Expert: Florence M Rollwagen - 12/29/2008

Question
QUESTION: "Factor VII is a zymogen which is converted to VIIa by thrombin" This is what the lecturer put in his notes about the extrinsic pathway, but I am doubtfull that this is correct. Other sources state that factor VII is converted to VIIa when in contact with tissue factor, and that Tissue factor and factor VIIa form a complex. The end result of this process produces thrombin which acts on fibrogen to form fibrin thats if the intrinsic pathway is ignored for learning purposes.
Please advise if my doubts were right.
Thank you

ANSWER: Hi Musa:  Thanks for your question.

As you know, the coagulation cascade is a dangerous process in which inactive enzyme precursors are activated to produce thrombin and clot the blood.

In the extrinsic pathway, Factor VII is indeed activated to VIIa by tissue factor.  Factor VIIa then goes on to activate thrombin via X to Xa conversion.

This is the way that coagulation is generally presented.  Wikipedia gives a more extensive explanation of what follows after FVII is bound by TF.  After the two factors are bound (following an injury, let's say) FVII can be activated by thrombin, FXa or by the FVII-TF complex.  (http://en.wikipedia.org/wiki/Factor_VII).  However, I was unable to find any published articles on this mechanism.

Here is more detail on FVII by emedicine:  (http://emedicine.medscape.com/article/209585-overview)

Factor VIII can be converted to VIIIa by thrombin, and I suspect that the handout from your professor may have included a typo, in which Factor VII was typed instead of Factor VIII.  You might ask your professor, and if you do, make sure to say that you researched the problem on your own (not that you asked AllExperts).  Teachers like self-motivated students.

Hope this helps.

FM Rollwagen, PhD

---------- FOLLOW-UP ----------

QUESTION:
Dear prof.
First of all, Thanks a lot for the answer and the tip about the professor, it was really helpful. I know this is unrelated to the topic, but I would like to know if you would recommend doing my medical residency in the United States. I am only a first year medical student in Ireland but it is best if I make a decision about this soon because there are some special exams and preparations needed to be made quite soon if I am to take this decision. As a professor in a medical subject yourself, I think that your opinion would be valuable. I would like to know things about the quality of teaching quality, duration of the programs, or anything else you can tell me about this topic. The reason I am so interested is because there has just been a major reform in the health system here in Ireland, and many privileges junior doctors (residence) used to enjoy are now revoked. This includes big payment cuts and more importantly increase in time of the training program, especially for non-EU nationals like myself. For instance a GP’s training period can reach up to 10 years for non-EU nationals as the training period is not fixed.
Kind regards.


Answer
Hi again, Musa:

Residency programs in the US vary by state, and can last from 3 to 10 years (for a complicated specialty like neurosurgery).  My husband was a pathology resident in New York for 4 years.  The pay will vary by state and specialty, with a range of $50,000 USD.  I should note that the median income in the US is about $40,000, so this salary is a little above average.  (Can’t say how it compares w/Ireland, for example).  For comparison, the median house cost in the US is about $170,000, and a reliable new car is about $25,000.

I should add that I’m a professor at the US military medical school, so what I know about the topic will be limited to that.  Our students are all military (army, navy, air force) and when they graduate, they get military pay plus physician’s bonus depending on their military rank.  As military medical students, all tuition, books, fees are waived and the student receives a salary of $45,000.  Of course, one needs to be a US citizen to apply.  (http://www.usuhs.mil/)


Here is some more information I found on the Internet.

http://www.internationaldoc.com/
http://en.wikipedia.org/wiki/Residency_(medicine)
http://www.studentdoc.com/

Good luck!

FM Rollwagen, PhD