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Renal Anatomy

Renal anatomy refers to anatomy of the kidneys. The two kidneys filter the blood and form urine, which is transported to the urinary bladder by the ureters. Each kidney is capped by a suprarenal gland, which is a major player in the endocrine system.

The two kidneys lie behind the peritoneum on the posterior abdominal wall near the 12th thoracic and first three lumbar vertebrae. The right kidney is slightly lower than the left kidney. Each kidney and suprarenal gland is encased in a perinephric fat capsule, which is covered by a membranous renal fascia. Paranephric fat lies outside of the renal fascia.

Each kidney is shaped like a kidney bean (surprised?) with an anterior and posterior surface. The renal hilum is located at the medial border and allows the renal artery to enter the kidney and the renal vein to leave. It also allows the ureter to exit the kidney. The internal part of the kidney includes a section called the medulla surrounded by a covering called the cortex. The medulla contains minor calyces that merge to form major calyces. The innermost renal pelvis is formed by the merger of the major calyces.

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Nerve supply to the kidneys comes from the renal plexus. The renal arteries leave the abdominal aorta around the level of the 1st or 2nd lumbar vertebrae. Each renal artery travels to the kidney, where it branches into segmental arteries that supply the segments of the kidney. Renal veins return from the kidneys to empty into the inferior vena cava. Lymph leaves the kidneys via lymphatic vessels that drain into the lumbar lymph nodes.

The ureters are long, narrow, muscular tubes that leave the renal pelvis and exit the kidney. They run along the posterior abdominal wall next to the transverse processes of the lumbar vertebrae. They cross the external iliac arteries to enter the pelvis and continue to the urinary bladder.

Nerve supply to the ureters comes from the renal nerve plexus. Arteries to the ureters branch off the renal, testicular, and/or ovarian arteries and the abdominal aorta. Veins to the ureters drain into the renal, testicular, and/or ovarian veins. Lymph drains from the ureters to the iliac lymph nodes.

Renal calculi, better known as kidney stones, are formed from crystals in the urine. Kidney stones are fairly common and can be quite painful when they move down the ureters. The pain is usually felt in the abdomen or the flank and often moves into the groin area. Additional symptoms may include blood in the urine, chills, fever, nausea, and vomiting. Renal calculi are detected by blood tests, urine tests, and imaging techniques such as ultrasound or X-rays. Treatment depends on the size of the stones. Small stones pass through the urinary tract. Pain medication and extra water can help. Large stones lodged in the kidney may require surgery or lithotripsy, a procedure that uses sound waves to break up the stones.

The suprarenal glands (or adrenal glands) are located between the superior part of the kidneys and the diaphragm. They’re encased in perinephric fat but are separated from the kidneys by fibrous connective tissue. The right suprarenal gland is more pyramid shaped, whereas the left one is more crescent shaped.

Each suprarenal gland is made up of two portions: the cortex and the medulla. The cortex produces corticosteroids (which affect immune system response, inflammation, metabolism, and electrolyte levels) and androgen hormones, and the medulla produces epinephrine and norepinephrine (which are hormones that affect heart rate and blood pressure).

Nerve supply comes from the celiac plexus and the abdominopelvic splanchnic nerves. Several suprarenal arteries bring blood to the suprarenal glands:

  • Superior suprarenal arteries: Six or eight branch off the inferior phrenic artery.

  • Middle suprarenal arteries: One or more branch off the abdominal aorta.

  • Inferior suprarenal arteries: One or more branch off the renal artery.

Venous drainage is provided by the suprarenal veins. The right suprarenal vein drains into the inferior vena cava, and the left suprarenal vein drains into the left renal vein. Lymph is drained into the lumbar lymph nodes.

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