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MD3002 > Jejunum, Ileum, and Large Intestine > Flashcards

Jejunum, Ileum, and Large Intestine Flashcards

1
Q

What is the longest part of the GI tract ? The longest part of this part ?

A

Small intestine

Jejunum and Ileum

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2
Q

What are the start and end of the jejunum/ileum ?

A

Duodenojejunal junction, to ileocecal valve

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3
Q

What is the boundary between jejunum and ileum ?

A

No clear boundary, gradual changes from jejunum to ileum

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4
Q

How much of the small intestine does the jejunum and ileum make up ?

A

Jejunum makes up proximal 40%, ileum makes up 60%

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5
Q

Where in the abdomen does the jejunum lie ? the ileum ?

A

Jejunum lies in the upper L abdomen while the ileum tends to be in the lower R and partly in the pelvis.
They both hang from the posterior abdominal wall by the mesentery (two layered peritoneum)

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6
Q

What structures does the base of the mesentery cross ?

A
  • 3rd part of duodenum
  • Aorta
  • IVC
  • Right gonadal vessels
  • Right ureter
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7
Q

Identify the content of the mesentery.

A
  • Branches of the superior mesenteric artery, forming anastomotic arcades
  • Branches of superior mesenteric vein
  • Lymph vessels
  • Nerves
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8
Q

Distinguish the main features which differentiate jejunum from ileum.

A

JEJUNUM

  • Wide
  • More plica circulares
  • No Peyer’s patches

ILEUM

  • Narrow
  • Less plica circulares (circular folds of mucous membrane)
  • Numerous Peyer’s patches (aggregations of lymphoid tissue along the antimesenteric border)
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9
Q

Describe the structure of the ileocecal valve.

A

Rudimentary structure consisting of 2 horizontal folds of mucous membrane that projects around the orifice of the ileum.

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10
Q

Explain the function of the ileocecal valve.

A

Limit the reflux of colonic contents into the ileum, and possible control the flow of ileal contents into the cecum

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11
Q

Identify the arterial supply of the jejunum and ileum.

A
  • Superior mesenteric artery has jejunal and ileal branches.
  • Superior mesenteric artery supplies the midgut (from Ampulla of Vater in duodenum to 2/3 along transverse colon), and forms a series of vascular anastomotic arcades within the mesentery.
  • In Jejunum, the branches make one or two arcades with long vasa recta (straight arteries coming off from arcades in the mesentery of the jejunum and ileum, and heading toward the intestines) in its mesentery.
  • In Ileum, the branches make many arcades with short vasa recta in its mesentery.
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12
Q

At what level does the superior mesenteric artery arise from the aorta ?

A

The superior mesenteric artery arises from the aorta at the level of L1.

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13
Q

Describe veinous drainage of the jejunum and ileum.

A

Jejunal and ileal veins drain into superior mesenteric vein which will eventually form the portal vein.

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14
Q

Describe lymphatic drainage of the jejunum and ileum.

A

Two systems:

1) Peyer’s patches → Mesenteric nodes → Superior mesenteric nodes → Intestinal trunk → Cisterna Chyli (sac from where thoracic duct starts)

2) Lacteals (vessel in center of each vilus) through mesenteric lymphatic channels, to Cisterna Chyli
For the absorption of digested fats & lipids (chyle)

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15
Q

What is the disadvantage of lacteals as a lymphatic route ?

A

If ingest something toxic that is soluble in fat, it will be absorbed in lacteals, to cysterna chyli, to thoracic duct, back to systemic veins so higher chance of getting poisoned.

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16
Q

Where is the cisterna chyli located ?

A

Upper abdomen

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17
Q

Describe the innervation of the jejunum and ileum.

A

Sympathetic: from greater and lesser Splanchnic nerves and T8-T11

Parasympathetic: from Vagus

Both sympathetic and parasympathetic fibers then → Ceoliac trunk → Superior mesenteric plexus

Sympathetic fibers then → myenteric plexus (peristaltic activity, sphincters)

Parasympathetic fibers then → Submucous plexus (secretion) + myenteric plexus (peristaltic activity, sphincters)

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18
Q

Where is pain from the jejunum/ileum referred ?

A

Referred pain from jejunum/ileum is periumbilical (T10)

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19
Q

Identify the main functions of the large intestine.

