Kingsnorth Vets – 11th February 2015: Pericardial Effusion

Although this evening was quite quiet at Kingsnorth Vets, I one particularly interesting case.

In the kennels, preparing to go home was a black Labrador. The previous week she had been spayed but been brought back in after she had suddenly become lethargic and was struggling to breath. The vets found that she had a muffled heartbeat so performed an echocardiogram. Using this, they diagnosed her with pericardial effusion.

Pericardial effusion is a condition where excess fluid builds up in the pericardium. The vet explained to me that the pericardium is a smooth membrane which surrounds the heart. Although its function is not known for certain, it is generally acknowledged that it has a lubricating purpose, ensuring that the contractions of the heart are not hindered by the lungs. However, if fluid (either blood or lymph) leaks into the pericardium, it can compress the heart making contractions difficult. In dogs, the right atrium is the first to be affected so appears squashed on the echo. The fluid often comes from a bleeding tumour on the heart so the prognosis for this poor dog wasn’t great.

Luckily there were no signs of a tumour on the echo, but nevertheless, they immediately withdrew as much of the fluid as possible to alleviate the pressure on the heart. Very often this will solve the problem, at least in the short term. However, now she had developed arrhythmia – her heart was beating irregularly. The vet had never come across this as a result of pericardial effusion but was more concerned that it had caused tachycardia – her heart rate had accelerated rapidly. She had been placed on two intravenous drips, both giving her doses of medication to reduce her heart rate. The nurse showed me that one of catheters had been placed in the left celaphic vein – the front leg normally used for IV, whilst the other had been placed in left saphenous vein – the back leg. This was because the original drip had been unsuccessfully placed in the right celaphic vein, bruising it.

The saphenous vein is not normally used for intravenous injections because it’s quite wobbly. So although it is easy to find and raise, it can be hard to steadily put a needle in. However, on some occasions it might it be the best option. If a dog is agitated or aggressive, the saphenous vein is useful as it is further away from the dog’s teeth. It can also be useful because there is more to hold onto, so the leg can be held steady for quick needle insertion in a restless animal. One of the vets mentioned that he found it easier to take blood from this vein on puppies whose celaphic veins were just too small, whilst someone else said that they had previously used it for euthanasia, giving the dog more space around it head so it remained calm, or so that its owners could be nearer. Another consideration is that bandaging is harder around the hock than the around the wrist, but a bandage is more likely to stay in place.

The Labrador was going to go home for the evening, with the decision made that she was in a stable condition and would be more comfortable at home. The nurse removed the drips, but left the catheters in place under bandages in case the dog was rushed in that night. The owners were sent home with medication to reduce the heart rate, and an appointment was made for tomorrow. If all was well the catheters would be removed and a course of action would be decided.

The final question left hanging, was whether this pericardial effusion could have anything to do with anaesthetic the dog had been under last week for her spay. This made me recognise how everything interlinks and no piece of information can be discarded when evaluating a case. This is just one of the things which makes veterinary medicine such a challenging career. It’s a good thing that I like challenges!

Sharks Asexually Reproducing

Last year, I visited the London Aquarium. I really enjoyed seeing all the sealife and was impressed at the emphasis they had put on conservation. All around the walls were ‘fun facts’ and one of these caught my attention. It said that sharks can asexually reproduce and immediately I wondered how this was possible.

Female sharks are able to reproduce without the need for a male shark through the process of parthenogenesis. Parthenogenesis is the process of a female gamete becoming an individual without fertilisation taking place. It is known to happen in wasps, bees and ants who do not have sex chromosomes as well as some species of reptile, fish and very rarely, birds.

Normal gametes are produced by meiosis and have half the number of chromosomes than their parent cell. This means that they are haploid. However, some offspring of parthenogenesis can be diploid. These are called full clones, whilst those which only have half the mother’s alleles are called half clones.
Full clones can only normally be formed without meiosis taking place and instead, the embryo is produced by apomictic parthenogenesis in which mature egg cells are formed by mitosis and then develop into embryos.
Half clones are formed by meiosis and therefore can be haploid. However, as haploid individuals are generally not viable, there are various mechanisms through which diploidy can be restored. These are called automictic parthenogenesis. Methods of automictic parthenogenesis include the duplication of DNA without cell division, before or after meiosis, as well as the fusion of two blastomeres.

