Recent Developments

A few months ago I was somewhat surprised to see a news story about scientists who had managed to get the natural balance just right to be able to support the growth of lamb foetuses in plastic bags (“BioBags”). This was not like anything I expected to see in this half of the century, and sounded like something from a science fiction movie, so you can understand my excitement at this achievement. In this blog post I will aim to explain the challenges the scientists faced in trying to get this system to support life and what this could mean in the future, not only for animals but for humans too.

The most obvious challenge when designing the Biobag was what to grow the foetus in. Amniotic fluid for a foetus is not only a cushion, protecting it from knocks and bumps, but it aids in bone and limb growth, and supplies the foetus with vital nutrients. Some also say that swallowing amniotic fluid helps to foster antimicrobial protection[1] and to develop the foetus’ gastrointestinal system[2]. Therefore, it is crucial to get the volume and composition of artificial amniotic fluid right. Complicating this is the fact that these conditions change throughout gestation to match the foetus’ stage of growth and needs.

The synthetic amniotic fluid used in the Biobags is a neutral electrolyte solution composed of hydrogen carbonate, sodium, chloride, potassium and calcium salts. These are all nutrients which the foetus needs to grow and develop. Although the initial experiments just used this simple electrolyte solution, the scientists’ future research will focus on improving and optimising the solution to be used in the Biobags [3].

Another challenge was how to get oxygen and nutrients to the foetus and remove any waste produced. Placental transfer is vital for the gas exchange and excretion of waste for the foetus. By inserting cannulas into the major veins and arteries in the lamb’s umbilical cord, these blood vessels can be attached to a filtering and exchange system for gases to be transferred to and from the lamb’s body[3]. This, however is not done by a man-made pump, but instead by the natural pump that exists in all mammals’ bodies; the heart. Using the foetal heart to drive the circulation instead of an artificial pump has many advantages, including a natural regulation of blood pressure, and simplicity – this is also closer to the natural situation. The heart of the foetus is able to pump the blood through the external gas exchange system at the perfect pressure to maintain the correct blood gas content but not too high that the blood vessels of the umbilical cord or the umbilical cord to machine interface are under threat of rupture.

However, the volume of the oxygenator is crucial. If too high or low a volume, then the foetus will become haemodynamically unstable (an instability in the flow of blood around the body[4]) and the system will not be able to deliver sufficient oxygen to the foetus.

Infection can be lethal to any foetus, even those cushioned safely inside a maternal uterus. However, this is a major consideration for foetuses in Biobags. The scientists lost many foetuses in their research because of sepsis (an infection), but have significantly reduced losses by having a ‘closed’ system with microbial filters and sterile access ports fitted for any addition of fluid or suction of meconium (faecal waste produced by the foetus).

Biobags have successfully grown infant lambs from a stage that would be equivalent to extremely premature human infants for up to 4 weeks. This may not sound like a long time, but this extra developmental time can be the difference between life and death or normal brain/lung function and life changing damage to human infants. It is also important to note that this 4 week period was not due to mechanical failure or a mishap in the system, the experiment had to be terminated at this time because of animal protocol limitations. The foetuses could be sustained in Biobags for much longer.

The scientists hope that Biobags could be used in the future to help human infants of just 23-25 weeks’ gestation[5] to have better outcomes, and to help treat conditions such as growth retardation caused by placental insufficiency. The trials for this could occur as soon as 3 years’ time. Although there may be some psychological barriers to overcome for parents seeing their baby ‘in a bag’, the possible applications of this breakthrough technology are potentially limitless, and truly in the realms of science fiction.

[1] BIOLOGY DICTIONARY. (2017) Amniotic Fluid. [Online] Available from: [Accessed: 15th September 2017]

[2] SANGILD, P. T. et al. (2003) Ingestion of Amniotic Fluid Before Birth: Does It Improve Intestinal Function? [Online] Available from: [Accessed: 15th September 2017]

[3] PARTRIDGE, E. A. et al. (2017) An Extra-uterine System To Physiologically Support The Extreme Premature Lamb. [Online] Available from: [Accessed: 17th September 2017]

[4] CHEGG. (2017) Signs And Symptoms Of Hemodynamic Instability. [Online] Available from: [Accessed: 17th September 2017]

[5] TAYAG, Y. (2017) How a Plastic Bag Became a Womb for Premature Lambs. [Online] Available from: [Accessed: 17th September 2017]


Bumblebees: A Man’s Best Friend?

