Friday, 21 June 2013

How Tongues Taste Part 2: Supertasters

Just a short post this time.

Taste researchers divide people into three groups:

  1. Non-tasters (around 25%)
  2. Medium tasters (around 50%)
  3. Supertasters (around 35% of women and 15% of men) (Wikipedia)
Studies suggest that women and people from Asia, Africa and South America are more likely to be supertasters. 

Testing for supertasters

These three groups are classified by their sensitivity to the bitter chemical 6-n-propylthiouracil (PROP). Non-tasters can't taste the bitterness all, medium tasters sense the bitterness but find it bearable, while supertasters find it revolting. Phenylthiocarbamide (PTC) was originally used for this test.

Children always seem to be able to taste PROP’s bitterness. This could be the reason why tastes for bitter foods such as coffee and dark chocolate are acquired with age. (BBC)

The term ‘supertaster’ was coined by Linda Bartoshuk in 1991, for people with acute PROP sensitivity. Supertasters are people with one or two dominant alleles for the gene TAS2R28. This results in a denser covering of fungiform papillae (one of the types of bumps on your tongue - see diagrams) and a therefore a higher number of taste receptors than non- and medium tasters (HowStuffWorks). 

You can see if you're a supertaster with this experiment.

The supertaster allele was probably an advantage in the past, allowing its possessors to detect poison more effectively, meaning more of them lived to reproduce and pass on their genes.   Even today, some studies have shown that supertasters still have an advantage but for different reasons: they tend to have a lower obesity rate (only in women) and risk of heart disease, because they also have a heightened sensitivity to fatty, salty and sugary foods so generally eat less of them.  

However, the supertaster gene can also affect people’s health negatively. Flavonoids, for example, taste unpleasantly bitter to supertasters, causing them to avoid certain fruit and vegetables. They often find common foods too strong, leading to extreme fussiness in some people.

If you do do the experiment, please let me know the results! 
For a basic overview on taste, please see the previous post :) 

Thursday, 20 June 2013

How Tongues Taste Part 1: Overview

The idea for the topic of this post came from an article on New Scientist, but it expired before I had the time to read it. If you’re subscribed to New Scientist you might want to go and look at it

Taste and flavour are different. Taste (like smell) is a reaction to the chemical composition of solutions (gustatory stimulation). Like all sensations, it begins with electrical impulses, becoming a perception when these reach the brain and are interpreted. Different stimuli activate different receptors.

The taste only partly contributes to actual 'flavour' of something. Flavour is the sensory impression of food (or anything you put in your mouth) and is determined by smell (olfaction) and trigeminal nerve stimulation (which also handles touch for texture, pain and temperature), as well as taste (Wikipedia). With very ‘hot’ food like pepper and chilies, the brain will even perceive pain as part of its flavour as the pain receptors in your mouth are activated.

This post will concentrate on taste by itself.  (Not the taste of tongues, which the title seems to suggest.  I don't even know what tongues taste like)

Five basic tastes

There are five basic tastes (these aren’t absolute - just ideas):
  •  Sour 
  •  Sweet 
  •  Bitter 
  •  Salty 
  •  Umami - salts of certain acids (e.g. monosodium glutamate) (BBC)

Taste is very subjective - things taste completely different to different people. Some people have inherited genetic traits that make certain foods taste disgusting. Supertasters, for example, have abnormally high concentrations of taste receptors.  This will be covered in the next post.

Taste buds

Taste buds are the smallest functional unit of taste. The chemoreceptors that detect taste in humans are called gustatory receptor cells. Each taste bud contains around 50 to 100 taste receptor cells (Wikipedia). These are contained in three of the four kinds of papillae (bumps), especially on the tongue.  

Most people have approximately 10,000 taste buds, mostly located on and around the bumps on your tongue, and the back of the throat and the roof of the mouth (Tasting Science).  Note that the little bumps on your tongue are NOT individual taste buds but simply bumps to increase friction - taste buds are actually little dips.

