(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
The actual unit of kidney function is the structure referred to as the nephron
(Figure 8-2). It is estimated that each kidney has about a million nephrons. Each
nephron consists of a renal corpuscle and a tubular system.
a. Renal Corpuscle. A nephron begins with a renal corpuscle. The renal
corpuscle is made up of a double-walled capsule and an arterial capillary network
known as the glomerulus. An afferent arteriole supplies blood to the glomerulus, and an
efferent arteriole drains blood from the glomerulus.
AFFERENT = carry to
EFFERENT = carry away from
The blood from the afferent arteriole fills the glomerulus. Because of a pressure
gradient, a large percentage of fluid in this blood passes through the wall of the
glomerular capillary. The fluid then passes through the inner wall of the capsule. This
brings the fluid into the hollow space between the inner and outer walls of the capsule.
b. Tubular System. The fluid, or filtrate, then passes through the tubular
system of the nephron. Here, the majority of the water, glucose, and other valuable
substances are reabsorbed from the fluid and returned to the cardiovascular system.