It was as I was mindlessly scrolling through the internet that something caught my eye which is the basis for my next blog post.

I am the first to admit that flying, stinging things are not my favourite type of insect, but I must say I always felt rather sorry for bees, unlike say wasps.

I’ve always been told that every bee’s approach is an all-or-nothing venture, and so although our relationship got off to a rocky start-after my first memory of bees is one being tangled in my hair, (which, let me tell you, was rather traumatic for a toddler and still would be now)- I don’t mind as much their fuzzy little black and yellow bodies buzzing along, because I now appreciate that they prefer to stay out of your way: to sting you is to condemn themselves to death. This is true of the well-known honeybee, however bumblebees have a slightly different story, as I shall explain later, yet I still prefer them to the furious looking wasps.

Thus, it shocked me a little to find out that the first bumblebee has been announced endangered in the U.S. I mean, it has been made very clear that bees are facing a tough time, but it never quite clicked that the fuzzy little things may not be the sign of summer anymore: may not be present at all.

This post looks at bumblebees and the Rusty Patched Bumblebee’s endangered status.


Bumblebees are members of the Bombus genus and now over 250 species of bumblebee are known [1].

They are classed as social insects that form colonies with a single queen, although their colonies are smaller than those of their relatives, the honeybees, as they can grow to as few as 50 individuals in a nest [1].

Bumblebees feed on nectar, like their relatives the honeybees. Bumblebees use their long hairy tongues to lap up the liquid and the proboscis (the elongated appendage from the head of an animal-in insects, this is typically an elongated sucking mouthpart which is usually tubular and flexible) is folded under their head during flight. Bumblebees gather nectar to add to the stores inside the nest and pollen is used to feed their young. They use colour and spatial relationships to identify flowers they use to feed from and some species of bumblebees ‘rob nectar’ by making a hole near the base of the flower to access the nectar without touching the pollen. Overall, they are essential agricultural pollinators and thus there is growing concern about their declining numbers in Europe, North America, and Asia [1].

As I have mentioned before, a honeybee generally dies after stinging a human because the barbs on her sting and the relative elasticity of our skin prevents her from pulling her sting out. Thus, she will either be swatted to death or so much of her sting, poison sac and abdominal contents will be left hanging from the stuck sting if she pulls away that she will fly to death (not a very pleasant death, if I say so myself) [2]. On the other hand, female bumblebees can sting repeatedly without injuring themselves because their stings lack the barbs and so they can pull their sting out of the wound. However, bumblebees are generally not normally aggressive and tend to ignore humans and other animals, although they may sting in defence of their nest or if harmed [1].

Rusty Patched Bumblebee

Recently, the U.S. Fish and Wildlife Service announced that the Bombus affinis -rusty patched bumblebee- is “now balancing precariously on the brink of extinction”, when “just 20 years ago,” it was “so ordinary that it went almost unnoticed as it moved from flower to flower”. The rusty patched bumblebee has experienced a swift and dramatic decline since the late 1990s, a shocking 87% decrease in numbers, leaving small, scattered populations in 13 states and one province in the U.S. [3].

The news should not have been surprising however, as only a few months before, the first ever bees were declared endangered in the U.S. In September of 2016, seven species of Hawaiian bees received protection under the Endangered Species Act [4].

We’ll now take a closer look specifically at the rusty patched bumblebee and its importance to us.

In case you ignored them, all rusty patched bumblebees have entirely black heads, but only the workers and males have a rusty-reddish patch located in the centre of their backs. Like the other bumblebees, this species lives in colonies that include a single queen and female workers, and it is only during late summer that the colony produces males and new queens. The queens can be easily distinguished by their larger size [5].


