Overview of GI system function Flashcards
Accessory digestive organs
(adnexa) - teeth, tongue, salivary glands, pancreas, liver, gallbladder
Gi tract
tube extending from mouth to anus and is constituted by: mouth, pharynx, oesophagus, stomach, small intestine, large intestine
Which layers of embryonic tissue is GIT made from?
Endoderm and mesoderm
Which embryonic layer forms epithelial lining of GIT?
endoderm, forms secretory cells (parenchyma) of glands
Which embryonic layer forms connective tissue, muscle and peritoneal covering?
Splanchnic (visceral) mesoderm
Divisions of GIT
- 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
Sections of foregut
pharynx, larynx, oesophagus, stomach, proximal half of duodenum, liver, gallbladder, pancreas
Sections of midgut
duodenum distal half, jejunum, ileum, cecum, ascending and transverse colon
Sections of hindgut
Hindgut: transverse colon, descending colon, sigmoid colon, rectum and anal canal
Vasculature of gut tube
Abdominal aorta
Vasculature of foregut
Coeliac trunl
Vasculature of midgut
Superior mesenteric artery
Vasculature of handgun
inferior mesenteric artery
Coeliac trunk
abdominal aorta at T12 (aortic hiatus), supplies foregut via common hepatic, left gastric and splenic branches
Superior mesenteric artery
from abdominal aorta at L1, supplies midgut via pancreaticoduodenal, jejunal, ileal, ileocolic and colic arteries
Inferior mesenteric artery
from aortic aorta at L3, supplies hindgut via left colic artery, sigmoid arteries, superior rectal artery
Ischaemic colitis
insufficient blood supply of splenic flexure of colon
Venous drainage
- 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
Physiological umbilical hernias
- Intestinal loops protrude through umbilical region of developing fetus to form hernia
Omphalocele
failure of inestinal loops to return to abdominal cavity after physiological herniation
Ileal diverticulum
- Ileal diverticulum: Embryological remnant of vitelline duct of yolk sac attached close to ileocecal junction (Meckel’s diverticulum)
Diverticula of colon
Small out-pouches from colon wall
Peritoneum
- 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
Peritoneal ligaments
- 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
Foramen of Winslow
- 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
Large intestine
Consists of cecum, appendix, ascending/transverse/descending colon, sigmoid colon, rectum, anal canal
Omental appendices
Small, fatty projections
Teniae coli
3 longitudinal smooth muscle bands
Haustra
Sacculations of wall of colomn between teniae
Variations in appendix position
- 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
Embryological derivative of anal canal
Endoderm cloaca of hindgut (upper 2/3) and ectoderm cloaca 0 lower 1/3
Rectum and anal canal delineated by
Pectinate line
Innervation of GIT
- 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
Stomach bed
- 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
Blood supply of stomach
Prepyloric vein of mayo ascends over pylorus identifies pylorus in surgery
Duodenum and pancreas
- 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
