In the human, there are two kidneys, one right and one left.
a. Location. Both kidneys are attached high up on the posterior abdominal wall. The left kidney is slightly higher than the right.
b. Shape. In the adult, each kidney measures about 1x2x4 inches. The kidneys have a kidney-bean shape. That is, they are notched on the medial side, they have a convex lateral curvature, and their front and rear surfaces are somewhat flat.
c. Capsule. Each kidney is surrounded by a dense FCT membrane called a capsule.
d. Internal Structure. When a kidney is cut from side to side, the internal structure is similar to that in Figure 8-1. There is a fleshy portion surrounding a central opening. The fleshy portion is divided into an outer cortex layer and an inner medulla.
(1) The medulla consists of a series of pyramids whose apices (peaks) point into the hollow center of the kidney. The apex (peak) of each renal pyramid is known as the papilla.
(2) The central cavity of the kidney is known as the renal sinus. Its opening on the medial aspect of the kidney is known as the hilus (or hilum). The sinus contains a number of structures:
(a) The spaces among these structures are filled with loose areolar FCT (fibrous connective tissue) and fat.
(b) The renal NAVL enter the kidney directly from the abdominal aorta, through the hilus, and into the renal sinus. They then continue in a regular pattern throughout the medulla and cortex of the kidneys.
(c) A funnel-shaped, cup-like tube, called a calix (or calyx), surrounds the papilla of each pyramid. All of the calices are continuous with and empty into a hollow structure called the renal pelvis.
e. Adherence to the Posterior Abdominal Wall. Each kidney is attached to the posterior abdominal wall on its respective side. Enclosing the kidneys and holding them in place are special perirenal fascial membranes and perirenal fats. During a "crash diet," an individual may lose some of this perirenal fat. This allows the kidney to move with the motions of the body. If the kidney should slump too far down, a kink may form in the ureter. This would prevent the normal flow of urine from the kidney to the bladder.
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