Fig. 2 Illustrations showing a rusty patched bumblebee queen (left), worker (centre) and male (right). [5]

Rusty patched bumblebees are generally not fussy eaters as they gather pollen and nectar from a variety of flowering plants, although since they emerge in early spring and are one of the last species to go into hibernation, they require a constant diverse supply of flowers blooming from April to September [5].

One of the reasons why the rusty patched bumblebees are flying ever closer the edge of extinction is because the habitat they once occupied is slowly being destroyed. The grasslands and tallgrass prairies of the Upper Midwest and Northeast, which the bumblebees once called home, have now been mainly converted to monoculture farms or developed areas, such as cities and roads, and the grasslands that are left are usually too small and isolated to provide the nesting sites (typically underground and abandoned rodent cavities or clumps of grass), overwintering sites (undisturbed soil) for queens and a large array of flowers to be a long-term solution [5].

Another reason for the bumblebees’ fading face from the earth is intensive farming, as many practices which have been adopted, such as increased use of pesticides, loss of crop diversity and loss of hedgerows with their flower populations and legume pastures, have harmed bumblebees. They are especially vulnerable to pesticides because they can absorb the toxins directly through their exoskeleton as through contaminated nectar and pollen [5] and this causes lethal and sub-lethal effects.

Furthermore, global climate change may also play a crucial card because the increased temperature and precipitation extremes; increased drought, early snow melt and late frost events may lead to more exposure or susceptibility to disease, fewer flowering plants [5]. There may also be fewer places for queens to hibernate and nest [5] which may be the final straw for the rapidly decreasing populations because the entire colony relies on the survival of their queen bee through winter-the only member of the colony which survives the season [3].

The Importance of Saying ‘Mi Casa Es Tu Casa’

Well, we all know the intricacies of ecosystems but the rusty patched bumblebees are in fact major contributors to our own food security. They are essential pollinators of blueberries, cranberries, and clover and almost the only insect pollinators of tomatoes. Overall, bumblebees are more effective pollinators than honey bees for some crops because of their ability to ‘buzz crop’, and this is one of the reasons why the economic value of pollination services by native insects (mainly bees) in the United States is around $3 billion per year [5].

One of the main ways people can help is by creating a more bee-friendly garden. Although this is mainly aimed at people living in areas native to the rusty patched bumblebees, you can very well apply this to your own home as almost everywhere there are issues with increasingly more important pollinators being endangered.

This can be as simple as adding a flowering tree or shrub to your garden, or more specifically to the rusty patched bumblebee, native plants such as lupines, asters, bee balm, native prairie plants and spring ephemerals. Or if you’re not one for gardening, just leave some ‘unmowed, brushy’ areas and tolerate bumble bee nests if you find them. On the other hand, if you are a garden enthusiast, try to keep away from pesticides and chemical fertiliser [5].

However, there is still hope as recently the giant panda has been downgraded from ‘endangered’ to ‘vulnerable’ [6], meaning as long as something is done in an effort to help, it may not all be doom and gloom.









Mind Over Matter

imageTaking a break from my monthly blog post about the fantastic Natural History Museum, I have decided to discuss one of my favourite and perhaps more controversial biological topics – the placebo effect. I am a massive fan of mental strength over physical prowess (I’m not the most athletic shall we say, so it works for me) and the placebo effect demonstrates just how strong the human mind can be. As perhaps one of the more complex of all of our organs, I’m going to talk about the brain and its role in numbing pain, reducing physical symptoms, and sometimes even curing disease.

Pain relief
This is one of the more obvious uses of placebos, as everyone has heard of someone withstanding cutting off a limb without anaesthesia in order to save their life; there has even been a film in which a man becomes trapped for 127 hours, only being released after cutting off his own hand. However, the more interesting side to this story is how we could potentially harness this effect in order to treat those with addictions to painkillers.

The statistics are shocking, with nearly 7,000 visits to A&E and 44 deaths each day caused by prescription painkiller addictions in America in a single year[1]. Pain clinics and monitoring prescription patterns are struggling to reduce this, so what if a solution could be found in a more unconventional place? Prescription painkillers have been put to the test, and some studies have shown that they do not work as well in bland, non-branded packaging [2], and also that their effects are reduced when the patient is unaware that they are taking them [1]. Additionally, the placebo effect can also have the opposite outcome – where no drugs are administered, placebo painkillers have been seen to affect the pain-related areas of the brain, and even stimulate the release of endorphins (which are pain relieving chemicals that the body produces).

