Key anatomy and physiology

Key anatomy and physiology

Dale Pinnock
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Published by
Quadrille Publishing
978 184949 541 7

To really understand the impact that your diet has upon your health and how it may relate to your specific health concerns, you need to be as informed as possible and to learn as much as you can about how it all works.

That is why we need to look at the background science a little bit here, paying particular attention to the structure and function of different tissues.

Structures and functions will be very important things to understand later on when it comes to actually putting all the pieces together and having this information down-pat for life. I want to give you enough information to empower you and help you to understand your body and your health a little better, but at the same time not to overload you.

So let’s begin with the base structure of every tissue in your body. That is your…


Cells are the smallest living components of our body, yet are some of the most mind-blowing and complex pieces of wizardry imaginable. They are the small components inside us that collectively make up the many tissues in the various different systems of our body. There are thousands of different types of cells in the body with all manner of weird and wonderful adaptations and specialised variations, and our bodies are composed of an estimated 37.2 trillion of them.

As a completely living unit, cells can replicate, regulate almost every aspect of their function and even suss out when is the best time to die for the good of the rest of the body. That’s pretty impressive! There are several components that make up the structure of each of our cells and familiarity with these will be very useful later on.

The membrane

The membrane is the flexible active outer bubble that separates all the intricate workings of the inside of the cell from the outer environment. The cell membrane is made from what is known as a phospholipid bilayer. This is a layer of two lipid (fatty) molecules back-to-back in a continuous sheet that surrounds the whole cell, keeping everything in place like a bubble.

It is designed to give the cell structure, shape and stability. It is also a very flexible structure, so the cell can move freely. It is designed both to regulate the movement of nutrients and oxygen into the interior of the cell and to safely and rapidly remove waste from within the cell. It is semi-permeable, meaning that some compounds can naturally diffuse across it to gain access to the internal environment of the cell (the ones with that ability are generally small, simple compounds).

There are, however, a huge array of different things that can affect the functioning of our cells. Most of these cannot freely enter the cell. Some that actually need to enter the cell to instigate their activities and stimulate changes require facilities for what is known as ‘active transport’. This is where a certain structure – a specific transport mechanism if you will – in the cell membrane can actually bind to the substance in question and pull it in. These transport systems are selective. They recognise the specific substance that they need to look after and that alone. This stops other potentially dangerous substances using the structures to gain entry to the cell at random.

There is a third category of things that can influence what happens within our cells: these compounds do not need to enter the cell physically in order to instigate their activity upon it. These compounds actually interact with the cells and cause a whole cascade of chemical reactions to take place within it, without even having physically to enter it to do so. These compounds, such as hormones, need…

Cell receptors

Cell receptors are specialised structures that are built into the cell membrane. They both project out into the extracellular (outside the cell) environment and into the intracellular (inside the cell) environment, too. Their role is to carry signals and messages that are sent from the outside, in order to stimulate changes inside the cell. They only bind to specific types of molecule. These may be hormones, neurotransmitters (chemicals that carry messages throughout the nervous system), cytokines (proteins that send specific commands to cells, often used by the immune system) and compounds that regulate tissue growth.

Receptors don’t just attach to any old communication compound. There are as many different receptors as there are compounds, and each is uniquely designed. It could be viewed as a lock-and-key system. Specific receptors can be likened to a lock that is a specific shape that can fit a specific key. Hormones, neurotransmitters, cytokines and growth factors are the key that will fit the specific lock, and are known as a ligand (the specific object that fits a receptor and instigates a response). When the ligand binds with the receptor, the receptor will set in motion a series of chemical responses inside the cell, that vary from a simple change through to an incredibly complex daisy chain of reactions, in order to bring about changes in the behaviour, growth or metabolism of the cell. Receptors and hormones are going to be cropping up a lot in this book. Especially the hormone insulin and its receptor!


Once we go into the cell, we find that there are a huge range of structures in there to perform every conceivable reaction necessary for life. There are many organelles, most that we don’t need to worry a great deal about here, but I will give you a little overview. Probably the most well-known of the organelles is the nucleus. This is the control centre of our cells and is the thing that is portrayed as a little dot or sphere in the centre of pictures and diagrams of cells (and that’s a pretty fair representation of the truth). The nucleus is where our DNA is found.

Other organelles are involved in facilitating chemical reactions, modifying, assembling and storing vital metabolic substances, and generally controlling a massive range of functions and events that take place in our cells during every moment of every day.

Probably the most important in terms of what we are discussing here is an organelle called the mitochondria. This is a small sausage-shaped structure that is the energy factory of our cells. This is really the final place where food becomes energy, or at least gives rise to the energy that our cells use to function. The mitochondria has an unique double-layered structure that is almost like a sac within a sac. Imagine one sac with many folds in it, placed inside another smooth sac. This curious double layering is vital to the mitochondria’s function and is there to allow two different stages of chemical reactions to take place in order for our cells to make the energy we need.

How cells make energy

This is the next important area for us to cover. It will also help drive some of the key points home a little later on and just give you a background for better understanding of the whole process. Things can get a little complicated, but don’t worry too much. I’m just trying to give you the broadest picture I can. There’s no test at the end. Honest!

Everyone knows that the food we eat is where our energy comes from. But it obviously has to go through many changes in order to be utilised. Cells require a lot of energy. The amount of complex chemical reactions that they undertake constantly is really rather mind-boggling. We are talking literally hundreds of thousands of things going on inside the cells and tissues of our body every second. This life-giving activity requires energy, and lots of it, too. I will go into greater detail later about how food is digested and how the energy is released from foods, but for now, what we need to know is that cells’ first choice of energy to run on is glucose. We can run very effectively on fats, too… more on that later. When we eat a meal, glucose, to a greater or lesser extent, will enter into the bloodstream and become available to the body. When glucose is available following a meal, the hormone insulin gets released from the pancreas and lets all our cells know that glucose is here and it is ready to use. Insulin then binds to its receptor and tells cells to take in glucose… and do it quickly. Glucose transporters open and in comes the glucose. Once inside the cells, the glucose needs to be put to use. Unfortunately, it isn’t as simple as cells simply running off glucose, more work needs to be done. Glucose needs to be converted into something called ATP (Adenosine Triphosphate). This is what gives the cell the energy it needs. It is the actual energy currency of the cell.

ATP has a specific structure. It consists of a substance called adenosine that is bound to three phosphates (again, don’t get too worried about the details, just the general concept). These are held together by very high-energy chemical bonds. When needed, one of the three phosphates can be chopped off to release the high energy found in these bonds to power chemical reactions within the cell. What’s left behind is something called ADP (Adenosine Diphosphate). Tri = 3, Di = 2; before it was a Triphosphate then, after one of the phosphates has been removed, it becomes a Diphosphate. This has to then have another phosphate attached to it, returning it to the triphosphate and restoring that huge amount of energy in the bond. This takes place in the mitochondria.

Sugars and fats contain many high-energy bonds. If you recall, the mitochondria is composed of a sac within a sac. In the space between the two sacs, these fuel substances (glucose and fats) are broken apart to release the high energy in them, as electrons. These electrons then activate pumps that force hydrogen across into the inner sac. These hydrogens in turn then move through something called ATP Synthase, and generate enough energy to bind a new phosphate on to the ADP.

OK, I know this sounds a little bit geeky and complex and you don’t need to know it inside out. The point I want to drive home is that cells respond to external signalling that lets them know that fuel is available. This fuel goes through a series of reactions that power our cells. That’s it in a nutshell.

Phew. Hopefully that is the hard part over. It will all be worth it, I promise: these key points will put some of the later information into context for you.

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