The Human Kidneys: Structure, Function, and Importance
Location and Structure
The kidneys are two bean-shaped organs located in the upper part of the abdominal cavity, on
either side of the backbone, just below the last two pairs of ribs.
Because of the large liver situated above the right kidney, it lies slightly lower than the left one.
The left kidney, however, is marginally larger to compensate for this difference.
A healthy adult kidney measures approximately 11 cm in length, 5 cm in width, and 3 cm in
thickness. The average weight is about 150 grams in men and 135 grams in women. Though
small in size, the kidneys perform vital and complex functions essential for life.
Blood Flow and Filtration
Each day, approximately 150–200 liters of blood pass through the kidneys. The 5–6 liters of
blood in the human body circulate through the kidneys 20 to 25 times per day.
Each kidney contains over one million nephrons, which are its functional units. A nephron
consists of two main parts: the glomerulus and the tubule.
● The glomerulus filters blood, separating waste materials from useful substances.
● The tubule reabsorbs essential nutrients such as glucose, amino acids, sodium, and
water back into the bloodstream.
From an initial 180 liters of filtrate, only about 1.5 liters of urine are ultimately produced. This
reabsorption process ensures that vital nutrients are retained in the body while waste products
are excreted.
Major Functions of the Kidneys
The kidneys perform multiple vital roles beyond waste removal:
● Maintaining fluid and electrolyte balance within the body.
● Activating vitamin D, which supports bone health.
● Releasing renin, a hormone that helps regulate blood pressure.
● Producing erythropoietin, a hormone that stimulates red blood cell production in bone
marrow.
These functions help maintain the body’s homeostasis—its internal balance necessary for
proper functioning.
Kidney Disorders and Treatment
When kidneys fail to function properly, harmful substances such as urea accumulate in the
blood, leading to a condition known as uremia.
To support patients with kidney failure, doctors use a process called dialysis, which artificially
removes wastes from the blood. There are two main types of dialysis:
1. Hemodialysis – Blood is passed through a machine that filters waste products before
returning it to the body.
2. Peritoneal Dialysis – The lining of the abdominal cavity acts as a natural filter, with a
special fluid used to remove wastes.
Dialysis is typically recommended when kidney function falls below 10–20% of its normal level.
Although it prolongs life, it cannot match the efficiency of healthy kidneys.
Kidney Transplantation
In cases of severe kidney damage, kidney transplantation may be necessary. During this
procedure, a diseased kidney is replaced with a healthy one from a living or deceased donor.
A living donor is often a close relative with a compatible blood type. Since a person can live with
one kidney, such donations can save lives.
After transplantation, the patient must take immunosuppressant medications for life to prevent
the body from rejecting the new organ. With proper care, a transplanted kidney can function
effectively for 10–20 years or more.
Kidney transplantation not only offers a second chance at life but also highlights the importance
of organ donation and medical care.
Care and Maintenance of Healthy Kidneys
To keep your kidneys healthy:
● Drink sufficient water daily.
● Eat a balanced diet low in excess salt and processed foods.
● Avoid smoking and excessive use of painkillers.
● Maintain a healthy weight and exercise regularly.
The kidneys silently work day and night to filter blood, remove wastes, balance fluids, and
produce essential hormones. Truly, they are the body’s natural purifiers and silent guardians.
Glossary
● Dialysis: A process that cleans the blood when the kidneys cannot do so effectively.
○ Hemodialysis: Uses a machine to filter blood outside the body.
○ Peritoneal Dialysis: Uses the lining of the abdominal cavity and a special fluid to
clean the blood.