This process of parthenogenesis is amazing and I find it incredible the number of species which can do it. Sharks were first found to asexually reproduce in 2001 with a bonnethead shark. After research, it was shown that this offspring contained only half of her mother’s DNA and therefore, automictic parthenogenesis must have taken place. Since then, several other recordings have been made in aquariums and zoos of parthenogenesis happening. Although this process of nature is a fantastic invention for overcoming the problem of females finding males, it prevents the formation of genetic diversity which is essential for species to stay alive and evolve in the changing world. All shark half clones produced are females so if parthenogenesis continues to happen, the male shark population will become depleted and asexual reproduction will happen even more, leading the shark population into a vicious cycle.
However, at present this has not been recorded as a problem so let us hope that nature’s phenomenon can remain just that for centuries to come.

Chromosomal Genetic Diseases

In biology, we are currently studying genetics, and I had the opportunity to some independent research into genetic diseases and in particular what causes a few of the many hundreds which exist.

The chromosomes in the genetic make up of an organism can be altered in a number of ways causing problems to occur within the growth, development and abilities of the organism.

  • Deletions are when a portion of the chromosome is missing or deleted.
  • Duplications happen when a portion of the chromosome is duplicated, resulting in extra genetic material.
  • Inversions are when a portion of the chromosome has broken off, turned upside down and reattached, therefore the genetic material is inverted.
  • Rings formed when a portion of a chromosome has broken off and formed a circle or ring. This can happen with or without loss of genetic material.
  • Translocations are when a portion of one chromosome is transferred to another chromosome. There are two main types of translocations. In a reciprocal translocation, segments from two different chromosomes have been exchanged. In a Robertsonian translocation, an entire chromosome has attached to another at the centromere. Only chromosomes 13, 14, 15, 21 and 22 in humans are acrocentric and therefore, only they can take part in Robertsonian translocation.

When considering this, it is needed to be known that all chromosomes are metacentric, submetacentric or acrocentric, depending upon where the pair of chromosomes are joined.

Only five chromosomes in humans are acrocentric as well as chromosome Y.

However, in dogs all but the sex chromosomes are acrocentric.

In cats none of the genes are acrocentric but are all metacentric.

A horse has 18 pairs of acrocentric chromosomes and 13 which are metacentric.

 

In humans, the five acrocentric chromosomes sometimes take part in Robertsonian translocation. When this happens, as shown in the picture, most people will be left with only 45 chromosomes. It often does not have any consequences, however, if an extra chromosome 13 is left this causes trisomy 13, Padua’s Syndrome. This is the same in chromosome 21 which results in Down Syndrome.

Robertsonian translocation allows mitosis to take place normally, however, it can affect meiosis, meaning that the offspring can have impairments.

 

These acrocentric chromosomes can also result in other genetic diseases:

Chromosome 13 – there are 13 diseases which are known to result from chromosome 13, including retinoblastoma which is a cancer in the cells on the retina.

Chromosome 14 – this can be linked to about 14 diseases including Alzheimer’s.

Chromosome 15  – this can account for about 11 diseases including Breast Cancer.

Chromosome 21 – about 12 diseases result from this, many which are cancers as a result of translocations of this chromosome.

Chromosome 22 – about 13 diseases can be associated with this chromosome, including schizophrenia. Many of these diseases result from deletions.

This is just a short summary of chromosomal diseases which can occur in humans, however, every chromosome in every organism can undertake a chromosomal change which can cause a very large number of diseases. But a lot is unknown and there is always more to discover about genetics and the diseases associated with them. I would like to be able to do more research into this, especially the affects upon different species, and have been enlightened by the opportunities I gained through school.

Otters’ Gestation Period – Delayed Implantation

The book The River People by Philip Wayre is about his lifelong involvement with otters. From Norfolk to Malaysia, he outlines the life of an otter. From recently reading this book, I picked up on the intriguing gestation period of a female North American otter.

The gestation period of the North American otter can vary from nine to twelve months. This astonishing variety is caused by delayed implantation of the foetus. After mating, the fertilised egg remains in the uterus in the form of a blastocyst. A blastocyst is a structure containing a mass of stem cells and surrounded by an outer layer of cells which will later form the placenta. Blastocysts are used in the process of IVF in humans to determine a more successful embryo.

However, when a blastocyst is formed in this species of otter, it does not anchor itself into the wall of the womb for some time causing its development to be halted. It could be several months before finally implanted, triggered by the production of certain hormones. The trigger of this is the amount of daylight, suggesting the advantageous gains of going through this process because of the benefits of raising young in a season rich in food and ideal conditions.

