Anatomy of the alimentary system 2 - Lecture 10

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1

Describe and identify the regions of the duodenum

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Duodenum is in general posterior to the transverse colon

Mesentary

  • 2 layers of peritoneum carrying a variable fatty CT, nerves, vessels and lymph nodes

1st/Superior part - Duodenal cap

  • Attached to greater and lesser omentum
  • Portal vein and bile duct are posterior (towards free edge of lesser omentum)
  • Quadrate lobe of liver and gall bladder are anterior
    • Undersurface of right lobe

2ns/descending part

  • Head of pancreas is medial
  • Bile duct and main pancreatic duct empty above greater duodenal papilla
    • Lesser may be present ~2cm above for the accessory pancreatic duct

3rd/Horizontal part

  • Upper R.psoas is posterior
  • Superior mesenteric vessels are anterior
    • Pass between uncinate process and head of the pancreas

4th/ascending part

  • Upper L.psoas is posterior
  • Duodeno-jejunal function at L2 medial to L.kidney
2

Give a brief overview of the small intestine and its most prominent features. Give distinctive differences between the Ileum and the Jejunum so as the separate them in dissection

Duodenum

  • ~25cm long
  • Composed of 4 sections which curve around the pancreatic head
  • Retroperitoneal except for proximal 2-3cm which are attached to greater and lesser omenta
  • Located above the level of the umbilicus
  • Permanent folds (plicae circularis) project into the lumen, most pronounced in the proximal section
  • Contains Brunner's glands
    • Bicarbonate producing cells

Jejunum

  • Proximal 2/5 of SI located mostly in umbilical region (L.upper abdomen)
  • ~3m long
  • Less Valvulae conniventes = mucosal folds
  • Small diameter ~2.5cm
  • Contains NEITHER Brunner's glands nor peer's patches
  • Long internal villi
  • Thicker more muscular wall
  • Increased plicae circularis
  • Less fat in mesentery

Ileum

  • ~2-4m long
  • Separated from caecum by the ileocecal valve (ICV)
  • NO LINE DEMARCATION BETWEEN JEJUNUM AND ILEUM
  • Contains peyer's patches
    • Aggregated Lymph nodules
  • Short vasa recta with an increase in arcades and mesenteric fat
  • Plicae circulares decrease in distal portion
3

Describe and identify the internal features of the duodenum and its blood & nerve supply

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Duodenal cap - proximal 2-3cm

  • Supply R.Gastric and R.gastroepiploic artery
  • Drainage prepyloric veins to portal vein

D1-mid D2

  • Supply Superior pancreaticoduodenal artery
    • Branch of gasproduodenal artery
  • Drainage Superior and Inferior pancreaticoduodenal vein
    • Drains to portal vein and inferior mesenteric vein respectively

Mid D2 to ligament of trietz

  • Supply Inferior pancreaticoduodenal artery
    • Branch of SMA
  • Drainage Superior and Inferior pancreaticoduodenal vein
  • Ligament - thin muscle connecting the junction between the duodenum, jejunum and duodenal flexure to the connective tissue surrounding the Superior Mesenteric Artery and the Coeliac
4

Describe and identify the nerve supply to and from the duodenum

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Image - Sympathetic = continuous black, Parasympathetic = dashed black, sensory = blue

Sympathetic nerve fibres

  • Coeliac trunk
  • Superior Mesenteric trunk

Parasympathetic nerve fibres

  • Anterior and posterior vagal trunks
5

Distinguish between the large and the small intestine

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The large intestine includes the:

  • caecum
  • appendix
  • ascending, transverse, descending and sigmoid colon

Features of the LI not in the SI

  • Sacculations/haustoria
    • regular expanded areas of colon interspersed with constrictions
  • Taenia coli
    • 3 thickenings of the longitudinal path of the external muscle (not in appendix or rectum)
  • Epiploic/omental appendices - present on transverse and sigmoid colon
  • Villi are NOT present
6

Describe the position and external features of the caecum

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Located in the R.iliac fossa

Suspended from ascending colon surrounded by peritoneum except where it connects with the ileum

Retrocaecal recess is behind/caecal fossa

Junction to ascending colon is at the level of the ileocaecal valve

Blind intestinal pouch with no mesentary

Superior margin - defined by ileocaecal ostium (opening from caesium to colon)

7

Describe the internal features and the blood and nerve supply of the caecum

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Horizontal ileocaecal vale is posteromedial

  • 2 flaps (valves) whose edges taper into horizontal elevations (frenulae)

Arterial supply

  • Anterior and posterior caecal arteries from colic artery from the superior mesenteric artery and ileocaecal artery from superior mesenteric artery

Venous supply

  • Anterior and posterior caecal veins into superior mesenteric vein and ileocaecal vein into superior mesenteric vein

Nerve innervation

  • Sympathetic - Superior mesenteric plexus
  • Parasympathetic - pelvic splachnic nerves (S2-4)
8

Identify and describe the variable position of the appendix

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Blind muscular tube that arises from the posteromedial caecum, 2-3cm inferior to the ileocaecal valve where tense coli merge

Lies on its own mesentery - the mesoappendix, in the retrocaecal recess

Variations

  • Duplex appendix
  • Position is hanging down over the pelvic brim close the the opening of the uterine tube i females
9

Describe the internal, external features, the blood supply/drainage and the nerve innervation

The opening of the appendix into the caecum is the McBurnerys point

  • Junction of lateral and middle this of line joining umbilicus with Anterior superior iliac spine

Suspended on mesoappendix attached to ill mesentary

Rings of lymphatic nodules in mucosa and submucosa are present

Arterial supply

  • Appendicular artery from the ileocolic artery from superior mesenteric artery

Venous drainage

  • Appendicular vein drains into ileocolic vein to portal venous system

Nerve innervation

  • Superior mesenteric plexus
10

Describe the regions of the colon

Ascending

  • Initial segment from ileocaecal valve to R.Colic Flexure
    • Flexure it anterior to R.kidney, descending duodenum and behind funds of gall bladder
  • Retroperitoneal though can have short mesentery

Transverse

  • Suspended between colic flexures in an inverted arch by transverse mesocolon (attaches to greater omentum and pancreas)
    • L.colic flexure is anterior to L.kidney, below spleen and pancreas
    • Attached to diaphragm at 11th rib by phrenjicocolic lig.
      • Passes laterally under spleen and is continuous with splenorenal ligament

Descending

  • L.colic flexure to pelvic inlet
  • Extends down lateral abdominal wall
  • Turns medially in L.iliac fossa to cross testicular and external iliac vessels

Sigmoid

  • Pelvic brim to S3 (middle sacrum)
  • Sigmoid mesocolon forms an inverted V (intersigmoidal recess) posterior to sigmoid mesocolon
  • Overlies L.ureter and external iliac veins
11

Describe the Arterial and venous drainage of the colon

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12

Describe the nerve innervation of the regions of the colon

...