total amount present in the amniotic sac.
Let’s look now at some other abnormalities
that can develop in the developing urinary
system. One possibility is that one ureteric
bud might fail to form altogether, or more
probably, fail to induce the surrounding mesoderm
to condense roundabout it. There is a complex
and increasingly well-understood process of
signaling by genes in gene products from
the ureteric bud to the surrounding metanephric
mesoderm, which brings about this condensation.
And this can fail to take place. If this happens
on one side, the corresponding kidney on the
other side will enlarge to increase its possible
function. But nonetheless, although this may
not normally affect function of the kidneys,
it does mean that that single kidney might
be more liable to infection as a result.
If kidneys failed to develop on both sides bilateral,
renal agenesis, then of course that would
be incompatible with normal life after birth.
But of course, during the time of pregnancy,
the mother would be handling all of the waste
products. Another possibility is that the
kidneys may come close together during the
course of development and if they come in
contact with each other, they may fuse. If
they fuse in this way, and this is a condition
called horseshoe kidney, then they’ll be unable
to shift their relative position because
they’ll be unable to clear the iliac artery
subsequently. So they remain down in the pelvis.
This is relatively common appearing in one in
1,500 live births or so. And because they’re
in the pelvis, it would still function normally
but they would not be detectable of course
in their normal position, which may cause
some confusion on ultrasound scan.
Again, because there’s effectively just one kidney,
it may be slightly more susceptible to infection
as a result. It’s also sometimes possible
to get an extra ureteric bud, and this will
bring about an extra or ectopic kidney. That
will normally be found in an abnormal position,
although it will develop as one blood supply
and be capable of functioning. Normally, it
would not shift its relative position in the
same way. Finally, there is a condition called
polycystic kidney disease occuring in one
in 800 live births. This is something which
is an underlying genetic basis. What happens in
this condition is that the embryonic patterns
of gene expression persist into the early
childhood and adulthood. As a result, multiple
cysts will form in the kidney as you can see
in the illustration. Eventually of course,
if these cysts are sufficiently common, and of
sufficiently large size, they will significantly
inhibit kidney function, and may even prove
fatal in the end. So then, to summarize what
we’ve covered in this particular lecture.
We’ve looked at the basics of development
of the urinary system. And we saw that there
are some common abnormalities that may arise
as a consequence of things going wrong during
the normal developmental pattern. In particular,
we focused on the common condition of either
too much or too little amniotic fluid due
to result of the disturbance of the
foetal amniotic fluid circulation.
That’s it for this lecture. Thank you very much.