Balance. In fact, it can’t survive without it.

I know that sounds quite “zen” (and you were probably expecting something scientific), but the reality is completely practical.

The human body is like a very picky machine. It needs specific conditions in order to work and it can’t deal with internal extremes for long. Just the same way your laptop or phone would be destroyed if you filled every space in it with water.

We are made up of cells and fibres in water. These are stuck together to make bones, joints, muscles, organs, nerves, lymphatics, blood vessels etc. All of our inner parts are nicely covered with fat, skin and hair so that being exposed to planet earth doesn’t kill us.

Our covers also stop us from terrifying small children (and them from traumatising us).

Before We Continue: cells are the smallest unit of all living things. Everything that’s alive is made up of one or more cells. So it’s impossible to learn how the human body works without understanding how cells work.

For comparison: a robot is made up of pieces of metal and/or plastic (and glass). They have electric wires running through them and they’re held together by nuts, bolts and solder. All of these inner parts are padded with insulation and then covered with an outer surface that the engineer chooses.

It takes a biologist to look at the body in such a practical way. Physicists will tell you that we’re made up of stardust and empty spaces. That sounds quite magical… until you start wondering where the empty spaces are.

The cells that make you and me come in thousands (if not millions) of varieties. They all do different things. They’re the reason why we can dance, taste chocolate, see in colour, feel the warmth of sunlight and hear the laughter of those we love. If our cells had an ice-cream shop equivalent, it would be the best ice-cream shop on earth.

Each of our cells is a little creature all on its own. It needs food, shelter, air, water and waste disposal. When it has them, it can survive, have babies and a full, lifelong career. Just like us. But if their surroundings aren’t just right, our cells die. This is true inside or outside our bodies.

Before We Continue: Physiology is the study of the functions of living things and the physical and chemical mechanisms that underlie them. Physiological parameters are features of living things that can be measured and used to assess their condition; e.g. temperature.

The environment outside our bodies changes all the time and we have very little say in it. But inside our bodies almost all of our cells work together to keep to their surroundings relatively constant.

Cells keep their surroundings inside the body flexibily “constant” by keeping different internal bodily conditions like blood pressure and temperature etc. in normal ranges. Things like blood pressure and temperature are called physiological parameters. Loads of physiological parameters are controlled by our bodies.

They include the amount of waste products like carbon dioxide and urea in our blood. And nutrients like glucose. The amount of glucose in our blood is kept in check by the infamous hormone, insulin. See figure 1.4:

Graph from Guyton and Hall Textbook of Medical Physiology, 13th edition.

As figure 1.4 shows, our blood glucose levels go up after we eat. The bigger the meal, and the more carbohydrates (potatoes, pasta, rice, bread etc.) in it, the more glucose it releases into our blood. But every time, our bodies take our blood glucose levels back to the baseline. This baseline glucose level is called our fasting blood glucose; it’s the amount of glucose that’s always supposed to be in our blood, even when we haven’t eaten.

Other things that are kept in normal ranges include the amount of ions like sodium, potassium and magnesium in our body fluids, the pH (i.e amount of acid and base) of our body fluids, the number of times our hearts beat in a minute (which changes depending on what we’re doing)… etc. Many other physiological parameters are managed this way.

Our bodies’ tendency to keep physiological parameters within normal ranges, this balance it needs and maintains, is called homeostasis.

The first person to write about the idea of homeostasis was a French physiologist called Claude Bernard. But the one who came up with the name was an American physiologist called Walter Cannon.

The practical use of homeostasis is that doctors work out what’s wrong with us by finding which physiological parameters are unexpectedly higher or lower than their normal range. This is why they ask for samples of our blood, urine and other fluids whenever we’re sick and we go to see them.

As I said before, most but not all of our cells play a part in maintaining homeostasis. Our reproductive cells, those lazy little brats, don’t help… They’re only interested in one thing. And they’re very single-minded about it. They’re not the only ones. The cells in our eyes are so busy helping us to see that they don’t care about anything else.

I’ll go into detail about how the different systems in our bodies play a part in homeostasis as I talk about each system. The details will be simpler to understand and easier to remember that way. Trust me.

Next time, I’ll continue to explain why homeostasis is so important for body function. I could give you a preview now, but I won’t. After all, you need a reason to come back!

Joanna xx

References: