Recruiting Guest Bloggers For Medical Blog -Would you like to guest blog on this site

We are currently recruiting guest bloggers for this medical blog.

If you are working in a field of medicine or alternative medicine or if you are a medical student or student studying medicine or a related subject and would like to guest blog for this medical blog then please get in touch to kate@adtuk.co.uk or simply register and post in comments and we will contact you.

If you are planning to apply for medical school we would also love to hear from you as we have and many student bloggers who have gone on to study at medical school. Many of them have found that writing blogs a helpful way to increase their knowledge of areas of medicine and to share it with others. Some have written about their experiences of applying to for medicine.

 

 

Compare and contrast the role of endothelial cells and platelets in haemostasis and coagulation

Haemostasis is the process by which blood vessels with a hole in them produce a stable plug to fill in the hole and prevent haemorrhage. Coagulation is the process by which a soluble protein called fibrinogen, produced by the liver and normally present in the blood is converted into insoluble polymers of fibrin monomers. These fibrin polymers are interwoven into a plug to increase its stability. Both endothelial cells and platelets have essential roles in the processes of haemostasis and coagulation. But as we shall see the role of endothelial cells is more in signalling the need for the formation of a haemostatic plug, whilst platelets actually form the haemostatic plug.

 

The Primary Haemostatic plug

Healthy endothelial cells are incredibly important for preventing the formation of a haemostatic plug in a healthy blood vessel. But if for some reason the endothelial cells are damaged then a primary haemostatic plug forms. When endothelial cells are injured the collagen of the basement membrane of the endothelial cells and the collagen of the extra cellular matrix (depending on how severe the injury is) are exposed on the luminal surface of the blood vessel. In addition the injured endothelial cells begin to produce and secrete a protein called Von Willebrand factor onto the surface of the exposed collagen where it binds. Platelets, also called thrombocytes which are in the circulation possess a surface glycoprotein called gp1B which will bind to the Von Willebrand factor. Hence a layer of platelets will form over the exposed collagen. This is known as platelet adhesion.

 

In addition the exposed collagen will activate the platelets and cause them to secrete granules which are stored in their cytoplasm. These granules contain many substances but some particularly important ones are Thromboxane A2, Serotonin (also called 5-Hydroxytryptamine) and ADP. Both Thromboxane A2 and Serotonin are vasoactive and produce vasoconstriction of the arterioles leading to the damaged blood vessel. Hence less blood will be reaching the damaged wall and this will help to reduce blood loss due to the injury. Similarly injured endothelial cells also take action to try and reduce blood flow to the affected area, but rather than producing a vasoconstrictor, they instead stop secreting the vasodilator Prostacyclin.

 

The final of the products that platelets release is ADP. Platelets have on their surface receptors for ADP and when ADP binds to this receptor it activates the platelet. Activated platelets will then bind to other platelets; specifically they will bind to the platelets which have formed a layer over the exposed collagen, to produce a multilayered structure of platelets. This structure is known as the primary haemostatic plug. The antithrombotic drug Clopidogrel works by binding to the receptor for ADP on the surface of platelets and not stimulating it, i.e. it is an antagonist and simply prevents ADP binding and activating the receptor.

 

Overall with regards to the formation of the primary haemostatic plus we can see that platelets and endothelial cells have vastly different functions. The platelets actually form the structure which will plug the hole. Whilst endothelial cells are essential for preventing the formation of such a structure in healthy blood vessels and ensuring that it is only produced at sites of injury. So their role is more in coordinating haemostasis.

 

 

Coagulation

The purpose of the coagulation cascade is to transform the primary haemostatic plug into a secondary haemostatic plug. A primary haemostatic plug as previously described consists of a multilayered structure of platelets. Whilst a secondary haemostatic plug is a multilayered structure of platelets but with a dense meshwork of fibrin between the platelets holding them in position. The secondary haemostatic plug is far more stable than the primary haemostatic plug and prevents haemorrhage more effectively.

 

In order to produce such a dense meshwork of fibrin it is necessary to turn fibrinogen which is a soluble protein in the blood plasma into these fibrin strands. The enzyme which converts fibrinogen into fibrin monomers is called Thrombin and the inactive precursor of thrombin, called Prothrombin is constitutively present in the blood plasma. Another enzyme called Factor XIIIa then converts the fibrin monomers into Fibrin strands. Hence in order to produce the fibrin strands it is necessary for Prothrombin to be converted into thrombin and the series of reactions by which this conversion occurs is known as the coagulation cascade.

 

Similarly to in the formation of the primary haemostatic plug it is the damaged endothelial tissue which starts the coagulation cascade. Damaged endothelium does this in two ways. The first way is through the intrinsic pathway, when there is damage the protein HMW kinin, standing for heavy molecular weight kinin is produced. This converts factor XII into XIIa. The activated factor XII then in turn activates XI to XIa and XIa activates IX into IXa. Then comes the important stage which is the activation of factor X. Factor X is activated by factor IXa, but it must be in the presence of factor VIIIa, calcium and phospholipids. This is important because it is the activated platelets which release calcium ions and it is also the platelets which act as a surface of phospholipids on which this reaction can occur. Hence this stage means that the coagulation cascade can only occur on platelets surfaces, i.e. it ensures that the fibrin is going to be produced in the primary haemostatic plug.

 

Factor X has two stages of activation. The first we have just seen and the second is done by Factor Va. Once factor X is activated to factor Xa, it will catalyse the conversion of prothrombin to thrombin and hence coagulation can begin. Thrombin then further activated factor V to Va to produce a positive feedback loop.

 

The second pathway by which endothelial cells can activate the coagulation cascade is through the extrinsic pathway. In this pathway, the endothelial cells along with any damaged cells in the interstitum underneath produce a protein called tissue factor. Tissue factor converts factor VII to factor VIIa and factor VIIa can undertake the first portion of factor X activation. Again though this transformation must take place on a phospholipids surface and in the presence of calcium, which helps to ensure that fibrin deposition occurs actually within a primary haemostatic plug and not just in the free circulation.

 

Conclusion

Overall we have seen that in both the formation of the primary haemostatic plug and its conversion to a secondary haemostatic plug, via the coagulation cascade, endothelial cells have a regulatory function. Indeed they help in both cases to ensure that both processes only occur when there is damage. They do this by preventing exposure of the underlying collagen in the case of platelet adhesion and by expressing surface molecules like Antithrombin which inactivates thrombin in the case of coagulation. Platelets on the other hand play a more active role in the case of primary plug formation, since they are the structures which will actually bind together to form the plug. With regards to coagulation they are more similar to endothelial cells and play a guiding role, i.e. they ensure that fibrin deposition happens at the correct site.

A short introduction

Hello readers,

I am a new Valuemed blogger hoping to contribute to this site as ‘mLukon’.

An aspiring doctor wanting to read medicine at university, I am going to apply for medical school this October. I am currently undertaking my A-Levels at Sixth Form, all of which are thoroughly engaging.

I became interested in writing medical-related posts for ‘Valuemed’ after an intriguing summer neurosurgery placement sparked an interest in the brain and degenerative neurological disorders. Through the placement, I became familiar with research papers and so, I would now like to take to ‘Valuemed’ to write a few of my own articles which concern areas of medicine and healthcare that I am fascinated by.

I hope to write interesting and thought-provoking articles soon and would appreciate any feedback and discussion on my blogs.

The UKCAT

I sat the UKCAT last year and received a score of 680. (Average being 600). So it wasn’t a bad score but I’m now faced with sitting it again. Advice for the UKCAT:
Verbal Reasoning – Some say you should read the passage first and get an idea of it and where different parts are within the text. Others say to read the question first then skim read through the text. Personally, I read the question first because the texts sometimes are very long. I think the point of this section is to see your ability to cut out the unnecessary and get to the point.

Quantitative – Personally my worst section. Many say the actual test is easier than the practice questions. Personally, last year I found that the difficulty level was the same in the practices and the actual test. Therefore, my advice would be to make sure you can do all the practice questions and know the basics which will definitely come up. Such as % changes. And practice on your computer calculator only.

