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

Jean-Louis Petit

Jean Louis Petit
(1674 – 1750)

French surgeon and anatomist, Jean Louis Petit was born in Paris in on March 13, 1674.  His family rented an apartment at his house to Alexis Littre (1658 – 1726), a French anatomist. Petit became an apprentice of Littre at seven years of age, helping him in the dissections for his lectures and at an early age became the assistant in charge of the anatomic amphitheater.

Because of Petit’s dedication to anatomy and medicine, in 1690 at the age of sixteen, became a disciple of a famous Paris surgeon, Castel.

In 1692, Petit entered the French army and performed surgery in two military campaigns. By 1693 he started delivering lectures and was accepted as a great surgeon, being invited to the most difficult operations.  In 1700 he was appointed Chief Surgeon of the Military School in Paris and in the same year he received the degree of Master of Surgery from the Faculty of Paris.

In 1715 he was made a member of the Royal Academy of Sciences and an honorary member of the Royal Society of London. He was appointed by the King as the first Director General of the Royal Academy of Surgery when it was founded in 1731.

Petit’s written works are of historical importance.  “Traite des Maladies des Os” ( A Treatise on Bone Diseases);  “Traite des Maladies Chirurgicales et des Operation” (A Treatise on Surgical Diseases and their Operations” This last book was published posthumously in 1774. He also published a monograph on hemorrhage, another on lachrymal fistula, and others.

He was one of the first to perform choIecystotomy and mastoidotomy. His original tourniquet design for amputations saved many in the battlefield and the design of the same surgical instrument today has not changed much since its invention by him.

His name is remembered in the lumbar triangle, also called the "triangle of Petit", and the abdominal hernia that can ensue through that area of weakness, the lumbar hernia or "Petit's hernia".

Sources:
1. “Jean Louis Petit – A Sketch of his Life, Character, and Writings” Hayne, AP San Fran Western Lancet 1875 4: 446-454
2. “Oeuvres compl?tes de Jean-Louis Petit” 1837 Imprimerie de F. Chapoulaud
3. Extraits de l'eloge de Jean-Louis Petit Ius dans Ia seance publique de I' Academie royale de chirurgie du 26 mai 1750” Louis A. Chirurgie 2001: 126 : 475- 81

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Layers of the GI tract

Published: Wednesday, January 31, 2018 07:00 | Written by: Efrain A. Miranda, Ph.D. | Hits: 33232

Layers of the gastrointestinal tract
Layers of the GI tract

The gastrointestinal (GI) tract is formed, with a few exceptions, by four concentric layers of tissue. These are, from deep to superficial, the mucosa, submucosa, muscular (or muscularis) and the serosa layers. This is the simplified version. The fact is that there are more sublayers.

The mucosa layer is characterized by the presence of intestinal villi, which in the stomach and small intestine contribute to absorption of the digested food. The mucosa has a thin layer of connective called the "lamina propia" and external to it a thin layer of smooth muscle, the muscularis mucosae.

The submucosa layer is formed by irregular connective tissue and contains on its most external region a plexus of nerves and neurons, the "submucosal plexus of Meissner", which provides parasympathetic innervation to glands and the muscularis mucosae.

The muscular layer, also known as the "muscularis" is composed of two sublayers of smooth muscle. The deep layer contains circular fibers and is known either as the "circular muscle layer" or the "muscularis interna", the superficial layer contains longitudinal smooth muscle fibers and is known as the "longitudinal muscle layer" or the muscularis externa. Between both muscle layers lies the "myenteric plexus of Auerbach", a layer of sympathetic and parasympathetic nerves and neurons that provides nerve supply to the muscular layer. The combined action of this plexus on the muscular layer is responsible for peristalsis.

The serosa layer is the outer or external layer and is formed by a layer of peritoneum. As such, this layer can also be called "visceral peritoneum".

There are variations from GI organ to GI organ in the arrangement, content, glands, thickness of the layers, etc. The most important differences can be found in the thoracic esophagus and most of the rectum which are devoid of a serosa layer, and in the stomach, where there is a third muscular layer, deep to the circular layer, called the "oblique layer" that contributes fibers to the lower esophageal sphincter found at the esophagogastric junction.

An important point to make is the presence of two interconnected ganglionated plexuses that are represented in the GI tract by the submucosal plexus of Meissner and the myenteric plexus of Auerbach which form the GI intrinsic autonomic nervous component . These two plexuses extend from the esophagus to the rectum and allow for the GI tract to operate almost independently from the extrinsic autonomic nervous system which moderates their activity. Ganglionated plexuses are present in organs that have rhythmic activity, such as peristalsis. Ganglionated plexuses are also present in the heart.

Sources:
1. "The bowel and beyond: the enteric nervous system in neurological disorders" Rao, M & Gershon, M. Nat Rev Gastroenterol Hepatol. 2016 Sep; 13(9): 517–528. 
2. "Advances in Enteric Neurobiology: The “Brain” in the Gut in Health and Disease" Kulkami, S et al. Journal of Neuroscience 31 October 2018, 38 (44) 9346-9354
3. "The Brain-Gut Connection" John Hopklins Health
4. "Think Twice: How the Gut's "Second Brain" Influences Mood and Well-Being" Hadhazy, B. Scientific American February 2010

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