The Anatomy of a Kidney
The Structure of the Kidney
The kidneys are reddish-brown, bean-shaped organs situated retroperitoneal on the posterior abdominal wall. They extend from lumbar vertebra T12-L3. Normally the kidney is about the size of a mouse and measures approximately 11-12 cm in length, 5-6 cm in width and 2.5-3 cm in thickness.
The kidneys have a superior and inferior pole, medial and lateral margins, and an anterior and posterior surface. The superior pole of each kidney is deep to the rib cage. For the right kidney, its superior pole is at the 12th rib and for the left the superior pole is at ribs 11 and 12.
On the medial margin of the kidney is concave region called the renal hilus. The renal hilum is the entrance to the renal sinus. Structures such as the renal veins, artery, nerves and lymphatic vessels are located in the renal hilum.
The renal sinus is a fat-filled cavity inside the kidney that extends from the hilum. At the hilum the ureters also exit the kidney. The kidney is covered by a fibrous renal capsule. Each kidney is completely surrounded by perirenal fat which extends in the renal pelvis.
Around the perirenal fat, is a layer of renal fascia called the Gerota’s fascia. The Gerota’s fascia has an anterior and posterior layer. The anterior layer continues medially and fuses with the adventitia of the aorta and the inferior vena cava (IVC). The posterior layer fuses with the psoas major fascia.
If one should take a knife and cut the kidney in halves from the superior pole to the inferior pole, you would find two distinct internal regions of the kidney, the cortex and the medulla. The cortex is the superficial outer layer of the kidney located underneath the capsule. The medulla is the inner layer and it extends from the renal cortex to the renal sinus. The medulla is divided into various cone-shaped structures called the renal pyramids. The renal pyramids extend from the cortex to the renal papilla. These papillae extend into a space called the renal pelvis.
Renal pelvis is a funnel-shaped structure that is continuous with the ureter. The renal pelvis is divided into calyces. Each pelvis receives about 2 major calyces, which in turn receive minor calyx, which in turn collect urine from the papilla.
Due to the location of the kidney, it comes into contact with various structures in the body.
Posteriorly, the kidneys are related to the diaphragm, quadrates lumborum muscle, transversus abdominis muscle, 11th and 12th rib (left kidney), 12th rib (right kidney), costodiaphragmatic recess, subcostal, iliohypogastric and ilioinguinal nerves. Anteriorly, the right kidney is in relation to the right suprarenal gland, liver, descending portion of the duodenum, and the right colic flexure. Anteriorly, the left kidney is related to the stomach, spleen, pancreas, jejunum and left colic flexure.
The Blood Supply To The Kidney
Each kidney receives its blood from the renal artery. The renal artery is a direct branch of the abdominal aorta at L1-L2. The renal artery enters through the hilum and branches into segmental arteries. Segmental arteries then divide into interlobar arteries which penetrate the renal pyramids. Upon penetrating the pyramids the interlobar arteries divides into arcuate arteries. Each arcuate artery gives rise to interlolular artery that enters the cortex and branch intro afferent arterioles. These afferent arterioles supply the nephron. Inside the nephrons, the afferent arterioles leads to a network of capillaries called the glomerulus.
Blood then leaves the glomerulus through the efferent arterioles and back to the renal vein and empties into the IVC . Renal veins lies anterior to renal arteries. The left renal vein is longer than the right and it passes between the aorta and the superior mesenteric artery.