18 Anatomy of jejunum, ileum and large intestine

Question 1

What is the jejunum and ileum suspended on?

Answer 1

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

Question 2

How long is the jejunum and ileum?

Answer 2

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

Question 3

Where does the jejunum begin? Where does ileum end?

Answer 3

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

Question 4

Difference between jejunum and ileum

Answer 4

Jejunum:

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

Question 5

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

Answer 5

• 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

Question 6

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

Answer 6

• 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

Question 7

What are Peyer’s patches?

Answer 7

• Aggregations of lymphoid tissue

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

Question 8

What is the ileocaecal valve?

Answer 8

• 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

Question 9

Jejunum and ileum arterial blood supply?

Answer 9

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

Question 10

Jejunum and ileum venous blood supply?

Answer 10

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

Question 11

Jejunum and ileum lymphatic supply?

Answer 11

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

Question 12

Jejunum and ileum nerve supply?

Answer 12

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

Question 13

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

Answer 13

Periumbilical - T10

Question 14

Superior mesenteric artery arises from where?

Answer 14

Arises from aorta at L1

Question 15

Superor mesenteric artery carries which nerves?

Answer 15

Carries nerves (sympathetic) derived from T10 and T11

Question 16

What does superior mesenteric artery supply?

Answer 16

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

Question 17

What does the superior mesenteric artery form?

Answer 17

Forms a sequence of vascular anastomotic arcades in THE mesentery

Question 18

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

Answer 18

• Jejunum:

• less arcades
• long vasa recta

• Ileum:

• many arcades
• short vasa recta

Question 19

Intestinal lymph drainage via THE mesentery (digestion and protection)

Answer 19

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

Question 20

What is Meckel’s diverticulum?

Answer 20

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

Question 21

Where does large intestine start and end?

Answer 21

From caecum to the rectum and anal canal

Question 22

How long is the large intestine?

Answer 22

~ 1.5 m

Question 23

What structures make up the large intestine?

Answer 23

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

Question 24

Which parts of the large intestine are retroperitoneal?

Answer 24

Ascending and descending colon

Question 25

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

Answer 25

Transverse and sigmoid colon

Question 26

What is the function of the large intestine?

Answer 26

* Absorbs fluid and salts | * Dries out the chyme to form faeces

Question 27

What are the macroscopic external features of the large intestine?

Answer 27

* 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

Question 28

What are the macroscopic internal features of the large intestine?

Answer 28

* Lacks villi | * Lacks plicae circularis

Question 29

``` Caecum: • Location? • Continuous with? • Width? • Covering? • Relevance of peritoneal recesses around it? • What converges? ```

Answer 29

* 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

Question 30

How to find appendix during surgery?

Answer 30

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

Question 31

What and where is McBurney's point?

Answer 31

* Root of vermiform appendix | * 1/3 up from ASIS to umbilicus

Question 32

What is the vermiform appendix?

Answer 32

Narrow blind ended tube hanging from the caecum

Question 33

What is the vermiform appendix packed full of?

Answer 33

Lymphoid tissue

Question 34

Where is the vermiform appendix suspended from?

Answer 34

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

Question 35

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

Answer 35

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

Question 36

Caecum and vermiform appendix blood supply?

Answer 36

All derived from the ileocolic artery of the SMA: 1. Anterior caecal a. 2. Posterior caecal a. 3. Appendicular a.

Question 37

Caecum and vermiform appendix lymph drainage?

Answer 37

To the nodes on the SMA

Question 38

What may be affected by appendicitis?

Answer 38

* Appendicular artery - close and parallel to appendix | * May become obstructed => gangrene and rupture of the vermiform appendix

Question 39

What is the appendicular artery derived from?

Answer 39

* Ileocolic branch of the SMA | * Nerves derived from T10/ T11

Question 40

Early appendicitis refers pain to...

Answer 40

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

Question 41

Describe the features of ascending colon

Answer 41

* ~ 13cm long in the right lumbar region * Retroperitoneal * Related to the liver at the hepatic (right colic) flexure

Question 42

Describe the features of the descending colon

Answer 42

* ~ 25cm in the left lumbar region * Retroperitoneal * Related to the spleen at the splenic (left colic) flexure

Question 43

Describe the features of the transverse colon

Answer 43

* ~ 38cm long * Intraperitoneal * Suspended by the transverse mesocolon

Question 44

Describe the features of the sigmoid colon

Answer 44

* ~ 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

Question 45

What does the root of the transverse mesocolon cross?

Answer 45

Crosses the inferior edge of the pancreas

Question 46

What happens when a mobile sigmoid colon rotates upon itself?

Answer 46

Sigmoid volvulus

Question 47

What is the result of colonic diverticula?

Answer 47

May become obstructed and mimic left sided "appendicitis"

Question 48

List the blood supply of the large intestine?

Answer 48

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

Question 49

Superior mesenteric artery

Answer 49

``` Branches: • Ileocolic • Right colic • Middle colic - to caecum, ascending colon, hepatic (right colic) flexure and 2/3 of the transverse colon ```

Question 50

``` Inferior mesenteric artery: • Supplies? • Carries which nerves? • Forms which anastomosis? • Forms collateral in the event of what? ```

Answer 50

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

Question 51

What is the marginal artery (of Drummond)?

Answer 51

* Important anastomosis between IMA and SMA | * May form a collateral circulation should the IMA become obstructed

Question 52

What does the inferior mesenteric artery end up as?

Answer 52

Superior rectal artery | - supplies rectum and anal canal

Question 53

What is the venous drainage of the large intestine?

Answer 53

Veins run with arteries and drain into the portal vein

Question 54

What is the lymphatic drainage of the large intestine?

Answer 54

Into the nodes on the superior and inferior mesenteries arteries

Question 55

What is the referred pain of the abdomen?

Answer 55

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)

Question 56

Why can't the brain localise visceral pain?

Answer 56

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

Question 57

What is Hirschsprung Disease?

Answer 57

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

Question 58

Describe the features of the rectum

Answer 58

* ~ 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

Question 59

Describe the features of the anal canal

Answer 59

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