Expectations play a great role in this effect. This is where ‘mind over matter’ plays a more prominent role. During a study, three groups of patients were given a placebo. One group had no expectation of analgesia (pain relief), another group had a positive expectation of analgesia, and the third had a negative expectation of analgesia (in the sense that they expected the pain to worsen). When the patients were asked to rate their pain, the patients expecting a positive result experienced twice the analgesic effect than the patients with no expectation of pain relief. Also, the patients expecting a negative result experienced no pain relief at all [3]. And this leads me quite nicely onto my next point for discussion.

The Ceremony
Placebos rely quite heavily on the art of pomp and ceremony, and this is quite clear to see when the placebo ‘form’ is examined in more detail.

As aforementioned, the packaging of a placebo makes a huge difference in the level of expectation and therefore the experience of the enclosed pill. On reading “Bad Science” by Ben Goldacre, I was interested (but perhaps not surprised) to read that patients responded better to placebos found in bright and flashy, branded packaging as opposed to bland, neutral boxes. An even greater effect was seen when patients were given aspirin in differing packaging.

However, external packaging is not all that matters when packaging a placebo. The colour of the pill itself has been found to play a role in this ever so fascinating and developing effect. For a drug called Oxazepam, its effects differed when the tablets were differently coloured. In a green tablet form it was better at treating anxiety, whereas the same drug was found to be more beneficial at treating depression when yellow. Colours have been assigned meanings by society, and these societal norms are influencing the way we perceive the world. Blue for sedatives, pink for stimulants. This was seen to be the case when a group of college students were given a placebo, told to be either a sedative or a stimulant. Those given pink pills experienced higher maintained concentration levels than those given blue pills. Two pills were also observed to have a greater effect than one (side effects included) [2].

This explains the pomp, but what about the ceremony? Well, again, this relates back to what we perceive to be ‘more effective’. The best example of this is the vaccine. In three separate experiments, pills have been out done by the salt-water injection. Not because sugar pills have any less of a biological effect than salt-water, but purely because it was seen as a more dramatic treatment. Much the same was seen when a sugar pill was put up against an acupuncture style ‘ritual’ treatment [2]. Ceremony wins.

This is perhaps the more controversial side of any placebo discussion. Is it ethical to supply a patient in pain, or with a disease, a placebo knowing that it has no active ingredient to treat the ailment? The answer is no. At least if you don’t discuss it with them first.

In a recent meeting of the school’s vets and medics society, we discussed in some detail the ethics behind full disclosure and some scenarios in which it was difficult, from an ethical stand point, to determine what exactly was the best way and thing to tell your patient. I was very much on Team Full Disclosure and my opinion hasn’t changed. When it comes to a patient’s health, they have a right to know exactly what is going on, which is why my whole viewpoint on the placebo effect changed when I discovered this next fact.

The placebo effect will have a very limited real life application if the patient must remain in the dark about the contents of the mysterious looking pill sat in front of them in order to feel its effects. It’s unethical. However, the placebo does not just work because the brain is tricked into thinking it has received a drug. Patients have been fully aware that they are taking a placebo and have still experienced the same effects as if they had been unaware. In a study, 80 patients suffering from irritable bowel syndrome (IBS) were split into two groups. One group was given no treatment, and the other given a placebo. The placebo group were told that they were being given a placebo, and that meant that all the pills would contain was sugar. To avoid confusion, ‘placebo’ was even printed on the bottle. Defying all expectation, the placebo group doubled the average rate of improvement to that expected from the most powerful IBS medications [4]. Presumably, this has something to do with the ritual of taking a pill, whether it contains medication or not, and the mind being deceived by the mere action. However, the sheer size of the effect experienced was somewhat incredible.

