Gastrointestinal Tract

  • foregut (pharynx>mid 2nd part duodenum)
  • midgud (>2/3 transverse colon/splenic flexure)
  • hindgut (>rectum)
  • Layers include mucosa (epithelium, lamina propria and mascularis mucosae), submucosa (vascular and lymphatics, autonomic nerve plexus), muscularis propria (inner circular and outer longitudinal layers) and serosa/adventitia (apart from oesophagus). Lymphatics in mucosa (mucosa-associated lymphoid tissue MALT) and submucosa.

Oesophagus ~25cm

  • cricoid @ C6>cardiac orifice of stomach @ T10
  • cervical, thoracic and abdominal portions
  • sling of muscle from right crus of diaphragm
  • oesophageal groove on posterior liver
  • fibrous adventitia, muscular, submucous and mucous layers, no serosal layer
  • superficial longitudinal and inner circular (forming functional GOJ sphincter) muscles (upper 1/3 striated, lower 1/3 smooth)
  • longitudinal folds (3mm)
  • tracheoesophageal fistula (V)
  • duplication of oesophagus (V)


  • A cervical = recurrent laryngeal n, trachea; A thorax = L main bronchus, right PA, LA, upper LV, pericardium, vagal plexus; A abdo = liver
  • P cervical = prevertebral mm; P thorax = thoracic duct, azygos and hemiazygos v, R posterior intercostal aa; P abdo = right crus, aorta
  • lat cervical = thyroid, carotid sheath
  • R thoracic = azygos, R lung, thoracic duct; R abdo = right crus
  • L thoracic = L SCA, ao.arch, L lung; L>P = descending aorta; L abdo = sling from R crus, L crus

Arterial Supply

  • upper < inferior thyroid <subclavian a
  • middle <oesophageal branches < descending aorta
  • lower < oesophageal branches <left gastric a

Venous Supply

  • upper> inferior thyroid vv > brachiocephalic vv
  • middle > azygos
  • lower > left gastric v


  • upper > deep cervical nodes
  • middle > paraoesophageal plexus > posterior mediastinal nodes > supraclavicular nodes
  • lower > left gastic and coeliac pre-aortic nodes

Radiological Anatomy

  • constrictions on Ba swallow: cricopharyngeus (C5/6 with cricoid ant), submucosal plexus of v (= postcricoid venous plexus; ant), (aberrant right/left subclavian), aortic arch (ant-L), (anomalous left PA), left main bronchus (ant-L), (enlarged LA), oesophageal hiatus
  • Distal oesophageal rings:
    • A ring (muscular ring) = tubulovestibular junction, muscular ring, inferior oesophageal sphincter
    • oesophageal vestibule – just above OGJ/B ring/Z line. Mid vestibule in oesophageal hiatus, opens and moves superior with swallowing.
    • B ring – mucosal ring, move up to 10mm above diaphragm on swallowing. Schatzki’s ring when pathlogically narrowed causing dysphagia.
    • Z line = ragged mucosal junction (OGJ) between oesophageal suqamous and gastric columnar epithelium, at level of B ring.

Stomach ~1500mL

  • lesser and greater curvatures
  • incisura angularis (at inferior lesser curve)
  • cardiac orifice at gastro-oesophageal junction
  • cardia (at GOJ), fundus (above GOJ), body (betw cardia and incursura) and pyloris (antrum + canal)
  • pyloric antrum (section from incisura)
  • pyloric canal (L1, 2.5cm R of midline
  • rugae (3-5mm thick, longitudinal at lesser = magenstrasse, mosaic at greater curve)
  • areae gastricae (2-3mm nodular elevations esp antrum, may be fine reticular to coarse nodular pattern)
  • serosa, muscular layer, submucosa and mucosa
  • inner oblique m (incomplete, form magenstrasse)
  • middle circular m (forming pyloric sphincter)
  • outer longitudinal m (at greater and lesser curves, from gastro-oesophageal shpincter)
  • Parietal cells (produce HCl) and cheif cells (pepsin precursors) in fundus and body.


