The kidneys consist of a vast network of blood vessels that are part of a complex filtration system. Blood travels through this network of blood vessels and is filtered in the functional unit of the kidney called the nephron. It is here that the blood is filtered, blood pH is balanced, and blood fluid volume is controlled.
Location of the Kidneys
The kidneys are located in the retroperitoneal space on either side of the vertebral column, or the spine. The retroperitoneal space is the cavity behind the abdominal cavity, which is the part of the body where abdominal organs such as the liver, spleen, and bowel are located. The right kidney is located behind the lower portion of the liver. The left kidney is adjacent to the spleen and is often slightly higher than the right kidney.
Kidney Anatomy
The kidney is shaped like a kidney bean. The ureters and blood vessels enter the kidney in the middle of the side nearest to the spine. This is called the renal hilum. The ureter enters the kidney and opens into a funnel-like space called the renal pelvis. The pelvis divides into two or three sections called major calyces. The major calyces further divide into minor calyces. Renal papillae are openings that project into the minor calyces.
The renal medulla is the middle region of the kidney between the pelvis and the outer layer of the kidney, which is called the cortex. Within the medulla, little tubules branch off of the minor calyces. These tubules form triangular groups called renal pyramids. The renal cortex extends into the medulla between the pyramids. The kidney is covered by a membrane called the renal cortex.
Renal Blood Circulation
Blood enters the kidney via the renal artery through the renal hilum. The renal artery branches into the interlobar arteries which pass through the renal pyramids. At the renal cortex, the interlobar arteries branch into arcuate arteries, which further branch into interlobular arteries and then into afferent arterioles that lead to nephrons.
The blood is filtered in the nephrons and returns via the interlobular veins that merge into the arcuate, and the interlobar veins. The interlobar veins return blood to the renal vein that exits the kidney through the renal hilum.
How Urine Forms and Flows Out
Urine forms around the nephrons and passes through collecting ducts and renal papillae into the calyces. It collects in the renal pelvis and moves into the ureter. The ureters are tube-like structures that carry urine from the kidneys to the bladder for excretion.
The renal pelvis, calyces, medulla, and cortex can be easily seen during a renal ultrasound and the visual appearance of the kidney can indicate a physiological problem. The anatomy of a kidney allows it to efficiently filter the blood of waste and maintain fluid and electrolyte balance within the body. For this reason, the kidneys are vital to maintaining homeostasis, which is the maintenance of an internal environment that is conducive to cellular metabolism.
Reference
Shier, D., Butler, J., Lewis, Ricki. Hole's Human Anatomy & Physiology. New York: McGraw-Hill, 2002.
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