The placebo effect is a wonderful demonstration of the power of the human mind, which I have always been deeply fascinated by. The social perceptions of colour and packaging, along with the ritualistic ceremony linked to how our brains not only receive medicine but also see the world is brilliantly clever, but also a little terrifying – perhaps the role of society in our lives is not as small as we once thought! I hope you have found this little insight into the placebo effect as interesting as I have, and I hope you now realise how truly amazing your brain is.


[1] MARCHANT, J. (2016) A Placebo Treatment for Pain. [Online] Available from: [Accessed: 30th January 2017]

[2] GOLDACRE, B. (2010) Bad Science. 1st ed. New York: Faber and Faber.

[3] NOVELLA, S. (2011) Placebo Effect for Pain. [Online] Available from: [Accessed: 30th January 2017]

[4] JHA, A. (2010) Placebo effect works even if patients know they’re getting a sham drug. [Online] Available from: [Accessed: 30th January 2017]

Eating a Rainbow


I have always been interested in food, but in recent years I have become more conscious (most of the time!) about what it is I’m putting into my body. This led to a lot of research over a long period of time around what is and is not good for your body, how to tell, and in what quantities. A phrase I have repeatedly come across is ‘eat your rainbow’. As a borderline vegan, this is quite an easy feat for me, I love fruit and veg and they are the star of most of my meals. However, I thought I would share the benefits of eating a variety of different coloured fruit and veg, and that eating more of a rainbow can bring to anyones diet.

I began this article wanting to explain why all these foods can have positive effects, however it would end up a short (or even long) novel! Therefore, I have settled for telling you what benefits different coloured foods can have, and examples of each. As each different colour of fruit and veg (natural foods) relates to the quantities of antioxidants, vitamins and minerals alongside pigments it contains, eating a variety of different coloured foods gives your body a huge amount of different antioxidants, vitamins and minerals. All of which nourish your body. It is recommended that you eat at least 3 different colours of food at every meal, as these different colours play different roles within your body – this may be aiding your immune system, digestion, or contributing to the strength of your bones. These fruit and veg are nutrient dense and contain a whole load of fibre, both of which will do your body a lot of good!

So while technically this post is a little unorthodox, and not entirely biology related, I’ve figured that it relates to the benefits we can get from our foods, all due to biological processes. I apologise to any hard biologists who find this slightly insulting …. but if anything I think it is an interesting topic, which many people are not hugely educated on!


Red foods are packed with phytochemicals such as lycopene, and thus help improve heart and circulatory health alongside memory. For instance, cherries are high in antioxidants which can help protect against heart disease, diabetes and arthritis. Red bell peppers are high in vitamin C and fibre, and have been linked to increased immunity, improved digestion and to lower cholesterol. Tomatoes are also notably high in lycopene, and have been shown to reduce damage done to our cells, and decrease the risk of diabetes.


These tend to be particularly high in antioxidants such as vitamin C and carotenoids. Orange foods have been linked to skin and eye health as well as increased immunity and a healthy heart. Carrots for example, are high in vitamin A, helping to maintain the integrity of the skin and oranges are high in vitamins A and C, again linked to increased immunity, heart health and healthier skin. Oranges also have a high magnesium content, which can help strengthen bones and improve digestion.


These commonly contain nutrients which promote good digestion, and as they are high in alpha and beta carotenes, have been linked to improved immunity, healthy eyes and skin. Examples of these are in pineapple, which is cholesterol and fat-free, and high in bromelain. Bromelain, is an enzyme which helps to regulate and neutralise body fluids, aiding digestion. Yellow peppers are also high in vitamins C and A, aiding the immune system and contributing to healthy skin.


Green foods are definitely my favourite, and anything with spinach, avocado or kale in is a winner for me. These contain phytochemicals such as lutein, and have benefits such as improved eye health and strong teeth. Spinach is high in antioxidants and vitamin K, which helps to strengthen bones, while broccoli is high in calcium and iron, linking it to stronger bones and muscles. Kiwi however, is high in folate and vitamin E, which help to decrease the risk heart disease.


