Abdomen VIII - Large Intestine

Question 0

Superior mesenteric plexus: what kind of nerve fibers & where do they come from?

Answer 0

Sympathetic: from lower thoracic spinal nerves Parasympathetic: from vagus nerve

Question 1

The mesoappendix derives from the posterior side of what mesentery?

Answer 1

Mesentery of the terminal ileum

Question 2

The position of the appendix is variable but it is usually…?

Answer 2

Retrocecal

Question 3

What is the McBuney point on the spinoumbilical line?

Answer 3

Appendix is deep to this point

Question 4

What is the usual cause of appendicitis in young people?

Answer 4

Hyperplasia of lymphatic follicles in appendix (occludes lumen)

Question 5

What is the usual cause of appendicitis in older people?

Answer 5

Obstruction from a FECALITH (Concentration formed around fecal matter) - trapped secretions from appendix cause swelling

Question 6

Why is appendicitis related pain usually periumbilical?

Answer 6

Afferent nerve fibres from appendix enter spinal cord at T10 level

Question 7

Acute appendicitis may result in..?

Answer 7

Thrombosis in appendicular artery (may result in ischemia, gangrene, and perforation of appendix)

Question 8

What nerve has to be retracted during an appendectomy?

Answer 8

Iliohypogastric nerve

Question 9

What separates the ascending colon from the anterolateral abdominal wall?

Answer 9

Greater omentum

Question 10

Right paracolic gutter

Answer 10

Deep vertical groove between lateral aspect of ascending colon & adjacent abdominal wall

Question 11

Juxtacolic artery (marginal artery)

Answer 11

Anastomoses between ileocolic a., right colic a., middle colic a., left colic a., sigmoid a. branches (parallels length of colon close to mesenteric border)

Question 12

Volvulus of the colon:

Answer 12

Obstruction of intestine resulting from twisting

Question 13

Cecopexy:

Answer 13

• may help avoid volvulus & colon obstruction - procedure: tenia coli of cecum + proximal ascending colon sutured to abdominal wall

Question 14

Compare the splenic flexure to the hepatic flexure

Answer 14

Splenic: - more superior - more acute - less mobile

Question 15

What attaches the transverse colon to the diaphragm?

Answer 15

Phrenicocolic ligament

Question 16

Transverse mesocolon is fused with what structure as it loops down inferiority?

Answer 16

Posterior wall of omental bursa

Question 17

The root of the transverse mesocolon is continuous with…

Answer 17

Parietal peritoneum posteriorly (along inferior border of pancreas)

Question 18

Left paracolic gutter:

Answer 18

Deep v-shaped crevice between descending colon & adjacent abdominal wall

Question 19

Sigmoid colon extends from:

Answer 19

Iliac fossa to S3 segment (joins rectum) RECTOSiGMOID junction: termination of teniae coli (approx. 15cm from anus)

Question 20

Root of sigmoid mesocolon:

Answer 20

• inverted v-shaped attachment - medially, superiorly along external iliac vessels - medially, inferiorly from bifurcation of common iliac vessels to anterior aspect of sacrum

Question 21

Which branches of the IMA anastomose to form the marginal artery?

Answer 21

Superior branch of most superior sigmoid artery + descending branch of left colic artery

Question 22

What is the only organ that is both retroperitoneal & subperitoneal?

Answer 22

Rectum

Question 23

Colitis

Answer 23

Chronic inflammation (ulcerative colitis, Crohn’s disease) - colectomy may be performed (terminal ileum, colon, rectum, anal canal removed) = ileostomy

Question 24

Diverticulosis

Answer 24

Multiple false diverticula along intestine - 60% in sigmoid colon (fibres change direction here) - Middle Aged + elderly - colonic diverticula = not true diverticula b/c protrusions = mucosa only, not entire colon wall

Question 25

Diverticulosis

Answer 25

Most commonly on mesenteric side of 2 nonmesenteric teniae coli - nutrient arteries perforate muscle coat to reach submucosa - diverticula can get infected/rupture = diverticulitis; can erode nutrient arteries = hemorrhage

Question 27

main functions of LARGE INTESTINE

Answer 27

• water is absorbed from indigestible residues of liquid chyme
• converted into semisolid stool/feces
• stored temporarily + accumulates until defecation occurs

Question 28

large intestine consists of:

Answer 28

cecum

appendix

ascending colon

transverse colon

descending colon

sigmoid colon

rectum

anal canal

Question 29

The large intestine can be distinguished from the small intestine by:

Answer 29

1. Omental appendices: small, fatty, omentum-like projections

2. Haustra: sacculations of the wall of the colon between teniae

3. A much greater caliber (internal diameter)

**4. Three teniae coli: **

• *Mesocolic = *transverse + sigmoid mesocolons attach
• Omental = omental appendices attach
• Free (libera) = neither mesocolons nor omental appendices attach

Question 30

TENIAE COLI

Answer 30

thickened bands of smooth muscle (most of longitudinal coat)

• begin: base of appendix; thick longitudinal layer of the appendix splits to form three bands
• run the length of the large intestine
• end: merge at rectosigmoid junction into a continuous longitudinal layer around rectum
• teniae are shorter than intestine = colon becomes sacculated between teniae = haustra

Question 31

CECUM

Answer 31

1st part of large intestine; continuous with ascending colon

• blind intestinal pouch (7.5 cm in length/breadth)
• right lower quadrant (lies in iliac fossa inferior to junction of terminal ileum + cecum)
• usually lies within 2.5 cm of inguinal ligament
• almost entirely enveloped by peritoneum
• can be lifted freely; has no mesentery (can be displaced)
• may be bound to lateral ab. wall by one or more cecal folds of peritoneum

Question 32

terminal ileum enters the cecum obliquely and partly invaginates into it. What does this form?

Answer 32

• ileocolic lips (superior and inferior) at the ileal orifice, which form the ileal papilla
• folds meet laterally = ridges = “frenula of the valve”
• when cecum is distended or contracts, frenula tighten = closing the valve to prevent reflux from the cecum into ileum

Question 33

ileal orifice

Answer 33

• circular muscle is poorly developed around the orifice; valve is unlikely to have any sphincteric action that controls passage of intestinal contents from ileum into cecum
• **probably does prevent reflux from the cecum into the ileum **
• orifice is usually closed by tonic contraction = appears as the ileal papilla on the cecal side

Question 34

APPENDIX

Answer 34

(vermiform appendix)

• blind intestinal diverticulum (6-10 cm in length); contains masses of lymphoid tissue
• arises from posteromedial aspect of cecum inferior to the ileocecal junction
• has a short triangular mesentery, mesoappendix; derived from posterior side of mesentery of terminal ileum
• mesoappendix attaches to cecum + proximal part of appendix

Question 35

ileocolic artery &

ileocolic vein

Answer 35

ileocolic artery:

• terminal branch of superior mesenteric artery
• supplies cecum
• branch = appendicular artery; supplies appendix

ileocolic vein:

• tributary of superior mesenteric vein
• drains blood from cecum & appendix

Question 36

The lymphatic vessels from the cecum and appendix pass to which lymph nodes?

Answer 36

• lymph nodes in mesoappendix
• ileocolic lymph nodes that lie along ileocolic artery

*Efferent lymphatic vessels pass to superior mesenteric lymph nodes

Question 37

The nerve supply to the cecum and appendix derives from…

Answer 37

sympathetic and parasympathetic nerves from the superior mesenteric plexus

• sympathetic origin = lower thoracic spinal cord
• parasympathetic = derive from vagus nerves

Afferent nerve fibers from appendix accompany sympathetic nerves to T10 segment of spinal cord