Midgut Reading- Dr. Morton

The midgut consists of, what?

duodenum (third and fourth parts), \n jejunum, ileum, cecum, ascending colon, and the proximal half of the transverse colon

The superior mesenteric arteries \n and veins provide, what?

primary vascular supply for the midgut

Lymph from the midgut drains into, where?

superior mesenteric nodes surrounding the superior mesenteric artery

The duodenum chemically digests food, how?

by the secretion of pancreatic enzymes

The parts of the duodenum associated \n with the midgut are:

1. Third Part (horizontal)
2. Fourth Part (ascending)


1. Suspensory ligament of the duodenum (ligament of Treitz)

Third Part (horizontal) crossed anteriorly by, what?

superior mesenteric artery and vein

The distal portion of the fourth part \n is transitional, from where to where? in what region?

retroperitoneal to intraperitoneal in the \n region of the duodenojejunal junction

Suspensory ligament of the duodenum (ligament of Treitz) is a structure composed of, what?

composed of smooth muscle and connective \n tissue

Suspensory ligament of the duodenum (ligament of Treitz) arises from?

the left crus of the diaphragm

Suspensory ligament of the duodenum (ligament of Treitz) courses, where?

to the duodenojejunal junction, marking the transition from duodenum to jejunum

The jejunum and ileum are, what?

intraperitoneal organs

The jejunum and ileum are tethered to the posterior abdominal wall via, what?

the mesentery

Mesentery, the double-layered peritoneum serves, as what?

conduit for the mesenteric neurovascular structures

The jejunum is, what?

second part of the small intestine

The jejunum has the most, what?

highly developed circular folds lining \n the lumen

Highly developed circular folds lining \n the lumen of the jejunum, increase what?

the surface area of the mucosal \n lining for absorption

In contrast to the ileum, the jejunum also has a greater, what?

number of vasa recti

the jejunum lacks, what compared to duodenum and ileum?

lacks Brunner’s glands \n (like the duodenum) or Peyer’s patches (like the ileum)

The ileum is what?

third part of the small intestine that contains large lymphatic aggregates known as Peyer’s \n patches

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In some conditions, such as lymphomas, what happens to these Peyer’s patches?

they may enlarge and cause intestinal obstruction

In contrast to the jejunum, the ileum has fewer, what? more of what?

fewer circular folds lining the lumen and more vascular arcades

The terminal end of the ileum has, what?

thickened smooth muscle layer known as the ileocecal valve (sphincter)

ileocecal valve (sphincter) does what?

prevents feces from the cecum to move backward from the large intestine into the small intestine

Approaching the distal end of \n the ileum is, what?

the site of the embryonic vitellointestinal duct attachment

If a remnant of the vitellointestinal duct persists, it presents as what?

Meckel’s diverticulum

Meckel’s diverticulum is important clinically how?

* it may contain ectopic gastric mucosa, which secretes acid
* may result in inflammation, bleeding from intestinal mucosa, bowl obstruction, intussusception, or perforation

Meckel’s Diverticulum, follows the 2s rule, how?

* occurs in 2% of the population
* is 2 inches in length
* may contain 2 types of ectopic tissue(Gastric and Pancreatic)
* found within 2 feet of the ileocecal valve


* most become symptomatic before 2 years of age

The cecum is, what? where is it located?

* blind-ended sac at the beginning of the large \n intestine
* located inferior to the ileocecal valve
* in the right lower quadrant of the abdomen
* within the iliac fossa

Attached to the cecum is what?

vermiform appendix, which has an unknown function in humans

The appendix is variable in, what?

* length and position
* usually lies deep to the cecum \n but may extend down into the pelvis

The surface projection of the appendix is, what?

McBurney’s point

Where is McBurney’s point?

is located 1/3 of the distance between the right anterior superior iliac spine and the umbilicus.

Ascending colon arises from where and courses where?

* from the cecum
* courses vertically to the liver, where the colon bends at the right colic (hepatic) flexure

The parietal peritoneum covers the ascending colon’s what?

its anterior surface

Ascending colon is considered a what organ?

secondary-retroperitoneal organ

The transverse colon is an ------- organ, and is located where?

intraperitoneal organ located between the right and left colic flexures

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Gastrocolic ligament connects what to what?

the transverse colon to the stomach

Transverse mesocolon is what?