These are brightly coloured due to anthocyanins, which have anti-acing properties in the body. They can help promote bone health and have been shown to improve memory and increase urinary-tract health. Although, the main benefit of purple and blue foods is increased circulation. Blueberries for instance, are high in fibre, vitamins E and C, antioxidants and are sometimes referred to as a ‘superfood’. They have been linked to an improved cholesterol and a boost in brain activity. Blackberries are packed with vitamin K which promotes calcium absorption and bone health, alternatively eggplant is high in phosphorus and calcium, again promoting strong bones and teeth.


Hopefully this has made you think about what colour the foods that you eat are, and the benefits that expanding your diet and ‘eating a rainbow’ can have. Hopefully when you sit down for dinner tomorrow there will be a little less beige, and your plate will look a bit more like a rainbow!

sources: as I mentioned, much of this has come from a notebook I have been adding to for a long time, so the exact sources I am not entirely sure of. However, I have found some interesting websites containing similar information.

Colour change in a teacup

As the revision period looms (I mean, when is there a time when we don’t have to revise?), tea becomes my constant companion. Whether this may be in the form of offering a shoulder to cry on as maths questions refuse to make sense or, by living up to its expectations, that tea can, in fact, solve all your problems by creating the polite deception of wanting to boil the kettle for everyone when you just wish to escape the confining shackles of textbooks.

It was as I was pouring over my chemistry notes on hydrogen and hydroxide ions that tea made another unlikely addition to its already enviable personal statement; it is a real-life example of a colour change.

I am sure this has limitations. For example, I drink my tea with lemon and no milk.

However, I was still intrigued about this magic in my tea cup and here is what I found in my educational revision break.

50 shades of tea

By adding a lemon slice or juice, black tea lightens significantly (shown by figures 1 and 2), and although I have never tried this, by adding lemon to green tea, the tea loses its signature colour and becomes colourless [1].


Fig 1. Tea before lemon has been added.


Fig 2. Tea after lemon has been added.

Lemon juice is an example of citric acid, which has the chemical formula of C6H8O7. It is a weak tricarboxylic acid that is found mainly in citrus fruit, but also a variety of different fruit and vegetables. Lemons and limes have a particularly high citric acid content as it can make up to 8% of the dry mass of the fruit and the concentration can reach 0.30 mol/L whereas this is significantly lower in fruit such as oranges and grapefruit where the concentration amounts to 0.005 mol/L.  Citric acid itself was isolated by the chemist Carl Wilhelm Scheele in 1784 by crystallising it from lemon juice. The acid can exist in both an anhydrous form, which is formed when it is crystallised from hot water, and a monohydrate form which is created when the acid is crystallised from cold water instead.

Anyway, back to tea.

Tea leaves are rich in polyphenols-a group of chemicals that accounts for almost one third of the mass of a dried leaf and much of the tea’s colour and flavour is due to these compounds. One group of polyphenols is called thearubigins and they are the red-brown pigments which are found in black tea. This group of polyphenols can make up between 7% and 20% of the total mass of dried black tea, and more interestingly, these thearubigins are weak ionising acids, and the anions (otherwise known as negatively charged ions) they produce are highly coloured. For example, if the water used to brew the tea is alkaline, then the colour of the tea will be deeper because of the greater ionisation of the thearubigins, and because the colour of black tea is influenced by the concentration of hydrogen ions in the water [3].

This means that if lemon juice, i.e. citric acid, is added to the tea, then the hydrogen ions will suppress the ionisation of the thearubigins and this will make the tea a lighter colour [3]. Sorry – no real magic this time.

On a side note, however, you may be interested to know that theaflavins-the yellow-coloured polyphenols present in black tea-are not actually involved in the colour change that is associated with a change in acidity [3].


The colour change that you see in your tea cup as you sip slowly in order to extend the tea-drinking break is in fact just evidence of a change in acidity-much like a change in litmus paper that you may have seen in a Chemistry lab.





Why does Christmas dinner make us sleepy?

I hope you all had a lovely Christmas, and are looking forward to the New Year. At about 5pm on Christmas day I looked round our living room to see my sister, dad and grandparents all fast asleep – the annual post Christmas lunch nap. Something which caused me to ponder why, so I thought I’d do a bit of research and share it with you in a quick blog post.