On further research, I found that about 100 mammals go through delayed implantation, or embryonic diapause, including rodents, bears, marsupials and mustelids, such as the otter. There are actually two types of delayed implantation. The one I described as occuring in North American otters is called Obligate Diapause and is controlled by seasonal changes.
In contrast to this, Facultative Diapause is controlled by the period of a mother’s lactation. This is a brilliant strategy in order to prevent two litters needing milk at once.

I think that this is an amazing evolutionary step towards preserving one’s young.

References

http://en.wikipedia.org/wiki/Embryonic_diapause

Wild Mammals of North America: Biology, Management, and Conservation by George A. Feldhamer, Bruce C. Thompson, Joseph A. Chapman

The River People by Philip Wayre

The Functions of the Tongue

After researching about the muscles in the tongue and the amazing ways in which they work together to move, I wanted to find out more about the functions of the tongue. I believe that this is especially evident in dogs because of the prominent and significant role of the tongue lolling out of a dog’s mouth in a cheerful ‘grin’.

Blood Vessels

Dog’s pant when they are hot because they cannot sweat like humans because of their fur. Therefore the tongue is vital in keeping them cool and ensuring that they cannot overheat. To act this important role, the tongue has a rich supply of blood vessels, and when too hot, these dilate and the tongue swells and expands because of this. This causes the blood vessels to be nearer the surface of the tongue where the heat can be conducted into the colder air around the dog. However, this also means that if punctured when in this state, the tongue will bleed profusely. In order to stop this bleeding,  the dog needs to cool down so that the blood vessels constrict and a blood clot can quickly form due to the many platelets in the many blood vessels.

Taste Buds

The tongue is also vital for tasting. This is because of the taste bud receptors found in small bumps across the tongue, called papillae. Dogs have different areas of the tongue which detect different chemicals with particular sensitivity, which are then interpreted by the brain as different flavours. These are as follows:

Sour – across the top of the tongue

Salt – along the lateral edges and rear of the tongue

Sugar – along the edges and front of the tongue. These respond to a chemical called furaneol which is found in many fruits. Cats do not taste this.

Bitter – the rear of the tongue

Meat – dog’s have a particular sensitivity for chemicals associated with meats and fats. This is found across the top of the tongue.

Water – the tip of the tongue is used to taste water… Why? Dog’s and other carnivores have an ability to taste the chemicals and impurities in water whilst humans cannot. This could be as a result of the salty meats which they are accustomed to eating and therefore the higher levels of water they need to drink.

Although humans have about 9000 taste buds, compared to 1700 in dogs, cats only have about 470.

Salivary Glands

The four major dog salivary glands can be seen on this diagram, these are responsible for making the dog’s mouth wet. They secrete two different types of saliva, mucoid and serous. Their functions are as follows:

Parotid – produce serous saliva which is thin, watery and amylase-rich. This is the only gland which can be examined from the outside of a dog’s mouth.

Mandibular – the acinar cells here are both serous and mucous, therefore this saliva is more viscous and mucous. If these glands are lacerated, they can leak saliva into the surrounding tissue, forming a cyst called a mucocele. This has to be drained.

Sublingual – produce mucous saliva which is very thick and viscous.

Zygomatic – acinar cells consist mainly of mucous secreting cells and only a few serous. They are foun only in carnivores. This is where salivary gland infection can occur and can only treated by removing the gland.

The surface of a dog’s tongue is also covered in tiny salivary glands which contribute to a wet mouth resulting in cooling by evaporation and helping to overcome the problem of sweating.

 

All tongues are amazing pieces of anatomy which have the purpose of carrying out many tasks, vital for function in the body of humans and dogs alike.