Abstract – I think the more you practice the section the easier it becomes. Many times the same patterns come up again and again. Last year I had questions which were the same as the ones in the practice book. And don’t forget the simple patterns like counting the number of sides! This actually comes up more than you think.

Decision Analysis – Personally, I think this is quite fun. One thing I’ve learnt is that every single word from the coded line will be in the answer. EVERY SINGLE WORD. They may have extra words in the answer, but the correct answer will contain all the words in the coded line. Watch out for hints like ‘personal’ meaning ‘I’ or ‘Me’ will be in the answer.

Most of all, it is true, practice makes perfect. Keep practising. You’ll find you reach a stage when you can’t practice any more. You’ve done all the questions you possibly can. That’s when you know you’re ready. And, every time you practice. Try and stick to the time limit. It’s a good idea to get used to the timing.

Wishing you all the best.

– Rabia

A male contraceptive pill?

Recently the BBC had an exciting news article that we may soon have an effective male contraceptive pill. Scientists in USA have been testing a drug ‘JQ1’ on mice. These tests have shown that whilst consuming the drug, the mice were rendered temporarily infertile, due to low sperm count and low motility levels. But of course, there are a lot of tests still to be done including on humans before you see this pill behind the Pharmacy counter.

But even before this prospective pill could be found and tested, scientists had to go deeper into the genome to find the ‘contraceptive gene.’ Known as ‘Katnal1’ this gene responsible for sperm production was found in mice. It is then this drug ‘JQ1’ which will interrupt Katnal1 to make a reversible contraceptive. This drug stops protein production meaning the male gametes do not fully form and the body disposes of them. Meaning, no fertilisation. (Or reduced chance, as one should say.)
It is reversible in the sense that it does not stop the early stages of sperm production and the organisms ability to produce them. It just stops them from fully forming in the later stages, whilst taking the drug.

But, another study has found that ultrasound to the testicles can stop sperm production. First proposed in the 1970’s it is only now being pursued. It has been found that two 15 minute doses, two days apart and through warm salt water “significantly reduced” the number of sperm. After being tested on rats, their sperm count dropped to ‘below 10 million per millilitre’.

But how good is this? Yes there will be fewer unplanned pregnancy but will this increase the rates of under-age sex? And will this lead to reduced use of the condom? Which the global world has taken years to raise awareness of. But then also, will there be any need for condoms?

– Rabia

5% Discount Coupon Code

Just a quick reminder that we have a 5% discount coupon aut5 active at www.valuemed.co.uk until the end of this month. 1st class UK Delivery at Valuemed is free when you spend over £25 until the end of this month

The 5% discount coupon code aut5 can also be used at:

our fertility website www.accessdiagnostics.co.uk

our drug testing website www.ukdrugtesting.co.uk

and our breathalyser website www.value-breathalysers.co.uk

Should you pay for a flu jab at your local pharmacy or chemist ?

For the last 2 years I have paid to have a flu jab at a local pharmacy. This is a fairly recent service that some pharmacies have been offering and I welcomed it initially, having had a particularly bad bout of flu several years ago which left me ill on the sofa for a good week and took several weeks to fully recover from.

Having worked previously in the NHS for many years I had been eligible for flu vaccination through my occupational health service or my local GP. When I changed jobs this was no longer part of the package and I went for several years with no flu vaccination. I had asked at my local GP surgery if I could pay to have a flu vaccine, but this was not a service that they were offering.

I was very excited last year when I spotted a pharmacy in a nearby town offering the service so I went along and booked an appointment to have the jab later that day. The young pharmacist was very nervous and had clearly not done many of these (I later found out I was his first paying customer ) He encountered a problem getting the air bubble out of the syringe and after trying several pre-loaded flu vaccine syringes he advised me he would be unable to do the flu vaccination, and that I would have to come back another day when they had more of the pre-loaded syringes in. I returned several weeks later  as I thought by this time he would have gained in expertise, but he was still very nervous, but did thankfully manage to successfully give me the vaccination. He later told me that I was his second successful flu vaccine paying customer as the uptake had been very poor in the area. He had been on a training course to learn injection techniques but I wonder how much practice he had had on live humans (it is very different to injecting an orange or dummy)

