UNIT 3: The midgut

Question 1

What is the ileocaecal junction?

Answer 1

Where the small intestine (ileum) joins to the large intestine at the ileocaecal valve.

Question 2

What is the duodenojejunal flexure?

Answer 2

Where the duodenum turns at a sharp angle to join the jejunum. The suspensory muscle of the duodenum contracts to widen the opening and add the passage of chyme between the two structures.

Question 3

Is the small intestine intra or retroperitoneal?

Answer 3

The iuem and jejunum are completley intraperitoneal.
The duodenum first 3cm are intraperitoneal but the rest is retroperitoneal.

Question 4

What is the ileocaecal valve?

Answer 4

Where the ileum invaginates into the cecum marking the end of the small intestine and the beginning of the large intestine.
This structure is too weak to control the flow of material into the cecum but can reduce reflux from the large intestine back into the ileum.

Question 5

In surgery what are some key features to identify the ileum?

Answer 5

Located in the lower right quadrant
More arcades than jejunum
Pink in appearance.
Thin intestine wall
Shorter vasa recta than the jejunum

Question 6

What are vesa recta in the ileum or jejunum?

Answer 6

Straight arteries that originate from arcades in the mesentery of the ileum and jejunum, connect up to the organs.

Question 7

What are arcades in the ileum or jejunum?

Answer 7

Scale shaped circular branches from a major artery, anastamose back onto themselves and to others (mesnetric artery) that lead into vesa recta which then supply the organ.

Question 8

What are some key features to identify the jejunum in surgery?

Answer 8

Appear red
Located in the upper left quadrant.
Has a thick intestinal wall
Has fewer arcades
Has longer vesa recta

Question 9

Explain the vasculature of the duodenum.
Why is this important?

Answer 9

The proximal section is supplied by a branch of the gastroduodenal artery (coeliac branch).
The distal section is supplied by the inferior pancreaticoduodenal artery (superior mesenteric artery).
Veins follow the same naming and patterns as the arteries.
This chance is important because the boundary is marked by the major duodenal papilla where the foregut becomes the midgut.

Question 10

Explain the lymphatic drainage of the duodenum.

Answer 10

Drains into the pancreatoduodenal or the superior mesenteric nodes.

Question 11

Describe the vasculature of the ileum and jejunum.

Answer 11

Supplied by the superior mesentric artery, which arise at T1 immediately inferior to the coeliac trunk, splits into twenty branches within the mesentry, supplying tje organs by a patterns of arcades and vesa recta.
Veins follow the same naming and pattern.

Question 12

Describe the lymphatics of the ileum and jejunum.

Answer 12

Drain into the superior mesenteric nodes

Question 13

What is the cecum?

Answer 13

the most priximal part of the large intestine, located after the ileum and before the ascending colon.
Is intraperitoneal.
Evolutionary history in digesting cellulose, main function transport role now is holding chyme

Question 14

Explain the vascuclar supply of the cecum.

Answer 14

Supplied by the superior mesentric vessels.
Arterial blood comes from the iliocolic artery which splits into posterior and anterior parts.
The veins in the body follow a similar pattern.

Question 15

Explain the nervous supply to the cecum.

Answer 15

Supplied by the ileocolic branch of the superior mesenteric plexus. Carries vagal and parasympathetic nerve fibres.

Question 16

Describe the lymphatic drainage of the cecum.

Answer 16

Drains into the ileocolic lymph nodes which are located around the ileocolic vein.

Question 17

Give an overview of the appendix.

Answer 17

The appendix is split into the probe and free end, The free end is external to the cecum and can be found in multiple positions, most commonly recto cecal. The probe is found internal to the cecum.
The appendix is mainly lymphoid tissue but has no specific function.

Question 18

What hold the appendix in place?

Answer 18

It is held in place by mesentery connected to the terminal end of the ileum, this fold of mesentery is called the mesoappendix.

Question 19

What is the most common position of the appendix?

Answer 19

Rectocecal
Found posterior to the cecum, described as 11 o’clock.

Question 20

What are the many different positions of the appendix?

Answer 20

Pre ileal - one o’clock posterior to the terminal ileum
Post ileal - two o’clock anterior to the terminal ileum
Sub ileal - parallel to the terminal ileum described as three o’clock
Pelvic - five oclock descinding over the plevic brim
Sub cecal - 6 o’clock below the cecum.
Para cecal - 10 o’clock lateral border to the cecum
Recto cecal - 11 oclock posterior to the cecum

Question 21

Describe the vascular supply to the appendix.

