Maintaining Water & Nitrogen Balance in the Body

cells swelling as water moves into them, this has a diluting effect and can lead to cell lysis (bursting)

problems of too much water in the blood

cells lose water by osmosis, this has a dehydrating effect and can lead to cell death

too little water in the blood

water as a result of aerobic respiration

water in the diet

sources of water

exhalation

Sweat

How water is lost from the body

process of breaking down excess protein

Deamination

Liver

Place of deamination

Process of deamination

Enzymes in the liver split up amino acid molecules, - part containing carbon turned into glycogen and the other part containing nitrogen (the amino part) turned into ammonia. Ammonia is toxic so it is immediately converted to urea

kidney

Help to control the water content of the body and the concentrations of substances dissolved in the fluids of the body

Kidney structure

highly branched capillary networks that form filters which contain pores

Filtration

high-pressure mass flow forces molecules that are small enough to pass through the pores out of the bloodstream in the kidneys

glucose, urea and water with ions dissolved in it

Substances forced out into the blood in the kidneys

Liquid formed called a filtrate

What happens to larger molecules in the kidneys

• Larger molecules (such as RBCs or proteins) are too big to pass out of the filter and so remain in the blood plasma

• The kidneys then selectively reabsorb substances needed by the body back into the bloodstream (this is an active process)

Urine

Molecules not absorbed by the kidneys

filtrate passes through on its way to the bladder

Water reabsorption occurs along these tubules; if the water content of the blood is too high then less water is reabsorbed, if it is too low then more water is reabsorbed

Tubules

pituitary gland releases less ADH which leads to less water being reabsorbed in the tubules of the kidney (the tubules become less permeable to water)

High water content of blood

blood is too concentrated, the pituitary gland releases more ADH which leads to more water being reabsorbed in the tubules of the kidney (the tubules become more permeable to water)

Low water content of blood

Dialysis

Treatment for someone with kidney failure

Unfiltered blood is taken from an artery in the arm, pumped into the dialysis machine and then returned to a vein in the arm

Inside the machine the blood and dialysis fluid are separated by a partially permeable membrane – the blood flows in the opposite direction to dialysis fluid, allowing exchange to occur between the two where a concentration gradient exists

How Dialysis works

Glucose concentration similar to a normal level in blood

A concentration of salts similar to a normal level in blood

No urea

In dialysis fluid

No chance of rejection of the organ

Not enough donors

Benefits of Dialysis vs Transplant

Less restricted diet

Much more freedom (no dialysis several times a week)

Dialysis machines are expensive

Kidney transplants are a long term solution

Problems of Dialysis vs Transplant