Download BRS Embryology 6th Edition PDF Free [Direct Link]
- Outline format highlights the most tested topics for USMLE Step 1
- More than 280 board-style questions to help test your memorization and mastery
- Online access-offers greater study flexibility
The sixth edition of BRS Embryology includes improvements based on suggestions and comments from the many medical students who have used this book in preparation for the USMLE Step 1 examination and those students who have reviewed the book. I pay close attention to these suggestions and comments in order to improve the quality of this book. The goal of BRS Embryology is to provide an accurate and quick review of important clinical aspects of embryology for the future physician. In addition, we have added color to the diagrams. In this regard, I have used the following color scheme. The ectoderm / neuroectoderm and derivatives are colored blue. The neural crest cells and derivatives are colored purple. The mesoderm and derivatives are colored red. When multiple mesodermal structures are involved (e.g., reproductive systems), I used light red and dark red. The endoderm and derivatives are colored yellow.
Many times in the history of science, certain biological concepts become entrenched and accepted as dogma even though recent evidence comes to light to challenge these concepts. One of these concepts is the process of twinning. Recent evidence calls into question the standard figures used in textbooks on how the process of twinning occurs. In particular, it is becoming increasingly difficult to ignore the fact that dizygotic twins are sometimes monochorionic. Although we by far do not know or attempt to explain exactly how twinning occurs, it seems that the interesting cell and molecular events involved in twinning occur in the first few cell divisions during first three or four days after fertilization. You are not a twin because the inner cell mass splits. The inner cell mass splits because you are a twin. This evidence warrants a new twinning figure (Figure 6.6) that does not comport with the standard figures but tries to embrace recent evidence, although many may call it controversial. Progress in our scientific understanding of twinning will never occur if our concept of the twinning process is overly simplistic and reinforced by standard figures repeated over and over in textbooks. Some published references that speak to this twinning issue include Boklage,1,2 Yoon et al.,3 Williams et al.,4 and Hoekstra et al.5
I understand that BRS Embryology is a review book designed for a USMLE Step 1 review and that you will not be faced with a question regarding this twinning concept, but I know my readers are sophisticated enough to appreciate the scientific and clinical value of being challenged to question traditional concepts as “grist for the mill” in discussions with your colleagues.
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