Mouse kidneys are located on the upper wall of the abdominal cavity and are held in place by fibrous capsules. Similar to other mammalian kidneys, mouse kidneys appear bean shaped, brownish red, granular, and have a firm consistency. The outer region of the kidney is termed the cortex and the inner area is known as the medulla. Tiny structures called nephrons, which consist of even smaller and more intricate elements, stretch across both sections. The nephrons are the functional units of the kidneys, responsible for filtering blood, reabsorbing water and nutrients, and secreting wastes.