 

References:

http://www.petmd.com/dog/general-health/evr_dg_anatomy_of_a_dogs_tongue

http://www.psychologytoday.com/blog/canine-corner/201104/how-good-is-your-dogs-sense-taste

http://flipper.diff.org/app/items/info/367

http://pets.webmd.com/dogs/dog-drooling-salivary-gland-problems

http://en.wikivet.net/Zygomatic_Gland_-_Anatomy_%26_Physiology

Animal Chromosomes – Numbers and Reproducing

Since I began to learn about genetics in biology last year, I have become very interested in how they work and the science behind them. Furthermore, this was encouraged by one of my first posts on owl classification when I talked about the differences in tytonidae and strigidae owl families. During the time when I researched that, I began to look into the genetic differences, and although finding none in these two species, I was eager to learn more. In terms of chromosomes, all I know is that humans have 23 pairs in every cell of their body except the gametes (sex cells) which only have one set of 23 meaning that when the sperm and egg fuse a complete set of 46 will be made. I also know that different animals have different numbers of chromosomes, which determines if they can reproduce with one another or not. However, I am interested to know how many chromosome pairs different animals have and the limitations between breeding because of this.

http://en.wikipedia.org/wiki/List_of_organisms_by_chromosome_count

This wikipedia link lists a cross-section of different animal, plant and protist (eukaryotic (organism whose cells contain complex structures within a membrane) microorganisms) groups. The highest count of diploid ( 2 complete sets of haploid (number of complete chromosomes in a gamete)) is 1440, found in a fern called Adders-tongue.

Whilst the organism with least diploid chromosomes is the Jack Jumper Ant in which the female has 2 and the male is haploid so only has 1!

From the sites I am researching, I feel out of my depth because of the vocabulary being used and need to clear up the different types of ‘ploidy’. Ploidy is the number of sets of chromosomes in an individual cell. The haploid number is referred to as and this is the number of chromosome sets in a gamete. But monoploid is the number of unique chromosomes within a single complete set. A pair of chromosomes is called a homologous pair. As the sets of chromosomes increase so does the name given to them, triploid (three sets), tetraploidy (four sets – common in plants), hexaploid (six sets) etc. Species, such as the Jack Jumper Ant, where one sex is haploid whilst the other is diploid are called haplodiploid. (http://en.wikipedia.org/wiki/Ploidy#Homoploid)

Although I am now overwhelmed with new vocabulary, I am beginning to understand the differences between different species and the number of chromosomes, as well as the number of sets of chromosomes, they have. But what determines these numbers?

But as no one really knows, this is a hard question to ask. However, related species generally have similar chromosome numbers. So how similar do they have to be to able to reproduce?

I decided to look at the example of the mule. In the list of animal chromosome numbers, horses have 64 and donkeys have 62, so a mule has 63. Therefore, the numbers of chromosomes have to be similar, although this does not mean that a dolphin could reproduce with a badger because they both have 44 chromosomes. The other thing that makes a difference is the similarities between the strands of DNA themselves. The genes have to be similar in lengths. A horse and donkey genes are similar enough to fuse, however they are not similar enough for mules to go through meiosis in order to make gametes. In this process, chromosomes have to match up and with different genes this cannot happen so mules cannot reproduce. Read more about mules: http://genetics.thetech.org/ask/ask225

In conclusion, the number of chromosomes, which range from 1 – 1,400, the number of sets and the length of the chromosomes determine the relationships animals can have with one another. However, when genetic mistakes occur, problems can arise. For example Down’s Syndrome is caused in humans by the presence of an extra chromosome number 21.

The Muscular Tongue

The other day, when casually watching my dog lick my hand, I noticed what an amazing piece of anatomy the tongue really is. Having never considered it much before I know little, however, I am already aware that it is a muscle, the only one in the body only attached at one end. Although tongues are quite special, they are limited in flexibility, mainly used for shaping words to enable talking, not to mention tasting. But what I really want to know is how a dogs tongue can be so flexible, able to wrap around almost any object whilst taking its shape. I find this especially puzzling when comparing it to other muscles which move in one direction only and require an antagonistic pair.

In the tongue there are also muscle pairs. These are called extrinsic, on the outside of the tongue attached to other structures, and intrinsic, entirely within the tongue. There are four pairs of each.

 

Extrinsic Muscle names and function:

Genioglossus muscle – protudes the tongue as well as depressing its centre

Hyoglossus muscle – depresses the tongue

Styloglossus muscle – elevates and retracts the tongue

Palatoglossus muscle – depresses the soft palate and elevate the back of the tongue

 

This diagram shows the extrinsic muscles outlined in blue and labelled. It can be seen where they attach to other structures in comparison to the tongue. There are a couple of other muscles labelled as well. These are the stylohyoid and geniohyoid muscles, which although they contribute to the movement of the tongue, they are no attached to it so do not count as tongue muscles. The Mandible and Hyiod bone are structures within the throat whilst the Frenulum attaches the tongue to the base of the mouth. Tongue and tooth are self-explanatory!

