Medical Terminology Daily (MTD) is a blog sponsored by Clinical Anatomy Associates, Inc. as a service to the medical community. We post anatomical, medical or surgical terms, their meaning and usage, as well as biographical notes on anatomists, surgeons, and researchers through the ages. Be warned that some of the images used depict human anatomical specimens.

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A Moment in History

Andreas Vesalius Bruxellensis (1514- 1564)

A Flemish anatomist and surgeon, Andreas Vesalius was born on December 31, 1514 in Brussels, Belgium. He is considered to be the father of the science of Anatomy. Up until his studies and publications human anatomy studies consisted only on the confirmation of the old doctrines of Galen of Pergamon (129AD - 200AD). Anatomy professors would read to the students from Galen's work and a demonstrator would point in a body to the area being described, if a body was used at all. The reasoning was that there was no need to dissect since all that was needed to know was already written in Galen's books. Vesalius, Fallopius, and others started the change by describing what they actually saw in a dissection as opposed to what was supposed to be there. 

Vesalius had a notorious career, both as an anatomist and as a surgeon. His revolutionary book "De Humani Corporis Fabrica: Libri Septem" was published in May 26, 1543. One of the most famous anatomical images is his plate 22 of the book, called sometimes "The Hamlet". You can see this image if you hover over Vesalius' only known portrait which accompanies this article. Sir William Osler said of this book "... it is the greatest book ever printed, from which modern medicine dates" 

After the original 1543 printing, the Fabrica was reprinted in 1555. It was re-reprinted and translated in many languages, although many of these printings were low-quality copies with no respect for copyright or authorship.

The story of the wood blocks with the carved images used for the original printing extends into the 20th century. In 1934 these original wood blocks were used to print 617 copies of the book "Iconaes Anatomica". This book is rare and no more can be printed because, sadly, during a 1943 WWII bombing raid over Munich all the wood blocks were burnt.

One interesting aspect of the book was the landscape panorama in some of his most famous woodcuts which was only "discovered" until 1903.

Vesalius was controversial in life and he still is in death. We know that he died on his way back from a pilgrimage to Jerusalem, but how he died, and exactly where he died is lost in controversy. We do know he was alive when he set foot on the port of Zakynthos in the island of the same name in Greece. He is said to have suddenly collapsed and die at the gates of the city, presumably as a consequence of scurvy. Records show that he was interred in the cemetery of the Church of Santa Maria delle Grazie, but the city and the church were destroyed by an earthquake and Vesalius' grave lost to history. Modern researchers are looking into finding the lost grave and have identified the location of the cemetery. This story has not ended yet.

For a detailed biography of Andreas Vesalius CLICK HERE.

Personal note: To commemorate Andrea Vesalius' 500th birthday in 2014, there were many scientific meetings throughout the world, one of them was the "Vesalius Continuum" anatomical meeting on the island of Zakynthos, Greece on September 4-8, 2014. This is the island where Vesalius died in 1564. I had the opportunity to attend and there are several articles in this website on the presence of Andreas Vesalius on Zakynthos island. During 2015 I also attended a symposium on "Vesalius and the Invention of the Modern Body" at the St. Louis University. At this symposium I had the honor of meeting of Drs. Garrison and Hast, authors of the "New Fabrica". Dr. Miranda


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Conduction system of the heart

Cardiomyocyte-based conduction system of the heart
Conduction system of the heart

[UPDATED] The conduction system of the heart a binary system that includes a cardiomyocyte-based component which acts as an automatic base, and an autonomic nervous system component which acts as a modulator.

The classic description of the conduction system of the heart emphasizes only the cardiomyocyte-based component and refers to a group of specialized cardiac muscle structures that serve as pacemakers and distributors of the electrical stimuli that make the heart beat coordinatedly. It is important to stress the fact that this primary "conduction system of the heart" is not formed by nerves but rather by specialized cardiac muscle cells.

Components of the cardiomyocyte-based conduction system of the heart:

• SA node: The sinoatrial (SA) node is a small nodule of cardiac muscle tissue, somewhat horseshoe-shaped that is found at the junction of the superior vena cava and the right atrium. It receives blood supply from the SA node artery, a branch of the right coronary artery. Later research indicates that the pacemaker function of the SA node includes areas of the lateral wall of the right atrium which are involved in different heart rate speeds.

• AV node: The atrioventricular (AV) node is found at the junction of atria and ventricles in an area known as the "Triangle of Koch". Its function is to delay the electrical impulse passing from the atria to the ventricles by 1/10th of a second, enabling the sequential pumping action of the heart. The eponymic name for the AV node is "node of Aschoff-Tawara", and it receives its blood supply by way of the AV node artery, a branch that usually arises from the right coronary artery

• AV bundle: Also known as the "Bundle of His", this thick bundle of specialized myocardial cells is found in the interventricular septum. It divides into the right and left bundle branches

• Bundle branches: Sometimes known as the "crura" of the bundle of His, these two divisions of the AV bundle help distribute the electrical stimuli to the ventricular walls. The right bundle branch has an extension that crosses the lumen of the right ventricle, from the base of the anterior papillary muscle to the interventricular septum, forming a cord of tissue known as the "moderator band" or "septomarginal trabecula"

• Purkinje Fibers: These thin fibers are the terminal end of the conduction system of the heart and finish the distribution of the electrical stimuli to all parts of the ventricular walls

Although the structural components of the conduction system of the heart were known, it was Dr. Sunao Tawara (1873-1952) who discovered the AV node and described the connections between the components of what he called the "Reitzleitungssytem" (conduction system) of the heart.

A separate article on the secondary conduction system of the heart will be published shortly

Click on the image for a larger version. Image modified from the original: "3D Human Anatomy: Regional Edition DVD-ROM." Courtesy of Primal Pictures.