INTERNAL STRUCTURE OF THE KIDNEY
In a coronal or frontal section of the kidney, three areas can be distinguished (Fig. 18–2). The lateral and middle areas are tissue layers, and the medial area at the hilus is a cavity. The outer tissue layer is called the renal cortex; it is made of renal corpuscles and convo-luted tubules. These are parts of the nephron and are described in the next section. The inner tissue layer is the renal medulla, which is made of loops of Henle and collecting tubules (also parts of the nephron). The renal medulla consists of wedge-shaped pieces called renal pyramids. The tip of each pyramid is its apex or papilla.
Figure 18–2. (A) Frontal section of the right kidney showing internal structure and blood vessels. (B) The magnified section of the kidney shows several nephrons. (C) Vascular cast of a kidney in lateral view. Red plastic fills the blood vessels. (D) Vascular cast in medial view. Blood vessels have been removed; yellow plastic fills the renal pelvis. (Photographs C and D by Dan Kaufman.)
QUESTION: Which main parts of a nephron are found in the renal cortex? Which areas of a kidney have many blood vessels?
The third area is the renal pelvis; this is not a layer of tissues, but rather a cavity formed by the expansion of the ureter within the kidney at the hilus. Funnel-shaped extensions of the renal pelvis, called calyces (singular: calyx), enclose the papillae of the renal pyr-amids. Urine flows from the renal pyramids into the calyces, then to the renal pelvis and out into the ureter.
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