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Kidney stones (nephrolithiasis or kidney stone disease) are small deposits that build up in the kidneys. The disease could be found accidentally (when there is no pain or crisis) by X-ray of the abdominal area or by ultrasound of the abdominal organs. Kidney stones vary in shape, size and number, ranging in size from a few millimeters to 5-6 cm.

The clinical picture in patients with kidney stones is different and depends on the size and location of the stone itself. Some patients have complaints of dull, slight pain in the lower back, which is not connected with physical activity or body position. In others, kidney stones are presented by changes in the color of urine or frequent urinary tract infections.

Nephrolithiasis may be asymptomatic (without discomfort to the patient). Renal colic is the most common clinical appearance of kidney stone disease, and it occurs most often when a stone begins to move down through the narrowest part of the urinary system.

Types of kidney stones

Very often kidney stones have a mixed chemical composition and are varied in shape and color. Some of them are:

  • Calcium oxalate – the most common kidney stones. The main reasons for their formation are: increased absorption of calcium in the small intestine from food, increased excretion of calcium from bones, hyperparathyroidism, vitamin D intoxication, dehydration, taking certain medications, increased intake of oxalates with food
  • Calcium phosphate stones
  • Struvite stones – they are formed in frequent bacterial infections of the urinary tract
  • Urate stones (uric acid stones) – formed by increased urinary acid excretion in the urine and in people who do not drink enough fluids


The nephron, the functional unit of the kidneys, is responsible for removing waste from the body. Each kidney is made up of over one million nephrons, which intersperse the renal cortex, giving it a granular appearance.

It is a microscopic tubular formation that consists of a renal (Malpighian) body and a curved tubule. The Malpighian body itself consists of a capillary ball called a glomerulus and the enveloping capsule, also called a Baumann capsule.

There are three main processes in the nephron: filtration, back-suction, and secretion. These processes are extremely important for maintaining the internal fluid environment and the alkaline-acid balance in the body. During glomerular filtration, water and particles dissolved in it and leave the vascular system. After that they enter the space between the two leaves of the Bauman capsule and from there into the lumen of the renal tubules, while filtration takes place only in the glomeruli.

There are two types of nephrons:

  • cortical (their glomeruli are located in the outer 2/3 of the cortex, their loops are short and reach the outer medulla) and
  • juxtamedullary (their glomeruli are located in the inner 1/3 of the cortex, their loops are long and reach the inner medulla – to the renal papillae).

Within a day, a large amount of blood passes through the kidneys, from which 170 liters of primary urine are excreted. This filtrate, passing successively through the other structures of the nephron than undergoes resorption of water and ions, as the amount of final urine is reaching an average of 1200 ml. per day.




There are two blood vessels leading from the abdominal aorta to the kidneys. The renal artery is one of these two blood vessels. The renal artery enters through the hilus, which is situated where the kidney curves inward into the concave shape. The renal artery and the renal vein pass through this hilus. The flow of oxygen-enriched blood passes through the renal artery, which the heart pumps to the kidneys in order to be filtered. After that process is finished already filtered blood is delivered back to the heart by the kidneys.

Under normal circumstances, once the renal artery enters through the hilus, it divides into two main branches, which then divide into a number of smaller arteries that supply blood to different areas of the kidney known as nephrons. The main structural and functional unit of the kidney is the nephron. The total number of nephrons in both kidneys is about 1-2 million. A normal person’s kidneys receive approximately a quarter of the heart’s blood, or 1.2 liters of blood, every minute. The body has self-regulating mechanisms that increase or decrease blood flow to adapt to stress. Receptors located in the smooth muscle wall of the renal artery allow the arteries to dilate or contract in order to compensate for the high or low blood pressure.

Due to its vital function, which includes constant contact with toxins, the kidneys are prone to a variety of problems.



As one of the most important water-soluble non-enzymatic antioxidants, vitamin C consists of ascorbic acid and its oxidized form, dehydroascorbic acid. Vitamin C has a wide range of metabolic functions and significantly enhances cellular immunity. One of its best benefits is its ability to increase iron absorption, thus preventing problems such as iron deficiency anemia.

Compared to the general population, plasma vitamin C levels range from 30 to 60 μmol / L. Plasma levels of vitamin C in patients on hemodialysis are usually lower than in the general population, which is mainly associated with increased inflammation, anemia, oxidative stress and secondary hyperparathyroidism. Because it is excreted by the kidneys, intake above 100-200 mg / day should be restricted in patients with CKD in order to avoid oxalosis, which is an accumulation of a metabolic by-product of ascorbic acid. Many organs and tissues of the body can be affected by oxalate deposits, including the kidneys.

The supplement of vitamin C is provided by potassium-rich foods such as citrus fruits, orange juice, strawberries and broccoli, commonly limited to hemodialysis patients for whom it is important to follow a potassium-restricted diet. Loss of this vitamin is also possible during dialysis, as about a few hundred mg of it can be removed in one dialysis treatment.