Abdomen: Small and Large Intestines Flashcards
Mesentery of small intestines
- Jejunum
- Ileum
Duodenum
- Widest, least mobile of the SI (mostly retroperitoneal)
- Derived from foregut and midgut
- “Cs” the head of the pancreas
4 parts of the duodenum
- Upper
- Descending
- Horizontal or inferior
- Ascending
Upper (1st part) duodenum
- Intraperitoneal
- Portal triad and IVC are posterior
Descending (2nd part) duodenum
- Receives bile and pancreatic ducts (division between fore- and midgut)
Horizontal/inferior (3rd part) duodenum
- Anterior to IVC, aorta, vertebral column
- Posterior to SMA and SMV
Ascending (4th part) duodenum
- Joins jejunum at the duodenojejunal flexure
- Supported by suspensory muscle of duodenum (ligament of Trietz)
Ligament of Trietz
- Fibromuscular band originating from the right crus of diaphragm
Duodenum blood supply
- Branches from celiac trunk and superior mesenteric artery
- Branches from gastroduodenal
- Branches from SMA
Branches from gastroduodenal supplying blood to duodenum
- Supraduodenal
- Anterior superior pancreaticoduodenal
- Posterior superior pancreaticoduodenal
Branches from SMA supplying blood to duodenum
- Anterior inferior pancreaticoduondenal
- Posterior inferior pancreaticoduondenal
Jejunum and Ileum
- 6-7 m long
- Suspended from posterior abdominal wall by mesentery
Jejunum
- Proximal 2/5 of small intestines
- Often empty (after death, hence its name)
Jejunum (compared to ileum)
- Thicker wall
- Greater vascularity
- Circular folds are more dense/taller
- Less mesenteric fat
Ileum
- Distal 3/5 of small intestines
Blood supply of jejunum and ileum
- Expansive
- Superior mesenteric artery (jejunal and ileal branches)
Superior mesenteric artery (SMA)
- Originates from abdominal aorta (~1cm below celiac trunk)
- Travels in the small intestine mesentery
Arteries of jejunum
- Fewer arcades
- Longer vasa recta
Arteries of ileum
- Many arcades
- Shorter vasa recta
Large intestines function
- Water absorption
- Fecal storage
Large intestine consists of
- Cecum
- Appendix
- Colon (ascending, transverse, descending, sigmoid)
- Rectum
- Anal canal
Omental appendices
- Small fatty projections
- Not really present on appendix, cecum, rectum
Tenia coli
- 3 bands of longitudinal muscle
- Begin at base of appendix
- Blend with longitudinal muscle of rectum
Haustra
- Wall sacculations that give the colon a segmented appearance
Cecum
- Blind end pouch below the ileocolic (ileocecal) junction
- Right lower quadrant
- Very mobile (covered by peritoneum)
- Internal: Ileocecal valve (passive valve)
Blind end pouch below the ileocolic/ileocecal junction (cecum)
- 2nd most common site of volvulus
Right lower quadrant of cecum
- Lies in the iliac fossa on the psoas and iliacus muscles
Internal: Ileocecal valve (passive valve) of cecum contains
- Ileal orifice
- Lips and frenulum of ileocecal valve
- Orifice of appendix
Appendix (vermiform appendix)
- Worm-like diverticulum (6-10cm)
- Variable location
Appendix (vermiform appendix) lacks
- Tenia coli and haustra
Appendix (vermiform appendix) contains
- Lymphoid tissue
- Has its own mesentery (mesoappendix)
Appendicitis
- Inflammation of the appendix
Appendicitis is caused by
- Obstruction (fecalith)
- Lymph follicle hyperplasia
Signs and symptoms of appendicitis
- Early dull pain in the peri-umbilical region
- Later severe pain in right lower quadrant
- Tenderness around McBurney’s point
Reason for early dull pain in the peri-umbilical region in appendicitis
- Afferent fibers enter cord at T10
- Referred pain
Reason for later severe pain in right lower quadrant in appendicitis
- Parietal peritoneum irritation
McBurney’s point
- About 1.5 - 2 inches on a line from the ASIS to the umbilicus (spino-umbilical line)
Techniques used for removal of appendix
- Muscle splitting technique of McBurney (open appendectomy)
- Laparoscopic appendectomy is commonly performed
Ascending colon