A
  • Fluid-electrolyte balance (absorbs water and salts)

- Dries out the chyme to form faeces

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20
Q

Identify the proximal and distal boundaries of the large intestine. How long is the large intestine ?

A

From the caecum, to the rectum and anal canal.

1.5 m long

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21
Q

Identify the main parts of the large intestine.

A

Caecum, ascending colon, hepatic (right colic) flexure, transverse colon, splenic (left colic) flexure, descending colon, sigmoid colon

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22
Q

Is the large intestine retroperitoneal or intraperitoneal ?

A

Ascending and descending colons are retroperitoneal while transverse and sigmoid colon are on a mesentery (i.e. intraperitoneal)

23
Q

Which of the small or large intestine is larger in diameter ?

A

Large intestine is larger in diameter, unless contracted by a wave of peristalsis

24
Q

Describe the main structural features of the large intestine.

A
  • Larger in diameter proximally than distally
  • 2 layers of muscle: circular muscle fibers (inside) + longitudinal smooth (outside) muscle fibers which thicken to form 3x taenia coli (free taenia, omental taenia, mesenteric taenia)
  • Taenia coli are shorter than the large intestine, which means sacculations/pouches called haustra (mobile) are formed
  • Epiploic/omental appendices (appendices epiploicae), tags of fat (their number increases distally)
  • Lacks Peyer’s patches
25
Q

What is the result of infection of the epiploic/omental appendices ?

A

Mimics appendicitis

26
Q

What is the widest part of the large intestine ?

A

Caecum

27
Q

Describe the anatomical location of the caecum.

A
  • Lies below the junction of the ileum with the large intestine in the right iliac fossa
  • Continuous with the ascending colon.
  • Covered with peritoneum but NOT on a mesentery
28
Q

Describe the anatomical relation between caecum and ileum.

A

Ileum enters the caecum obliquely and partly invaginates into it, forming ileocecal orifice

29
Q

Define vermiform appendix, stating its location.

A
  • Blind intestinal diverticulum
  • From the posteromedial aspect of the caecum.
  • Suspended on a short but highly variable mesoappendix that transmits the appendicular vessels
  • Can be found in retrocecal (65%), pelvic (30%), subcecal, retroileal, and pre-ileal anatomical positions.
30
Q

Define McBurney’s point.

A

Point over the right side of the abdomen that is one-third of the distance from the anterior superior iliac spine to the umbilicus. Also where root of vermiform appendix is.

31
Q

What is the anatomical relationship between base of vermiform appendix and taenia coli ?

A

The base of the appendix most often lies deep to a point that is one third of the way along the oblique line joining the right anterior superior iliac spine to the umbilicus (McBurney’s point).
The 3 taenia coli converge at the root of the vermiform appendix, at McBurney’s point

32
Q

What is so special about the mucosa of the vermiform appendix ?

A

Submucosa of the vermiform appendix is full of lymphoid tissue.

33
Q

Describe the anatomical location of the ascending colon.

A
  • Right lumbar region
  • Between caecum and hepatic flexure
  • Secondary retroperitoneal
34
Q

Define right and left paracolic gutter, describing their location.

A

Right paracolic gutter is a space, formed between ascending colon and posterior abdominal wall
Left paracolic gutter is a space, formed between descending colon and posterior abdominal wall

35
Q

Describe the anatomical location of the transverse colon.

A
  • Extends between the hepatic and splenic flexures
  • Suspended by the transverse mesocolon
  • Intraperitoneal
  • Shape of it can vary depending on its mesentery
36
Q

What organ is each of splenic and hepatic flexure related to ?

A

Splenic flexure is related to the spleen

Hepatic flexure is related to the liver

37
Q

Define mesocolon. Describe the anatomical location of the root of the transverse colon.

A
  • Broad, meso-fold of peritoneum which connects the transverse colon to the posterior wall of the abdomen.
  • Root of the transverse mesocolon crosses the inferior edge of the pancreas
38
Q

Describe the anatomical location of the descending colon.

A
  • L lumbar region, hidden anteriorly by small intestine

- Retroperitoneal

39
Q

Describe the anatomical location of the sigmoid colon.

A
  • Continuation of the descending colon in front of the pelvic inlet
  • Intraperitoneal
  • Suspended by the sigmoid mesocolon
  • Continuous with the rectum in front of the 3rd sacral vertebrae
40
Q

Describe the anatomical location of the rectum.

