Abdomen: Small & Large Bowel Flashcards
Parts of the Small Bowel
Duodenum
Jejunum
Ileum
Parts of the Duodenum
D1 - Superior (L1)
D2 - Descending (L1-L3)
D3 - Inferior (L3)
D4 - Ascending (L3-L2)
Superior part of duodenum
L1
Ascends upwards from pylorus of stomach
Connected to liver by hepatoduodenal ligament
Most common site of duodenal ulcers
Initial 3cm covered anteriorly and posteriorly by visceral peritoneum. The remainder is retroperitoneal
Descending part of duodenum
L1-L3
Curves inferiorly around head of pancreas
Posterior to transverse colon and anterior to right kidney.
Marked by major duodenal papilla
Inferior part of duodenum
L3
Travels laterally to the left over inferior vena cava and aorta
Located inferiorly to pancreas, posterior to superior mesenteric artery & vein
Ascending part of duodenum
L3 - L2
After crossing aorta ascends and curves anterior to join jejunum at sharp turn: duodena-jejunal flexure
at DJ flexure is suspensory muscle of duodenum (ligament of Trietz)
Blood supply to duodenum
Proximal to major duodenal papilla - gastroduodenal artery (branch of common hepatic artery from coeliac trunk)
Distal to major duodenal papilla - inferior pancreaticoduodenal artery (branch of SMA)
Blood supply to duodenum
Proximal to major duodenal papilla - gastroduodenal artery (branch of common hepatic artery from coeliac trunk)
Distal to major duodenal papilla - inferior pancreaticoduodenal artery (branch of SMA)
Venous drainage of duodenum
Veins follow arteries
Drain into hepatic portal vein
Lymphatic drainage of duodenum
Pancreatoduodenal nodes
Super mesenteric nodes
Origin of jejunum
Duodenojejunal flexure
Jejunum and Ileum peritoneal relations
Intraperitoneal
Attached to posterior wall by mesentery
Jejunum versus Ileum: Location
Jejunum: upper left quadrant
Ileum: lower right quadrant
Jejunum versus Ileum: Wall
Jejunum: thick intestinal wall
Ileum: thin intestinal wall
Jejunum versus Ileum: blood flow
Jejunum: Longer vasa recta
Ileum: shorter vasa recta
Jejunum versus Ileum: Arcades (arterial loops)
Jejunum: Less arcades
Ileum: more arcardes
Jejunum versus Ileum: colour
Jejunum: Red
Ileum: Pink
Blood supply to Jejunum and Ileum
Super mesenteric artery
Venous drainage from Jejunum/Ileum
Superior mesenteric vein
Lymphatic drainage from Jejunum/Ileum
Superior mesenteric nodes
Ileocaecal valve
Junction of ileum and cecum
Function is to prevent reflux of lateral back into ileum
Functions of the small bowel
Digestion
Absorption
Layers of the small bowel wall
Mucosa (epithelium, lamina propria, muscularis mucosae)
Submucosa
Muscular externa (two smooth muscles layers: inner circular, outer longitudinal. Myenteric plexus)
Adventitia
Cells of the epithelium in small bowel
Enterocytes: tall columnar, function: absorption
Goblet cells: exocrine glands, secrete mucin
Crypts of Lieberkuhn: contains cells to produce news cells to relish lining. Enteroendocrine cells also.
Paneth cells: secrete protective agents
Peyers patches: ileum containing MALT (mucosal associated lymphatic tissue)
Crypts of Lieberkuhn, Enteroendocrine cells
I cells: cholecystokinin (CCK)
S cell: secretin
K cells: gastric-inhibitory peptide (GIP)
Enterochromaffin Cells: Serotonin
Function of cholecystokinin (CCK)
Produced by I cells in response to fat in small intestine
Stimulates:
1. contraction of gallbladder (pushes bile into cystic duct)
2. Release of pancreatic enzymes
Functions of secretin
Produced by S cells
In response to low pH of chyme in small intestine
Secretin induces HCO3- secretion in pancreas and inhibits gastric emptying
Functions of gastric-inhibitory peptide
Produced by K cells
In response to chyme entering small intestine
Stimulates insulin release
Functions of serotonin in small bowel
Produced by Enterochromaffin Cells
In response to presence of chyme in small bowel
Acts on enteric nervous system to activate cystic fibrosis transmembrane regulators (CFTRs). Ion channel secretes Cl- into intestinal lumen with Na + and H2O. Na+ is required for absorption of certain nutrients
Secretions small bowel receives for digestion
Bile
Pancreatic Enzymes
Alkaline juice
Hepatopancreatic ampulla
Ampulla of vater
Formed from common bile duct and pancreatic duct
Opens into duodenum at major duodenal ampulla.
Secretions regulated by sphincter of Oddi
Carbohydrate digestion and absorption in the small bowel
Starch digested by amylase (salivary and pancreatic) to form disaccharides.
