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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

Johann Gottfried Zinn

Johann Gottfried Zinn
(1727–1759)

Anatomist and botanist, Johann Gottfried Zinn was born on December 6, 1727 in the city of Ansbach, Germany. He started his medical studies in his native city, becoming later a student of Dr.  Albrecht von Hallers at the University of Göttingen, and received his MD in 1749.

He left for Berlin to continue his studies but came back shortly thereafter. He became a professor of anatomy at the University of Göttingen and in 1753 he also became the director of the botanical garden in the same city.

He is known for his anatomical treatise on the anatomy of the human eye: “Descriptio anatomica oculi humani iconibus illustrata”. Because of this, his name has become an eponym in the “Zonule of Zinn”, a ring of strands that forms a fibrous band connecting the ciliary body with the capsule of the lens of the eye. Zonule of Zinn is sometimes referred to as the suspensory ligaments of the lens, or the “ligament of Zinn”. His name is also attached to the anular ring tendon found in the posterior aspect of the eye, the "anular tendon of Zinn". This ring serves as attachment for all the extraocular muscles of the eye and the optic nerve passes through the center of the ring.

Carol Linné (Carolus Linneaus) named a genus of flowers in the family Asteraceae known vernacularly today as “Zinnia” in his honor. Hover your cursor over his portrait to see the flower.

The chapter on orbital anatomy of his anatomy book, taken from the second edition in 1780, has been translated and the first of three parts is published in an issue of “Strabismus”

His book "Catalogus Plantarum Horti Academici Et Agri" can be seen online here.

His life was short, dying at the early age of 32, but his name lives on in the name of a beautiful flower.

Sources:
1. “Johann Gottfried Zinn" Simonz, HJ Strabismus – 2004, Vol. 12, No. 2, p. 125 
2. "Anatomical Description of the Human Eye" Zinn, JG Strabismus, 13:45–52, 2005 
Images: Public Domain by Wikipedia Commons. 1. Own work I_am Jin, and H. Wilhem Dietz


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Respiratory Diaphragm

The respiratory diaphragm is a musculotendinous dome-shaped shelf that divides the thoracic cavity from the abdominal cavity. It is one of the four named diaphragms in human anatomy. This is why it is proper to call it the "respiratory diaphragm" instead of just "diaphragm".

The name comes from the Greek, where the prefix [dia-] means "complete" or "through" and [phragm] means "a partition". In Latin, Celsus called it the "septum transversum", meaning "the transverse partition". The root term for [diaphragm] is [-phren-], as in phrenic nerves and cardiacophrenic vessels.

The respiratory diaphragm has a club-shaped central tendon (as in a card suit) which has a large hiatus for the inferior vena cava. The muscular portion is formed by skeletal (voluntary) muscle and descends skirt-like to attach to the internal aspect of the sternum and ribs anterolaterally, and a complex system of lumbocostal tendinous arches posteriorly.

Respiratory diaphragm (www.bartleby.com)
Images and links courtesy of Bartleby.com
It receives its blood supply through branches of the intercostal arteries, the musculophrenic artery, and the pericardiacophrenic arteries. It is innervated by the phrenic nerves, which descend through the mediastinum in relation to the pericardium.

The respiratory diaphragm has not one, but seven openings (hiatuses) to allow for passageway of many structures:

• Esphageal hiatus
• Aortic hiatus
• Inferior vena cava hiatus
• Hiatuses (2) for the superior epigastric vessels, which are the inferior continuation of the internal thoracic (mammary) vessels. Also known as the hiatuses of Morgagni.
• Hiatuses (2) for the splanchnic nerves

The most common site for an internal abdominothoracic herniation is the esophageal hiatus, but there are other respiratory diaphragm hernias, including the retrosternal hernia of Morgagni (through the superior epigastric hiatus), and the hernia of Bochdalek (a congenital hernia through an incomplete central tendon of the respiratory diaphragm).