Anatomy of the kidney

Location of the kidney:

The kidneys are situated behind the peritoneum on each side of the vertebral column. It extends from twelfth thoracic vertebra (T12) to the third lumbar vertebra (L3). The right kidney is usually lower than the left because of the presence of the liver. Each kidney is about 12cm long and weighs about 50g.

 Location of the kidney at horizontal plane at L1 level

Figure 1: Location of the kidney at L1 level

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Surrounding structures of the kidney

Figure 2: Surrounding structures of the kidney

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The main structural features of the kidney:

Figure 3: A longitudinal section of the right kidney

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 Longitudinal section of the left kidney

Description: 1) Renal pyramid 2) Interlobar artery 3) Renal artery 4) Renal vein 5) Renal hylum 6) Renal Pelvis 7) Ureter 8) Minor Calyx 9) Renal capsule 10) Inferior renal capsule 11) Superior renal capsule 13) Nephron 14) Minor calyx 15) Major Calyx 16) Renal papilla 17) Renal column

(no distinction for red/blue (oxygenated or not) blood, arteriole is between capillaries and larger vessels)

Figure 4: A longitudinal section of the left kidney

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On the medial surface of the kidney (the concave surface), it is the renal hilus, through which pass the renal artery and vein, renal nerve and the renal pelvis, which is the funnel-shaped upper end of the ureter.

If a kidney is bisected from superior to interior, the cut surface shows 2 distinct coloured regions, a dark outer region which is the cortex, and a paler inner region which is the medulla, which is further divided into a number of conical areas called the renal pyramids. The renal pelvis is lined by transitional epithelium and is the expanded upper part of the ureter. Extension of the pelvis, the calyx extends towards the papilla of each pyramid and collect the urine draining from it.

The ureters, about 30cm long, are muscular tubes which conect the renal pelvis to the bladder.

Blood supply of the kidney

The kidney receive 20-25 percent of the total cardiac output. In normal healthy individuals, about 1200ml of blood flows through the kidneys each minute. The blood supply to each kidney is usually a single renal artery originates along the lateral surface of the adominal aorta near the level of the superior mesenteric artery. However, there may sometimes be additional small vessels from superior mesenteric, adrenal, spermatic or ovarian arteries.

Almost all of the blood which enters the kidneys at renal hilus, via the renal artery. The renal artery branches to form several interlobar arteries which radiate outward through the renal column between the renal pyramids. The interlobar arteries subdivide themselves to arcuate arteries, which pass along the boundary between cortex and medulla. Each arcuate artery branches and travel out at a right angle, through the cortex towards the capsule and gives rise to a number of interlobular arteries, which supply the cortical portions of the adjacent renal lobes. Branching from each interlobular artery are numerous afferent arterioles, which deliver blood to the capillaries supplying individual nephrons (also called glomerular capillaries)

The glomerular capillaries are the site of filtration of the blood. The filtrate will enter the Bowman’s capsule of the nephron by the hydrostatic pressure of the capillary. The glomerular capillaries do not drain into a vein; instead they drain into a second arteriole, called the efferent arteriole.

The efferent arterioles from the nephrons in the outer two-thirds of the cortex branch to form a dense network of peritubular capillaries, which surround all the cortical tubular elements. The efferent arterioles in the one-third of the cortex give rise to capillaries which have a hairpin course into and out of the medulla, where they are adjacent to the loops of Henle and collecting ducts. These medullary capillaries are vasa recta. The peritubular capillaries and vasa recta eventually drain into the renal vein which leaves the kidney at the hilus.

The blood supply of the kidney is illustrated in Fig.5