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.

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:

• Esophageal 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).

Sources:
1 "Tratado de Anatomia Humana" Testut et Latarjet 8 Ed. 1931 Salvat Editores, Spain
2. "Anatomy of the Human Body" Henry Gray 1918. Philadelphia: Lea & Febiger Image modified by CAA, Inc. Original image by Henry Vandyke Carter, MD., courtesy of bartleby.com

Jejunoileal vascular supply

The jejunum is an intraperitoneal organ, it is the second portion of the small intestine and part of the digestive tract. It begins at the duodenojejunal junction  where it is related to the ligament of Treitz, and extends 8 to 9 feet, continuing distally with the ileum.

Being intraperitoneal, it is anchored to the posterior abdominal wall by the double-layered mesentery through which the jejunum receives its blood and nerve supply. At the root (base) of the mesentery are the superior mesenteric vessels.

The Latin word [jejunis] means "empty" or "fasting". The Latin term [jejunum] was used by the Romans to denote the first meal of the day, breakfast, when you have an "empty" stomach. The term was associated with this segment of the small intestine, as it is most of the time found empty in cadavers being dissected.

There is no clear anatomical boundary between the jejunum and ileum, as they blend smoothly one into the other. There are several gross changes from jejunum to ileum, one of them being that the complexity of the mesenteric arterial arches increases from proximal to distal. See the accompanying image. Click on it for a larger depiction.

Two interesting side notes: In English, the term for the first meal of the day is self-explanatory: [break - fast], adding to the Roman concept of "fasting" or "jejunum". In Spanish, the term for breakfast is [desayuno], where the word [ayuno] means "fasting", therefore the word [des-ayuno] also means "the end of fasting". Look at the evolution (in Spanish) from [jejunum] to [yeyuno] (the Spanish term for the organ) to [ayuno], meaning "fasting" or "empty".

Sources:
1. "The Origin of Medical Terms" Skinner, HA 1970 Hafner Publishing Co.
2. "Clinically Oriented Anatomy" Moore, KL. 3r Ed. Williams & Wilkins 1992
3 "Tratado de Anatomia Humana" Testut et Latarjet 8 Ed. 1931 Salvat Editores, Spain
4. "Anatomy of the Human Body" Henry Gray 1918. Philadelphia: Lea & Febiger Image modified by CAA, Inc. Original image by Henry Vandyke Carter, MD., courtesy of bartleby.com

1. Right tendinous aortic crus 2. Left tendinous aortic crus
IVC= Inferior vena cava

The word [crus] is Latin (cruris) and refers to the leg, or region of the shin. It is commonly used to mean "leg" or "pillar". The plural form is [crura].

Several authors suggest a relation of [crus] with another Latin term [crux] meaning "cross" as if a cross is formed by two [crura] (legs).

The term crus is widely used in human anatomy:

- crus cerebri: there are two crus cerebri in the anterior aspect of the mesencephalon
- crura of the penis: the posterior aspect of the corpora cavernosa firmly attached to the ischiopubic rami
- crura of the clitoris:  the posterior aspect of the corpora cavernosa firmly attached to the ischiopubic rami
- crura fornix cerebrii: the posterior converging bands that form the fornix of the cerebrum

Special mention is deserved by the crura of the diaphragm. There are two pairs of diaphragmatic crura. The esophageal crura (right and left) which bound the passageway of the esophagus from the thorax into the abdomen, the esophageal hiatus. The esophageal crura have a muscular structure. The aortic crura (righ and left) allow for passage of the aorta into the abdomen, and although muscular superiorly, they are mostly tendinous. The accompanying image shows an anteroinferior view of the respiratory diaphragm. Click on the image for a larger picture.

Sources:
1. "The Origin of Medical Terms" Skinner, HA 1970 Hafner Publishing Co.
2. "Medical Meanings - A Glossary of Word Origins" Haubrich, WD. ACP Philadelphia
3 "Tratado de Anatomia Humana" Testut et Latarjet 8 Ed. 1931 Salvat Editores, Spain
4. "Anatomy of the Human Body" Henry Gray 1918. Philadelphia: Lea & Febiger
Image modified by CAA, Inc. Original image by Henry Vandyke Carter, MD., courtesy of bartleby.com