  • A = abdominal wall, diaphragm, left liver
  • P = lesser sac
  • P/I = stomach bed: diaphgram, aorta, CT (with nodes and plexus), L suprarenal, L kidney, splenic a, pancreas, spleen, transverse colon
  • L = splenic flexure
  • R = L lobe liver

Vascular supply

  • left and right gastric arteries
  • left and right gastroepiploic arteries
  • short gastric arteries
  • anastomoses within stomach wall


  • left gastric > coeliac lymph nodes
  • right gastric, gastroepiploic > retroduodenal > coeliac nodes
  • short gastric and L gastroepiploic > splenic hilum nodes > retropancreatic > coeliac nodes

Duodenum ~25cm

  • first 2.5cm intraperitoneal, rest retroperitoneal
  • plicae circulares = valvulae conniventes (encircle 2/3 inner mucosa)
  • outer longitudinal and inner circular muscle layers
  • reversed rotation (V, transverse colon behind vessels and duodenum in front, causing duodenal obstruction from peritoneal fold)

First/Superior part ~5cm, L1

  • duodenal cap/bulb (first 2cm; conical with rugae; gallbladder impression; attached to greater and lesser omentum)
  • passes S-R-P from pylorus


  • A = segment 4 of liver, GB
  • P = lesser sac, GDA, bile duct, portal v, splenic v, SMV, IVC
  • S = epiploic foramen
  • I = pancreatic head

Second/Descending Part ~8cm, L2-3

  • aortic impression
  • (major) duodenal papilla = ampulla of Vater (P/med, 2/3 down, 8-10cm from pylorus)
    • sphincter of Oddi around ampulla of Vater
    • superior hooded fold and distal longitudinal folds
  • minor duodenal papilla (V; accessory duct 2cm proximal and more anterior to major papilla)
  • valvulae conniventes proper begin (constant despite hypotonic agents)


  • A = GB, right liver, transverse mesocolon, jejunum
  • P = R adrenal, kidney and ureter
  • P/med = pancreatic and bile ducts
  • med = pancreatic head
  • lat = ascending colon, hepatic flexure, right liver

Third/Inferior/Horizontal Part ~8cm, L3


  • A = SMA/V, root SB mesentery, jejunum
  • P = R ureter, psoas, gonadal vessels, IVC, aorta, L3
  • S = pancreas
  • I = jejunum

Forth/Ascending Part ~4cm, L2

  • ligament of Treitz = suspensory muscle of duodenum (DJ flexure @ highest 4th part [L and same/sup level to 1st part]> left crus)
  • paraduodenal fossa (betw ligament of Trietz and peritoneal fold from inferior mesenteric vessels)


  • A = jejunum, root SB mesentery, stomach
  • P = aorta, left psoas
  • med = aorta
  • lat = paraduodenal fossa, IMA/V

Vascular Supply

  • duodenal cap < R gastric and R gastoepiploic aa; >prepyloric vein (of Mayo)> portal vein
  • superior (>mid 2nd part) and inferior pancreaticoduodenal arteries


  • proximal pancreaticoduodenal nodes > gastroduodenal/pyloric nodes > coeliac nodes
  • distal pancreaticoduodenal nodes > superior mesenteric nodes

Small Intestine 3-10m, ~6m

  • jejunum proximal 2/5 (3.0-3.5cm), ileum distal 3/5 (2.5cm)
  • duodenojegunal flexure
  • root of mesentery L L2>R sacroiliac joint, 15cm
  • plicae circulares = valvulae conniventes become thinner (2>1mm) and less prominent, deeper and more numerous through ileum
  • lymphoid follicles may aggregate into Peyer\’s patches on antimesenteric border of ileum, becoming smaller and more numerous (feather-like in jejunum)
  • wall of SB (~3mm)gets thinner in ileum


