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3002 > 18 Anatomy of jejunum, ileum and large intestine > Flashcards

18 Anatomy of jejunum, ileum and large intestine Flashcards

1
Q

What is the jejunum and ileum suspended on?

A

On THE mesentery from the posterior abdominal wall - carries blood, lymph and nerve supply

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2
Q

How long is the jejunum and ileum?

A

~6 m long (2/5 jejunum and 3/5 ileum)

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3
Q

Where does the jejunum begin? Where does ileum end?

A
  • Jejunum begins at: duodenojejunal flexure/ junction (upper left abdomen)
  • Ileum ends at: ileocaecal junction - right iliac fossa (lower right + pelvis)
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4
Q

Difference between jejunum and ileum

A

Jejunum:

  • Wider bored
  • Thicker walled : plicae circulares are larger, more numerous, and more closely set in the jejunum
  • Redder
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5
Q

Within the mesentery the superior mesenteric artery branches as a series of anastomotic arcades. Describe the jejunal mesentery

A
  • Its base starts just left of L2
  • One or two arcades with long vasa recta reaching the intestine
  • The fat is deposited near the root and is scanty near the intestinal wall
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6
Q

Within the mesentery the superior mesenteric artery branches as a series of anastomotic arcades. Describe the ileal mesentery

A
  • Its bade passes obliquely downwards to the right ending just above the right sacroiliac joint
  • Many arcades with short vasa recta reaching the intestine
  • The fat is deposited throughout extending from the root to the intestinal wall
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7
Q

What are Peyer’s patches?

A
  • Aggregations of lymphoid tissue

* Predominantly present in the mucous membrane of the distal ileum along the anti mesenteric border

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8
Q

What is the ileocaecal valve?

A
  • Rudimentary structure
  • 2 horizontal folds of mucous membrane that project around the orifice of the ileum
  • Situated at the junction of ileum and caecum
  • Its function is to limit the reflux of colonic contents into the ileum and possibly control the flow of ileal contents into the caecum
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9
Q

Jejunum and ileum arterial blood supply?

A

Jejunal and ill arteries arise from the superior mesenteric artery and its ileocolic branch

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10
Q

Jejunum and ileum venous blood supply?

A
  • Veins correspond to the branches of the superior mesenteric artery
  • Drain into the superior mesenteric vein that forms the portal vein
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11
Q

Jejunum and ileum lymphatic supply?

A

Lymphatic drainage is to the superior mesenteric nodes that are situated around the origin of the superior mesenteric artery

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12
Q

Jejunum and ileum nerve supply?

A

Nerve supply derived from:
• Sympathetic lesser splanchnic nerve T10-T11
• Parasympathetic (vagus) nerves via the superior mesenteric plexus

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13
Q

Mid gut (jejunum and ileum) derived structure send referred pain to…

A

Periumbilical - T10

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14
Q

Superior mesenteric artery arises from where?

A

Arises from aorta at L1

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15
Q

Superor mesenteric artery carries which nerves?

A

Carries nerves (sympathetic) derived from T10 and T11

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16
Q

What does superior mesenteric artery supply?

A

Supplies midgut (from ampulla of Water in duodenum to 2/3 along the transverse colon)

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17
Q

What does the superior mesenteric artery form?

A

Forms a sequence of vascular anastomotic arcades in THE mesentery

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18
Q

What is the difference between the arcades and vasa recta of jejunum and ileum?

A

• Jejunum:

  • less arcades
  • long vasa recta

• Ileum:

  • many arcades
  • short vasa recta
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19
Q

Intestinal lymph drainage via THE mesentery (digestion and protection)

A

Digestion:
• Mucous membrane of small intestine is raised in multiple villi to increase absorptive SA
• Lacteal in centre of each villus for the absorption of digested fats and lipids (chyle)
• Chyle passes from lacteals –> mesenteric lymph channels (don’t pass trough lymph nodes but converge on cisterna chylli that lies in upper abdomen, and passes through diaphragm as the thoracic duct - absorbed lipid molecules too big for lymph node “filters”)

Protection:
• Intestinal wall is packed with lymphocytes
• In distal ileum these aggregate as Peyer’s patches
• Lymph absorbed from the intestinal wall passes into mesenteric lymph channels but the filter through the mesenteric nodes
• Afferents from the mesenteric nodes converge on –> nodes at the root of the SMA
• Afferents from the nodes on SMA pass –> cisterna chyli

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20
Q

What is Meckel’s diverticulum?