Two-layered peritoneum that connects the transverse colon to the posterior wall of the abdomen, that contains its associated neurovascular structures

Transverse Mesocolon is continuous with what?

the two posterior layers of the gastrocolic ligament.

The superior mesenteric artery arises immediately where?

inferior to the celiac trunk at the L1 vertebral level

The superior mesenteric artery courses where?

anteriorly and inferiorly at an acute angle

The superior mesenteric artery supplies what?

the midgut

The superior mesenteric artery’s branches are:

* Inferior pancreaticoduodenal arteries.
* Jejunal arteries.
* Ileal arteries.
* Middle colic artery
* Right colic artery
* Ileocolic artery
* Appendicular artery

Inferior pancreaticoduodenal arteries

* Supplies the distal duodenum and pancreatic head
* pancreatic head; superior and inferior pancreaticoduodenal arteries form an anastomosis between foregut and midgut

Jejunal arteries

* Supplies the jejunum via seven to nine \n branches with a few large arterial arcades and long vasa recti

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Ileal arteries

* Supplies the ileum via seven to nine branches \n with numerous short arterial arcades and short vasa recti

Middle colic artery

* Supplies part of the transverse colon
* forms anastomoses with the left and right colic arteries in the marginal artery (of Drummond)

Right colic artery

* Supplies the ascending colon
* forms anastomoses with the ileocolic and middle colic arteries in the marginal artery (of Drummond).

Ileocolic artery

* Supplies the cecum
* forms anastomoses with the ileal and right colic arteries

Appendicular artery

* A branch off the ileocolic that courses \n within the mesoappendix
* supplies the appendix

Lymph is drained from----- to------?

* organs of the gastrointestinal (GI) tract \n to the lymph nodes along the arterial supply to that organ
* the next set of lymph nodes is located at \n the origin of the artery to an organ

Lymph from midgut organs drains into ?

* Superior mesenteric lymph nodes surrounding the superior mesenteric artery
* From which, it passes to the celiac nodes, cisternal chyli, the thoracic duct
* its termination in the formation of the left brachiocephalic vein

The hindgut consists of what?

distal half of the transverse colon, descending colon, sigmoid colon, and proximal rectum

Branches of the inferior mesenteric artery and vein provide vascular supply to?

hindgut

Lymph from the hindgut drains into the?

inferior mesenteric nodes surrounding the inferior mesenteric artery

The transverse colon transitions from where to where?

from midgut to hindgut somewhere between the left and right colic flexures

The colon continues vertically down \n the left wall of the abdomen as the, what?

descending colon

The parietal peritoneum covers only what in descending colon?

anterior surface of the descending colon

the descending colon is considered a, what?

a secondary retroperitoneal structure

Sigmoid colon is, what?

* The continuation of the descending colon as \n it courses into the left side of the pelvis


* makes an S shape
* it’s intraperitoneal

The curving nature of the sigmoid colon enables, what?

gases to be stored in the superior arch, thus expelling gas without defecating is possible

Sigmoid mesocolon, is what?

A fold of peritoneum that attaches the \n sigmoid colon to the pelvic wall

What course between the layers, sigmoid colon and sigmoid mesocolon?

sigmoid and superior rectal vessels

The inferior mesenteric artery arises at the? supplies?

* L3 vertebral level
* the hindgut

Branches of IMA are?

* Left colic artery.
* Sigmoidal arteries
* Superior rectal artery

Left colic artery

* Supplies the descending colon
* forms anastomoses with the middle colic and sigmoidal arteries.

Sigmoidal arteries

* Supplies the sigmoid colon

Superior rectal artery

* Supplies the superior region of the rectum

From Inferior mesenteric lymph nodes, lymph passes where?

* to the superior mesenteric nodes, celiac nodes, cisterna chyli, the thoracic duct and \n its termination in the left brachiocephalic vein

The rectum is what?

* terminal, straight portion of the \n colon
* becomes the anal canal as it traverses through the pelvic floor muscles

the rectum lacks, what?

