Describe the division of regions/quadrants of the GIT
Regions:
- right and left hypochondrium, and epigastric regions - separated into each other by midclavicular plane
- divided from lumbars/umbilicals by subcostal plane
- divided from iliacs/pubic region by intertubercular plane
- quadrants divided by transumbilical and sagittal planes
Note: McBurney’s point: start of appendix
Note 2: umbilicus location changes with weight
Recall the layers of peritoneum
Recall the two layers of peritoneum
- parietal
- visceral
- mesentery is a continuation of visceral
Note some organs are intraperitoneal i.e. surrounded by both layers, while other lies retroperitoneal.
Describe the retroperitoneal space and list the organs within
- The retroperitoneal space sits between the peritoneum and posterior abdominal wall (psoas major and quadratus lumborum), and extends from T12 and 12th rib to sacrum and iliac crest
- suprarenal glands
- aorta
- duodenum
- pancreas
- ureters
- colon - ascending and descending
- oesophagus
- rectum
Describe some peritoneal relationships
- omentum is connected to stomach - lesser and greater omentum
- mesentery has two main portions
- mesocolon - transverse and sigmoid
- mesentery of small intestine
- peritoneal ligaments, thicking of pertitoneum, help keep organs in place
- falciform
- hepatogastric
- hepatoduodenal
- gastrosplenic
- gastrocolic
- gastrophrenic
DESCRIBE THE LESSSER OMENTUM AND OMENTAL BURSA
- lesser omentum is made of peritoneum
- contains? hepato-duodenal ligament and hepato-gastric ligament
- omental bursa or omental sac, lesser sac
- inferior: stomach, duodenum, transverse colon, right colic/hepatic flexure, right kidney, R adrenal gland
Describe the position (and changes) of liver
- the diaphragmatic surface fits under the dome of the diaphragm
- ascends with expiration, descends with inspiration
- occupies both of right hypogastric and epigastric regions
Describe the anterior surface of the liver and key structures
- irregular, wedge-like shape
- covered by peritoneum
- diaphragmatic i.e. superior anterior surface, is convex, fits under the dome of the diaphragm
- key features include:
- diaphragm
- coronary ligament
- L triangular ligament
- falciform ligament
- R and L lobes
- round ligament, recall left-over from fetal circulation
Describe the visceral surface of the liver and key structures
- has four margins: anterior, posterior, left and right
- portia hepatis
- hepatic artery proper
- hepatic portal vein
- hepatic ducts
- key features include:
- R and L lobes
- caudate lobe
- quadrate lobe
- IVC
- bare area - uncovered by peritoneum, rougher texture
- portia hepatis: cystic duct, hepatic artery proper, hepatic portal vein
- R triangular ligament
Describe the biliary tree
- from hepatocytes
- biliary canaliculi
- interlobular bile duct
- R and L hepatic ducts
- common hepatic duct (into which drains cystic duct)
- common bile duct (into which drains pancreatic duct) through head of pancreas
- ampulla of Vater, surrounded by sphincter of Oddi
- inserts into greater duodenal papilla
Describe the differences between jejunum and ileum
- jejunum mainly occupies upper quadrants
- ileum mainly occupies lower quadrants
- jejunum has longer vasa recta
- ileum has larger arterial arcades
- jejunum has thicker mucosa/submucosa
- ileum has aggregated lymphoid nodules, jujunum does not
jejunum is deeper red, ileum is paler pink
- calibre is similar: 2-4 vs 2-3 cm
- wall is thick and heavy vs thin and light
- vascularity is greater vs less
- vasa recta is long vs short
- arcades: few short loops vs many short loops
- less mesenteric fat vs more
- circular folds are large, tall, and closely packed vs low distal and sparse – completely absent in distal part
- few lymphoid nodules or Peyer’s patches vs many
Describe the features of the large intestine
- has five parts
- caecum (where ileum opens into)
- appendix - taenia coli can help identify
- colon: taeniae coli (three bands of smooth muscle: omental (only along transverse), mesocolic (posterior) and free(anterior)), haustra, omental appendage
