Structure of the kidney
The kidneys are among the most vital organs of the human body.
Malfunction of the kidneys can lead to serious illness or even death.
Each kidney has a very complex structure and function.
They have two important functions namely: to flush out harmful and
toxic waste products and to maintain balance of water, fluids, minerals
and chemicals i.e., electrolytes such as sodium, potassium, etc.
Structure of the Kidney
The kidney produce urine by removing toxic waste products and excess
water from the body. Urine formed in each kidney passes through the
ureter, flows into bladder before finally being excreted through the
Most people (males and females) have two kidneys.
The kidneys are located at upper and back side of the abdomen, on
either side of the spine (see diagram). They are protected from damage
by the lower ribs.
The kidneys lie deep inside the abdomen so normally one cannot
The kidneys are a pair of bean shaped organs. In adults, a kidney is
about 10 cm long, 6 cm wide and 4 cm thick. Each kidney weighs
approximately 150-170 grams.
Urine formed in the kidneys flow down to urinary bladder and then
through the ureters. Each ureter is about 25 cm long and is a hollow
tube- like structure made up of special muscles.
The urinary bladder is a hollow organ made up of muscles, which lie
in the lower and anterior part of the abdomen. It acts as a reservoir
The adult urinary bladder hold about 400-500 ml of urine; when
filled to near capacity, a person feels the urge to pass urine.
The urine in the bladder is excreted through the urethra during the
process of urination. In females, the urethra is relatively short, while
it is much longer in males.
Location, structure and functions of the kidneys
are the same in males and females.
Functions of the kidney
Why are the kidneys essential for living?
What are the functions of the kidney?
- We consume different kinds and quantities and kind of food every
- The quantity of water, salts, and acids in our body also varies every
- The continuous process of converting food into energy produces
harmful toxic materials.
- These factors lead to changes in the amount of fluid, electrolytes and
acids in the body. The accumulation of unwanted toxic materials
can be life threatening.
- Each kidney carries out the essential job of flushing out harmful and toxic by-products. At the same time, they also regulate and maintain
the right balance and levels of water, acids and electrolytes.
The primary function of
he kidney is to make
urine and purify the
blood. Each kidney
materials, and other
chemicals which are not
equired by the body.
mportant functions of
he kidney are
1. Removal of waste products
Purification of blood by removal of waste products is the most important
function of the kidney.
The food that we consume contains protein. Protein is necessary for
the growth and repair of the body. But as protein is utilized by the body
it produces waste products. Accumulation and retention of these waste
products is similar to retaining poison inside the body. Each kidney
filters blood, and toxic waste products which are eventually excreted in
Creatinine and urea are two important waste products, that can easily
be measured in the blood. Their “values” in blood tests reflects the
function of the kidney. When both the kidneys fail, value of creatinine
and urea will be high in blood test.
2. Removal of excess fluid
The second most important function of the kidney is the regulation of fluid balance by excreting excess amount of
water as urine while retaining the necessary
amount of water in the body, that is essential for
When the kidneys, fail they lose the ability of
removing this excess amount of water. Excess
water in the body leads to swelling.
3. Balance minerals and chemicals
The kidneys play another important role of
regulating minerals and chemicals like sodium,
potassium, hydrogen, calcium, phosphorus,
magnesium and bicarbonate and maintains
normal composition of body fluid.
Changes in the sodium level can affect person’s
mental state, while changes in the potassium level
can have serious adverse effects on the rhythm
of the heart as well as functioning of the muscles.
Maintenance of normal level of the calcium and
phosphorus is essential for healthy bones and
4. Control of blood pressure
The kidneys produce different hormones (renin,
angiotensin, aldosterone, prostaglandin etc)
which help regulate water and salt in the body, which plays vital roles in
the maintenance of good blood pressure control. Disturbances in
hormone production and regulation of salt and water in a patient with
kidney failure can lead to high blood pressure.
5. Red blood cells production
Erythropoietin is another hormone produced in the kidneys, it plays an
important role in the production of red blood cells (RBC). During kidney
failure, production of erythropoietin is decreased, which in turn leads to decreased production of RBC resulting in low hemoglobin (anemia).
This is the reason why in patients with kidney failure, the hemoglobin
count does not improve despite supplementation with iron and vitamin
6. To maintain healthy bones
The kidneys convert vitamin D into its active form which is essential for
the absorption of calcium from food, growth of the bones and teeth,
and keep the bones strong and healthy. During kidney failure, decreased
active vitamin D leads to decreased, growth of bones and they also
become weak. Growth retardation may be sign of kidney failure in
How is blood purified and urine formed?
In the process of blood purification, the kidneys retain all necessary
substances and selectively removes excess fluid, electrolytes and waste
Let us understand this complex and amazing process of urine formation.
- Did you know that every minute, 1200 ml of blood enters the kidneys
for purification, which is 20% of the total blood pumped by the
heart? So in one day, 1700 liters of blood is purified!
- This process of purification occurs in small filtering units known as
- Each kidney contains about one million nephrons, and each nephron
is made up of glomerulus and tubules.
- Glomeruli are filters with very tiny pores with the characteristic of
selective filtration. Water and small-sized substances are easily filtered
through them. But larger-sized red blood cells, white blood cells,
platelets, protein etc. cannot pass through these pores. Therefore
such cells are normally not seen in the urine of healthy people.
The kidney’s chief function is to remove waste and
harmful products and excess water in the form of urine.
Can there be variation in the volume of urine in a person with
- The first step of urine formation occurs in the glomeruli, where 125
ml per minute of urine is filtered. It is quite astonishing that in 24
hours, 180 liters of urine is formed. It contains not only waste
products, electrolytes and toxic substances, but also glucose and
other useful substances.
- Each kidney performs the process of reabsorption with great
precision. Out of 180 liters of fluid that enters the tubules, 99% of
fluid is selectively reabsorbed and only the remaining 1% of fluid is
excreted in the form of urine.
- By this intelligent and precise process, all essential substances and
178 liters of fluid are reabsorbed in the tubules, whereas 1-2 liters
of fluids, waste products, and other harmful substances are excreted.
- Urine formed by the kidneys flow to the ureters, and passes through
the urinary bladder and is finally excreted out through the urethra.
- Yes. The amount of water intake and atmospheric temperature are
major factors which determine the volume of urine that a normal
- When water intake is low, urine tend to be concentrated and its
volume is decreased(about 500 ml) but when a large volume of
water is consumed, more urine is formed.
- During the summer months, because of perspiration caused by high
ambient temperature, the volume of urine decreases. During winter
months it is the other way round – low temperature, no perspiration,
- In a person with a normal intake of water, if the volume of urine is
less than 500 ml or more than 3000 ml, it could indicate that the
kidneys need closer attention and further investigation.
Too little or too much volume of urine formation, could be an
indication that the kidney seeks attention and investigation.