trunk, with positions of the organs show, and<unk> s seen at the vertebral level of T12 to L3. In humans, the<unk> s are located high in the abdominal cavity, one on each side of the spine, and lie in a retroperitoneal position at a slightly oblique angle. The asymmetry within the abdominal cavity, caused by the position of the liver, typically results in the right<unk>  being slightly lower and smaller than the left, and being placed slightly more to the middle than the left<unk> . The left<unk>  is approximately at the vertebral level T12 to L3, and the right is slightly lower. The right<unk>  sits just below the diaphragm and posterior to the liver. The left<unk>  sits below the diaphragm and posterior to the spleen. On top of each<unk>  is an adrenal gland. The upper parts of the<unk> s are partially protected by the 11th and 12th ribs. Each<unk> , with its adrenal gland is surrounded by two layers of fat: the perirenal fat present between renal fascia and renal capsule and pararenal fat superior to the renal fascia. The<unk>  is a bean-shaped structure with a convex and a concave border. A recessed area on the concave border is the renal hilum, where the renal artery enters the<unk>  and the renal vein and ureter leave. The<unk>  is surrounded by tough fibrous tissue, the renal capsule, which is itself surrounded by perirenal fat, renal fascia, and pararenal fat. The anterior (front) surface of these tissues is the peritoneum, while the posterior (rear) surface is the transversalis fascia. The superior pole of the right<unk>  is adjacent to the liver. For the left<unk> , it is next to the spleen. Both, therefore, move down upon inhalation. Sex Weight, standard reference range Right<unk>  Left<unk>  Male Female A Danish study measured the median renal length to be on the left side and on the right side in adults. Median renal volumes were on the left and on the right. Gross anatomy 1. Renal pyramid • 2. Interlobular artery • 3. Renal artery • 4. Renal vein 5. Renal hilum • 6. Renal pelvis • 7. Ureter • 8. Minor calyx • 9. Renal capsule • 10. Inferior renal capsule • 11. Superior renal capsule • 12. Interlobular vein • 13. Nephron • 14. Renal sinus • 15. Major calyx • 16. Renal papilla • 17. Renal column The functional substance, or parenchyma, of the<unk>  is divided into two major structures: the outer renal cortex and the inner renal medulla. Grossly, these structures take the shape of eight to 18 cone-shaped renal lobes, each containing renal cortex surrounding a portion of medulla called a renal pyramid. Between the renal pyramids are projections of cortex called renal columns. Nephrons, the urine-producing functional structures of the<unk> , span the cortex and medulla. The initial filtering portion of a nephron is the renal corpuscle, which is located in the cortex. This is followed by a renal tubule that passes from the cortex deep into the medullary pyramids. Part of the renal cortex, a medullary ray is a collection of renal tubules that drain into a single collecting duct. The tip, or papilla, of each pyramid empties urine into a minor calyx; minor calyces empty into major calyces, and major calyces empty into the renal pelvis. This becomes the ureter. At the hilum, the ureter and renal vein exit the<unk>  and the renal artery enters. Hilar fat and lymphatic tissue with lymph nodes surround these structures. The hilar fat is contiguous with a fat-filled cavity called the renal sinus. The renal sinus collectively contains the renal pelvis and calyces and separates these structures from the renal medullary tissue. The<unk> s possess no overtly moving structures. File:Right<unk>  seen on abdominal ultrasound.Normal adult right<unk>  as seen on abdominal ultrasound with a pole to pole measurement of 9.34 cm. File:CTscankidney.A CT scan of the abdomen showing the position of the<unk> s. The left cross-section in the upper abdomen shows the liver on the left side of scan (right side of body). Center: cross-section showing the<unk> s below the liver and spleen. Right: further cross-section through the left<unk> . File:Slide42222.Image showing the structures that the<unk>  lies near. File:Left<unk> .Cross-section through a cadaveric specimen showing the position of the<unk> s. Blood supply The<unk> s receive blood from the renal arteries, left and right, which branch directly from the abdominal aorta. Despite their relatively small size, the<unk> s receive approximately 20% of the cardiac output. Each renal artery branches into segmental arteries, dividing further into interlobar arteries, which penetrate the renal capsule and extend through the renal columns between the renal pyramids. The interlobar arteries then supply blood to the arcuate arteries that run through the boundary of the cortex and the medulla. Each arcuate artery supplies several interlobular arteries that feed into the afferent arterioles that supply the glomeruli. Blood drains from the<unk> s, ultimately into the inferior vena cava. After filtration occurs, the blood moves through a small network of small veins (venules) that converge into interlobular veins. As with the arteriole distribution, the veins follow the same pattern: the interlobular provide blood to the arcuate veins then back to the interlobar veins, which come to form the renal veins which exiting the<unk>  . Nerve supply The<unk>  and nervous system communicate via the renal plexus, whose fibers course along the renal arteries to reach each<unk> . Input from the sympathetic nervous system triggers vasoconstriction in the<unk> , thereby reducing renal blood flow. The<unk>  also receives input from the parasympathetic nervous system, by way of the renal branches of the vagus nerve; the function of this is yet unclear. Sensory input from the<unk>  travels to the T10-11 levels of the spinal cord and is sensed in the corresponding dermatome. Thus, pain in the flank region may be referred from corresponding<unk> . Microanatomy Renal histology is the study of the microscopic structure of the<unk> . Distinct cell types include:<unk>  glomerulus parietal cell<unk>  glomerulus podocyte<unk>  proximal tubule brush border cell *Loop of Henle thin segment cell *Thick ascending limb cell<unk>  distal tubule cell *Collecting duct principal cell *Collecting duct intercalated cell *Interstitial<unk>  cells Gene and protein expression About 20,000 protein coding genes are expressed in human cells and almost 70% of these genes are expressed in normal, adult<unk> s. Just over 300 genes are more specifically expressed in the<unk> , with only some 50 genes being highly specific for the<unk> . Many of the corresponding<unk>  specific proteins are expressed in the cell membrane and function as transporter proteins. The highest expressed<unk>  specific protein is uromodulin, the most abundant protein in urine with functions that prevent calcification and growth of bacteria. Specific proteins are expressed in the different compartments of the<unk>  with podocin and nephrin expressed in glomeruli, Solute carrier family protein SLC22A8 expressed in proximal tubules, calbindin expressed in distal tubules and aquaporin 2 expressed in the collecting duct cells. Development The mammalian<unk>  develops from intermediate mesoderm.<unk>  development, also called nephrogenesis, proceeds through a series of three successive developmental phases: the pronephros, mesonephros, and metanephros. The metanephros are primordia of the permanent<unk> .
Kidney
Liver
Lung
Heart
Peripheral nervous system
Central nervous system
Brain
Adrenal gland