The kidneys (from the Latin ren, renis) are organs that are part of the urinary system. They ensure the filtration of the blood by eliminating waste therein through the production of urine. They also maintain the body’s water and mineral content.

The nothings, two in number, are located in the rear part of the abdomen at the level of the last two ribs, on each side of the spine. The right kidney, located under the liver, is a little lower than the left, which is located under the spleen.

Each kidney, bean-shaped, measures on average 12 cm in length, 6 cm in width and 3 cm in thickness. They are surmounted by an adrenal gland, an organ belonging to the endocrine system and not involved in urinary function. They are each surrounded by a protective outer shell, the fibrous capsule.

The interior of the kidneys is divided into three parts (from the outside to the inside):

• The cortex, the outermost part. Pale in color and about 1 cm thick, it covers the medulla.
• The medulla, in the center, is reddish brown in color. It contains millions of filtration units, the nephrons. These structures have a glomerulus, a small sphere where blood filtration and urine production takes place. They also consist of tubules directly involved in changing the composition of urine.
• The calyces and pelvis are urine collecting cavities. The calyces receive urine from the nephrons which is then poured into the pelvis. The urine then flows through the ureters to the bladder, where it will be stored before being evacuated.

The inner edge of the kidneys is marked by a notch, the renal hilum where the renal blood vessels and nerves as well as the ureters end. The “used” blood arrives to the kidneys through the renal artery, which is a branch of the abdominal aorta. This renal artery then divides inside the kidney. The blood that comes out is sent to the inferior vena cava through the renal vein. The kidneys receive 1,2 liters of blood per minute, which is about a quarter of the total blood volume.

In the event of pathologies, only one kidney can perform the renal functions.

The kidneys have four main functions:

• The development of urine from the filtration of blood. When the blood arrives to the kidneys through the renal artery, it passes through the nephrons where it is cleared of certain substances. Waste products (urea, uric acid or creatinine and drug residues) and excess elements are excreted in the urine. This filtration makes it possible at the same time to control the water and ion content (sodium, potassium, calcium, etc.) in the blood and to keep it in balance. In 24 hours, 150 to 180 liters of blood plasma are filtered to produce approximately 1 liter to 1,8 liters of urine. Urine is ultimately made up of water and solutes (sodium, potassium, urea, creatinine, etc.). Some substances are not, in a healthy patient, present in the urine (glucose, proteins, red blood cells, white blood cells, bile).
• Secretion of renin, an enzyme that helps regulate blood pressure.
• The secretion of erythropoietin (EPO), a hormone that stimulates the formation of red blood cells in the bone marrow.
• The transformation of vitamin D into its active form.

Kidney stones (kidney stones) : commonly called “kidney stones”, these are hard crystals that form in the kidneys and can cause severe pain. In almost 90% of cases, urinary stones form inside a kidney. Their size is very variable, ranging from a few millimeters to several centimeters in diameter. A stone formed in the kidney and in transit to the bladder can easily obstruct a ureter and cause severe pain. This is called renal colic.

Malformations :

Renal malrotation : congenital anomaly that can affect only one kidney or both. During embryonic development, the kidney moves up the column to its final location and rotates. In the case of this pathology, the rotation is not done correctly. As a result, the pelvis, normally located on the inner edge of the nothing, is found on its anterior face. The anomaly being benign, the renal function is intact.

Renal duplicity : rare congenital anomaly, it corresponds to the presence of an additional kidney on one side of the body. This kidney is independent, with its own vascularity and its own ureter that leads directly to the bladder or joins the ureter of the kidney on the same side.

Hydronéphrose : it is a dilation of the calyces and the pelvis. This increase in volume of these cavities is due to a narrowing or an obstruction of the ureter (malformation, lithiasis…) which prevents urine from flowing.

Horseshoe kidney : malformation which results from the union of the two kidneys, generally by their lower pole. This kidney is located lower than the normal kidneys and the ureters are not affected. This condition does not lead to any pathological consequences, it is usually evidenced by chance during an X-ray examination.

Renal function abnormality :

Acute and chronic renal failure : gradual and irreversible deterioration of the kidneys’ ability to filter blood and excrete certain hormones. The products of metabolism and excess water pass less and less in the urine and accumulate in the body. Chronic kidney disease results from complications from diabetes, high blood pressure, or other illnesses. Acute kidney failure, on the other hand, comes on suddenly. It often occurs as a result of a reversible decrease in renal blood flow (dehydration, severe infection, etc.). Patients may benefit from hemodialysis using an artificial kidney.

