The urinary system
The urinary system

The urinary system
consists of two
kidneys, two ureters,
one bladder and one
urethra. Urine is
formed in each of the
kidneys as waste
product from blood
filtration and passes
through a ureter
through to the bladder
Renal Structure

About 1cm of the outside of the kidney is
called the renal cortex layer. The inside of
the kidney is called the medulla and it is
here that blood is filtered. The medulla is
composed of between 8 and 18 renal
pyramids and you can see a representation
of these in this slide. You can also see how
urine drains into the ureter
Renal Pyramid

Each renal pyramid has many thousand nephrons.
You can see a representation of one in this slide.
Blood enters the glomerulus where filtration
commences. It is labelled “G” in this slide. The
filtrate then passes through the Proximal
convoluted tubule then down the thin descending
limb of Henle’s loop, then through the Distal
convoluted tubule), the Collecting tubule and
finally into the Collecting duct. We will look at
the microscopic structure in each of these
structures to come to terms with urine formation
The nephron

This slide also shows a nephron and you
can see how different substances are
reabsorbed back into the blood during urine
formation. Essentially, urine is on the
inside of the tube in this diagram and its
composition varies as it passes down
through the tube until it comes to the
collecting ducts where its composition has
been finalised
Glomerulus (Renal Corpuscle)

First point of blood filtration is in the glomerulus. It is a
tuft of capillaries. Blood enters via afferent arteriole and
leaves via efferent arteriole. Plasma is filtered into
Bowman’s space across the networked capillaries. The
filtrate flows into the Proximal Convoluted Tubule. You
can note that these cells have cilia on them. Filtered
plasma passes back into the efferent arteriole whilst the
filtrate containing much of the liquid component of blood
flows out of the glomerulus into the proximal convoluted
tubule. No protein should be present in filtrate
Proximal Convoluted Tubule

The Proximal convoluted tubule is lined by
cuboidal epithelium most of the water that
was filtered out of the blood now passes
across the epithelial layer and back into the
blood. The epithelial membrane contains
special enzymes that can digest any
peptides present so amino acids are not lost
into the urine
Loop of Henle

Urine now passes through the Loop of
Hele, which consists of thin walled tubules.
Much of the salt in the urine is reabsorbed
back into the blood by active transport
Distal Convoluted Tubules

The Distal convoluted tubule contains
numerous mitochondria to provide ATP for
active transport of sodium back into
interstitial fluid.
Collecting Ducts

Finally urine passes through the collecting
ducts. These ducts are very important
because of their role in regulating the
amount of urine formed
Proximal Ureter

The urine now flows from the kidney into
the ureter. This is lined by transitional
epithelium, fibroelastic lamina and circular
smooth muscle, which helps move the fluid
into the bladder.
Bladder

The bladder has a thick muscular wall, a
thin layer of smooth muscle and is lined by
transitional epithelium. The transitional
epithelia change shape as the bladder
distends