Simple Science Shorts #2

Science shorts 2

I made several promises that I would continue to write this blog after I left to go travelling. I had every intention of chilling in some internet café in Asia, having coffee and typing away but of course, at no stage did that actually happen. I have been lazy, and I intend on changing that now. Without diving straight into a full post on a specific topic I will try to piece together an easy to write, easy to read set of explanations for day to day occurrences or subjects that I have thought about over the past week. Ease myself back into it!

I like this picture. Its even relevant to the first section of this blog. DO NOT GIVE CHOCOLATE TO PUPPIES.

Why is chocolate toxic to dogs?

It is fairly wide known to anyone that owns a dog, not to give it chocolate. I was curious as to the specific reason for this however as it would be interesting if the particular substance that causes this toxicity is present in other things that could come into contact with dogs. It turns out that the poisonous substance contained within chocolate is theobromine, a xanthine alkaloid. Not only is this substance lethal to dogs, it is also poisonous to us, albeit in significantly larger doses. The lethal dose (LD₅₀) of theobromine in dogs is ~300mg/Kg body mass whereas in humans, LD₅₀ = ~1000mg/Kg. Take into account the significantly larger body weight of people and it is obvious how little chocolate is needed to poison a dog (and obviously it would take much less chocolate to kill a Chihuahua than a Great Dane). Theobromine increases metabolic rate, cardiovascular activity and neural activity which can result in cardiac arrest, hyperventilation and seizures in canines. This becomes fatal when the chemical pushes the body to function far beyond its capabilities resulting in permanent damage. Theobromine is found in chocolate because it is produced by the cocoa plant. This means that it can also be traced in coffee (and other caffienated beverages), cocoa powder as well as in tea leaves so again, avoid letting your dog come into contact with anything associated with cocoa plants!

One thing that is also very peculiar is that cats actually have a lower theobromine LD₅₀ than dogs. However, they do not possess the necessary receptors on their tongues to taste sweetness, and are therefore at a lower risk of ever experiencing theobromine poisoning.

The moral of this section is don't risk giving chocolate to a dog, even a small amount can be deadly. Think of the puppies.

Goosebumps

Hot dogs or legs?

Everyone at some stage has experienced Goosebumps. These small bumps on your skin and erect hairs arise from exposure to cold temperatures or even experiencing strong emotions such as fear, arousal or euphoria. Goosebumps, termed medically as “horripilation”, is innervated from the sympathetic branch of the autonomic nervous system and facilitated via contraction of arrector pili muscles attached to the hair follicles. This involuntary contraction responds to a variety of stresses for a number of reasons. The primary function is considered to be for insulation. Air becomes trapped between the erect hairs which enables the individual to retain heat. However, this trait has underwent expatation and is therefore not exclusively developed for heat retention. The sympathetic nervous system is synonymous with the ‘fight or flight’ response. There are strong hypotheses to suggest that under stressful situations, the contraction of the arrector pili muscles is being utilised to make the individual appear bigger and therefore more intimidating to a potential predator (such is the case in the porcupine raising its spines). It seems however that this trait has become a vestigial response to humans. This means that it has lost its original function. Humans no longer have much body hair to provide much added warmth, nor enough to increase body size a noticeable amount.

Interestingly, the colloquial name “Goosebumps” derives from the appearance of the bumps under a microscope. Evidently, they look very similar to the head and bill of a goose.

A simple representation of the effect of the arrector pili muscles causing a lump in the skin and erection of hair.

When Tanning Stops and Sunburn Begins

Showcasing melanogenesis in response to UVB radiation.

Everyone I know is different. Some people cannot get a tan if they pay for it; other turn golden brown looking out the window; and some people burn watching Thomas cook adverts. Why does the sun affect our skin so differently and what sort of damage is it actually doing to us? As with everything good in life, it is harming us in some way. Melanin pigmentation of the skin protects the body by absorbing solar radiation to a certain extent. The direct cause of tanning is exposure to UV rays from the sun (UVA, UVB or a combination of both) which results signalling to increase protection. The first mechanisms involved, is UVA radiation causing oxidative stress to melanin already present in your skin, resulting in oxidisation and rapid darkening of the skin tone. The second phase is triggered by UVB radiation which initiates melanogenisis (production of melanin). This is the body’s reaction to direct and indirect DNA damage within the skin and the increase of melanin present causes the skin colour to darken. Although the redness of sunburn appears to be the damaged consequence of exposure to UVB radiation, it is actually your body’s photoprotection response. By preventing UV protons from disrupting chemical bonds, melanin inhibits both direct and indirect alternation of DNA and the production of harmful free radicals. The damage of sunburn is mainly the formation of a thymine dimer which triggers several defence mechanisms like melanogenisis as well as apoptosis to kill and remove irreparably damaged cells and an inflammation process. Inflammation produces prostanoids and bradykinin which increase sensitivity to heat (making showering with sunburn particularly unpleasant) and also results in the overproduction of CXCL5 protein, activating nerve fibres, causing pain.

At some stage I intend on covering skin cancer associated with severe sunburn but that will require a post in itself.

There was going to be another section in this blog about allergies however it became very clear early on that this topic is much too large for a "shorts" post. I will make a full post on allergies sometime soon!

As always, feedback and ideas for other topics are very welcome.

Cheers!