Answer 21

As classified as mid gut supply is from the superior mesentric vessels.
First branches into the ileocolic artery then the appendicular artery.
Travels to the appendix through the mesoappendix.

Question 22

Describe the nerve supply to the appendix.
How does this link to the pain from appendicitis?

Answer 22

Supplies by the ileocolic branch of the superior mesenteric plexus.
Sympathetic fibres originate from T-10, often where the first pain from appendicitis is felt.

Question 23

Explain the lymphatic drainage of the appendix.

Answer 23

Drains into lymph nodes found in the mesoappendix then into the ileocolic lymph nodes.

Question 24

Describe the location of the ileocolic lymph nodes?

Answer 24

Surround the ileocolic vessels.
Travel from the bottom right near the cecum to the top left near the left colic flexure.

Question 25

Give an overview of the colon.

Answer 25

Also known as the large intestine, is part of the midgut.
Composed of four parts, the cecum, ascedning c, transverse c, descending c and sigmoid colon.
Creates a c -shape surrounding parts of the jejunum and ileum.
Is roughly around 150cm in length in adults.

Question 26

What is another name for the right colic flexure?

Answer 26

The hepatic flexure

Question 27

How and when is the colon attached to the diaphragm?

Answer 27

Attaches to the diaphragm at the left colic flexure by the phrenicocolic ligament.

Question 28

Is the colon intra or retroperitoneal?

Answer 28

The transverse colon, sigmoid and caecum is intraperitoneal
The descending and ascending colon are retroperitoneal.

Question 29

Give an overview of the sigmoid colon.
Location
peritoneum links

Answer 29

Extends from the left iliac fossa to S3 on the sacrum.
Is attached to the parietal peritoneum by the sigmoid mesocolon - allows large mobility.

Question 30

What are the paracolic junctions?
Why are they important clinically?

Answer 30

Spaces between the ascending and descending colon and the posterolateral abdominal wall.
Important as substances release from other inflamed or infected parts of the abdomen will collect in these areas.

Question 31

What are omental appendices?

Answer 31

Small pouches of peritoneum filled with fat.
Attach to the colon.

Question 32

What is the tenai coli?

Answer 32

Three strips of muscle that run along the colon, made up of the mesocolic, free and omental coli.
They contract to shorten the wall of the bowel producing haustra (bubble like sections in bowel structure).

Question 33

What features differentiated the colon from the small intestine?

Answer 33

colon has a larger diameter
Colon has tenai coli
Colon has omental appendices.

Question 34

What is the rectumsigmoid junction?

Answer 34

Where the sigmoid colon joins up with the rectum.
Distinctive features of the colon ends.
The tenai coli of the sigmoid colon widen to attach fully to the rectum.

Question 35

How does the kidney relate location wise to the colon?

Answer 35

Located posteriorly to the ascending and descedning colon. ( or colic flexure typically )

Question 36

How is the location of the uterus and bladder related to the colon?

Answer 36

Located inferiorly to the sigmoid colon and anteriorly to the rectum

Question 37

How does the colon fit into the foregut, midgut and hindgut classifications?

Answer 37

The ascending colon and proximal two third of the trasnverse colon are part of the midgut.
The remainder of the colon is part of the hindgut.

Question 38

What is the blood supply to the ascending colon?

Answer 38

Supplied by the superior mesentric artery, which splits into the branches the ileocolic and right colic arteries.
The ileocolic splits further into the colic, anterior cecal and posterior cecal which supply the ascending colon.

Question 39

What is the blood supply to the transcending colon?

Answer 39

The right colic artery (from the superior mesenteric artery)
The middle colic artery from the superior mesenteric artery.
The left colic artery from the inferior mesenteric artery.

Question 40

What is the blood supply to the descending colon?

Answer 40

The left colic artery (a branch of the inferior mesentric artery)

Question 41

What is the blood supply to the sigmoid colon?

Answer 41

The sigmoid arteries which are a branch of the inferior mesenteric arteries)

Question 42

What is the marginal artery?

Answer 42

Anastomoses of the superior and inferior mesenteric artery join together to form one long arteries channel that runs the length of the colon.

Question 43

Describe the venous drainage of the colon.