- rectum
- anal canal
Describe the various positions of the appendix and its clinical significance
- end of appendix can sit in several positions including
- preileal
- postileal
- prececal
- retrocecal
- subcecal
- pelvic
- promonteric
- clinical significance: size and position can vary — influences where pain is perceived
Describe the supply territory of the superior mesenteric
- midgut: duodenum, jejunum, ileum, large intestine to transverse colon
- several branches
- jujunal
- ileal
- vasa recta–> arterial arcades
- ileocolic
- colic branch
- anterior and posterior caecal
- appendicular
- right colic
- middle colic
- inferior pancreaticoduodenal
Describe the supply territory of the inferior mesenteric
- hindgut: part of transverse, descending and sigmoid colon, rectum
- branches include:
- left colic
- asc and desc branches
- sigmodial aa
- superior rectal
- left colic
Describe teh lymphatic draingage of the lower GIT
- many including
- paracolic
- superior mesenteric
- inferior mesenteric
- intermediate colic
- ileocolic
- lateral aortic
- epicolic
- appendicular
- coeliac
- everything ends up in celiac
Describe the features of the rectum
- note adjacent to prostate: DRE
- divided from intestine by rectosigmoid junction
- three lateral curves, created by rectal folds
- expanded to form rectal ampulla
- lacks taenia coli, omental appendices and haustra
- key features include: rectal ampulla, folds, jucntion
Conrast the rectum and anal canal
- anal canal is not anus
- rectum and anal canal divided by pectinate line
- above pectinate line
- inferior mesenteric artery supplies
- mainly superior rectal drains; also inferior mesenteric and portal
- internal iliac lymph nodes
- visceral motility and sensation - no pain on incision
- columnar epithelial mucosa
- below pectinate line
- internal iliac artery
- mainly inferior rectal vein drainage; also internal ilaic and IVC
- superficial inguinal lymph nodes
- somatic motor/sensory – does have pain
- squamous epithelial mucosa
- note: internal and extenal sphincter muscle
- extenal is skeletal
- deep
- superficial
- subcutaneous
- internal is smooth
- extenal is skeletal
- note levator ani near rectum
Describe blood inflow to liver and outflow
Inflow
- (Hepatic) portal vein (75%)
- Drains blood from stomach, intestines, pancreas and spleen
- O2-poor nutrient-rich blood. **portal vein drains blood into the liver not from the liver.
- Hepatic artery (25%)
- Branch of the celiac trunk from the descending aorta.
- O2 rich blood.
- Outflow
- Hepatic veins (R and L) drain blood from the liver into the inferior vena cava.
List veins of GIT
- note also L gastric straight to portal
- g omental v into inferior mesenteric V
Describe the consequences of the portal systemic anastomoses
- portal vein and tributaries have no valves
- portal hypertension leads to venous enlargement or varices at portosystemic anastomoses
- three main presentations
- Oesophageal varices at the gastroesophageal junction
- Caput medusae at the umbilicus
- Haemorrhoids at the anorectal junction (can have without PH)
Descrieb teh roles of sympathetic and parasympathetic innervation of the GIT
- sympathetic which inhibits contraction muscle excitability
- PSY which enhances muscle excitability
- head, neck, thorax and body wall: paravertebral ganglia (Sympathetic trunk)
- abdomen and pelvis: paravertebral ganglia, coeliac, SMG, IMG
Describe sources of sympathetic innervation of the lower GIT
- greater splanchnic nerve
- celiac ganglian
- stomach, liver, ?intestine, adrenal glands and kidneys
- lesser
- superior mesenteric ganglion
- small intestine
- lumbar splanchnic
- inferior mesenteric ganglion
- large intestine
Describe sources of enteric innervation
- System: mechanical and chemical receptors –> enteric reflex
- myenteric plexus: muscle motility
- submucous plexus: secretion and absorption
Describe Hirschprung’s disease
- congenital disease
- intestinal obstruction shortly after birth
- chronic constipation, swelling of abdomen
- absence of ganglion cells at Meissner’s/submucosal plexus