Each taste bud can detect all five tastes (see diagram below). The ‘tongue map’, that you might have learnt about at school is now outdated; in 1974, Virginia Collings determined that although the areas of the tongue do have varying degrees of sensitivity (different taste bud density), they all respond to multiple tastes (gustatory stimulations).   You can taste any taste wherever there are receptors.

Gustatory receptor cells
Every gustatory receptor cell includes a protrusion called a gustatory hair, which pokes out through a taste pore.

The gustatory impulse is activated when:

1. Food molecules mix and dissolve in saliva to form a solution;

2. This solution enters a taste pore (in the top of the taste bud) and interacts with the gustatory hairs at the tops of the receptor cells (How Stuff Works);

3. Electrical signals pass this impulse through nerves up to the gustatory area of the cerebral cortex (Tasting Science). 

4. The brain then interprets these signals as taste.

The next post looks at supertasters.

Wednesday, 19 June 2013

Newt Pierces Its Sides With Its Own Ribs

Spanish (or Iberian) ribbed newts are large newts, reaching 30cm in length in the wild (source: Caudata Culture).  They are found in a range of freshwater habits across Spain, Portugal and Morocco (source: Dudley Zoo).  They get their name from their characteristic defence mechanism. 

When attacked, the newt swings its ribs forward, increasing their angle to the spine by up to 50 degrees.  "The forward movement of the ribs increases the body size and stretches the skin to the point of piercing it," says zoologist Egon Heiss of the University of Vienna in Austria.  (source: BBC Earth News
On their sides, along the rib tips, the newts have small yellow/orange dots (see picture).  These are paratoid glands, external skin glands on the back, neck, and shoulder of toads and some frogs and salamanders  (source: Reptile Apartment).  They contain a milky alkaloid substance which acts as a neurotoxin (source: Wikipedia).  The newts rupture these glands with the points of their ribs when attacked, releasing the toxin. The poison can be almost injected into the thin skin within the mouth when grabbed by an attacker, causing severe pain and/or death.

This poison can seep into the body tissue of the newt, but apparently doesn’t hurt it at all.  "The combination of the poisonous secretion and the ribs as 'stinging' tools is highly effective," says Heiss.  (source: BBC Earth News)

Thanks for reading!

Strange HTML again so sorry if it looks weird!

Tuesday, 18 June 2013

Hairy Frog Breaks Its Own Toes To Make Claws

There is a small piece of bone nestled in connective tissue in the top of the frog's toe. When sheathed, the claw's sharp point is anchored to this bone with strands of collagen.  Gerald Durrell, naturalist and author of the famous Corfu Trilogy, discovered first hand that when the frog is threatened, it can quickly break this connection and force the sharp point through the skin (source: Wikipedia). This is possible because the proximal end of the claw is connected to a muscle. David Blackburn and his colleagues at Harvard have discovered that when attacked, the frog contracts this muscle and pulls the claw downwards. This causes the sharp point to break away from the bone and cut through the toe pad, emerging on the underside. (source: New Scientist)

Blackburn and his team only researched on dead T. robustus frogs, so they didn't discover how the claws are retracted. In 2011 the retraction method was still unknown and there seems to be no information on it now in 2013, so I assume it still is.  The most likely explanation is that the claw retracts by itself when the muscle is relaxedand the tips of the toes heal over (amphibian skin heals extremely quickly).

David Blackburn and other scientists at Museum of Comparative Zoology at Harvard University have researched the strange behaviour of Trichobatrachus robustusthe Hairy Frog. This is a central African species of frog of the Arthroleptidae family. It has a rather unusual and seemingly painful defence mechanism: it can intentionally break parts of the toes of its hind feet and puncture the bones through its toe pads to make retractable claws. (New Scientist)

David Cannatella, a herpetologist at the University of Texas, Austin, questions whether these bone claws are actually meant for fighting: they could simply exist to allow a frog's feet "to get a better grip on whatever rocky habitat they might be in." (source: Daily Mail)  However, this seems slightly random and highly unlikely; according to Wikipedia, its natural habitats are subtropical or tropical moist lowland forests, rivers, arable land, plantations, and heavily degraded former forest - not exactly places where rocks are a huge problem.  However, other amphibians in different habitats could have spines for this purpose.