Initially, the only answer I found was that large meals obviously take a long time to digest, thus blood is diverted away from other body areas to help digest the food at a faster rate. However, after a bit of digging I found some interesting websites and articles which gave more in-depth alternatives. The conclusion I came to is as follows…

Eating triggers the PNS  (parasympathetic nervous system) responsible for preparing the body for rest and increasing the activity of the digestive system. The PNS is part of the autonomic nervous system (thank you 3rd Form biology!) which is responsible for involuntary actions. Fundamentally, the actions of the PNS trigger hormones and neurotransmitters which are what make us feel sleepy.

An old New Scientists article says that ‘high blood glucose levels, similar to those after eating a big meal, can switch off the brain cells that normally keep us awake and alert.’ Additionally to this, high blood glucose levels cause the PNS to stimulate the pancreas to produce insulin – converting these sugars to be stored.  This increased level of insulin consequently stimulates the action of tryptophan, an essential amino acid within the brain. In turn, when the tryptophan is in the brain, it leads to an increased level of serotonin – the universally known ‘happy hormone’. Serotonin is an neurotransmitter which passes electrical signals between connecting neurones, and has many functions, including controlling mood and lethargy. Around 90% of serotonin within the body is found in the abdomen, and is responsible for regulating intestinal movements. However, the remaining 10% is found in the brain.

In short, high blood glucose levels trigger the production of insulin. This stimulates the action of tryptophan in the brain, consequently triggering an increase in the levels of serotonin within the body.

Therefore, it is the increased level of serotonin, responsible for mood and ‘sleepiness’ which makes you feel like all you can do is nap after Christmas dinner!



Nerves, aka the not-so-good wires

Author’s note:

So, just before we explore the workings of message transfer in the human body, I would like to clarify the origins of this blog post. On Saturday 5th November 2016, Cambridge University held a Medicine Taster Day at the Lady Mitchell Hall. This consisted of sample lectures and a run through of the teaching system, among other tips for entry. One of the lectures was titled something along the lines of “How do nerves work?”. As fabulous and interesting as the other lectures were, this one really gave me the most “food for thought”, as they say, and it is on the notes that I made during the lecture that is blog post is based.

Thus, I implore you to understand that writing notes on a topic which a lecturer is comfortably pacing through and later trying to make out the beginning and end of your scrawls is no easy feat (as I’m sure we’ll all find out about in a few years’ time and become masters of note taking). I admit that I wanted to write this solely on my notes to a) review the lecture and b) to see if I understood anything that was being said.

But before any of you future Biology stars start panic (or panic further as may be the case), I did ask for my Biology teacher to look over this post. The message is this: this is a very simplified version of what is happening in real life, especially in the case of amplification. We shall, of course, come to study the topic of nerves in more detail and finesse further in the A Level course.

Oh, and another thing. If any of you dear readers come to learn that any of the figures are incorrect, I sincerely apologise and please do not hesitate to let me know. In the meantime, feel free to blame my poor eyesight (I did find out a while later that my right eye has deteriorated 🙂 ) or my incomprehensible handwriting for any mistakes made.


Nerves work in a similar fashion to wires, but when you look at their basic structure, to be honest, they’re a bit of a disappointment to the wire family.

So, if nerves are the “ok” version of copper wires, how do we manage to stay alive?

Firstly, we’ll look at how nerves work, then the problems they encounter and finally how they try to overcome the issues of transferring current.

Trying hard to be a wire

When a pain fibre is stimulated, pain channels are opened and sodium ions (which have a positive charge) enter at one end of the nerve while the rest remains negatively charged. The next stages are similar to those of a battery, as, the differently charged ions create a current which spreads positive charge through the nerve and this results in the potential of activating something else, such as a synapse.

In comparison to a copper wire in which the speed of this is 28,000,000 m/s, the nerve’s speed is between 0.6 to 100 m/s. However, although this is significantly lower, this is not a limiting factor in the body’s reactions, as the message still travels in milliseconds.

The difficulties begin

As usual, there are problems with all wires, however this is particularly true of nerves, and the problem nerves face is that current leaks out.


Fig 1. Diagram showing longitudinal and membrane resistance in a nerve.