Answer 43

Similar in naming to the arterial supply.
AC - ieocolic and right colic veins drain into superior mesenteric vein
TC - middle colic vein drains into superior mesenterc vein.
DC - left colic vein which drains into the inferior mesenteric vein
SC - sigmoid branches of the inferior mesenteric vein.
All drains into the hepatic portal vein.

Question 44

Explain the innveration of the midgut derived section of the colon.

Answer 44

Up to and including the proximal two thirds of the transverse colon.
Supplied by the superior mesenteric plexus.
Includes the sympathetic, parasympathetic and sensory nerve supply.

Question 45

Explain the innervation of the hindgut derived sections of the colon.

Answer 45

From the distal 1/3 of the transverse colon onwards.
Via nerves from the inferior mesenteric plexus.
In particular the parasympathetic innervation from the pelvic splanchnic nerves.
The sympathetic nerves from the lumbar splanchnic nerves.

Question 46

Explain the lympathic drainage of the colon.

Answer 46

Midgut derived structures drain into the superior mesenteric lymph nodes.
Hindgut derived structures drain into the inferior mesenteric lymph nodes
Pass into the intestinal lymph trunk into the cisterna chyli then the thoracic duct.

Question 47

What is the mesentery?
Why is it classified as an organ?

Answer 47

A double fold of peritoneal tissue that suspend the small and large intestine from the posterior abdominal wall.
Is considered an organ as it a contiguous structure meaning it all has one shared floor or gathering point.

Question 48

What is the role of the mesentery?

Answer 48

Suspends the small intestine and the colon from the posterior abdominal wall.
Used for passage of mesenteric vessels, nerves and lymphatics.
Plays a pathological role in inflammatory diseases.

Question 49

What is the bare area of the mesentery?

Answer 49

Where all seperate sections os mesentery gather together at the posterior abdominal wall.
It is long thin and oblique in structure.
Runs from the left of L2 to the sacroiliac.

Question 50

What are the different sections of the mesentery in the GIT?

Answer 50

The mesentery of the small intestine - attaches loops of the ileum and jejunum to the posterior abdominal wall, id very flexible.
The right mesocolons - pins ascedning colon to the posterior abdominal wall.
The para mesocolon (transverse)- gives the transverse colon a large range of flexibility.
The left mesocolon - gives the descending colon a large range of flexibility.
The mesosigmoid - has a medial proportion flattened against the posterior wall whilst the part associated with the sigmoid itself is very flexible.
The mesorectum - anchors the rectum through the pelvis.

Question 51

What is Toldts fascia?

Answer 51

Relates to mesentery that is flattened against the posterior abdominal wall ( right and left mesocolon etc).
An additional layer of connective tissue containing lymphatic vessels.

Question 52

Where are the superior and inferior mesenteric vessels located?

Answer 52

Branch off from the abdominal aorta (arteries) or the portal triad vein (veins).
Located within the mesentery.

Question 53

Explain the location of the superior mesenteric arteries in relation to digestive organs.

Answer 53

Anterior to the artery is the pylorus of the stomach, the splenic vein and the neck of the pancreas.
Posterior to the artery is duodenum and the left renal vein.

Question 54

What is the inferior pancreaticduodenal artery?

Answer 54

The proximal branch of the superior mesenteric artery.
Anastamoses with the superior pancreatic duodenal artery to supply the inferior head and uncinate part of the pancreas and duodenum,

Question 55

What is the ileocolic artery?

Answer 55

The distal branch of the superior mesenteric artery.
Supplies the ascending colon, the cecum and the ileum.

Question 56

What makes up the midgut viscera?

Answer 56

The duodenum, the jejunum, the ileum, the cecum, the ascending colon, the transverse colon.

Question 57

In what relation do the superior mesenteric vessels pass over the duodenum?

Answer 57

Anteriorly.

Question 58

Which dermatome will pain from the appendix initially appear?

Answer 58

T10 - around the umbilicus

Question 59

From which vertebrae does the superior mesenteric artery arise from?

Answer 59

L1

Question 60

Why is the left colic flexure higher than the right colic flexure?

Answer 60

The right colic flexure is compressed inferiorly due to the presence of the liver in the right hypochondriac region.

Question 61

What part of the small intestine can be removed with the fewest complications?

Answer 61

The proximal sections of the ileum.
Ileum and jejunum can adapt to play a helper role if the other is removed. Most of the absorption happens in the jejunum, the distal part of the ileum is needed for absorption of vitamin b-12.