The Kidneys and Dialysis

The kidneys

• The kidneys make urine by taking waste and unwanted products out of the blood. Substances are filtered out of the blood as it passes through the kidneys. This is called filtration. Useful substances like glucose, some ions and the right amount of water are then absorbed back into the blood. This process is called selective reabsorption.
• One substance in urine is urea. Proteins, and the amino acids they break down into, can't be stored in the body- so any excess amino acids are converted to fats and carbohydrates, which occurs in the liver and invloves a process called deamination. Ammonia is produced as a waste product from this process. Ammonia is toxic so it's converted into urea in the liver. Urea is then transported to the kidneys, where it is filtered out of the blood and excreted as urine.
• Ions are also a substance in urine. Ions such as sodium are taken into the body in food, and then absorbed into the blood. If the ion content is wrong, this could upset the balance between ions and water, meaning too much or too little water is drawn into cells by osmosis. Having the wrong amount of water can damage cells or mean they don't work as normal. Some ions are lost in sweat , however this amount is not regulated, so the right balance of ions in the body must be maintained by the kidneys. The right amount of ions is reabsorbed into the blood after filtration and the rest are removed as urine.
• Another substance in urine is water. The body has to constantly balance the water coming in against the water coming out. We lose water from the skin in sweat and from the lungs when breathing out. We can't control how much we lose in these ways, so the amount of water is balanced by the amount we consume and the amount removed…