anatomy of lower gastrointestinal tract
DESCRIPTION
Anatomy of Lower Gastrointestinal Tract. Thanasil Huanmanop MD, M.Sc Anatomy Chula. LGIT = duodenojejunal junction - anus : Jejunoileum, large intestine & anal canal. Embryology : Foregut, Midgut, Hindgut. Vitelline duct. - PowerPoint PPT PresentationTRANSCRIPT
Anatomy of Lower Gastrointestinal Tract
Thanasil Huanmanop MD, M.ScAnatomy Chula
LGIT = duodenojejunal junction - anus :
Jejunoileum, large intestine & anal canal
Embryology : Foregut, Midgut, Hindgut
Vitelline duct
Small intestine - Jejunoileum :
> duodenojejunal junction - ileocaecal junction ( 20 ft )> proximal 1/3 LUQ , middle 1/3 periumbilical , distal 1/3 pelvis
Ligament of Treitz :
duodenojejunal flexure (L2) - Rt. crus of diaphragm
duodenum
jejunum
Ligamentof
TreitzCeliac trunk
Right crusof diaphragm
Lower GI tract
Ileocaecal junction :
Line ( Rt. ASIS - umbilicus ) X Rt. linear semilunaris , L5
Jejunoileum
Intraperitoneal organ
Anterior : greater omentum ( omental apron )
Posterior : mesentery proper to post. abdominal wall
• double-layered peritoneal fold • root 6-7 inches
Mesentery proper
Root of mesentery
Characteristic jejunum ileum
Length 8 ft (proximal 2/5 ) 12 ft (distal 3/5 )
Diameter 2 – 4 cm 2 – 3 cm
Wall Thick and heavy Thin and light
Color Deeper red Paler pink
Vascularity Greater Less
Vasa recta Long Short
Arterial arcade A few large loop Many short loops
Fat in mesentery Less More
Plicae circulares( circular folds )
Large,tall & closely packed Low & sparse
Villi Large & many Small & discrete
Peyer’s patches Few Many
Jejunum Ileum
Clinical consideration :
• Resect mesentery of jejunoileum -> intestinal mobile • Resection of small bowel : short bowel syndrome (80%)
• Cancer, Inflammation, hemorrhage, obstruction
• Remnant of vitelline duct
• Organ of 2 = 2% , 2 ft from IC valve , 2 inches, 2 special types of mucosa (gastric & pancreatic)
• Bleeding / diverticulitis
MECKEL’S DIVERTICULUM
Large intestine : 5 ft ; ileocaecal junction - anus
Ileocecal junction
Vermiform appendix
Caecum
Ascendingcolon
Hepatic flexureSplenic flexureTransverse colon
Descendingcolon
Sigmoidcolon
RectumAnal canal
General features of large intestine : Small intestine Large intestine
1. Villi 2. Mucosal fold
3. Taenia coli4. Haustra coli (sacculation)5. Appendices epiploicae6. Peritoneal relation
7. Peritoneal fold
+Circular folds
(plicae circulares)---
Intraperitoneal organ(except duodenum)
Mesentery proper(except duodenum)
-Semilunar folds
(plicae semilunares)+(except appendix & rectum)
++ (except caecum & rectum)
Retroperitoneal organ(except caecum, transverse colon,
sigmoid colon & rectum) Transverse mesocolon Sigmoid mesocolon
Caecum : 7.5 x 6 cm., blind intestinal pouch, Rt. iliac fossa (L5)
Ileocaecal orifice : ileocaecal valve (superior & inferior lips), frenulum
Appendicular orifice
Mesenteric support :
- Superior ileocaecal (vascular) fold & fossa
- Inferior ileocaecal fold & fossa
- Rectocaecal fossa
Clinical consideration :
• Fecal reflux at IC valve
• Intussusception
10 cm., blind intestinal diverticulumsearch by following taenia coliIntraperitoneal organ – mesoappendix
Vermiform appendix
RLQ at McBurney’s point : Lat. 1/3 & med. 2/3 of line ( Rt. ASIS - umbilicus )
malrotation or nonrotation, situs inversus
Position : retrocaecal , pelvic
Clinical consideration :
Acute appendicitis
• common abdominal emergency• lymphoid hyperplasia & fecolith• appendiceal mass/abscess• appendectomy• McBurney’s incision…?