  • A = anterior abdo wall
  • P = D3/4, aorta, IVC, R gonadal vessels, ureter, psoas

Vascular and Lymphatic Supply

  • SMA, jejunal, ileal and ileocolic arteries and veins
  • jejunal mesenteric arcades (1-2) with long infrequent branches, ileal arcades (3-4) with numerous short branches > vasa recta (end arteries) that enter wall
  • lymph > superior mesenteric group of preaortic nodes


  • Meckel’s diverticulum (2%, remnant vitellointestinal duct at antimesenteric border of ileum 60[15-350]cm/2ft from ileocaecal valve, up to 15cm/usually 2in long, may contain gastric mucosa, hepatic or pancreatic tissue at apex)
  • persistent vitellointestinal fistula, cyst (along path) or raspberry tumour (of umbilicus)
  • duplication of lumen or stenosis = abnormal recanalisation
  • volvulus neonatorum (volvulus around narrow pedicle of SB mesentery from non-descended caecum)
  • malrotation
    • nonrotation (SMA to right of SMV, small intestine on right and colon on left)
      • incomplete rotation (failure of midgut to rotate final 90°; caecum inferior to pylorus)
    • exomphalos (persistent midgut herniation)

Large Intestine = Colon ~1.5m

  • caecum 9cm, transverse colon 5.5cm
  • taeniae coli (3 bands: anterior, posteromedial and posterolateral, converge on appx and rectum, thickenings of longitudinal m; 30cm shorter than colon)
  • haustra = sacculations (incomplete separations, may be absent hindgut)
  • appendices epiploicae (multiple in sigmoid, sparse in caecum and rectum; with perforating arteries)
  • intestinal glands/crypts of Lieberkuhn (mucous glands in colon mucosa, 1mm deep)
  • innominate grooves (from linear collections of lymphoid tissue connecting crypts)
  • lymphoid follicles (1-3mm elevations, larger in rectum 4mm dia)
  • Chilaiditi syndrome (V, asymptomatic hepatodiaphragmatic interposition of intestine, commoner in chronic lung disease)

Caecum ~6cm

  • vascular fold of caecum (containing anterior caecal a)
  • superior ileocaecal fossa/recess (betw vascular fold and terminal ileum)
  • ileocaecal fold = bloodless fold of Treves (inf to iliocaecal junction)
  • inferior ileocaecal fossa (post to ileocaecal fold)
  • retrocaecal fossa
  • ileocaecal valve (P/med junction of caecum and ascending colon)
    • upper and lower folds/lips
    • frenula of valve (lateral extensions of folds, thickend posterior ends of 1st haustral fold)
    • sphincter (thickening of circular muscle of ileum)
  • anterior and posterior caecal arteries < ileocolic a
  • terminal branches colic artery < ileocolic a
  • lymph > epicolic nodes (med to gut) > paracolic nodes > superior mesenteric group of para-aortic nodes
  • Ladd’s band (V, caecum fails to descend and peritoneal fold fixes to duodenum causing obstruction)


  • A = SB, greater omentum, abdo wall
  • P = psoas, iliacus, femoral nerve, lateral cutaneous nerve of the thigh, appendix
  • P/med = appendix origin

(Vermiform) Appendix ~12-24cm

  • post-med caecum 2.5cm below ileocaecal junction
  • mesoappendix
  • appendix tip retrocaecal (64%, may be fused to caecum or posterior abdo wall), inferomedial (36%) or superomedial (0.5%)
  • lumen of appendix wide in infant, obliterated after mid-adult life
  • faecoliths and fluid levels in appendix seen in 10%
  • appendicular artery < posterior caecal artery
  • appendicular vein > posterior caecal vein
  • lymph > paracolic nodes > superior mesenteric group

Ascending/Right Colon ~15cm

  • >hepatic flexure
  • ileocolic, right colic and middle colic aa
  • lymph > epicolic nodes > peripancreatic > superior mesenteric group of para-aortic nodes


