Urine formed in the kidneys are paired organs that lie near the back wall of the abdominal cavity, at a distance of hands from the lumbar spine:
Each human kidney weighs about 150 grams. But despite its small size, the kidneys are richly supplied with blood: 5 minutes through the kidneys have time to go through the entire volume of blood contained in the body (in an adult is about 5 liters). All blood fluid per day manages to filter approximately 20 times.
Blood enters the kidney through the renal artery. In the kidneys it is cleared from the products of metabolism. These products kidney is removed from the body through urine. And purified the blood leaves the kidney through the renal vein.
The kidney is covered outside of a solid by a capsule of connective tissue. On the longitudinal section of the kidney clearly distinguished two layers that make up the kidney - brain and cortex.
A functional unit of the kidney is the nephron. Each kidney contains about 1 million nephrons. Each nephron consists of a renal bullock and systems tubules.
The structure of the nephron
In the cortical substance are the glomerular nephrons. In them the blood is filtered: each glomerulus of the nephron under the action of blood pressure skips the liquid with the dissolved substances, but does not allow proteins and blood cells remain in the blood. And the filtered liquid enters the system of tubules that are found in the medulla of the kidney.
This filtered liquid is called the primary urine. In the kidney for 1 minute produces 130 ml of primary urine, or 8 liters per hour. But we take only 1-1,5 litres of urine per day - where does the rest of the primary urine?
In the system of tubules, most of the water is taken back into the blood (this process is called reabsorption, or backward induction). Together with water are absorbed back into the blood of many valuable substances that the body cannot afford to lose is glucose, vitamins, amino acids and others. In the bone is absorbed into the blood 7/8 volume of fluid filtered in the glomeruli!
Thus, the kidneys have the ability to concentrate urine, that is, to take water from it and give it back into the blood. This property is especially important in conditions of difficult access to water, for example, in the deserts.
Formed in the bone filtered liquid is called secondary urine. It comes in collective tubules, and then into the pelvis of the kidney. Of the pelvis urine through the ureter enters the bladder, and from there out.