A
  • Retroperitoneal
  • Begins in front of the 3rd sacral vertebrae
  • Ends in front of the tip of the coccyx by piercing pelvic diaphragm and becoming continuous with the anal canal
41
Q

True or False: Rectum follows the curvature of the sacrum and coccyx.

A

True

42
Q

What is the function of the rectum ?

A

Store faeces

43
Q

Compare the microscopic features of the rectum with those of the large intestine.

A

Rectum lacks taenia, haustra, or appendices epiploica

44
Q

How long is the anal canal ?

A

Approximately 4 cm

45
Q

Where does the anal start, and end ?

A

From the pelvic diaphragm, to the anus (to the outside world)

46
Q

Mention any important structures with the anal canal, explaining why they are important.

A

Internal and external anal sphincters

External one helps maintain continence and keep stool in the rectum

47
Q

Describe the arterial supply of the large intestine + rectum/anal canal.

A

1) SUPERIOR MESENTERIC ARTERY BRANCHES supply part of large intestine, from vermiform appendix to proximal 2/3 of transverse colon.

  • Ileocolic artery: Caecum
  • Appendicular artery (branch of ^, running close and parallel with appendix and supplying it)
  • Right colic artery: Ascending colon
  • Middle colic artery: Transverse colon

→ There are anastomoses between these branches (so if one blocked, others provide collateral circulation).

2) INFERIOR MESENTERIC ARTERY BRANCHES supply distal 1/3 of transverse colon, the splenic flexure, descending colon, and sigmoid colon.

  • Left colonic artery: splenic flexure, descending colon
  • Sigmoid artery: Sigmoid colon
  • Superior rectal artery: Rectum and anal canal (inferior mesenteric artery ends as superior rectal artery)

3) Marginal artery (of Drummond) is an anastomosis between inferior and superior mesenteric arteries
→ forms a collateral circulation should the inferior mesenteric artery become obstructed

48
Q

Where does the superior mesenteric artery originate from ?
The coeliac trunk ?
the inferior mesenteric artery ?

A
  • Superior mesenteric artery originates from lower border of L1 vertebrae
  • Coeliac trunk originates at the superior border of L1 vertebrae
  • Inferior mesenteric artery arises from aorta at L3
49
Q

Which of the arteries of the large intestine has no collateral circulation ? Why ?

A

Appendicular artery, because it’s a terminal branch.

50
Q

Describe the veinous drainage of the large intestine.

A

Veins of the colon run with arteries:

1) Superior rectal vein, sigmoid vein and left colic vein into inferior mesenteric which drains into splenic vein which drains into hepatic portal vein
2) Ileocolic vein + R and middle colic veins + appendicular vein drain into superior mesenteric, which drains into splenic veins which drains into hepatic portal vein

51
Q

Describe the lympathic drainage of the large intestine.

A

Lymphatic drainage is into the nodes along the arteries → nodes around the origins of the superior and inferior mesenteric arteries

52
Q

Describe the nerve supply of the large intestine.

A

Autonomic nerves run with the three arteries:

1) Coeliac trunk to foregut:
- Sympathetics from T5-T9 (greater splanchnic)
- Parasympathetics from vagus

2) Superior mesenteric to midgut
- Sympathetics (around superior mesenteric artery) are from T10-T11 (lesser splanchnic)
- Parasympathetics from vagus

3) Inferior mesenteric to hindgut
- Sympathetics from T12-L3 (least splanchnic and lumbar splanchnic nerves)
- Parasympathetics from S2-S4

53
Q

Explain why referred pain occurs, and where pain from different organs in the abdomen is referred ?

A

♦ Afferents from abdominal viscera run with the sympathetic nerves
-Brain cannot localise visceral pain (unlike somatic pain), so pain localisation occurs when the overlying parietal peritoneum is involved

♦

  • Pain from areas supplied by the celiac trunk refers to epigastric region (T7-T9)
  • Pain from areas supplied by the superior mesenteric refers to the periumbilical region because that part of intestine receives sympathetic from T10, so pain will refer to T10 dermatome (T10-T11) (appendicitis pain in the first 6-8 hours)
  • Pain from areas supplied by the inferior mesenteric refers to the suprapubic region (T12)

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