Kidneys are located below your ribs, in normal conditions, their size is the same as a human fist and they are mainly comprised of:
Nephrons: They are the most important structures inside the kidneys because they are in charge of filtering blood. They also metabolize nutrients
Renal cortex: This is the outer part of the kidney, where capillaries and tubules are located. It is also surrounded by the renal capsule, which is a layer of fatty tissue that houses and protects the inner kidney.
Renal medulla: It is the smooth, inner skin of the kidney.
Renal pelvis: It is a funnel-shaped space that works as a pathway for fluids to when they are on their way to the bladder.