- Up to right colic (hepatic) flexure
- Secondarily retroperitoneal
Transverse colon
- Up to left colic (splenic) flexure
- Very mobile
- Phrenicocolic ligament
Transverse colon is very mobile because of
- Transverse mesocolon (variable position)
Phrenicocolic ligament of transverse colon
- Peritoneum that connects left colic flexure to the diaphragm
Descending colon
- Up to left iliac fossa
- Secondarily retroperitoneal
Sigmoid colon
- S-shaped
- Iliac fossa to S3, joins rectum
- Has a mesentery (sigmoid mesocolon)
Sigmoid colon is the most common site of
- Volvulus
Rectosigmoid junction
- Site where sigmoid colon (from iliac fossa to S3) joins rectum
- Termination of teniae coli, lack of omental appendices
Colon primary blood supply
- Superior mesenteric artery
- Interior mesenteric artery
- Marginal artery (of Drummond)
- Vasa recta
Branches of SMA supplying colon
- Ileo-colic
- Right colic
- Middle colic
Ileo-colic artery supplies
- Cecum
- Ascending colon
- Appendix
- Ileum
Branches of ileo-colic artery supplying parts of the colon
- Colic and ilieal branches
- Appendicular
- Anterior and posterior cecal
Right colic artery primarily supplies
- Ascending colon
Branches of right colic artery supplying parts of the colon
- Ascending and descending branches
Middle colic artery primarily supplies
- Transverse colon
Branches of middle colic artery supplying parts of the colon
- Left and right branches
Branches of interior mesenteric artery
- Left Colic
- Sigmoid artery
- Superior rectal artery
Branches of left colic artery supplying parts of the colon
- Ascending and descending branches
Sigmoid artery primarily supplies
- Sigmoid colon
Superior rectal artery supplies
- Rectum
- Continuation of inferior mesenteric
Marginal artery (of Drummond)
- Continuous artery along the inner border of colon
- Connects SMA and IMA
- Allows for collateral blood flow in case of stenosis/blockage or ligature
Vasa recta
- Straight vessels that supply colon
Lymph drainage of colon invovles
- Superior mesenteric nodes
- Celiac nodes
- Inferior mesenteric nodes
Midgut lymph drains to
- Superior mesenteric nodes
Foregut lymph drains to
- Celiac nodes
Hindgut lymph drains to
- Inferior mesenteric nodes
All lymph drains from nodes to
- Intestinal lymph trunk > cisternal chyli > thoracic duct
Venous drainage of GI tract
- IMV drains into Splenic vein
- Splenic vein joins SMV to form portal vein
- Can have tri-union with IMV
Venous drainage of foregut
- Directly into portal vein
- Superior mesenteric vein
- Splenic vein
Venous drainage of midgut
- Superior mesenteric vein
Venous drainage of hindgut
- Inferior mesenteric vein
Portal vein (PV)
- Union of SMV and splenic veins
- Posterior to pancreas neck
- Runs in hepatoduodenal ligament
Portal-systemic (caval) anastomoses
- Connections between veins that drain into portal system with systemic venous system
- Collateral circulation if portal venous system becomes obstructed
Obstruction of portal venous system may cause
- Portal hypertension
Portal-systemic (caval) anastomoses connect to
- Left gastric (portal) and esophageal veins (systemic)
- Superior (portal) and inferior rectal veins (systemic)
- Paraumbilical veins (portal) and superficial epigastric veins (systemic)
- Veins of the GI tract and renal, lumbar, phrenic, suprarenal
Varicose veins
- Dilation of the systemic veins
Portal hypertension
- Increased pressure in portal vein
Liver cirrhosis can cause the following observable symptoms (example of portal hypertension)
- Ascites in the peritoneal cavity due to blood stasis of portal vein tributaries
- Internal hemorrhoids via the superior rectal vein
- Esophageal varices via the esophageal vein of the left gastric vein
- Caput medusa via superficial veins on the abdomen
Treatment for liver cirrhosis caused by portal hypertension
- Portosystemic shunts
- Transjugular intrahepatic portosystemic shunt (TIPSS)
- Liver transplant
