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Hydrogen is everywhere.
It's in the air we breathe, the water we drink, and the stars that fill our galaxy.
But not all molecules treat hydrogen the same way.
While some happily soak up hydrogen ions (bases), others are keen to palm them off at the earliest opportunity (acids).
This balance is measured by pH (power of hydrogen) — a logarithmic sliding scale between 1 (meaning very acidic) and 14 (meaning very basic).
If blood pH moves outside the normal range of 7.35-7.45, we risk disrupting the chemical reactions and structures that sustain life.
Thankfully, the renal and respiratory systems play an important role in stabilising the body's overall pH:
But there's another important factor that influences pH (and many other functions).
Electrolytes are substances that ionise in water, producing electroconductive solutions.
They play several roles in the body:
Each time blood passes through the kidneys, electrolytes are pulled between the urine and vasculature through various ion channels.
The net effect, in a functioning kidney, is to retain/excrete the right amounts of the right electrolytes, ensuring that all upstream factors keep functioning as they should.
Let's explore these mechanisms in more detail.
Concentration describes the quantitify of a substance per unit volume of a solution.
As with pressure gradients, substances tend to move from areas of high to low concentration.
Which leads us to the different kinds of membrane transport:
Passive Transport
This type of transport occurs along concentration gradients.
We call the passive transport of water "osmosis". In most other instances, it's referred to as "diffusion".
"Facilitated diffusion" is like regular diffusion, but uses certain membrane proteins to allow substances through. Some of these proteins ("ion channels") only allow specific ions to pass.
As the name implies, passive transport requires no energy.
But things aren't always this easy.
Active Transport
Active transport occurs against concentration gradients.
To do this, cells use stored chemical energy from a molecule known as ATP ("primary active transport"), or ride the coat-tails of nearby ATP expenditure ("secondary active transport").
This is useful, but fragile.
When there's enough energy, active transport helps keep us alive. But if the plug is pulled, things can go sideways:
An AKI is a sudden, significant decrease in kidney function.
There are three types:
You can imagine how, in an untreated AKI, the regulation of pH and electrolytes could become life-threateningly dysregulated.
Especially when it occurs as a complication of another pathology, such as sepsis.