  • A = SB, greater omentum, abdo wall
  • P = iliac crest, iliacus, quadrates lumborum m, origin transversalis abdominis, iliohypogastric n, ilioinguinal n, genitofemoral n
  • med = right infracolic space
  • lat = R paracolic gutter

Transverse Colon ~45cm

  • >splenic flexure
  • transverse mesocolon
  • phrenicocolic ligament
  • gastrocolic ligament and greater omentum
  • middle colic artery (prox 2/3-all) < SMA
  • ascending branch of left colic artery (dist 1/3-none) < IMA
  • lymph > superior and inferior mesenteric nodes


  • A = liver, greater omentum, spleen, abdo wall
  • P = inferior R kidney, D2, pancreas, inferior L kidney, SB

Descending Colon ~30cm

  • lymph > inferior mesenteric nodes


  • A = SB, greater omentum, abdo wall
  • P = left kidney, origin transversalis abdominis, quadrates lyumborum, iliac crest, iliacus, left psoas, iliohypogastric n, ilioinguinal n, genitofemoral n, lateral cutaneous n of the thigh, femoral n

Sigmoid Colon ~45cm

  • pelvic brim > rectum
  • sigmoid mesocolon
  • loss of haustra, becoming featureless with age
  • sigmoid branches of the IMA (3-4)
  • lymph > inferior mesenteric nodes


  • A = bladder or uterus and upper vagina
  • P = rectum, sacrum, terminal ileum

Rectum ~13cm

  • S3>anal canal
  • peritoneum over front and sides in upper 1/3, over the front in middle 1/3, none in lower 1/3
  • valves of Houston = horizontal shelves/valves (2 on left, 1 on right)
  • rectal ampulla (distal rectum storing faeces)
  • perirectal space/fat
  • perirectal/mesorectal fascia (Denonvillier\’s fascia = anterior part, separating from seminal vesicles and prostate)
  • pararectal fat
  • postrectal space <1.5cm
  • superior rectal artery < IMA
  • middle rectal artery < internal iliac artery
  • inferior rectal artery > lower 1/3
  • median sacral artery (post) <aorta
  • lymph > pararectal nodes in perirectal connective tissue; upper 2/3 > inferior mesenteric nodes; lower 1/3 > internal iliac nodes


  • A = sigmoid, ileum, rectouterine pouch (F), uterus, occasionally ovaries; lower 1/3 A = Denonvillier’s fascia, bladder, vas deferens, seminal vesicles, prostate gland, vagina
  • P = sacrum, coccyx, piriformis, coccygeus, levatores ani m, sacral plexus, sympathetic trunk

Anal Canal ~3cm

  • pelvic floor > skin
  • puborectal sling causes anorectal junction angled 90° posteriorly
  • mucous membrane upper 2/3, skin lower 1/3
  • anorectal line (upp margins of columns)
  • anal columns (of Morgagni) = vertical folds (6-10)
  • anal valves = valves of Ball (joined lower anal columns)
  • pectinate/anocutaneous/mucocutaneous/dentate/Hilton’s white line (lower margins of columns; boundary between upper 2/3 and lower 1/3 marking division of a/v/lymph supply)
  • internal sphincter (upper 2/3, smooth m, thickening circular m, thicker anteriorly)
  • external sphincter (lower 2/3, striated m, blends with levator ani)
    • subcutaneous (beneath skin)
    • superficial (anococcygeal raphe [tip coccyx>post anus] > perineal body)
    • deep (annular) > puborectalis m
  • inferior rectal artery < internal pudendal a < IIA (lower half; anastamoses with middle rectal @ anorectal junc)
  • lymph > inferior mesenteric nodes, medial group of superficial inguinal nodes
  • anorectal junction at rest @ level of ischial tuberosities; defaecation descends 30mm and anorectal angle 90°>115°


  • A = perineal body, membranous urethra, bulb of penis, lower vagina
  • P = anococcygeal body
  • lat = ischiorectal fossae