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Kidney Anatomy and Function


Kidney Anatomy and Function

Renal System Anatomy

Kidneys, Ureters, Bladder

This image shows the kidneys, ureters, and bladder. The adrenal glands (part of the endocrine system) sit on top of the kidneys and release renin which affects blood pressure, and sodium and water retention. The bean-shaped kidneys are about the size of a closed fist. They lie against the back of the abdominal wall, outside the peritoneal cavity, just above the waistline in the lumbar area. The right kidney sits slightly higher than the left one because of the position of the liver. The kidneys are aout 4 1/2 inches long and 2 1/2 inches wide. The kidneys are highly vascular (contain a lot of blood vessels) and are divided into three main regions: renal cortex (outer region which contains about 1.25 million renal tubules), renal medulla (middle region which acts as a collecting chamber), and renal pelvis (inner region which receives urine through the major calyces).

The kidneys are protected in front by the contents of the abdomen and behind by the muscles attached to the backbone. They are further protected by a layer of fat.


The Renal System

Kidney Anatomy

Anatomy of the Kidney

Kidney Function

Every minute 1300 mL of blood enter the kidneys, 1299 mL leave the kidney. and 1 mL leaves as urine.The kidneys have many functions. The kidneys are the major organs that maintain homeostasis (balance of the various body functions) in the body and help control blood pressure. They maintain balance in electrolytes, acid-base, and fluid in the blood. The kidneys remove nitrogenous waste from the body (creatinine, urea, ammonia) and keep essential substances the body needs to function as it should. The kidneys produce the hormone erythropoietin that stimulates the production of red blood cells and enzymes.

When the kidneys aren’t working as they should, there is a failure of homeostasis which can cause death if not corrected. A panel of blood tests, called a Kidney Function Profile, is used to monitor the kidneys, detect kidney problems or make a diagnosis.

Nephron Anatomy

Anatomy of a Nephron

Nephron Function

Individual nephrons cannot be seen by the naked eye.The nephron is the basic structural and functional unit of the kidney. Each kidney has about 1 million nephrons. The walls of the nephron are made of a single layer of epithelial cells. Blood containing urea and metabolic waste products enters the kidney from the liver. The blood is mechanically filtered to remove fluids, wastes, electrolytes, acids and bases into the tubular system while leaving blood cells, proteins and chemicals in the bloodstream. The nephrons also reabsorb and secrete ions that control fluids and electrolyte balance.

The blood enters the kidney and goes to the glomerulus. Pressure forces fluid out of the blood through membrane filtration slits creating a cell-free fluid (plasma) of water and small molecules that enters into the renal tubule. Large cells and proteins stay in the blood. This plasma is taken to the nearest (proximal) convoluted tubule. This runs down into the medulla into the loop of Henle and then back to the farthest (distal) convoluted tubule to join with other tubules. In the distal tubule most of the salts are reabsorbed. What is left is further modified until it becomes concentrated urine which contains urea and other waste products at the end of the collecting duct. (See Anatomy Terms to understand proximal and distal.)

The kidneys collect and get rid of waste from the body in 3 steps:

The glomerular filtration rate (GFR) is the rate at which the glomeruli filter the blood. The normal GFR is 120 ml/minute. The most accurate measure of the GFR is done by measuring creatinine clearance. Clearance is the complete removal of a substance from the blood. Creatinine is a good measure because it is filtered by the blood but not reabsorbed by the tubules.

What is urine made of?

Urine is made of water, urea, electrolytes, and other waste products. The exact contents of urine vary depending on how much fluid and salt you take in, your environment and your health. Some medicines and drugs are excreted in urine and can be found in the urine.


What is in urine is not as important as how much urine is made or how the amounts of the individual components change in order to keep the body in balance (homeostasis). This balance is done in the kidneys, no matter how much we eat or drink. The kidneys keep this balance by reworking the blood 15 times a day. If the body is dehydrated, the kidneys put less water is in the urine. When the body becomes too acid, the kidneys remove more acid into the urine. If the potassium levels get too high, the kidneys remove more potassium into the urine.

Urine is formed in the nephrons in three process: glomerlular filtration, tubular reabsorbtion and tubular secretion. The amount of urine varies based on fluid intake and climate.

Kidney Disease and Disorders

Kidney disease and kidney problems are usually treated by a nephrologist. Kidney stones are sometimes treated by a urologist. | Anatomy, Surgery, Pregnancy, Nutrition, Fitness