Kidneys are the organs in the body that regulate blood pressure, electrolytes, acid-base homeostasis and other homeostatic functions.

Formation and Orientation

Kidneys can be found in the abdominal cavity, one on each side of the spine in the retroperitoneum, located at the back of the abdominal cavity. Kidneys are usually 11 to 14 centimeters long, six centimeters wide and four centimeters thick.

The parenchyma of the kidney is made up of the renal cortex and the renal medulla. These form together to create the renal pyramid. Between these pyramids, renal columns are formed. The pyramids are covered in nephrons which produce urine in the kidneys. These nephrons are created by the combination of renal corpuscle that filter and the renal tubule that transport. The area beneath the glomeruli, which is the main area for filtration, is referred to as the interstitum which absorbs fluids from the urine. On the tip of the pyramids, papilla connect to the ureter through calyces and the renal pelvis.

At one point, the ureter leaves the kidney while at the same point, the renal artery goes into the organ. The renal sinus surrounds this area and is created from hilar fat, lymphatic tissue and lymph nodes.

Blood comes from interlobar arteries that provide blood to renal capsules, columns and pyramids as well as from arcuate arteries that supply blood to the cortex and medulla. Both the interlobar arteries and arcuate arteries stem from renal arteries. Lastly, the afferent arterioles provide blood flow to the glomeruli.


The kidneys have a number of functions such as the excretion of waste, acid-base homeostasis, osmolality regulation, blood pressure regulation, and hormone secretion.

They excrete wastes that are created by the human metabolism like the nitrogenous bases of urea and uric acid. As these toxins are filtered out, the kidneys create urine as a mode of transport to relieve the body of those toxins. With acid-base homeostasis, the kidneys have a sort of interaction with urine as they reabsorb bicarbonate from the urine, all the while releasing hydrogen ions into the urine. As mentioned before, the kidneys rid the body of urea, but in the case of osmolality, when the volume of plasma in the blood is lower than normal, the kidneys’ glands release antidiuretic hormones.

Image Caption: Human kidneys viewed from behind with spine removed. Credit: Wikipedia