A
  • Congenital abnormality in ileum
  • 2% of people
  • Remnant of the vitalise duct
  • It may ulcerate causing signs/ symptoms similar to appendicitis
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21
Q

Where does large intestine start and end?

A

From caecum to the rectum and anal canal

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22
Q

How long is the large intestine?

A

~ 1.5 m

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23
Q

What structures make up the large intestine?

A
  • Caecum
  • Ascending colon
  • Hepatic (right colic) flexure
  • Transverse colon
  • Splenic (left colic) flexure
  • Descending colon
  • Sigmoid colon
  • Rectum and anal canal
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24
Q

Which parts of the large intestine are retroperitoneal?

A

Ascending and descending colon

25
Q

Which parts of the large intestine are on a mesentery (i.e. intraperitoneal)?

A

Transverse and sigmoid colon

26
Q

What is the function of the large intestine?

A
  • Absorbs fluid and salts

* Dries out the chyme to form faeces

27
Q

What are the macroscopic external features of the large intestine?

A
  • Larger in diameter than the small intestine unless contracted by a wave of peristalsis
  • Posesses:
  1. Epiploic/ omental appendices (appendices epiploicae) that are tags of fat
  2. Taeniae coli (3) that are longitudinal bands of smooth muscle
  3. Haustra that are sacculations/ pouches

• Lacks: Peyer’s patches

28
Q

What are the macroscopic internal features of the large intestine?

A
  • Lacks villi

* Lacks plicae circularis

29
Q 
Caecum:
• Location?
• Continuous with?
• Width?
• Covering?
• Relevance of peritoneal recesses around it?
• What converges?
A
  • 1st part of large intestine
  • Lies below the junction of the ileum with the large intestine in the right iliac fossa
  • Continuous with the ascending colon
  • A pouch of ~ 7.5cm
  • Covered by peritoneum but NOT on a mesentery
  • Variable peritoneal recesses may form adjacent to it, but these are more important in relation to the vermiform appendix that may be found in any of these recesses
  • 3 taeniae coli converge in the caecum at the root of the vermiform appendix
30
Q

How to find appendix during surgery?

A

3 taeniae coli converge in the caecum at the root of the vermiform appendix

31
Q

What and where is McBurney’s point?

A
  • Root of vermiform appendix

* 1/3 up from ASIS to umbilicus

32
Q

What is the vermiform appendix?

A

Narrow blind ended tube hanging from the caecum

33
Q

What is the vermiform appendix packed full of?

A

Lymphoid tissue

34
Q

Where is the vermiform appendix suspended from?

A

Suspended on a short but highly variable mesoappendix that transmits the appendicular vessels

35
Q

What are the different possible anatomical positions of the vermiform appendix?

A
  1. Pelvic
  2. Subcaecal
  3. Retrocaecal
  4. Retroileal (postileal)
  5. Preileal
36
Q

Caecum and vermiform appendix blood supply?

A

All derived from the ileocolic artery of the SMA:

  1. Anterior caecal a.
  2. Posterior caecal a.
  3. Appendicular a.
37
Q

Caecum and vermiform appendix lymph drainage?

A

To the nodes on the SMA

38
Q

What may be affected by appendicitis?

A
  • Appendicular artery - close and parallel to appendix

* May become obstructed => gangrene and rupture of the vermiform appendix

39
Q

What is the appendicular artery derived from?

