A projecting ridge or fin on the bottom of the hull of a boat or ship that improves directional control and is often weighted for added stability. 2. The principal structural member of an aircraft, resembling a ship's keel in shape and function.
The outer, reddish region, next to the capsule, is the renal cortex. This surrounds a darker reddish-brown region called the renal medulla. The renal medulla consists of a series of renal pyramids, which appear striated because they contain straight tubular structures and blood vessels.
Each kidney is reddish-brown, bean shaped organ and is about 4 inches long and 2 inches wide. It has a medial concave surface and a lateral convex surface. On the medial concave border of each kidney, there is a vertical slit called hilum, which is bounded by thick lips of the renal substance.Inside the kidney, the hilum extends into a large cavity called renal sinus.All structures that enter or exit the kidney pass through the hilum. From front backwards, these structures are: 1  Renal vein. 2  Two branches of renal artery. 3  Ureter. 4  Third branch of renal artery. 5  Lymph vessels.nside the kidney, the hilum extends into a large cavity called renal sinus. All structures that enter or exit the kidney pass through the hilum. From front backwards, these structures are: 1  Renal vein. 2  Two branches of renal artery. 3  Ureter.