THE NEPHRON:
Is the functional unit of the kidney (Fig. 1.2). Each kidney contains
approximately one million nephrons. The first part of the nephron is the
glomerulus (renal corpuscle) which lies mainly in the renal cortex,
followed by proximal convoluted tubule which also lies mainly in the renal
cortex. This is followed by a loop of Henle which is partly in the cortex
and partly extends deep into the medulla. Loop of Henle is composed of a
thin part and a thick part. This is followed by the distal convoluted tubule
which lies in the renal cortex. Part of the distal convoluted tubule comes
into contact with the hilum of the glomerulus and afferent arteriole. Cells
in the hilum of the glomerulus and those in distal convoluted tubule and
afferent arteriole are modified to form the Juxta glomerular apparatus.
Distal convoluted tubule ends into the collecting duct which lies partly in
the cortex and partly in the medulla. In the medulla, collecting ducts
descend in the pyramids, at the renal papillae collecting ducts unite
together to form ducts of Bertini which discharge urine into renal pelvis.The glomerulus (renal corpuscle):
The renal corpuscle is formed essentially of two modified
structures of different embryonic origins:
A. The first is the Bowman's capsule which is present at the beginning
of the proximal convoluted tubule and is formed of a space lined by
basement membrane and flat epithelial cells.
B. The second is modification of the end of the afferent arteriole,
which divides into several primary branches. These in turn give
rise to several lobules of capillaries (tuft of capillaries). The other
end of this capillary tuft gives rise to the efferent arteriole. Each
capillary is lined with basement membrane, lined from inside by
endothelial cells and from outside by epithelial cells which lie on
the capillary basement membrane by foot process (so it is called