In the diagram above (Fig 1.), RL (red line) is the longitudinal resistance and it is a measure of the resistance the current encounters as it travels along the nerve. The lower this resistance, the easier it is for the current to travel.

Rm (blue line) is the membrane resistance and this is a measure of the resistance given to the current by the cell membrane. The higher this resistance, the less current will escape.

How far can a nerve conduct?

Voltage decreases exponentially, meaning it leaks less.

The distance at which the voltage has decreased by half is called lambda (λ), and it is a ratio of the two resistances aforementioned. In effect, it is a ratio of how much voltage continues travelling along the nerve to how much has leaked out.


This means that high membrane resistance and low longitudinal resistance results in a good signal.

We must also remember that resistance is calculated by:

R = p x l/A


  • R is resistance
  • p is resistivity
  • l is length
  • A is cross-sectional area


Nerves are very narrow as they normally have a diameter between 0.2 to 2.0 micrometres, meaning that RL is large.

The cell membranes are also very thin, typically between 7.0 to 9.0 nanometres, so Rm is small. This is due to the fact that the membrane is made of two molecules – specifically two phospholipids, as cell membranes are bilayers.

In addition, the axon, which is mainly cytoplasm, has a resistivity of 50 To put this into perspective, copper wires have a resistivity of 1.7×108 The poor axon resistivity is because, since nerves are part of the body, they have to be able to change shape, which is the advantage of a conducting liquid.

As a result, a 1 metre long, 1 micrometre diameter nerve has the same resistance as a 22-gauge copper wire, which in other words is a 0.65 nanometre diameter piece of copper stretching to Saturn and back. Five times.

A much-needed rescue

To put it nicely, nerves are probably not the material you would be reaching for if you wanted to transfer some current. As a result of their physical properties of being narrow, thin-walled and not very conductive, their resistance is high, and even non-physics students know that this is not ideal for conducting electricity.

After reading all of this, I’m sure your question is: how are we still alive? This was my question too.

Thankfully, nerves have some tricks up their sleeves, something similar to pulling a rabbit out of a hat.


One of these features is myelination of the nerve fibre. The myelin sheath increases the membrane resistance and it means that the signal can travel 3 millimetres more. However taking into consideration that the length of a nerve fibre running from your foot to the central nervous system can be around 1 metre, in the grand scheme of things, 3 millimetres are not that helpful, although certainly much appreciated.


The real show stopper trick and literal life saver is the nerve’s power of amplification. This process keeps allowing ions to enter the nerve cell by sodium gated voltage channels in order to sustain the voltage. This makes the signal bigger, as when the channel opens, more positive sodium ions enter and this increases the concentration gradient, as there is more positive charge. Furthermore, the channel is also charged, meaning it moves if voltage changes. This means the channel itself detects a change in the voltage and is able to react to make it greater. Figure 2 demonstrates this process.


Fig 2. Graph showing the effect of amplification [1].

Problems persist

Because the amplification process requires sodium channels, and channels are required to stimulate pain, the myelin sheath cannot be too thick, as otherwise the sodium channels could not be present, meaning the effect of myelination is not at its highest potential, as it needs to compromise with the other processes.

Moreover, the transmission takes time because the passive movement of the signal (i.e. when the signal is not aided by amplification) is still faster than the active movement (the points where amplification takes place) since the amplification process, as we now know, involves sodium channels opening, moving and opening again, which overall is time consuming. 

In addition, there is also the factor of positive feedback. The main idea is that it is triggered by something that it causes and so it is an all or nothing response. What this means is that as one sodium channel opens, then more will open. If the stimulus is not powerful enough, then nothing happens, so the stimulus must be greater than the threshold.


Overall, the structure of the nerve results in it being a poor conductor, however it is because of features such as myelination and amplification that we are still here today, reading this biology blog post.


As I have mentioned before: this post has been written from my notes which I took during the lecture: “How do nerves work?” as part of the Medicine Taster Day at Cambridge University. The information is from the lecturer given on the day: 5Th November 2016.



With thanks to:

·Cambridge University for organising the taster day and to the lecturer for providing the fascinating information.

·Miss Lasouska who kindly read this post.