Disaccharides converted to glucose by brush border enzymes (lactase, sucrase, trehalase).
Glucose and galactose absorbed across apical membrane by secondary active transport (Na-Glucose co transporter SGLT1). Fructose enters by facilitated diffusion through GLUT5. Sugars transported to blood via GLUT2 receptors.
Protein digestion and absorption in the small bowel
Protein digestion starts in stomach from pepsin (active form of pepsinogen released by chief cells).
Proteins –> amino acids + oligopeptides
Digestion completed in small intestine with brush border and pancreatic enzymes.
Amino acids are absorbed by Na cotransporter.
Lipid digestion and absorption in the small bowel
10% - lingual/gastric lipase
90% - emulsification via bila acids to smaller fat goblets (micelles)
Pancreatic lipase, phospholipase A2, cholesterol ester hydrolase: hydrolyse micelles = fatty acids + monoglycerides + cholesterol + lysolecithin
Lipids packaged inside cells to form chylomicron and enter lymphatic system via lacteals
Water absorption in the small bowel
Most water and electrolyte absorption occurs in small intestine
Na+ is reabsorbed from intestinal lumen with cotransported Glucose/Amino acids
H2O follows Na via osmosis
Parts of the large bowel
Ascending Colon
Transverse Colon
Descending Colon
Sigmoid Colon
Blood supply to the cecum
Ileocolic artery (Branch of SMA)
Venous drainage from Cecum
Ileocolic vein (drains into superior mesenteric vein)
Lymphatic drainage from Cecum
Ileocolic lymph nodes
Ascending colon anatomical position
Rises from cecum to right colic (hepatic) flexure
Retroperitoneal
Blood supply to the ascending colon
Ileocolic artery
Right colic artery
(both branches of SMA)
Venous drainage from the ascending colon
Ileocolic and right colic veins (draining into SMV)
Lymphatic drainage from the ascending colon
Superior mesenteric lymph nodes
Nerve supply to ascending colon
Sympathetic, parasympathetic, sensory from superior mesenteric plexus
Transverse colon anatomical position
Extends from right colic (hepatic) flexure to the left colic (splenic) flexure
Attached to diaphragm at splenic flexure by phrenicocolic ligament
Intraperitoneal. Enclosed by transverse mesocolon
Blood supply to Transverse colon
Right colic artery (SMA)
Middle colic artery (SMA)
Left colic artery (IMA)
Venous drainage from transverse colon
Middle colic vein, drains into SMV
Lymphatic drainage to transverse colon
Superior mesenteric nodes
Innervation to transverse colon
Proximal 2/3: superior mesenteric plexus
Distal 1/3: inferior mesenteric plexus (parasympathetic: pelvic splanchnic nerves. Sympathetic: lumbar splanchnic nerves)
Innervation to transverse colon
Proximal 2/3: superior mesenteric plexus
Distal 1/3: inferior mesenteric plexus (parasympathetic: pelvic splanchnic nerves. Sympathetic: lumbar splanchnic nerves)
Descending colon anatomical position
Descends inferior from the left colic (splenic) flexure
Retroperitoneal in majority
Anterior to left kidney
Blood supply to descending colon
Left colic artery (branch of IMA)
Venous drainage from descending colon
Left colic vein (drains into IMV)
Lymphatic drainage from descending colon
Inferior mesenteric nodes
Innervation to descending colon
Inferior mesenteric plexus (parasympathetic: pelvic splanchnic nerves. Sympathetic: lumbar splanchnic nerves)
Sigmoid colon anatomical position
Left lower quadrant.
Forms when the descending colon turns medially.
Left iliac fossa to S3 vertebra
Attached to posterior wall by mesentery (sigmoid mesocolon)
Blood supply to sigmoid colon
Sigmoid artery (branches of IMA)
Venous drainage from sigmoid colon
Sigmoid veins (drains into IMV)
Innervation to sigmoid colon
Inferior mesenteric plexus (parasympathetic: pelvic splanchnic nerves. Sympathetic: lumbar splanchnic nerves)
Characteristics of large bowel wall
Mental appendices (pouches of peritoneum, filled with fat) Teniae coli (3 strips of longitudinal muscle along surface of large bowel): mesocolic, free and mental coli. Haustra (sacculations formed from teniae coli contraction) Wider diameter (9cm cecum, 6cm large bowel, 3cm small intestine)
Cell types in the epithelium of large bowel
Crypts of Lieberkuhn: glands and mucus-producing goblet cells
GALT (gastrointestinal associated lymphoid tissue)
Water and Ion absorption in the large bowel
Na+: Na/H antiporter, epithelial sodium channels, enhanced absorption of short-chain fatty acids via specialised symporters
Cl-: Cl follows Na+ absorption, in exchange for bicarb (net bicarb loss)
H2O: absorbed following osmotic gradient
K+: diffuses down electrochemical gradient caused by Na+/H2O absorption
Vits: B6, B12, K are produced by digestion of chyme by commensal guy flora
