Final answer:
The kidneys are located in the retroperitoneal space on either side of the spine, under the ribs and protected by muscle, fat, and multiple tissue layers. They extend from the T12 to L3 vertebral levels, with the right kidney slightly lower than the left due to the liver's position.
Step-by-step explanation:
The kidneys are situated in the retroperitoneal space of the abdomen, which is behind the peritoneal lining and against the posterior abdominal wall. This positioning offers considerable protection from muscle, fat, and the lower ribs. Each kidney is roughly the size of a person's fist, with males typically having slightly larger kidneys than females. The right kidney is positioned a bit lower than the left due to the presence of the liver, while the left kidney is situated near the spleen. The kidneys extend from the T12 to L3 vertebral levels, and each one is located beneath the diaphragm and encased in multiple protective layers, including a fibrous capsule, adipose tissue, and the renal fascia.
Both kidneys are bean-shaped and well vascularized, receiving about a quarter of the body's cardiac output when at rest. The upper parts are partially under the eleventh and twelfth ribs, and each kidney is surmounted by an adrenal gland. The asymmetry in the abdominal cavity due to the liver results in the right kidney being slightly lower than the left, which is slightly more medial. They are surrounded by fat for additional cushioning and protection from physical trauma.