Abdomen VIII - Large Intestine Flashcards
Superior mesenteric plexus: what kind of nerve fibers & where do they come from?
Sympathetic: from lower thoracic spinal nerves Parasympathetic: from vagus nerve
The mesoappendix derives from the posterior side of what mesentery?
Mesentery of the terminal ileum
The position of the appendix is variable but it is usually…?
Retrocecal
What is the McBuney point on the spinoumbilical line?
Appendix is deep to this point
What is the usual cause of appendicitis in young people?
Hyperplasia of lymphatic follicles in appendix (occludes lumen)
What is the usual cause of appendicitis in older people?
Obstruction from a FECALITH (Concentration formed around fecal matter) - trapped secretions from appendix cause swelling
Why is appendicitis related pain usually periumbilical?
Afferent nerve fibres from appendix enter spinal cord at T10 level
Acute appendicitis may result in..?
Thrombosis in appendicular artery (may result in ischemia, gangrene, and perforation of appendix)
What nerve has to be retracted during an appendectomy?
Iliohypogastric nerve
What separates the ascending colon from the anterolateral abdominal wall?
Greater omentum
Right paracolic gutter
Deep vertical groove between lateral aspect of ascending colon & adjacent abdominal wall
Juxtacolic artery (marginal artery)
Anastomoses between ileocolic a., right colic a., middle colic a., left colic a., sigmoid a. branches (parallels length of colon close to mesenteric border)
Volvulus of the colon:
Obstruction of intestine resulting from twisting
Cecopexy:
- may help avoid volvulus & colon obstruction - procedure: tenia coli of cecum + proximal ascending colon sutured to abdominal wall
Compare the splenic flexure to the hepatic flexure
Splenic: - more superior - more acute - less mobile
What attaches the transverse colon to the diaphragm?
Phrenicocolic ligament
Transverse mesocolon is fused with what structure as it loops down inferiority?
Posterior wall of omental bursa
The root of the transverse mesocolon is continuous with…
Parietal peritoneum posteriorly (along inferior border of pancreas)
Left paracolic gutter:
Deep v-shaped crevice between descending colon & adjacent abdominal wall
Sigmoid colon extends from:
Iliac fossa to S3 segment (joins rectum) RECTOSiGMOID junction: termination of teniae coli (approx. 15cm from anus)
Root of sigmoid mesocolon:
- inverted v-shaped attachment - medially, superiorly along external iliac vessels - medially, inferiorly from bifurcation of common iliac vessels to anterior aspect of sacrum
Which branches of the IMA anastomose to form the marginal artery?
Superior branch of most superior sigmoid artery + descending branch of left colic artery
What is the only organ that is both retroperitoneal & subperitoneal?
Rectum
Colitis
Chronic inflammation (ulcerative colitis, Crohn’s disease) - colectomy may be performed (terminal ileum, colon, rectum, anal canal removed) = ileostomy
Diverticulosis
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
Diverticulosis
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
main functions of LARGE INTESTINE
- water is absorbed from indigestible residues of liquid chyme
- converted into semisolid stool/feces
- stored temporarily + accumulates until defecation occurs
large intestine consists of:
cecum
appendix
ascending colon
transverse colon
descending colon
sigmoid colon
rectum
anal canal
The large intestine can be distinguished from the small intestine by:
1. Omental appendices: small, fatty, omentum-like projections
2. Haustra: sacculations of the wall of the colon between teniae
- 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
TENIAE COLI
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
CECUM
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
terminal ileum enters the cecum obliquely and partly invaginates into it. What does this form?
- 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
ileal orifice
- 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
APPENDIX
(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
ileocolic artery &
ileocolic vein
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
The lymphatic vessels from the cecum and appendix pass to which lymph nodes?
- lymph nodes in mesoappendix
- ileocolic lymph nodes that lie along ileocolic artery
*Efferent lymphatic vessels pass to superior mesenteric lymph nodes
The nerve supply to the cecum and appendix derives from…
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
