There are two parts of a kidney nephron: the renal
corpuscle,
and the renal tubule.
(1) Renal Corpuscle
The renal corpuscle is the part of
the kidney nephron in which blood plasma is filtered.
The
term "corpuscle" means "tiny" or "small" body.
The renal corpuscle of each kidney nephron has two
parts - they are
the Glomerulus,
which is a network of small blood vessels called capillaries,
and the Bowman's Capsule (also
known as the Glomerular
Capsule), which is the double-walled
epithelial cup within which the glomerulus is contained.
Within the glomerulus are glomerular
capillaries that are
located between the afferent
arteriole bringing blood into
the glomerulus and the efferent
arteriole draining blood away from
the glomerulus. The (outgoing) efferent arteriole has
a smaller diameter than the (incoming) afferent arteriole.
This difference in arteriole diameters helps
to raise the blood pressure in the glomerulus.
The area between the double-walls
of the Bowman's Capsule is called the capsular
space.
The cells that form the outer edges of the glomerulus
form close attachments to the cells of the inner surface of
the Bowman's Capsule. This combination of cells adhered
to each other forms a filtration
membrane that enables
water and solutes (substances that are dissolved
in the
water/blood)
to pass through the first wall of the Bowman's Capsule
into the capsular space. This filtration process
is helped
by the raised
blood
pressure in
the glomerulus
- due to the difference in diameter of the afferent
and efferent arterioles.
So to summarise:
In the renal corpuscle blood is forced
through the glomerular capillaries at higher pressure than
the
pressure
at which
the blood
generally travels around the body (and also into the
kidney itself). Helped by the increased pressure in the
glomerular capillaries, a filtration process occurs in
which some blood fluid is forced out of the glomerulus
and into the capsular space of the Bowman's Capsule.
The fluid that is filtered into the Bowman's Capsule is
called the glomerular filtrate.
Click
here to read more about Glomerular Filtration.
Note: What is special about the glomerular capillaries
? They are the only capillaries in the body that
are located between two arterioles, rather than between
an arteriole (incoming
blood supply) and a venule (drainage
of blood from the capillary).
(2) Renal Tubule
The renal tubule is
the part of the kidney nephron into which the glomerular
filtrate passes after it has reached
the Bowman's capsule. The first part of the renal tubule
is called the proximal convoluted
tubule (PCT), which is
shown on the right-hand side of the diagram above.
The water and solutes that have passed through the proximal
convoluted tubule (PCT) enter the Loop
of Henle, which consists of two portions
- first the descending limb
of Henle, then the ascending
limb of Henle. In order to pass through
the Loop of Henle, the water (and substances dissolved
in it) pass from the renal cortex into the renal medulla,
then back to the renal cortex. When this fluid returns
to the renal cortex (via the ascending limb of Henle) it
passes into the distal convoluted
tubule (DCT), which
is shown on the left-hand side of the diagram above.
The distal convoluted tubules of many individual kidney
nephrons converge onto a single collecting
duct. The fluid that has passed through
the distal convoluted tubules is drained into the collecting
duct (far left-hand-side of the diagram above). Many collecting
ducts join together to form several hundred papillary
ducts. There are typically about 30 papillary
ducts per renal papilla (the
renal papillae being the tips of the renal pyramids - which
point towards the centre
of the kidney). At each renal papilla the contents of the
papillary ducts drain
into
the minor
calces - the
channels
through
which
the
fluid passes, via the major calyx,
into the centre of the kidney - called the renal
pelvis.
|