This behaviour is found in 9 of the 11 frogs of the Astylosternus genus, most of which live in Cameroon, where they presumably developed it to try and escape the tribes who want to feed them to their childless couples to make them fertile. (it didn't work - they use spears.)

These are not the only frogs with bony spikes or claws, but they have a unique way of 'producing' them. "Some other frogs have bony spines that project from their wrist, but in those species it appears that the bones grow through the skin rather than pierce it when needed for defence," Blackburn told New Scientist. The Japanese Otton Frog, among others, also has a false thumb which conceals a sharp spine used in combat and mating. (source: Daily Mail)

Another similarly strange and painful defence mechanism can be seen in the Spanish Ribbed Newt, which will be discussed in the next blog post.

p.s. something has gone a bit strange with the HTML.  Is everything in the right order?

p.p.s  sorry about my useless post titles.  Are you really meant to start every word with a capital letter?

Saturday, 15 June 2013

3D Printing Cells And Organs

3D printing has been everywhere recently - from food to models to customised implants, ears, and bits of skull


Gabriel Villar and colleagues at Oxford University have developed a material which behaves like biological tissue and resembles brain and fat tissue, according to (April 4 2013).    

A specially designed 3D printing machine ejected tens of thousands of individual droplets according to a 3D network.  Each droplet is about the same size as a drop of ink from an inkjet printer, and contains all the chemicals normally found in tissue cells.  They are coated in a layer of lipids, which form membranes similar to the phospholipid bilayers of animal cells. 

The 3D printer can also build pores into the already water-permeable lipid membrane, to act like the channel proteins of the plasma membranes of real cells, allowing the transport of molecules across the membrane. They allows communication between cells and therefore enables them to function together as a group

The shapes that the printed droplets formed had the consistency of soft rubber and remained stable for several weeks.  If the droplets were displaced they sprung elastically back to their original places, like soft tissue cells in animals.  They are held together by the network of lipid bilayers.
The hopes for these droplet networks are that they could one day be programmed to release drugs following a psychological signal.  Printed cells could then be integrated into damaged or failing tissue, replacing malfunctioning cells.  Medical engineers are currently trying to grow brain cells to treat diseases like Huntingdon’s.   


Currently thin layers of liver cells (assays) are used for testing in labs. These only last a few days and don’t have a wide enough range of functions. In San Diego, California, Organovo has developed a 3D bioprinter that can print mini livers when loaded with liver cells from spare tissue. These livers are 0.5mm deep and 4mm wide, and can perform most of the functions of a real liver.

  1. A tissue design is established;
  2. The protocols which are required to generate the multi-cellular building blocks (called bio-ink) from the cells that will be used to build the tissue are developed;
  3. The bio-ink droplets are then dispensed from a bioprinter in layers.  Bio-inert hydrogel can be used for support and fillers to create channels or spaces within tissues to copy features of real tissue.

The bioprinting process can be adapted to produce tissues in many different formats, from micro-scale tissues to larger structures (Organovo: the bioprinting process).  

The printer builds up about 20 layers of the two main types of liver cell, hepatocytes (see diagram above - cells that perform many of the liver’s main functions) and stellate cells (which provide both structure and repair capabilities).  It also adds cells from the lining of blood vessels, to form a network of channels to supply the liver cells with nutrients and oxygen.  The tissue “remained viable for 135 hours and retained key liver functions,” according to the company.  

The mini-livers produce albumin and cholesterol and the detoxification enzymes, cytochrome P450s, in the same way as real livers. Their realistic functioning means they act as good predictors of the toxicity of drugs and other substances. 

Organovo hopes to be able to create larger viable sections, stepping toward 3D printing of implantable liver tissue and whole replicated organs.  To reach this point, however, they still need to find a way to print larger blood vessel networks. 

These two new 3D printers - liver and and general tissue - could one day supply some of the organs used for the 1.5 million tissue transplants that take place in the USA each year.

