92. Small intestine Flashcards
length of small bowel
5X length of trunk 1-1.5 m cats2-5 m dogs
what and where is the root of the mesentery
attaches to L2contains –cranial mesenteric artery–intestinal lymphatics–large mesenteric plexus of nerves
mucosal layer of small intestine
contains microvili which increase surface area 8 fold in dogs and 15 fold in catstwo cell types:1. columnar epithelial—absorptive function2. goblet cells–mucus secretingepithelium is produced in the intestinal crypts, replacement occurs every 2-6 days (shed at apex), start out as secretory and as the migrate up ddx into absorptive cells that aid in digestion
common bile duct and major duodenal papilla in dogs vs cats
DOGSmajor duodenal papilla: CBD and adjacent pancreatic duct (duct of Wirsung) minor duodenal papilla: accessory pancreatic duct –major contributor (duct of Santorini)80% cats have a single pancreatic duct that FUSES with CBD and empties into major duodenal papilla
muscular layers of SI and motility
inner circular (thick); outter longitudinal (thin)2 movements (PSNS control–vagus):1. segmental (mixes): random, stimulated by stretch, slows transit2. peristaltic (moves aborally): cyclic q 1.5-2 hours
T/Freduced peristalsis leads to ileus, reduced segmental contractions leads to diarrhea
TRUE
what is the functional unit of small intestine
VILLI and associated crypts
ilium and jejunal absorptive capacity for water
jejunum 50%ilium 75%
mechanisms for sodium absorption in the small intestine
Na/Cl passive diffusionN/K/ATPaseNa/glucose (SGLUT1) or other electrolyte co-transporter
branches of cranial mesenteric artery that feed the SI
- jejunal arteries2. caudal pancreaticoduodenal3. ileocolic artery (cecal and antimesenteric arteries)4. right colic5. middle colic
where do digestive enzymes come from
- pancreas2. brush border of SI3. bile from GB for fat digestion
portion of SI in which the majority of chemical digestion takes place
duodenum
role of cholecystokinin (CCK) and secretin in digestion
produced in the small intestine in response to the presence of nutrientsCCK–stimulates gallbladder contraction for digestion of fatSecretin– causes release in bicarb from pancreas to help neutralize acid from stomach
breakdown/digestion of proteins/peptides
breakdown into amino acidsenzymes: trypsin, chymotrypsin (secreted by pancreas), carboxypeptidase (brush border)
breakdown/digestion of CHO
breakdown into simple sugarsenzymes: pancreatic amylase, brush border enzymes, sucrase, lactase, maltase
breakdown/digestion of lipids
breakdown into fatty acids and glycerolenzymes: pancreatic lipase, bile saltsnot water soluble: micelle formation using bile salts and bile acids is necessary (have both hydrophobic and hydrophilic domainsbile acids also increase the surface area of the oil-water interfaces which aids access by pancreatic lipaseinside enterocyte—form chylomicrons and taken into lymphatics thru lacteal
acid base disturbances with small intestinal obstruction
metabolic acidosis if loss of intestinal alkaline fluidsUNLESSproximal duodenal obstructions & vomiting leading to loss of HCl and hypochloremic hypokalemic metabolic alkalosis
objective vs subjective measures of bowel viability
subjective: color, pulse, peristalsis, thickness (may not always correlate to histologic results)objective: fluorescin (gold/green under UV light) 10-15 mg/kg IV. Nonviable areas are non fluorescent >3 mmsurface oximetry: compare with peripheral pulse ox but only measures a small surface