A
  • Ileocolic branch of the SMA

* Nerves derived from T10/ T11

40
Q

Early appendicitis refers pain to…

A
  • Periumbilical region (T10)
  • Pain moves to the right inguinal region over time when the parietal peritoneum is involved (same nerve supply as overlying skin)
41
Q

Describe the features of ascending colon

A
  • ~ 13cm long in the right lumbar region
  • Retroperitoneal
  • Related to the liver at the hepatic (right colic) flexure
42
Q

Describe the features of the descending colon

A
  • ~ 25cm in the left lumbar region
  • Retroperitoneal
  • Related to the spleen at the splenic (left colic) flexure
43
Q

Describe the features of the transverse colon

A
  • ~ 38cm long
  • Intraperitoneal
  • Suspended by the transverse mesocolon
44
Q

Describe the features of the sigmoid colon

A
  • ~ 25-38cm long
  • Intraperitoneal
  • Suspended by the sigmoid mesocolon
  • Continuation of the descending colon in front of the pelvic brim/ inlet
  • Continuous with the rectum in front of the 3rd sacral vertebra
45
Q

What does the root of the transverse mesocolon cross?

A

Crosses the inferior edge of the pancreas

46
Q

What happens when a mobile sigmoid colon rotates upon itself?

A

Sigmoid volvulus

47
Q

What is the result of colonic diverticula?

A

May become obstructed and mimic left sided “appendicitis”

48
Q

List the blood supply of the large intestine?

A
  1. Superior mesenteric artery: ileocolic, right colic + middle colic branches
  2. Inferior mesenteric artery: left colic + sigmoid branches
49
Q

Superior mesenteric artery

A 
Branches: 
• Ileocolic
• Right colic 
• Middle colic 
- to caecum, ascending colon, hepatic (right colic) flexure and 2/3 of the transverse colon
50
Q 
Inferior mesenteric artery:
• Supplies?
• Carries which nerves?
• Forms which anastomosis?
• Forms collateral in the event of what?
A
  1. Left colic
  2. Sigmoid branches
    - -> 1/3 of the transverse colon, the splenic (left colic) flexure, descending colon and sigmoid colon
  • IMA ends up as superior rectal artery - rectum and anal canal
  • Arises from aorta at L3
  • Carries sympathetic nerves derived from T12 (least splanchnic nerves) + parasympathetic from S2,3,4 (NOT vagus)
  • Forms an important anastomosis with the SMA known as the marginal artery (of Drummond) that may form a collateral circulation should the IMA becomes obstructed
51
Q

What is the marginal artery (of Drummond)?

A
  • Important anastomosis between IMA and SMA

* May form a collateral circulation should the IMA become obstructed

52
Q

What does the inferior mesenteric artery end up as?

A

Superior rectal artery

- supplies rectum and anal canal

53
Q

What is the venous drainage of the large intestine?

A

Veins run with arteries and drain into the portal vein

54
Q

What is the lymphatic drainage of the large intestine?

A

Into the nodes on the superior and inferior mesenteries arteries

55
Q

What is the referred pain of the abdomen?

A

Autonomic nerves run with the 3 arteries:

  1. Celiac trunk:
    - to foregut (lower oesophagus, stomach, duodenum)
    • Referred to upper abdomen (T7-T9)
  2. Superior mesenteric:
    - to midgut (duodenum to 2/3 transverse colon)
    • Referred pain to periumbilical region (T10)
  3. Inferior mesentericL
    - to hindgut
    • Referred to suprapubic region (T12)
56
Q

Why can’t the brain localise visceral pain?

A
  • Due to afferents running with the efferent sympathetic nerves derived from T7 to T12
  • Pain localisation occurs with involvement of the overlying parietal peritoneum
57
Q

What is Hirschsprung Disease?

A

Lack of normal development of the colonic innervation leads to a constricted aganglionic segment of bowel with a distended segment proximally the innervation of which is normal

58
Q

Describe the features of the rectum

A
  • ~ 13cm long
  • Retroperitoneal
  • Begins in front of the 3rd sacral vertebra
  • Follows the curve of the sacrum and coccyx
  • Ends in front of the tip of the coccyx by piercing the pelvic diaphragm and coming continuous with the anal canal
  • Stores faeces
59
Q

Describe the features of the anal canal

A
  • ~ 4cm long
  • From the rectal ampulla to the anus
  • Conduit to outside world

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