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Hello and welcome back to
The Fundamentals of
Human Physiology.
My name is Jessica Briffa.
Today, we'll be going
through the third lecture in
the 'Kidney Function' series,
which is on sodium balance.
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Before we delve into this topic,
I have a few
stop-and-think questions
that are designed as a refresher
for the content
already covered and
to get you started
thinking about this topic.
First, let's consider
the following question.
What tubular activity
do you think is bigger?
As you may recall from
the first lecture,
reabsorption and secretion
occurs throughout the nephron.
We also know that 20% of
plasma is filtered
into the nephron.
However, less than 1% of the
volume is excreted as urine.
It may not be too
surprising that
reabsorption is a
bigger tubular process.
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Now that we know
that reabsorption
is the biggest tubular activity,
let's consider the
following question.
Where do you think
tubular reabsorption
is of the greatest
along the nephron?
If you think back to the
structure of the nephron,
you'll appreciate that
the first segment
of the tubule that
the glomerular filtrate
comes into contact
with is the proximal
convoluted tubule.
It is not too surprising
that this is a site where
the majority of solute and
water reabsorption occurs,
which is responsible for
reabsorbing 50-60% of
glomerular ultrafiltrate.
The reabsorption that occurs in
the proximal
convoluted tubules is
primarily driven by the
reabsorption of sodium ions;
a topic which we will expand
upon in this lecture.