* taeniae coli

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Arteries that supply the rectum are?

* superior rectal, middle rectal, and \n inferior rectal arteries

Veins of the rectum are drained by what?

* the hepatic portal system (superior rectal vein)


* caval system (middle and inferior rectal veins to the internal iliac vein)

Lymph from the upper part \n of the rectum follows the path of what?

* path of the superior rectal artery into nodes surrounding the inferior mesenteric artery

Lymph from the middle part of the rectum follows the path of?

* middle rectal artery into nodes surrounding the internal iliac artery.

Lymph from the lower part of the rectum follows the path of?

path of the inferior rectal and along the internal pudendal artery into inguinal lymph nodes.

The transition from sigmoid colon to rectum occurs \n at approximately?

S3 vertebral level

The S3 vertebral level is where the rectum is?

covered anteriorly by parietal peritoneum and thus is a retroperitoneal structure

The marginal artery (of Drummond) is, what?

* an arterial anastomosis between the superior and inferior mesenteric \n arteries

The marginal artery courses, where?

* within the mesentery and parallels the ascending, transverse, and descending colon.

The anastomosis at marginal artery, is so complete that during the repair of an aortic \n aneurism, that what happens?

* inferior mesenteric artery often will not be \n regrafted to the aorta
* because the marginal artery will supply blood to the hindgut via the superior mesenteric artery

Near the left iliac fossa, the descending colon continues as what?

* sigmoid colon, which is an intraperitoneal structure

The vascular supply of the sigmoid colon is via what?

* sigmoid arteries from the \n inferior mesenteric artery

Autonomic innervation of the foregut and midgut is accomplished via, what?

the celiac and superior mesenteric ganglia and \n plexuses, respectively

These celiac and superior mesenteric plexuses receive sympathetic innervation via the, what?

* greater and lesser splanchnic nerves

parasympathetic innervation of the celiac and superior mesenteric plexuses is through what?

via the vagus nerves

Autonomic innervation of the hindgut is accomplished via, what?

the inferior mesenteric ganglia and plexus

Hindgut plexus innervation is from?

* receives sympathetic \n innervation via lumbar splanchnic nerves
* parasympathetic \n innervation via pelvic splanchnic nerves

Sympathetic motor innervation to the GI tract decreases, what?

* motility, peristalsis, sphincter muscle contraction, absorption, and \n glandular secretions
* causes vasoconstriction

Greater splanchnic nerve has preganglionic sympathetic neurons from where to where?

* T5–T9 spinal cord levels to the prevertebral \n plexus (celiac and superior mesenteric ganglia and plexuses)

Greater splanchnic nerve innervates?

* innervates the foregut and associated organs

Lesser splanchnic nerve has preganglionic sympathetic neurons from where to where?

* T10–T11 spinal cord levels to the prevertebral \n plexus (celiac and superior mesenteric ganglia or plexuses)

Lesser splanchnic nerve innervates what?

* the midgut

Least splanchnic nerve has preganglionic sympathetic neurons from where to where?

T12 spinal cord level to the prevertebral plexus \n (aorticorenal and inferior mesenteric ganglia or plexuses)

Least splanchnic nerve innervates what?

innervates the kidney and adrenal gland

Lumbar splanchnic nerve

* Has preganglionic sympathetic neurons from the L1–L2 spinal cord level to the prevertebral plexus (inferior mesenteric and inferior hypogastric ganglia or plexuses)
* innervates the hindgut

Parasympathetic motor innervation increases, what?

* GI tract motility, absorption, smooth muscle contraction, and glandular secretions

Parasympathetic motor GI innervation relaxes, what?

sphincter muscles

Vagus nerve (CN X):

* Has preganglionic parasympathetic \n neurons from the medulla to the prevertebral plexuses
* accompanies sympathetic neurons to regions of the foregut and midgut

Pelvic splanchnic nerves

* Have preganglionic parasympathetic neurons from the S2–S4 spinal cord levels to the prevertebral plexus (inferior hypogastric plexus)
* provide innervation to the hindgut and pelvic and perineal organs