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The medial border of the kidney is concave in the center and convex toward either extremity; it is directed forward and a little downward. Its central part presents a deep longitudinal fissure, bounded by prominent overhanging anterior and posterior lips. This fissure is a hilum that transmits the vessels, nerves, and ureter.
A CT scan of the abdomen showing the position of the kidneys. 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 kidneys below the liver and spleen. Right: further cross-section through the left kidney.
The renal medulla (Latin: medulla renis 'marrow of the kidney') is the innermost part of the kidney. The renal medulla is split up into a number of sections, known as the renal pyramids. Blood enters into the kidney via the renal artery, which then splits up to form the segmental arteries which then branch to form interlobar arteries.
The kidney is surrounded by a capsule separating the kidney from the echogenic perirenal fat, which is seen as a thin linear structure. [1] The kidney is divided into parenchyma and renal sinus. The renal sinus is hyperechoic and is composed of calyces, the renal pelvis, fat and the major intrarenal vessels.
The collecting duct system of the kidney consists of a series of tubules and ducts that physically connect nephrons to a minor calyx or directly to the renal pelvis.The collecting duct participates in electrolyte and fluid balance through reabsorption and excretion, processes regulated by the hormones aldosterone and vasopressin (antidiuretic hormone).
In multilobar kidneys, the pyramids are separated from each other by dipped into the kidney areas of cortical tissue known as the renal columns. [61] Blood enters the kidney through the renal artery, which in the multilobar kidney then branches in the region of the renal pelvis into large interlobar arteries that pass through the renal columns.
Cross-section of the kidney, with major structures labelled. The renal pelvis , located in the middle of the image, collects urine from the urinary calices. An image showing just the pelvis and calices of the kidneys, with the rest of the kidney removed, from a dissected cow and seal specimen.
Mammalian kidneys are susceptible to ischemic injury because mammals lack a renal-portal system, and as a result, vascular vasoconstriction in the glomeruli can lead to decreased blood supply to the entire kidney. The kidneys are susceptible to toxic injury, since toxins are reabsorbed in the tubules along with most of the filtered substances. [47]