This year I saw another local pharmacy was offering the flu vaccination service and decided to give it another go, as last year I did not succumb to flu. I booked an appointment and yesterday I had my vaccination. It was a very different experience but unfortunately not in a good way. The pharmacist rushed the injection and in fact injected me with a fairly large amount of air which alarmed both her and me (although I did not let on to her that I knew what she had done & she worryingly did not admit it to me) She then repeatedly asked me if i was ok and if I felt faint. I felt quite anxious following the experience but thankfully it is now 24 hours later and I am fine-touch wood apart from a large bruise & egg sized swelling on my upper arm ! (not usual after a flu injection)

This experience set me to thinking & concluding the following;

  • I wish that I had not gone to the pharmacy for the injection. I do not feel the staff that I dealt with this year or last year were competent enough at performing the injections unsupervised
  • I wish that GP’s would offer this service to their patients for a fee-the nurses at the local surgery are fully trained & are great at giving injections (they get plenty of practice)
  • I have had many injections over the years and these 2 were by far the worse experiences that I have had, and have put me off going to a pharmacy again for an injection
  • What training does a pharmacist have before they are allowed to administer injections to the public ?
  • Do the pharmacists feel competenet to be doing the vaccines or is it something they are being pressured in to by the company ?

If you do decide to have a flu shot at your local pharmacy it may be worth asking the pharmacist who is going to administer the shot the following:

  • How many vaccines they have given this year ?
  • How much training did they receive on live patients ?
  • How many flu vaccines have they given this autumn 2011 ?
  • Would they have a vaccine in a pharmacy or would they rather go to a practice nurse ?

I welcome your comments

Latest development in Neuroscience

Previously I had believed that synaptic pruning within the brain was something that happened only twice in your life: during the first years of life and during puberty. And that once this had happened your brain was moulded and set for life. However resent scientific advances, reported in the new scientist (20:08:11 edition) have suggested that this is not the case and in fact your brain is still remoulding its design, through synaptic pruning late into the twenties.

Moreover my belief that synaptic pruning was occuring in the first few years of life seems to have been wrong, as the article states that: “(dendritic) spine density increased rapidly during infancy reaching a peak before the 9th birthday”. Dendritic spines are small “door knob” shaped extensions of the dendrites, which have on their ends a PSD (post synaptic density). The role of the PSDs and therefore also the denritic spines is to recieve the incoming neurotransmitters, from an axon of another neuron and then send the message the signal to the neruon cell body (the soma).

By the age of nine then our brain has far too many connections between individual neurons. Over the next 20 years of our lives our brains are pruned so that half of these neurons are disconnected. this pruning is done to the crude: “Use it or loose it” principle. Therefore the neuron connectors we dont use – we loose. This neural pruning is believed to be crucial for learning and other cognative functions.

So whats the significance of this advancement? Well the disease schizophrenia is commonly developed whilst in the twenties. So now many neurologists and psychiatrists are theorizing that it may be due to a developmental complication, rather than a degenrative component. So we may be one step closer to curing a long incurable psychiatric disorder and who knows the further implications and applications this revelation could have – this is the beautiful ambiguity and mystery of science.

Medical Student Diagnostic set back in stock

After selling out almost immediately upon release, Valuemed is pleased to again be able to offer the Medical Student Clinical Starter Kit.

Offering everything needed for medical students starting clinical attachments the diagnostic sets include a quality stethoscope, aneroid sphygmomanometer with standard adult cuff, otoscope and opthalmoscope for ear and eye examination, A complete set of reflex hammers, 125,256 & 512Hz tuning forks, a pen torch and a tornique

Version 2 of the pack offers the following upgrades. Palm aneroid sphygmomanometer. Tenso medical Otoscope and Opthalmoscope units and additional name tags to allow labelling of the kit.

Purchased individually the original diagnotic equipment set would exceed £225.00 net of UK VAT, the pack is offered with a saving of over £50.00 at £175.00 plus VAT  and delivers free in the UK when purchased online

Thanks to a medical school in the north east, the original stock allocation sold out almost immediately, so demand is expected to be high.