The kidneys are found in all vertebrates. They are a pair of bean-shaped organs present in the abdomen. Their primary task is to remove waste products from the body while maintaining the electrolyte balance. They also regulate blood pressure. The kidneys are hence considered very important organs in the body.
Structure of the Kidney –
They are present at the back of the abdominal cavity, located on each side of the spine respectively.
To accommodate the liver, the right kidney is slightly smaller than the left kidney, both weighing around 125–170 grams in males and 115–155 grams in females.
There is a tough, fibrous capsule that surrounds each kidney. Kidneys have a layer of fat on them which serves are protection. Inside the kidney, a number of pyramid-shaped lobes are seen.
Each has an outer renal cortex and an inner renal medulla. Nephrons are present in between all these segments. Nephrons are the urine producing structures of the kidney. Blood flows through the renal arteries and leaves through the renal veins. Each kidney is connected to the bladder, which serves as a reservoir for the collection of urine.
Functions of the Kidney –
Primarily the function of the kidneys is to maintain homeostasis. They manage fluid levels and keep the electrolyte balance appropriate.
When there is kidney failure, the first line to treatment is dialysis. In case which has end-stage renal disease, the doctors advise for Renal Transplantation. The kidney transplant cost in India depends on –
- Type of transplant
- Donor availability
- The extent of the renal disease
- Choice of hospital
- Surgeon’s experience
- Length of hospitalization
- Room category
The various functions that Kidney serves are –
Waste excretion
The kidneys excrete a number of waste products through urine. The two major compounds that the kidneys remove are urea, resulting from the breakdown of proteins and uric acid which results from the breakdown of nucleic acids.
Reabsorption of nutrients
They reabsorb nutrients from the blood and transport them to different parts of the body. This keeps the homeostasis of the body in control. Reabsorbed products include:
- glucose
- amino acids
- bicarbonate
- sodium
- water
- phosphate
- chloride, sodium, magnesium, and potassium ions
Maintaining pH
The pH level between 7.38 and 7.42 are considered appropriate. Below this pH, it is acidemia, and above it is alkalemia.
Outside these ranges, the proteins and enzymes do not function properly, and they break down. This can be a fatal change for the body. The kidneys and lungs stabilize the pH in the human body.
The kidneys keep the pH in the range by –
Getting more bicarbonate from urine: The kidney reabsorbs a lot of bicarbonate, which helps neutralize acids. The kidneys then either retain it if the pH is tolerable, otherwise the release it through the urine.
Excreting hydrogen ions: Because of incomplete metabolism of the proteins and carbohydrates, fixed ions are released. These are acidic and kidney works in excreting them to keep the pH in good shape. These include lactic acid, sulfuric acid, and phosphoric acid.
Osmolality regulation –
Osmolality is the measure of the body’s electrolyte-water balance. This is the ratio between the water level and the mineral level in the body. Dehydration causes an electrolyte imbalance.
If the osmolality raises in the blood more antidiuretic hormone (ADH) is released by the pituitary gland. This causes a number of changes, including:
- increasing urine concentration
- increasing water reabsorption
- reopening portions of the collecting ducts to allow water back into the body
- retaining urea in the medulla of the kidney, because it attracts water
Regulating blood pressure
The kidneys regulate blood pressure when necessary, but they are only capable of making slight changes. They maintain the long-term pressure in the arteries by changing the extracellular fluid consistency. With the release of certain hormones which act as a vasoconstrictor, the blood vessels get narrower. Anything that alters the blood pressure of the body can damage the kidneys over time, including alcohol consumption, smoking, or obesity.
Secretion of active compounds
The Kidney releases:
Erythropoietin: This controls the production of red blood cells. The liver and the kidney are the main producers of this, and in adults, the kidney produces it at a higher rate.
Renin: This helps in managing the expansion of arteries. It is also required to maintain the volume of blood plasma, lymph, and interstitial fluid.
Calcitriol: This is the hormonal active metabolite of vitamin D, which controls the amount of calcium absorbed in the body.
Formation of urine
The main processes are involved in the creation of urine are –
Filtration – takes place at the renal corpuscle, the contents are filtered from the fluid that is collected. This filtered content will be pushed towards being reabsorbed or will be excreted. The filtered content includes some minerals and non-essential vitamins.
Reabsorption – at the re absorption stage, the remaining filtrate is absorbed. The number of nutrients required by the body is calculated, and they are absorbed by the kidneys before the urine is passed to the bladder.
Image courtesy: Vidal Balielo Jr.