Glomerulonephritis : inflammation or damage to the glomeruli of the kidney. The filtration of the blood no longer works properly, proteins and red blood cells are then found in the urine. We distinguish between primary glomerulonephritis (only nothings are affected) from secondary glomerulonephritis (consequence of another disease). Usually of unknown cause, it has been demonstrated that glomerulonephritis can, for example, appear following an infection, the taking of certain drugs (eg: non-steroidal anti-inflammatory drugs such as ibuprofen) or a genetic predisposition.

Infections

Pyelonephritis : infection of the kidneys with bacteria. In most cases, this isEscherichia Coli, responsible for 75 to 90% of cystitis (urinary tract infection), which proliferate in the bladder and ascend to the kidneys through the ureters (8). Women, especially pregnant women, are most at risk. Symptoms are the same as for cystitis associated with fever and lower back pain. The treatment is done by taking antibiotics.

Benign tumors

Cyst : A kidney cyst is a pocket of fluid that forms in the kidneys. The most common are simple (or solitary) cysts. They do not cause any complications or symptoms. The vast majority are not cancerous, but some can disrupt the functioning of the organ and cause pain.

Polycystic disease : hereditary disease characterized by the development of a multitude of renal cysts. This condition can lead to high blood pressure and kidney failure.

Malignant tumors 

Kidney cancer : it represents about 3% of cancers and affects twice as many men as women (9). Cancer occurs when certain cells in the kidney transform, multiply in an exaggerated and uncontrolled way, and form a malignant tumor. In the majority of cases, kidney cancer is detected incidentally during an examination of the abdomen.

Prevention. Protecting your kidneys is essential. While some illnesses cannot be completely prevented, healthy lifestyle habits can reduce the risk. In general, staying hydrated (at least 2 liters per day) and controlling your salt intake (through diet and sport) are beneficial for kidney function.

Other more specific measures are recommended to reduce the risk or prevent recurrence of kidney stones.

In the case of kidney failure, the two main causes are diabetes (type 1 and 2) as well as high blood pressure. Good control of these diseases greatly reduces the risk of progressing to a case of insufficiency. Other behaviors, such as avoiding alcohol, drug and medication abuse, can ward off the disease.

Kidney cancer. The main risk factors are smoking, being overweight or obese, and not having dialysis for more than three years. These conditions can promote the development of cancer (10).

Laboratory examinations : Determination of certain substances in the blood and urine allows kidney function to be assessed. This is the case, for example, for creatinine, urea and proteins. In the case of pyelonephritis, a cytobacteriological examination of the urine (ECBU) is prescribed to determine the germs involved in the infection and thus adapt the treatment.

Biopsy: test that involves taking a sample of the kidney using a needle. The removed piece is subjected to microscopic examination and / or biochemical analysis to determine whether it is cancerous.

POSTERS 

Ultrasound: imaging technique that relies on the use of ultrasound to visualize the internal structure of an organ. Ultrasound of the urinary system allows visualization of the kidneys but also the ureters and the bladder. It is used to highlight, among other things, renal malformation, insufficiency, pyelonephritis (associated with ECBU) or kidney stone.

Uroscanner: imaging technique which consists of “scanning” a given region of the body in order to create cross-sectional images, thanks to the use of an X-ray beam. It makes it possible to observe the entire device urinary tract (kidneys, excretory tract, bladder, prostate) in the event of renal pathology (cancer, lithiasis, hydronephrosis, etc.). It is increasingly replacing intravenous urography.

MRI (magnetic resonance imaging): medical examination for diagnostic purposes carried out using a large cylindrical device in which a magnetic field and radio waves are produced. It makes it possible to obtain very precise images in all dimensions of the urinary tract in the case of an MRI of the abdomino-pelvic area. It is used in particular to characterize a tumor or to make a diagnosis of cancer.

Intravenous urography: X-ray examination which makes it possible to visualize the entire urinary system (kidneys, bladder, ureters and urethra) after injection of a product opaque to X-rays which concentrates in the urine. This technique can be used in particular in the event of lithiasis or to compare the functioning of the kidneys.

Kidney scintigraphy: this is an imaging technique that involves administering a radioactive tracer to the patient, which spreads through the kidneys. This examination is used in particular to measure the renal function of the kidneys, to visualize the morphology or to assess the sequelae of pyelonephritis.

In Chinese medicine, each of the five fundamental emotions is connected to one or more organs. Fear is directly associated with the kidneys.