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Medical Terminology Daily (MTD) is a blog sponsored by Clinical Anatomy Associates, Inc. as a service to the medical community, medical students, and the medical industry. We will post a workweek daily medical or surgical term, its 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

Thomas Willis, MD
Thomas Willis
(1621-1675)

An English physician and anatomist, Willis was born on his parents' farm in Great Bedwyn, Wiltshire, where his father held the stewardship of the Manor. He was a kinsman of the Willys baronets of Fen Ditton, Cambridgeshire. He graduated M.A. from Christ Church, Oxford in 1642. In the Civil War years he was a royalist, and was dispossessed of the family farm at North Hinksey by Parliamentary forces. In the 1640's Willis was one of the royal physicians to Charles I of England. He obtained his medical degree in 1646.

Thomas Willis might well be one of the greatest physicians of the 17th century.He is one of the founders of the Royal Society of London. He is remembered by his many publications, especially "Cerebri Anatome: Cui accessit Nervorum Descriptio et Usu", where he describes the arterial anastomoses at the base of the brain. This work is also the first detailed description of the vasculature of the brain. Willis described nine cranial nerves.

He is considered as the father of Neurology as a discipline. He used the term "neurology" for the first time in 1664. He described several neurological conditions

The Arterial Circle of Willis is a famous eponymous structure found at the base of the brain. It represents an anastomotic roundabout that connects the right and left sides as well as the carotid and vertebral arterial territories that supply the brain. Named after Thomas Willis, this structure was known well before him, but it was Willis who described its function.  If you click on the image or here, you will be redirected to a detailed description of this structure.

Sources:

1. "The legendary contributions of Thomas Willis (1621-1675): the arterial circle and beyond" Rengachary SS et al J Neurosurg. 2008 Oct;109(4):765-75
2. "Thomas Willis, a pioneer in translational research in anatomy (on the 350th anniversary of Cerebri anatome)" Arraez-AybarJournal of Anatomy, 03/2015, Volume 226, Issue 3
3. " The naming of the cranial nerves: A historical review" Davis, M Clinical Anatomy, 01/2014, Volume 27, Issue 1
4. "Observations on the history of the circle of Willis". Meyer A, Hieros, R.Med Hist 6:119–130, 1962


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Ascending aorta

UPDATED: The ascending aorta is the first and most proximal portion of the aorta. About 5 cm. in length and 3 cm. in diameter at its origin, its proximal end begins at the superior aspect of the outflow tract of of the left ventricle, at the ventriculoaortic junction. 

The ascending aorta ends superiorly at an imaginary horizontal plane (blue dotted line) that passes through the sternal angle (of Louis), continuing distally with the aortic arch. This is an important anatomical landmark, as many surgeons use as the superior border of the ascending aorta an oblique plane that passes proximal to the brachiocephalic trunk (yellow dotted line). Although this landmark could be useful in surgery, it is not anatomically correct.

Since the sternal angle (of Louis) also indicates the superior border of the pericardial sac, it can be said that the ascending aorta is completely intrapericardial, and in surgery the pericardial sac should be the anatomical landmark used to separate the ascending aorta from the aortic arch.

From its point of origin at the ventriculoaortic junction, the aorta presents with a dilated region where the aortic valve is located. The aortic valve is one of the two  semilunar valves of the heart, and the dilation of this region is caused by the presence of the sinuses of Valsalva. This dilated bulbous segment is known as the aortic root.

Ascending aorta, anterior view
Ascending aorta. Click on the image for a larger version.
The dilated, sinus portion, or aortic root segment of the ascending aorta continues superiorly with the tubular portion of the ascending aorta. The area of transition between these two components is marked by a sharp crease known as the sinotubular junction (STJ). The dilation of the aortic root is caused by the presence of the sinuses of Valsalva, named after Antonio Maria Valsalva (1666 - 1723).

The tubular portion of the ascending aorta ascends with an inclination anteriorly and to the right. The ascending aorta presents with a slight anterior bulge causing the transverse section of this aortic segment to be slightly oval.

Only two arteries arise from the ascending aorta, both usually at the aortic root segment, just inferior to the STJ. These are the right coronary artery and the left coronary artery. There are anatomical variations where only one, or up to five different coronary arteries have been described.

Image property of:CAA.Inc.Artist:Dr. E. Miranda