(2) Structure. A coronal (frontal) section of the internal anatomy of the
kidney is called the cortex. The inner, reddish-brown region of the kidneys is called the
medulla. Eight to 18 striated, triangular structure termed renal pyramids are located in
the medulla. The characteristic tissue of the kidneys is made up of the cortex and the
renal pyramids. Tissue in each kidney is made up of about 1 million microscopic units
called nephrons, collecting ducts, and their associated vascular supply. The working
units of each kidney are the nephrons which help regulate the composition of blood and
the formation of urine.
Figure 4-1. The kidneys.
b. The Nephron Unit. The nephron is the functional unit of the kidney. The
estimation is that each kidney has about a million nephron units. A nephron is a long
tubular structure made up of successive segments of different structure and transport
functions. A nephron unit includes the following: renal corpuscle (Bowman's capsule
and the glomerulus), proximal tubule, Henle's Loop, distal tubule, and collecting duct