This is how the kidneys and urinary tract work

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Last Medical Review: April 1, 2020
Medically Reviewed by Dr. Elisabeth Vincent Hamelin
Kidneys and Urinary Tract (April 1, 2020)
What are the kidneys and urinary tract? (April 1, 2020)

The kidneys cleanse the blood from substances that are not needed in the body. Such substances are called residues. In the kidneys, urine is formed and the residual products leave the body with the urine. The kidneys are also important for regulating the water balance, salt balance and blood pressure in the body.

Kidney tasks

In the kidneys, urine is formed. The urine is transported through the ureters. Then the urine is collected in the bladder and then proceeds through the urethra as you urinate. How much urine is formed depends on how much fluid there is in the body.

The kidneys cleanse the body

The most important task of the kidneys is to cleanse the body from various substances. Urine and gall color are examples of substances that the body gets rid of through the urine.

The kidneys are also important for several other functions of the body:

  • They regulate the salt balance and the water balance.
  • They affect blood pressure.
  • They form hormones.
  • They stimulate the formation of red blood cells.
  • They regulate the balance of salt and acid in the blood.

So the kidneys are built up

The kidneys are located on either side of the spine, slightly above the navel level. Each kidney is shaped like a bean. A kidney is 10-12 centimeters long.

The kidney consists of the bark, marrow and renal pelvis

The kidneys are surrounded by thick, tight connective tissue and very protective fat. The outer layer of the kidneys is called the bark. Inside the bark lies the marrow.

The marrow is divided into 10 –15 so-called renal pyramids. The tips of the pyramids are called papillae. The papilla has contact with the so-called renal pelvis. The renal pelvis collects urine. The urine then leaves the kidney through the ureter.

The nephron cleanses the blood

Each kidney contains about 1 million nephrons. A nephron is the small unit where the blood is purified and the urine is formed.

The nephron consists of two parts:

  • The kidney body, which is a small vascular nose. The kidney body lies in the bark.
  • The renal ducts which are a system of ducts surrounded by small blood vessels. The ducts are emptied into the renal pelvis. The renal ducts are found in both the bark and the marrow.

Large amounts of blood pass through the kidney

About a quarter of the blood that the heart pumps out every minute when you are at rest goes to the kidneys. This means that about 1,500 liters of blood pass through the kidneys every day.

Urinary tract

The kidneys are connected to the urinary tract. The urinary tract includes ureter, bladder and urethra.

The ureters

Each ureter is 25-30 centimeters long and runs between the kidney and the bladder. The urine is then passed on through the ureter. The muscles in the walls of the ureters push the urine down towards the bladder.

The bladder can be stretched

The bladder lies in the pelvis behind the pubic bone. There, the urine is collected before you urinate it. The size of the bladder varies depending on how full it is. The bladder holds 3-4 deciliters, but it can also be stretched sharply.

The urine leaves the body through the urethra

The last part of the urinary tract is the urethra. The urethra is about 20 inches long in those with a penis. It goes from the bladder, through the prostate gland and penis. The opening of the urethra is located on the eyelid.

The urethra is 3-5 inches long in those with a sheath. It passes from the bladder and passes behind the pubic joint. The opening of the urethra is located in front of the slide opening.

The will only partially controls that you kiss

The bladder wall sends signals when it is stretched out of urine. The signals make you feel like you need to pee. The signals also cause an unconscious reflex to urinate. Then the muscles in the wall of the bladder are contracted. At the same time, the muscle cells relax around the inner opening of the urethra.

There is also a willpowered muscle around the urethra. It keeps the urethra closed. The muscle is contracted until you consciously decide to let the muscle relax so you can pee. But you cannot consciously hold on any longer if the bladder becomes too stretched.

Small children who have not yet learned to control the will-driven muscle pee as soon as the reflex to pee is triggered.

This is how urine is formed

Urine consists mostly of water with residual products and dissolved salts. The urine also contains substances that have been filtered out so as not to harm the body. Adrenal cortex hormones and pituitary hormones affect urine content.

Urine is formed in several steps:

  1. The kidney nephron is surrounded by small, thin blood vessels. The blood in the blood vessels is filtered as it passes through the vasculature of the nephron. What happens is that fluid is excreted from the blood vessel. The liquid is collected in a sack that surrounds the vessel socket.
  2. The sac is the first part of the renal canal. The fluid continues through the channels of the nephron.
  3. On the way through the canals, water and nutrients are absorbed by the blood into the blood vessels surrounding the renal ducts. It is water and nutrients that the body needs. At the same time, the blood in these vessels releases other substances that the body wants to get rid of. In this way, the kidneys regulate the body’s fluid balance, salt balance and acidity.
  4. The urine from the nephron’s ducts is collected in the renal pelvis. In most people, 1.5–2 liters of finished urine is produced per day.

It is important that the blood pressure is high enough

Blood pressure must be high enough for urine to be properly formed. The kidneys themselves can affect blood pressure by secreting hormones if the blood pressure is too low. One such hormone is renin.

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