Interesting (But Rather Useless) Facts I Learnt in Pre-Clinical Medicine

Interesting (But Rather Useless) Facts I Learnt in Pre-Clinical Medicine

I have now finished pre-clinical Medicine. This is the part of Medicine, usually lasting two years in the UK, where we learn information about the human body. There is a hell of a lot to learn and you end up forgetting most of it after exams. Apparently this isn’t too bad though, for most people do and end up making fine doctors.

Here are some interesting facts that I learnt in my pre-clinical years.

How much sperm males produce

It’s no secret that males produce a large number of sperm, but the numbers amazed me. Of course, the numbers are only estimates but that doesn’t make them any less effective.

It is estimated that per gram of testes, 300 – 600 sperm are produced per second.

To put it in another way, this equates to about 100 – 200 million sperm produced per day.

Otherwise, this equates to at least 1000 sperm being produced per heartbeat in males.

I find that rather amazing.

Why do we rub a part of our body that’s in pain?

You’re playing cricket and the ball hits you hard in the arm. You start rubbing it. Why do we do that?

One proposed mechanism is that of Gate control theory. To understand it, we need to understand a bit about the nervous system.

The nervous system is basically involved in sending signals to and from the brain. This is done through several complex mechanisms, and many different type of nerve fibres. Touch is sensed and transmitted through large Aβ nerve fibres (as well as others, but they’re less relevant to this question). Pain, however, is sensed and transmitted through large Aδ fibres and smaller C fibres.

Essentially, when we are feeling pain, these Aδ (and sometimes C) fibres are firing. However, the larger Aβ fibre, through various mechanisms, can inhibit the pain nerve fibres. This is known as ‘closing the gate’. To stimulate these Aβ fibres, you need touch – that is, to gently rub the site of pain. This can inhibit the pain, hence why we possibly do it.

Why are injuries in sport/in a fight more noticeable after?

If you play sports regularly or get involved in fights (which I hope you don’t by the way!), you may notice that any injuries you feel tend to be more painful after you complete your activity. Once again, there are probably several proposed theories for this. The one I want to talk about is the neural perception of pain.

When a painful stimulus is detected by the fibres mentioned above, it is eventually sent to the brain. When the pain is being processed and sent back down to the part of the body that it came from, it is inhibited by several structures to alter the perception of pain. These structures include things like the nucleus raphe magnus and (wait for it) nucleus reticularis paragigantocellularis. This is the basis for how opioids work to inhibit pain – they target some of these pain inhibitors to further inhibit the pain.

Also inhibiting pain as it travels back is something called the locus coeruleus. This is essentially a part of the brain involved in the sympathetic nervous system – that is, the fight or flight response. Therefore, when you are in a situation of fight or flight, this becomes active and inhibits pain perception. Once you stop exercising/fighting, this becomes less active and so more pain is felt.

Why can patients with lung cancer develop a hoarse voice?

Sadly, lung cancer has a poor prognosis and is absolutely devastating for anyone involved. Patients can present with a variety of symptoms, and one of these is a hoarse voice.

The reason why this happens is because in some cases, the tumour can end up compressing the recurrent laryngeal nerve, usually on the left side. The recurrent laryngeal nerve supplies most of the muscles of the larynx, or the voice box. Therefore, if this nerve is damaged or compressed in any way, it will affect the voice. In the case of lung cancer patients, it can cause hoarseness.

 The genetics of diabetes mellitus suggests something interesting

Diabetes mellitus (what most people mean when they just say ‘diabetes’) has two types: Type 1 and Type 2. Well, no, there are more than two types but these are the ones that are most well known.

Type 1 is caused when there is absolute insulin deficiency caused by destruction of the cells in the pancreas. It is unknown why this destruction takes place – although it is thought to be autoimmune and some evidence suggests that it may even be caused by a virus. Type 2 diabetes, however, is caused when cells become unresponsive to insulin. It was traditionally only seen in adults before, but it is now seen more often in children too. It is caused by things like obesity, but HOW obesity causes insulin resistance is not well understood.

What’s interesting is the genetics of these two types of diabetes. Type 1 diabetes has a 30-50% concordance, whilst type 2 had a nearly 100% concordance. What this means is that in identical twins, if one twin develops Type 2 Diabetes, the other will almost certainly develop it too. This is slightly surprising too, for Type 1 diabetes typically presents in children so on first impression, it may be tempting to think that Type 1 has a greater genetic component.

To me, this suggests something else. As already mentioned, obesity is a common cause of Type 2 diabetes. Does this mean that food intake and activity too is genetic? We don’t know for sure is the answer, but this genetic influence in Type 2 suggests it might be.

Final thoughts

All of this was written mainly from the top of my head so if anything interests you, be sure to research it properly. Let’s hope clinical years can also give me many more interesting things to see and learn!


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