Diagram of Anterior anatomical relations of both kidneys

The kidneys are retroperitoneal organs that are located in the perirenal retroperitoneal space with a longitudinal diameter of 10–12 cm and a latero-lateral diameter of 3–5 cm and a weight of 250–270 g.
In the supine position, the medial border of the normal kidney is much more anterior than the lateral border, The upper pole of each kidney is situated more posteriorly than the lower pole.

The right kidney,  anteriorly :
has a relation with the inferior surface of the liver with peritoneal interposition,and with the second portion of the duodenum without any peritoneal interposition since the second portion of the duodenum is retroperitoneal .
The left kidney, anteriorly :
has a relation with the pancreatic tail, the spleen, the stomach, the ligament of Treitz and small bowel, and with the left colic lexure and left colon . Over the left kidney, there are two important peritoneal relections, one vertical corresponding to the spleno-renal ligament (connected to
the gastro-diaphragmatic and gastrosplenic ligaments) and one horizontal corresponding to the transverse mesocolon.