Ascending colon : 20 cm., Rt. lumbar region
Rt. colic (hepatic) flexure
Secondarily retroperitoneal organ
Volvulus(L.volvo=to roll)
Transverse colon : 45 cm., umbilical region
intraperitoneal organ
hepatic flexure - Lt. colic (splenic) flexure (phrenococolic or sustenaculum lienis)
Transverse mesocolon
Greater omentum & gastrocolic lig.
Descending colon : 25 cm.,
Lt. hypochondriac, lumbar & iliac regions
splenic flexure to Lt. pelvic brim
Secondarily retroperitoneal organ
Sigmoid colon : 40 cm., S-shape, suprapubic region, intraperitoneal organ
Rectosigmoid junction (15 cm. from anus, S3)
Sigmoid mesocolon (reverse V-shape) & intersigmoid fossa
Clinical consideration :
• Variation
• Sigmoid volvulus
Rectum :
15 cm., extraperitoneal organ,
rectosigmoid junction to anorectal ring (pelvic diaphragm)
S3
3 parts of rectum andPeritoneal reflections : anterior, lateral & posterior
Rectum :
Rectovesical pouchRectouterine pouch
(pouch of Douglas or Cul-de-sac)
Pararectal fossa
Mesorectum
Rectovesical septum or Denonvillier’s fascia Rectovaginal septum
Rectum :
No mesentery, haustra coli, appendices epiploicae, taenia coli spread out and form longitudinal rectal muscle
Rectal ampulla : fecal storage before defecation
Transverse rectal folds (shelves) (Houston’s valves)
Levator ani muscle(pelvic diaphragm)
Rectal ampulla
Taenia coli spread to formLongitudinal rectal muscle
Right middle rectal valve*
Left lower (Infr) rectal valve
Left upper (Supr) rectal valve
* Anterior peritoneal reflection
Clinical consideration :
Colorectal carcinoma • Most at rectum • large bowel obstruction• Colectomy• Colostomy• Barium enema• Colonoscopy, sigmoidoscopy,
proctoscopy
Clinical consideration :
• Digital rectal examination (DRE) or PR(per rectum) ->
prostate gland, rectal mass
• Megacolon (Hirschprung’s disease) - congenital, absent of parasympathetic ganglion cell in myenteric plexus of intestinal wall
• Polyp / Diverticulum
Anorectal ring
Anus, anal verge
Levator ani muscle (pelvic diaphragm)
Anal canal :Terminal part of LGIT, 3-4 cm.
Anorectal ring (pelvic diaphragm) - anus (anal opening, anal verge)
Ant. : perineal body, urogenital diaphragm, bulb of penis or vagina
Post. : anococcygeal raphe’
Upper : pelvic diaphragm
Wall of anal canal :
Internal sphincter ani (involuntary)
External sphincter ani (voluntary)
Pelvic diaphragm(Levator ani muscle)
(rectal sling)
Internal sphincter
Ani (from inner circular muscle of rectum)
Conjoined longitudinal muscle
( from levator ani muscle & outer longitudinal muscle of
rectum)
Corrugator cutisani muscle
Deep external sphincter ani muscle
Superficialexternal
sphincter animuscle
Subcutaneous external sphincter ani muscle
* Anorectal ring : check sphincter tone by DRE, protect fecal incontinence
Mucosa of anal canal :
Anal columns (of Morgagni)
Anal valves
Anal crypts (sinuses)
Opening of anal glands
Dentate (pectinate) line
Transitional (intermediate) Zone or pecten
Hilton white line
Cutaneous zone
Rectal venous plexus
Dentate line Above Below
Development Hindgut (endoderm)
Proctodeum (anoderm)
Vein Portal IVC
Lymphatic drainage
Abdominal Inguinal
Nerve Autonomic(tone) Somatic(pain) (pudendal nerve)
Hemorrhoids Internal(bleed) External(pain)