Now, the bladder
develops from part of the urogenital sinus.
In this diagram, we can see the original cloaca,
which is a large space dividing into two different
components. The upper part, the more anterior
part is known as the urogenital sinus.
The anal canal or rectum is the posterior part
of this process. Later on in life, the bladder
and the urethra will both develop from the
urogenital sinus. The cranial part of this
urogenital sinus will give rise to the bladder.
What we should know is that this is connected
to the structure called the allantois. Now,
this may seem rather mysterious and it certainly
will not be the word that you’ve heard during
your studies of adult anatomy. The reason for
that is that the allantois is an evolutionary
remnant. In our ancestors who existed inside
eggs, one of the major problems was where
to sequester waste products. And what [inaudible 00:10:32] developed
inside eggs have evolved is a little impermeable
sac called the allantois in which they store
their waste products. It comes off from the
hind end of the gut in the way that we’ve
just seen. This of course is redundant in
humans, and therefore, it will eventually
become condensed to form a ligamentous like
structure. So it will close down to form a
structure like a ligament. And if you were
to follow that forward, what you’d find
is that that ligament now connected to the
inside of the umbilical cord is called the
urachus. By the time birth is taken place
and development proceeds, eventually, it would
be known as the medial umbilical ligament.
So the name of the structure changes from
allantois to urachus to medial umbilical ligament.
You can readily imagine that this process
of closing might not go completely properly.
Therefore, it’s imaginable that in some
babies, it will still be open at the time
of birth. And if that were to happen, what
would appear are little drops of urine appearing
at the umbilicus which was normally fairly
startling to individual, as we see it, but
this is relatively simple to resolve surgically.
But as we’re discussing these changes at
this point, it’s worth pointing out that
the process of separation between the urogenital
sinus and the anal canal is also something
which shows variation. There may be abnormal
connections, fistulas, which join the rectum,
the anal canal to the bladder or the urethra at
some other point during the course of development.
Let’s look at the insertions of these structures
into the bladder. In the initial picture on
the left hand side, we can see the mesonephric
duct, and from it, the ureteric bud, and these
two are still joined together but gradually,
this will become separate. In this view, we’re
looking at the posterior, the back wall of
the bladder. We can see that they are gradually
becoming separate in the nature of their insertions
between the two. If we’re to follow this
forward, what we would see is that the mesonephric
duct is now quite separate from the ureter.
In the male, the mesonephric duct will persist and
form the vas deferens of the reproductive system.
In the female, as we’ll see in another lecture,
the mesonephric duct will degenerate.
If we go back to the urogenital sinus, what
we can see is that in the part just below
the bladder, there will be little outgrowths
that develop. In the female, these little
outgrowths will form the urethral and paraurethral
glands. However, in the male, this will give
rise to the prostates and its supporting structures.
The remainder of the urogenital sinus will
form the membranous and penile urethra in
the male. So the prostate gland is coming
from these outgrowths from this lower part
of the urogenital sinus just below the bladder.