Kidney anatomy

The two kidneys are bean-shaped organs located on the posterior abdominal wall outside the peritoneal cavity, one on either side of the vertebral column at the level of the T12 to L1 vertebrae. The right kidney is slightly lower than the left kidney because of the large size of the right liver lobe. The kidney is enclosed by a thick, fibrous capsule that protects its delicate internal structures.

Kidney size and shape

The kidneys are reddish-brown in color. adult human kidney weighs about 150 grams and is about the size of a clenched fist. It measures approximately 10 cm in length, 5 cm in width, and 2.5 cm in thickness.

Gross anatomy of kidneys (internally):

Renal hilum and Renal sinus

The medial side of each kidney includes an indented area called the renal hilum, a vertical cleft present on the concave medial margin through which the renal artery and vein, lymphatics, nerve supply, and ureter pass. It is the entrance to space inside the kidney called the renal sinus. Thus, the renal sinus is occupied by the renal pelvis, calyces, veins, nerves, and a variable amount of fat.

Renal medulla

If the kidney is bisected from top to bottom, the outer cortex and the inner medulla regions are the two main regions that can be visualized. The medulla is divided into 8 to 10 cone-shaped mass of tissue called renal pyramids. The renal pyramids are triangular regions of renal tissue, which are 4–14 in number and divided from each other by cortical renal columns. Each pyramid has a base that is oriented towards the cortex, and an apex (or renal papilla) that protrudes into the renal pelvis and fits into a minor calyx.

Renal pelvis

The renal pelvis is a flattened funnel-shaped continuation of the upper end of the ureter. the outer border of the pelvis is divided into two (or three) parts, called major calyxes, which extend down and divide into several minor calyxes. The end of each minor calyx is shaped like a cup that collects urine from the tubes of each papilla. The walls of the calyces, pelvis, and ureter contain contractile elements that propel the urine to the bladder, where the urine is stored until it is emptied by micturition.

Renal cortex

The renal cortex is the outer tissue layer of the kidney, dark and granular in appearance. The renal cortex can be divided into two sections which are continuous with each other:

• Cortical arches or cortical lobules refer to the tissue between the base of the pyramids and the surface of the kidney.
• Renal columns or (Columns of Bertin) refer to the cortical tissue that reaches down into the medulla. lies between the pyramids separating them from each other.
• Lobe of the kidney (renal lobe) Each pyramid, surrounded by a cortex shell, is a lobe of the kidney. This lobulation is visible in the fetal kidney.