Premature Birth Complications - Lack Of Arachidonic Acid?

Premature birth is quite common and there are many reasons for it such as infections, poor diet, smoking, accidents and multiple pregnancies. Babies born prematurely are put in state-of-the-art incubators and cared for scrupulously and still they don't all survive.  Even if they do their problems aren't over: they grow slowly and are much more prone to disabilities and diseases such as cerebral palsy and blindness than those born normally.  

According to The Times of India, worldwide, the preterm birth rate is estimated at 9.6% and 1 million premature babies die every year.  "In the United States alone, the annual cost of caring for preterm babies and their associated health problems tops 26 billion dollars annually," says Dr. Jennifer Howse, President of the March of Dimes Foundation.

Could one of the reasons why there are so many problems with premature babies be the lack of arachidonic acid in their feed? 

Arachidonic acid is an essential omega-6 polyunsaturated fatty acid supplied by the mother through the placenta and continued through breast milk after birth.  Premature babies are suddenly cut off from this supply and the level of the chemical in their blood falls rapidly to less than half that of a baby still in the womb (John Emsley, Molecules at an Exhibition). 

In 1992, Michael Crawford of the Institute of Brain Chemistry at Hackney Hospital, London, showed that arachidonic acid is essential for the growth and function of the blood vessels within the brain and therefore the brain itself.

It is also involved in muscle growth: arachidonic acid is abundant in skeletal muscle membrane phospolipids, and is the main building block for prostaglandins.  Recent evidence suggests that the prostaglandin isomer PGF2a has a potent ability to stimulate muscle growth. (Mike Roberts

Adults make the arachidonic acid they need from another common omega-6 fatty acid, linoleic acid, but babies can only do the same once they have developed the right enzymes.  Arachidonic acid is not yet included in the formula feed for premature babies, and this seems to explain why they are so slow to develop and often have brain and muscle defects.

By the way, it's not arachnidonic.  Nothing to do with spiders!

Friday, 14 June 2013

Regenerated Lizard Tails: New Ones Are Different!

lizard line drawing
Regeneration is central to life and every animal is capable of it at the small scale of cells and tissues.  Some animals take this much further: the hydra flatworm, for example, can remodel whole sections of itself; if you cut one in half, you end up with two. 

Caudata, the order of tailed amphibians which includes newts, is probably the most adept vertebrate group at regeneration. They can regenerate tails, limbs, internal structures, and apparently even eyes! Autotomy (self amputation), is a defensive action seen in geckos, lizards and some salamanders. It allows them to drop tails or limbs when threatened by a predator. After the tail or limb has been dropped, cells at the site are activated and the tissues regenerate. This occurs in two stages:
  1. the cells work backwards - dedifferentiate - to become stem cells again;
  2. re-differentiate and multiply.
Tail regeneration in lizards has recently been extensively studied. Contrary to previous belief, the regenerated tail of a lizard is not a perfect replica of the orignial but a copy grown simply for aesthetic reasons. 

The new tail of the green anole lizard, studied by ASU's School of Life Sciences, consists of a single long tube of cartilage, with muscles spanning its whole length instead as opposed to the shorter fibres of the original. Pores in the regenerated cartilage allow blood vessels to pass through, but not nerves, which would normally pass through the gaps between the vertebrae of the original backbone. This suggests that the nerves grow from the tail stump into the regenerated part. "These differences suggest that the regenerated tail is less flexible, as neither the cartilage tube nor the long muscle fibers would be capable of the fine movements of the original tail, with its interlocking vertebrae and short muscle fibers," said Rebecca Fisher, an associate professor in ASU's School of Life Sciences. 
Regenerated lizard tail

To regrow an exact replica of the original tail, sections of vertebrae and spinal cord would have to be regenerated - a much more complicated process which would take up a lot more of the lizard’s time and resources. The simple regrown tail gives the lizard more balance than it would have with no tail at all, but is nowhere near as well engineered. As Fisher said, "The regrown tail is not simply a copy of the original, but instead is a replacement that restores some function." (ASU News