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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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Esophageal hiatus

UPDATED: The esophageal hiatus is one of the seven hiatuses found in the respiratory diaphragm allowing passage of structures between the thorax and abdomen. As it name implies, the esophageal hiatus is the passageway for the esophagus. It also allows passage of the anterior and posterior vagus nerves, (CN X).

The hiatus is bound by two muscular crura, both of which arise from the right tendinous aortic crus. Since the intraabdominal pressure is higher than the intrathoracic pressure, there is a series of structures at the phrenoesophagogastric junction to close the esophageal hiatus.

The infradiaphragmatic parietal peritoneum reflects off the diaphragm towards the stomach to form its serosa layer (visceral peritoneum). At the same time the infradiaphragmatic fascia, also known as the  endoabdominopelvic fascia, splits into two components or limbs. These are the superior and inferior phrenoesophageal ligaments or phrenoesophageal membranes. (the root [-phren-] means "diaphragm"). These phrenoesophageal ligaments create a disc-like plug between the abdomen and the thorax. This "plug" is reinforced by a circular infradiaphragmatic fat pad. The phrenoesophageal ligaments are reinforced on their thoracic aspect by the endothoracic fascia.

Esophageal hiatus

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

The lower esophagus has a dilation (evident in the image) called the "esophageal ampulla", in relation to this dilation the circular muscle layer of the esophagus slightly thickens creating the so-called "lower esophageal sphincter". This area is not a true anatomical sphincter, but rather is a functional sphincter. 

The esophagogastric mucosal junction shows a marked transition in the shape of a wavy line. This is called the Z-line or the ora serrata. Extensions of the gastric mucosa and submucosa inferior to the ora serrata create a valve-like flap called the "gastroesophageal flap valve". When viewing this mucosal flap through and endoscope, it looks corrugated and flower-like, hence it is also called the "rosette". 

The congenital or pathological dilation of the esophageal hiatus can predispose to esophageal hiatus hernia.