Main segments and boundaries
Anatomically, the small intestine (intestinum tenue) is situated between the stomach and the large intestine. It consists of three consecutive parts:
- Duodenum.
- Jejunum (jejunum).
- Ileum (ileum).
In routine clinical practice, this term most commonly refers specifically to the intraperitoneal part—the mesenteric small intestine, consisting of the jejunum and ileum. There is no clear visual or anatomical boundary between the jejunum and ileum. Meanwhile, the jejunum accounts for approximately two-fifths of the total length, and the ileum accounts for the remaining three-fifths.
Fixation and duodenojejunal flexure
The initial and terminal segments of the small intestine are securely fixed to the posterior abdominal wall and have a constant topographic position. Along the rest of its extent, the intestine is suspended by a mesentery of varying width, providing it with significant mobility.
The area of the duodenojejunal flexure (flexura duodenojejunalis) is located to the left of the body of the second or third lumbar vertebra, directly beneath the root of the transverse mesocolon. Here, the duodenojejunal recess (recessus duodenojejunalis) is formed, bounded by a peritoneal fold, the parietal layer of the posterior abdominal wall, the transverse mesocolon, and the upper margin of the flexure itself. Excessive enlargement of this recess can lead to the formation of a hernial sac and the development of a true internal hernia.
Surgical orientation and loop identification
To locate the duodenojejunal flexure during procedures, the Gubarev maneuver is used. The surgeon grasps the greater omentum along with the transverse colon using the left hand, puts them on a stretch, and retracts them upward. Using the fingers of the right hand, one slides along the transverse mesocolon toward the spine, then slips to the left and secures the initial intestinal loop.
To accurately distinguish the afferent loop from the efferent loop, the Wilms–Gubarev method is used:
- The retrieved loop is fixed in the surgical wound, and its mesentery is completely straightened, eliminating any twisting.
- The direction of the mesentery root is traced from top to bottom and from left to right.
- As a result, the left and upper parts correspond to the afferent intestine, while the right and lower parts correspond to the efferent intestine.
Meckel's diverticulum
A serious congenital anomaly is Meckel's diverticulum (diverticulum ilei), which represents a remnant of the abnormal regression of the embryonic vitelline duct. This blind pouch of the ileal wall may have a conical, cylindrical, or club-shaped form.
Main parameters of the formation:
- Frequency: found in 2–3% of people.
- Dimensions: length ranges from 1.2 to 10–12 cm.
- Localization: located on the ileum at a distance of 25 to 125 cm from the ileocecal junction (where it enters the cecum).
Briefly: answers to topical questions
Which arteries supply blood to the mesenteric part of the small intestine?
Blood supply to the mesenteric part of the small intestine is provided by the superior mesenteric artery system (a. mesenterica superior). It gives off 12–16 branches, which are subdivided into:
- Jejunal arteries (aa. jejunales) — supply the jejunum.
- Ileal arteries (aa. ileales) — supply the ileum.
The branches of these arteries anastomose with each other, forming 3 to 5 rows of vascular arcades. The final row of arcades forms a continuous marginal vessel, from which straight arteries (vasa recta) depart toward the mesenteric border of the intestine.
Where does venous drainage from the jejunum and ileum occur?
Venous drainage from the jejunum and ileum flows into the portal vein system. Blood is collected from the straight veins into:
- jejunal veins (vv. jejunales);
- ileal veins (vv. ileales);
- ileocolic vein (v. ileocolica).
These veins merge to form the superior mesenteric vein (v. mesenterica superior). The superior mesenteric vein runs in the root of the mesentery to the right of the artery of the same name, passes anterior to the horizontal part of the duodenum, passes beneath the head of the pancreas, and joins the splenic vein (v. lienalis) to form the portal vein.
To which lymph nodes does lymph drainage from the small intestine occur?
Lymph drainage from the small intestine occurs into the mesenteric lymph nodes (nodi lymphoidei mesenterici), which are arranged in three rows:
- First-row nodes — located along the mesenteric border of the intestine.
- Second-row nodes — lie at the level of the intermediate vascular arcades.
- Third-row nodes — located along the course of the main branches of the superior mesenteric artery.
Between the leaves of the mesentery, ileocolic nodes (nodi ileocolici) are also distinguished. Some lymphatic vessels may bypass the nodes and drain directly into the thoracic duct.
What is the innervation of the mesenteric part of the small intestine?
The mesenteric part of the small intestine receives autonomic innervation involving parasympathetic and sympathetic fibers.
- Parasympathetic innervation of the abdominal organs is provided by branches of the vagus nerve (n. vagus); the vagus nerve enhances the motility of the small intestine.
- Sympathetic innervation inhibits small intestinal motility.
Parasympathetic preganglionic fibers, together with sympathetic and viscerosensory fibers, form mixed autonomic plexuses. Below the celiac plexus along the course of the aorta lies the superior mesenteric plexus (plexus mesentericus superior).
By what macroscopic features can the jejunum be distinguished from the ileum?
The jejunum can be distinguished from the ileum by the characteristics of the mucosal folds, lymphoid apparatus, vascular architecture, and mesentery.
| Sign | Jejunum (jejunum) | Ileum (ileum) |
|---|---|---|
| Circular folds | High and frequent | Become lower, sparser, and disappear toward the end |
| Lymphoid apparatus | Solitary follicles are present in all parts of the small intestine | Aggregated lymphoid nodules—Peyer's patches—are characteristic |
| Vascular arcades | Few levels of arches | Multiple arcades |
| Straight vessels (vasa recta) | Long | Short |
| Mesenteric width | 1–2 cm at the initial part of the jejunum | Reaches a maximum of 20–25 cm in the lower ileum; decreases near the junction with the cecum |
Gubarev's maneuver: «Omentum upward, along the mesentery toward the spine, to the left — and the loop is in your hands». For loops according to Wilms — Gubarev: straighten the mesentery; the afferent loop is top-left, the efferent loop is bottom-right.
Class and exam questions
Where is the duodenojejunal flexure localized?
The flexure is located on the left at the level of the second or third lumbar vertebra, directly below the root of the transverse mesocolon.
How do the lengths of the jejunum and ileum relate to each other?
The jejunum constitutes approximately two-fifths of the total length of the mesenteric part of the small intestine, and the ileum accounts for the remaining three-fifths.
Where is Meckel's diverticulum most frequently localized?
It is located on the ileum at a distance of 25 to 125 cm proximal to its opening into the cecum (ileocecal junction).
What else to study on this topic
- Anatomical structure of the Treitz recess and its significance in internal hernias
- Step-by-step technique of Gubarev's maneuver for locating the duodenojejunal flexure
- Differential diagnosis of the afferent and efferent intestinal loops
- Variant forms and clinical manifestations of Meckel's diverticulum
- Blood supply and fixation features of the mesenteric part of the small intestine
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