 

Intrinsic Muscle names and function:

Superior longitudinal muscle – elevates, retracts or deviates the tip of the tongue.

Inferior longitudinal muscle

Verticalis muscle

Tranversus muscle

These intrinsic muscles are mainly responsible for maintaining the shape of the tongue rather than assisting movement.

 

This diagram is my interpretation of the intrinsic tongue muscles, extremely  simplified. It is based on the information that the superior longitudinal runs along under the surface, the inferior longituninal lines the sides, the verticalis joins the inferior and superior longitudinal muscles in the middle and the traversus divides the tongue at the middle, attached to the sides.

 

After doing this research into the human tongue, I can conclude that a dog, or any vertebrate, would have a very similar tongue. However, my prior assumptions have been proved wrong for many reasons. Firstly, a dog’s tongue only appears so much more flexible than ours because of the long length and thin depth. Also, I previously thought that the tongue was one muscle, therefore I was confused at how it could move as it does, especially as there is no apparent antagonistic pair. But now I know the complexity of the eight muscles, both inside and out, working together to fulfill the movements we need for talking, eating and many other activities our mouths would not be complete without.

From starting this research I began to look specifically into dogs. Although the muscular knowledge was sparse because of the similarity to humans, I found that there was a lot more to find out about a dog’s tongue. This has made me interested so I will expand my research into another post more on The Tongue.

 

References:

http://en.wikipedia.org/wiki/Tongue

http://en.wikipedia.org/wiki/Muscles_of_tongue

http://www.rci.rutgers.edu/~uzwiak/AnatPhys/APFallLect14.html

AIDS Illumination and Glowing Animals

After reading the February 2012 issue of National Geographic, an interesting picture of this cat caught my eye. I read how FIV causes AIDS in cats, just as HIV does in humans. A rhesus macaque gene, which produces an antiviral protein therefore preventing the FIV decimating infection-fighting cells, was inserted into unfertilized feline egg. To be able to monitor this gene within the kittens as they grew, they added a luminescent protein from a jellyfish causing the scientists to be able to observe the individual genes under microscopes and certain lights. This meant that the next generation of cats produce the antiviral and luminescent protein themselves, glowing in the dark and perhaps being immune to FIV!

I found this genetic modification, used in an effort to help both cats and humans alike, fascinating; so I did some more research to decipher the details of how it was done and how it may help us in aspects of veterinary and human medicine.

To put the macaque gene (TRIMCyp) and the jellyfish gene (GFP) into the egg cells (oocytes), a virus was used which doesn’t cause disease, otherwise known as the process of gamete-targeted lentivirus transgenesis. As they wereput into the same little bit of DNA, one would only occur if the other did as well. Therefore all cells containing the antiviral protein (and hopefully causing resistance to FIV) would also glow under ultra-violet light. This means that a kitten born with its whole body glowing has undergone the genetic modification successfully.

The macaque gene works by attacking the outer shell of the virus, beginning before the immune system has time to sense presence of an infection. This has worked in Petri dish so scientists hope that it will also work in the cats. Eventually, if the results are positive, the TRIMCyp gene (or one similar) may also be able to be inserted into humans to help fight HIV/AIDS. However, AIDS poses a parallel pandemic in cats to the one faced by humans. Millions of cats die of it everyday, especially feral cats as the virus is transmitted through bites. This could be a revolutionary process to transform the prevention of AIDS for those human and feline.

Green Flourescent Protein has also been used for other purposes in veterinary medicine. In fish it can be used to track the invasion path of the pathogen Edwardsiella tarda. But even better than this, it can be used to follow individual neurons in the brain.

Cerebral Cortex

This is called Brainbow and results in a beautiful multicoloured brain caused by random mixes of different colour proteins. This could help in research into neurodegenerative diseases like Altzheimers’ and Parkinson’s disease.

However, the access to GDF can result in experiments which have no need and are done ‘for fun’ at the animals’ expense. Like Ruppy the glowing beagle puppy:

Examples can be gained by just typing ‘glowing animals’ in Google Images and finding the horrors of genetically modified animals made to glow for no reason but to ‘look pretty’.

So although GDF can be used scientifically to uncover radical changes in medicine for both animals and humans, it has to be used carefully with the consideration of the animals being used…

…however, if this was done to hedgehogs could it reduce the chance of them being run over?!