Kidney and Adrenal Gland drawing
General Structure of the Kidney
The kidney is invested by a fibrous tunic, which forms a firm, smooth covering to the organ. The tunic can be easily stripped off, but in doing so numerous fine processes of connective tissue and small bloodvessels are torn through. Beneath this coat a thin, wide-meshed net-work of unstriped muscular fiber forms an incomplete covering to the organ. When the capsule is stripped off, the surface of the kidney is found to be smooth and even and of a deep red color. In infants fissures extending for some depth may be seen on the surface of the organ, a remnant of the lobular construction of the gland. The kidney is dense in texture, but is easily lacerable by mechanical force. If a vertical section of the kidney be made from its convex to its concave border, it will be seen that the hilum expands into a central cavity, the renal sinus, this contains the upper part of the renal pelvis and the calyces, surrounded by some fat in which are imbedded the branches of the renal vessels and nerves. The renal sinus is lined by a prolongation of the fibrous tunic, which is continued around the lips of the hilum. The renal calyces, from seven to thirteen in number, are cup-shaped tubes, each of which embraces one or more of the renal papillæ; they unite to form two or three short tubes, and these in turn join to form a funnel-shaped sac, the renal pelvis. The renal pelvis, wide above and narrow below where it joins the ureter, is partly outside the renal sinus. The renal calyces and pelvis form the upper expanded end of the excretory duct of the kidney.
The kidney is composed of an internal medullary and an external cortical substance.
The medullary substance (substantia medullaris) consists of a series of red-colored striated conical masses, termed the renal pyramids, the bases of which are directed toward the circumference of the kidney, while their apices converge toward the renal sinus, where they form prominent papillæ projecting into the interior of the calyces
The cortical substance (substantia corticalis) is reddish brown in color and soft and granular in consistence. It lies immediately beneath the fibrous tunic, arches over the bases of the pyramids, and dips in between adjacent pyramids toward the renal sinus. The parts dipping in between the pyramids are named the renal columns (Bertini), while the portions which connect the renal columns to each other and intervene between the bases of the pyramids and the fibrous tunic are called the cortical arches (indicated between A and A’ in Fig. 1127). If the cortex be examined with a lens, it will be seen to consist of a series of lighter-colored, conical areas, termed the radiate part, and a darker-colored intervening substance, which from the complexity of its structure is named the convoluted part. The rays gradually taper toward the circumference of the kidney, and consist of a series of outward prolongations from the base of each renal pyramid.
Each suprarenal (adrenal) gland consists of a cortical portion derived from the celomic epithelium and a medullary portion originally composed of sympatho-chromaffin tissue. The cortical portion is first recognizable about the beginning of the fourth week as a series of buds from the celomic cells at the root of the mesentery. Later it becomes completely separated from the celomic epithelium and forms a suprarenal ridge projecting into the celom between the mesonephros and the root of the mesentery. Into this cortical portion cells from the neighboring masses of sympatho-chromaffin tissue migrate along the line of its central vein to reach and form the medullary portion of the gland.
Vessels and Nerves
The arteries supplying the suprarenal glands are numerous and of comparatively large size; they are derived from the aorta, the inferior phrenic, and the renal. They subdivide into minute branches previous to entering the cortical part of the gland, where they break up into capillaries which end in the venous plexus of the medullary portion.
The suprarenal vein returns the blood from the medullary venous plexus and receives several branches from the cortical substance; it emerges from the hilum of the gland and on the right side opens into the inferior vena cava, on the left into the renal vein.
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Gray H. Anatomy of the human body. (1918) Philadelphia: Lea & Febiger.
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