GIT Flashcards

Question

small intestine

Answer 1

digests proteins, fats, carbs - does most of the nutrient absorption (sugars, AAs, fats, water, minerals) PARTS 1) duodenum: - extends from pylorus -> jejunum - receives ingesta from stomach, bile from liver, secretions from pancreas 2) jejunum - longest part of SI 3) ileum - short terminal part - connects to LI via ileocecal spincter LAYERS (in all parts) 1) luminal mucosa (simple columnar epithelium w/goblet cells) 2) submucosa (CT) 3) muscular layer (smooth muscle) 4) outer serosa (visceral peritoneum) MECHANISMS to increase mucosal surface: - large surface area exposed to lumen = more absorption - protected by mucus, just like stomach 1) long.... many loops and coils 2) mucosa folded into plications (villi above and intestinal crypts below surface). crypts are site of cell regeneration for SI. secrete fluid into intestine to dilute chyme. 3) villi between crypts 4) microvilli on each cell (tiny, on apical surface of epithelial cells on villi). brush border. cells have enzymes for digestion and carrier molecules for absorption in membrane MOTILITY 2 types of contractions: 1) peristalsis - progressive propulsive contractions to move ingesta 2) segmental - mixing, churning contractions - slow movements of ingesta - increase exposure of chyme to intestine wall ENZYMES - needed to break down carbs, fats, protein - produced in proportion to diet - sudden diet changes result in incomplete digestion -> diarrhea. must be gradual - 2 sources: 1) mainly from pancreas 2) enzymes on microvilli - carb digestion: 1) amylase - sometimes in omnivore saliva, always in pancreas - starch -> disacc 2) sucrase, maltase, isomaltase, lactase - in microvilli, amount dependent on diet - disacc -> monosacc -> absorbed through epithelium via 'second active transport' (low sodium in cells thanks to Na-K ATPase, sodium + glucose co-transported into cell down sodium concentration gradient, glucose absorbed efficiently) -> glucose leaves cells for blood by diffusion through basement membrane - protein digestion: 1) pepsin - breaks proteins into polypeptides in stomach 2) pancreatic proteases - incl. trypsin, chymotrypsin, elastase, carboxypeptidase - in SI - originally secreted as inactive substances -> activated in lumen of GIT - luminal digestion yields free AAs + small peptides -> peptidases in microvilli final stage -> produces AAs -> absorbed on carrier molecules in microvilli by secondary active transport (like glucose) -> leave for blood by diffusion through basement membrane - fat digestion: - fat clumps in droplets, emulsification breaks them up -> warmed and mixed in stomach -> bile acids added (secreted by liver through bile duct into duodenum, bipolar w/hydrophobic end for fat and hydrophilic end for water) -> droplets now smaller w/more surface area -> fat soluble vitamins (A D E K) can attach -> pancreatic lipases digest (dietary triglycerides hydrolyzed, free fatty acids and monoglycerides produced) -> monoglycerides, fatty acids, bile salts form water soluble micelles that transport the lipid to villi -> bile salt stays in lumen (only absorbed in ileum) -> monoglycerides and fatty acids diffuse into cell -> reassembled into triglycerides -> packaged w/protein + excreted from cell as chylomicrons (too big to enter capillaries) -> travel in lymph to vena cava * exception = medium chain triglycerides enter blood directly (shorter chain)

Answer 2

- recovers water + electrolytes (principle function of LI in cats and dogs, in small colon of horses) - stores feces - ferments fiber (to variable extent by species) PARTS: 1) cecum - blind diverticulum (sac) at beginning of colon (at ileocecal junction) - poor in carnivores, large in ruminants, very developed in horses/rats/guinea pigs/rabbits 2) colon - has numerous mucus secreting glands + uses peristaltic and segmental contractions for movement a. ascending - proximal, courses cranially b. transverse - courses R to L c. descending - connects transverse to rectum LAYERS - same as in SI but muscosa is not at folded and contains more mucous cells HORSE - cecum on right side of peritoneal cavity - ascending colon known as large colon (4 large banks traveling in pairs (one dorsal, one ventral)) - cecum + large colon divided into sacs called 'haustra' - longitudinal muscle forms bands called 'taenia' - descending colon known as small colon (longer than in carnivores) RUMINANT - ascending colon long + doubled into a spiral that supports the SI HIND GUT FERMENTORS - equids, rabbits, guinea pigs - fiber doesn't digest in SI - cecum and large colon ferment fiber - microbes + end products here identical to those in ruminants, VFAs absorbed across cecal and LI wall - differs from ruminants: much starch and protein digested and absorbed in SI, not in ruminants, and microbial protein can't be absorbed - bicarbonate directly secreted across cecal + large colon wall into lumen - microbes that ferment are sensitive to antibiotics!

Answer 3

stores feces - terminal portion of colon, continues into pelvic cavity - many mucus glands for lubrication - sensory receptors for stretch (stimulates defecation)

Answer 4

internal + external muscular sphincters to allow controlled passage of feces 1) internal spincter - ANS controlled - para relaxes (usually along w/increase in colon motility), symp constricts 2) external sphincter - voluntary control - internal relaxes -> fecal contents contact anal mucosa -> stimulates conscious need to defecate - voluntary relaxation of external sphincter causes defecation - rectum + anus muscle and nerves easily damaged by perianal surgery, tumors, and trauma. can cause incontinence

Answer 5

exocrine glands for digestion, secretions travel through pancreatic duct to duodenum secretes: - proteases, amylase, lipase from acinar cells - bicarbonate to neutralize acid

Answer 6

second largest organ! - caudal to diaphragm - divided into lobes -> subdivide into microscopic lobules - hepatic portal system drains intestine and delivers blood directly to liver - assists the phagocytic and nutrient processing functions of liver FUNCTIONS 1) filter + detoxify substances absorbed from GIT into blood (via phagocytic cells in hepatic sinusoids) 2) absorb + store vitamins, minerals, glucose from GIT 3) produces bile acids, cholesterol, bilirubin ('yellow') - bile collects in canaliculi -> drains into bile ducts -> merge to form hepatic duct -> connects to gallbladder (where bile is stored, horses don't have one) -> common bile duct drains gallbladder + liver -> merges w/pancreatic duct just before opening into duodenum 4) makes blood proteins - albumin: important for maintaining blood oncotic pressure (keeps water in our circulatory system, not leaking into our body!) 5) glucose metabolism - glycogenesis: making glycogen from sugars absorbed from gut - glycogenolysis: breaking glycogen down b/w meals to maintain blood glucose - gluconeogenesis: make glucose during starvation (all), constantly in ruminants and true carnivores, from AAs (cats), from propionate (herbivores) GALLBLADDER - contracts in response to cholecystokinin (released in response to fats + proteins in intestine, provides bile for fat emulsification when needed) - bile salts reabsorbed w/fats through hepatic portal system -> removed from blood by liver to make more

GIT Flashcards

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