This document is a summary of everything discussed as part of the GI Tract in the abdomen cluster. It corresponds to the educational activities given with the 'Surgery' OPCs. This covers all the learning goals (ie. gallstones, pancreatitis, cancers, anal pathology, etc), an example of a patient cas...
- Innervation:
- Sympathetic: thoracic splanchnic nerves
- Parasympathetic: vagus nerve
- Vascularization
- Arterial: left and right gastric arteries, left and right gastroomental arteries
- Histology
- Superficial epithelial: bicarbonate secretion => barrier
- Mucous neck: mucus production => barrier
- Parietal: HCl production
- Chief: pepsinogen, lipase production
- Enteroendocrine: chemical messengers into the interstitial fluid of the lamina
propria
- Hormones
- Gastrin:
- Stimulates: ECL cells to release histamine, motility
- Histamine:
- Stimulates: parietal cells to release HCl
- Serotonin:
- Stimulates: stomach muscle contraction
- Somatostatin:
- Decreases: secretions, absorption
- Ghrelin:
- Stimulates: hunger
- Pepsinogen:
- Requires low pH to be activated
- HCl forms it into pepsin -> active proteolytic enzyme
- Other
- Intrinsic factor: binds to vitamin B12
- Acid secretion
- Gastrin -> ECL histamine production -> parietal HCl production
- Parietal cells are also stimulated by ACh
- Works by hydrogen-potassium pump
- Liver
- Functions in digestion
- Bile production
- Storage of fat-soluble vitamins
- Gallbladder
- Bile secretion
- Fat emulsification: micelle formation
,- Pancreas
- Retroperitoneal, epigastric, left hypochondric regions
- Stomach: anteriorly, superiorly
- Duodenum: anteriorly, medially, curves around
- Spleen: posteriorly, laterally
- Aorta, vena cava: posterior to the head of the pancreas
- Blood supply: branches of celiac and superior mesenteric arteries
- Drainage: portal vein to liver
- Exocrine
- Tubuloacinar glands -> ducts -> main pancreatic duct
- Proteases: break proteins into amino acids
- Amylase: break polysaccharides into small sugar (maltose, glucose)
- Maltase: breaks maltose into monosaccharides
- Lipase: breaks triglycerides into fatty acids and monoglycerides
- Nuclease: breaks RNA/DNA into ribose/deoxyribose and 4
nitrogenous bases
- HCO3- neutralizes H+ arriving from the stomach
- Endocrine
- Islets of Langerhans (in the tail)
- Alpha cells: glucagon
- Beta cells: insulin
- D (delta) cells: somatostatin -> inhibit alpha and beta cells,
exocrine function
- PP (gamma) cells: pancreatic polypeptide -> inhibit exocrine
function
- Digestion
- Enzymes
- Intestinal brush border enzymes
- Hydrolyze maltose/sucrose/lactose to constituent
monosaccharides
- Carboxypeptidase: splits off amino acids
- aminopeptidase/dipeptidase: liberate final amino acids
- (Chymo)trypsin:
, - Cleaves proteins into smaller peptides
- Absorption
- Ileum: major absorption site
- Via blood stream or lymphatics
- Vitamin B12 absorbed in the terminal ileum when bound to intrinsic factor
- Bile salt cycling and secondary production
4. Large Intestine
- Ascending and transverse colon
- Water absorption
- Metabolite absorption
- Vitamine absorption: vitamin K, thiamine, riboflavin
- Recycling: fermentation of carbohydrates, short chain fatty acids, urea cycling
- Descending Colon
- Fecal storage
- Sigmoid Colon
- Muscular contraction to increase colon pressure and induce movement of stool
into the rectum
- Rectum
- Holds the feces awaiting elimination
- Hormones
- VIP (vasoactive intestinal peptide)
- Stimulates: secretions, capillary and smooth muscle dilation
- Decrease: gastric acid secretion
- Peptide YYY (postprandially)
- Decrease: appetite in the hypothalamus
5. Digestion and Absorption
- Carbohydrates
- Digestion
- Salivary amylase (stomach): to oligosaccharides
- Pancreatic amylase (duodenum): various oligosaccharides (ie. maltose)
- Intestinal brush border enzymes (intestine)
- Dextrinase, glucoamylase: to monosaccharides
- Maltase, sucrase, lactase: to monosaccharides via hydrolyzation
- Absorption
- Only mono/disaccharides can be absorbed
- Glucose/galactose:
- Into cells: secondary active transport (Na+)
- Exit cells: facilitated diffusion
- Into capillaries: intercellular clefts
, - Trypsin/chymotrypsin (small intestine): cleaves proteins to peptides
- Intestinal brush border enzymes: splits amino acids from the end of the
chain and liberate final amino acids
- Absorption
- Carriers: coupled to active Na+ transport
- Short chains: active absorption via H+ - dependent cotransport
- Into capillaries: diffusion
- Lipids
- Digestion
- Emulsification: formation of micelles
- Monoglycerides + fatty acids + bile salts + lecithin
- Pancreatic lipases: cleave fatty acid into free fatty acids and
monoglycerides
- Absorption
- Micelles: diffusion between microvilli to apical cell surface -> lipid
dissociation -> pass through plasma membrane via diffusion
- Reconversion to triglycerides
- Chylomicron formation: triglycerides + lecithin + cholesterol +
phospholipids + protein coating
- Enter lacteals -> venous blood (via thoracic duct)
- Iron
- Ferrous (Fe2+) -> binds to transferring -> absorption
- Role of cytochrome B
- Haem: facilitated diffusion
- Calcium
- Mainly active transport ; passive (in high concentrations)
- Basolateral membrane: Ca2+ ATPase, Na+/Ca2+ exchange
- Ca2+ n chyme to binds to brush border proteins
- Ca2+ in cells binds to calbindin
6. Anal Anatomy
- Anal triangle of perineum between right and left ischioanal fossae
- Zones:
- Columnar (upper half): simple columnar epithelium
- Zona hemorrhagic
- Zona cutanea
- Pectinate line
- Boundary between visceral and somatic nerve supply
- Vascular supply
- Upper ⅔: superior rectal arteries (from inf. mes. aa)
- Lower ⅓: inf. rectal artery from internal pudendal artery
II. Dyspepsia and GERD
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