Overview of GI system function

Question 1

Accessory digestive organs

Answer 1

(adnexa) - teeth, tongue, salivary glands, pancreas, liver, gallbladder

Question 2

Gi tract

Answer 2

tube extending from mouth to anus and is constituted by: mouth, pharynx, oesophagus, stomach, small intestine, large intestine

Question 3

Which layers of embryonic tissue is GIT made from?

Answer 3

Endoderm and mesoderm

Question 4

Which embryonic layer forms epithelial lining of GIT?

Answer 4

endoderm, forms secretory cells (parenchyma) of glands

Question 5

Which embryonic layer forms connective tissue, muscle and peritoneal covering?

Answer 5

Splanchnic (visceral) mesoderm

Question 6

Divisions of GIT

Answer 6

• Foregut: pharynx
• Extends from mouth to hepatopancreatic ampulla entering duodenum - has oro-pharyngeal, thoracic and abdominal parts
• Midgut
• From where hepatopancreatic ampulla enters duodenum to junction between proximal 2/3 and distal 1/3 of transverse colon
• Hindgut
• Extends from junction of proximal 2/3 and distal 1.3 of transverse colon to anus

Question 7

Sections of foregut

Answer 7

pharynx, larynx, oesophagus, stomach, proximal half of duodenum, liver, gallbladder, pancreas

Question 8

Sections of midgut

Answer 8

duodenum distal half, jejunum, ileum, cecum, ascending and transverse colon

Question 9

Sections of hindgut

Answer 9

Hindgut: transverse colon, descending colon, sigmoid colon, rectum and anal canal

Question 10

Vasculature of gut tube

Answer 10

Abdominal aorta

Question 11

Vasculature of foregut

Answer 11

Coeliac trunl

Question 12

Vasculature of midgut

Answer 12

Superior mesenteric artery

Question 13

Vasculature of handgun

Answer 13

inferior mesenteric artery

Question 14

Coeliac trunk

Answer 14

abdominal aorta at T12 (aortic hiatus), supplies foregut via common hepatic, left gastric and splenic branches

Question 15

Superior mesenteric artery

Answer 15

from abdominal aorta at L1, supplies midgut via pancreaticoduodenal, jejunal, ileal, ileocolic and colic arteries

Question 16

Inferior mesenteric artery

Answer 16

from aortic aorta at L3, supplies hindgut via left colic artery, sigmoid arteries, superior rectal artery

Question 17

Ischaemic colitis

Answer 17

insufficient blood supply of splenic flexure of colon

Question 18

Venous drainage

Answer 18

• Hepatic veins drain venous blood from major GIT parts through hepatic portal venous system into IVC
• Hepatic portal vein receives drainage from abdominal part of GIT, pancreas, spleen and gallbladder via gastric, splenic and mesenetric veins to liver
• Venous drainage from mesenteric veins corresponds to pattern of mesenteric arterues

Question 19

Physiological umbilical hernias

Answer 19

• Intestinal loops protrude through umbilical region of developing fetus to form hernia

Question 20

Omphalocele

Answer 20

failure of inestinal loops to return to abdominal cavity after physiological herniation

Question 21

Ileal diverticulum

Answer 21

• Ileal diverticulum: Embryological remnant of vitelline duct of yolk sac attached close to ileocecal junction (Meckel’s diverticulum)

Question 22

Diverticula of colon

Answer 22

Small out-pouches from colon wall

Question 23

Peritoneum

Answer 23

• 2 layers - parietal and visceral (v is inner)
• Parietal layer: lines inner surface of walls of abdomen)
• Visceral layer: covers abdominal viscera
• Peritoneal cavity: space between layers
• Intraperitoneal: organs covered by visceral peritoneum
• Retroperitoneal: organs behind peritoneum and partially covered on anterior surface only - kidneys or pancreas

Question 24

Peritoneal ligaments

Answer 24

• Mesenteries: double layers of peritoneum that enclose organs and connect them to either anterior or posterior abdominal walls
• Greater omentum (gastrocolic ligament) - connects stomach and transverse colon
• Lesser comentum: connects stomach and duodenum sections to liver
  Falciform ligament: connects liver to ant abdominal wall

Question 25

Foramen of Winslow

Answer 25

- Anterior border: bile duct, hepatic artery and portal vein = portal triad - Posterior border: inferior IVC - Inferior border: first part of duodenum - Superior border: caudate lobe of liver

Question 26

Large intestine

Answer 26

Consists of cecum, appendix, ascending/transverse/descending colon, sigmoid colon, rectum, anal canal

Question 27

Omental appendices

Answer 27

Small, fatty projections

Question 28

Teniae coli

Answer 28

3 longitudinal smooth muscle bands

Question 29

Haustra

Answer 29

Sacculations of wall of colomn between teniae

Question 30

Variations in appendix position

Answer 30

- Retro-colic (it is behind colon) - Retro-caecal - Sub-caecal - Pelvic - towards pelvic cavity - Retro-ileal - Pre-ileal - Surgical importance - normally located at McBurney's point - retro-colic or retro-caecal

Question 31

Embryological derivative of anal canal

Answer 31

Endoderm cloaca of hindgut (upper 2/3) and ectoderm cloaca 0 lower 1/3

Question 32

Rectum and anal canal delineated by

Answer 32

Pectinate line

Question 33

Innervation of GIT

Answer 33

- Splanchnic nerves carry autpnomic visceral efferent and afferent fibres to and from GIT respectively - Abdominopelvic splanchnic nerve (T5 to L2/3) carry sympathetic fibres - lower thoracic splanchnic (greater (T5-9/10), lesser (T10-11) and least (T11/12)) and lumbar splanchnic (L1-2/3) - Vagus and pelvic splanchnic nerves S2-4 carry parasympathetic and visceral afferent fibres to and from GIT respectively

Question 34

Stomach bed

Answer 34

- Cardial notch to angular incisure is lesser curvature - Superior to inferior: left dome of diaphragm, spleen, left kidney and suprarenal gland, splenic artery, pancreas, transverse mesocolon - Posterior gastric ulcer can erode into stomach bed - Pancreatic pseudo-cysts and abscesses in omental bursa may push stomach anteriorly - Inflammation of pancreas may lead to adhesion of posterior wall of stomach to omental bursa

Question 35

Blood supply of stomach

Answer 35

Prepyloric vein of mayo ascends over pylorus identifies pylorus in surgery

Question 36

Duodenum and pancreas

Answer 36

- Pancreatic head is in duodenum cavity - Duodenum has 4 parts - initial, vertical, horizontal and vertical rising - Pancreas near inferior mesenteric vessels - Cancer of head of pancreas compresses and obstructs bile duct and hepatopancreatic ampulla = enlargement of gallbladder and jaundice, Whipple's procedure performed