urine will be produced because you don't sweat.

High pressure squeezes everything from blood into Bowman's capsule.

Allowed through:

• water
• urea
• ions
• glucose

NOT:

• proteins
• blood cells

(these stay in the blood because they're TOO BIG to pass through cell membranes)

Useful substances reabsorbed as filtrate flows through nephron:

• All sugar (active transport)
• Enough Ions (active transport)
• Sufficient Water

> Blood from renal artery into nephron

> Blood flows to glomerulus (ultrafiltration in Bowman's capsule)

> Filtrate flows through capillary network (big surface area for reabsorption)

> Blood flows up to renal vein 

> All excess ions and urea flows to collecting duct and then is excreted

If kidneys don't work, waste products build up and control over ion and water levels is lost.

This can be treated with either a kindney transplant of dialysis.

Keeps the concentration of dissolved substances the same and to remove waste substances.

>Blood flows next to selectively permeable barrier surrounded by dialysis fluid.

- permeable to things that would normally be filtered from the blood by the kidneys.

> Dialysis fluid is the same concentration of dissolved ions as the blood.

- means that nothing useful is lost from the blood.

- only waste substances and excess ions and water are lost.

Time consuming.

May cause blood clots.

May cause infections. 

Can be rejected by immune system - closely matched tissue - anti rejection drugs > make patient more prone to illnesses.