The following excerpt is taken from the first chapter of the publication 'Kidney Failure Explained' (1st edition) written by Dr. Andy Stein and Janet Wild. For details on how purchase the 2nd edition of this book, please see the details in the side menu.

Kidney failure - What is it?
Kidney failure is a condition in which the kidneys are less able than normal to perform their usual functions. These functions are:

• Removing toxic wastes
• Removing excess water
• Helping to control blood pressure
• Helping to control red blood cell manufacture
• Helping to keep the bones strong and healthy

This book is about the long-term condition known as chronic kidney failure or chronic renal failure. There is also another condition, known as acute kidney failure, in which the kidneys suddenly stop working. Short term treatment may be needed for acute kidney failure, but the kidneys usually get better on their own. This book does not tell you about acute kidney failure.

When someone has chronic kidney failure, the kidneys become less and less able to do their work. This happens gradually, usually over a period of many years. Eventually the kidneys stop working almost completely - a condition called end-stage renal failure or ESRF. Treatment is then essential to take over the work of the kidneys and so keep the patient alive. The treatments for ESRF are dialysis - either peritoneal dialysis (PD) or haemodialysis -or a kidney transplant. These treatments cannot 'cure' kidney failure but they can improve health and prolong life.

Introduction
Chronic kidney failure is a serious, long-term medical condition. At the present time, there are approximately 30,000 people in the UK who are either on dialysis or who have received a kidney transplant to treat chronic kidney failure. This is approximately one person in 2000, making it a rare condition.

Kidneys - What and where are they?
Most people have two kidneys. These important organs are shaped like 'kidney beans' and are about 12 cm long, 6cm wide and 3cm thick. They lie under the ribs at the back of the body, just above the waist.

The Kidneys' Main Job: Making urine
The main job of the kidneys is to make urine. Blood is pumped by the heart to each kidney. The kidneys then 'sieve' the blood to remove water and toxins and make urine.

Each kidney has a drainage system that takes urine from the kidney to the bladder through a tube called the ureter. Urine is stored in the bladder before being passed from the body via another tube called the urethra. The bladder holds about 400ml or urine when 'full'. People normally pass about 2 litres of urine a day.

Why make urine?
The kidneys make urine in order to perform their 2 most important functions. These are
1. removing toxic wastes from the blood - a process called clearance (More details in Ch.2)
2. removing excess water from the body. A process called ultra filtration (More details in Ch.3).

Removing toxic wastes
The kidneys play a very important role in getting rid of the waste products of food. The food that we eat is normally digested in the stomach and the bowels. During digestion the food is broken down into simple substances that can be carried round the body in the blood. These 'good things' in the bloodstream provide every part of the body with the energy that it needs for work, and with the substances that it needs for growth and repair.

When the different parts of the body make use of the various 'good things' in the blood, they also produce waste products. These wastes are toxins (poisonous) to the body and make people unwell unless they are removed. Like the 'good things' these 'bad things' also travel around the body in the blood stream.

When the waste products of food reach the kidneys it is the job of the kidneys to get rid of them in the urine. What the kidneys do is to sieve and filter the blood, removing the wastes and putting them in the urine, but leaving the 'good things' in the blood.

In people with kidney failure, however, the levels of toxins build up in the blood. It is this build up of toxins that makes people with kidney failure feel unwell. When someone is in the early stages of kidney failure, there are usually no symptoms because the toxin levels are not high enough to cause them (this can be true even when the kidneys are working at less that 25% of their normal capacity).

Removing excess water
The second most important function of the kidneys is to remove excess water from the body. as well as getting rid of the waste products of food, healthy kidneys also remove excess fluids from the body. Like the food that we et, the water (and tea, coffee, beer and all other liquids) that we drinks is digested in the stomach and bowels and absorbed into the blood. When the blood reached the kidney, the normal sieving and filtering process removes any excess water and puts it into the urine. So, normal urine contains not only the waste products of food but also any excess water that has been drunk.

In people with kidney failure, water cannot be so easily be put into the urine. Excess fluid can therefore build up in the body, causing it to become 'waterlogged' - a condition called fluid overload (More details in Ch.3) . this may lead to swelling of the ankles and shortness of breath due to excess fluid in the lungs.

Other functions of the kidneys
As well as making urine to perform their two main functions (removing toxic wastes and removing excess water) the kidneys have 3 important 'extra' functions. These are:

1. Helping to control blood pressure
The blood pressure is usually finely controlled by the kidneys. When someone's kidneys fail, their blood pressure usually goes up, although it is not really known why. High blood pressure does not usually cause symptoms unless the blood pressure gets very high but it increases the risk of a stroke or heart attack and can cause the kidneys to deteriorate more rapidly, (More details in Ch.4).

2. Helping to control the manufacture of red blood cells
The kidneys help to control the many of red blood cells in the bone marrow. The red blood cells float in the liquid part of the blood (called plasma). Their job is to carry oxygen around the body. Every part of the body needs oxygen to function properly.

When someone has kidney failure, they make fewer red blood cells than normal. As a result, most people with kidney failure become anaemic (i.e. they are short of red blood cells). This anaemia contributes to the tiredness suffered by most people with kidney failure - it is not only high toxin levels that cause tiredness (More details in Ch.5).

3. Helping to keep the bones strong and healthy.
Calcium and phosphate are two minerals found in the blood and the bones. If the bones are to stay strong and healthy, there must be a correct balance of these minerals in the body. The kidneys help to maintain this balance. When someone develops kidney failure, the normal balance between calcium and phosphate in the body is lost. The level of calcium in the blood goes down, while the level of phosphate in the blood goes up. Unless this imbalance is treated, it will result in a condition called renal bone disease. This may cause aches and pains in the bones, and even fractures (More details in Ch. 6).