L13 Abs And Mobil In S And LI Flashcards
LO1: desc gross and micro anat of S and LI, rel to func.
-int role- abs nutr, water, electrolytes. Abs= movem water, water and nutr gut lumen to blood- cellul through enterocs or paracellul in btw.
-req large SA and length- perman folds plicae circulares and mucosa folded into villi. Surf cov in mvilli. Slow movem for abs, precise contr.
Plicae- more dense proxim as more abs. Termin ileum narr and decr folds.
-int epith-enterocs. Goblet cells. Mucosa shed ev 3-6d, chemo affs rap div.
int gl/crypt in btw villi- cont SC at base- mig to surf and mat. Rap dig. Mvilli has enzs.
Crypt: SC bottom and parietal cells- part inv in innate def-prod antibacterial/vir tox. Up to transit amplifying cells-still flexib. Enteroendoc cells=horm to blood. Goblet. At top differentiated enterocs-Slough after few days-anoitis= prog to die when detatch.
LO2: desc mechs of abs in SI of sug, AA, fat, salt, water.
-cells on villi v active. Sec enzs to brush border- breakd carb and prot to compl dig and abs. Lip dig- Michelle to enterocs, built back up bit=chylomicron to lacteals to thoracic duct to L subclavian vein.
-CARB DIG- polysacc eg starch, cellul. Oligo 4-10. Disacc. Mono only ones abs by gut- fructose, galactorea, gluc. Final enz dig brush border.
-dig starch- amylose Lin gluc alpha 1-4. Alpha amylase saliva and panc amylase= gluc and maltose.
Amylopectin br alpha 1-6. Isomaltase=alpha dextrins and disaccharide.
Brush border enz=monosacc for abs. Maltose, alpha dextrinase, sucrose, lactase.
-monosacc abs- (see diag)
SGLT1 apical mem sod gluc linked transp is secondary AT. Na bind allow gluc/galac bind, alt conf, molecs in dissoc. Apical mem also GLUT5 facil diff fructose in.
Basolat mem GLUT2 facil diff frac, gluc and galac then gluc diff to capill. Also Na/K ATPase pump 3 Na out makes grad for Na in via SGLT.
LO3: princip of oral rehyd therap.
-upt Na gen osmot grad- water follow. Gluc upt stims Na upt- mix gluc and salt stim max water upt- oral rehyd fluid. Diffic abs just water. More gluc and Na in= more Na out. So mixt gluc and Nacl drives max abs of osmot active solute= water foll.
LO2 prot
PROT DIG:
-only AA, dipep and tripep abs. Diff lev of breakd to carb.
-in stom- pepsinogen rel from chief cell, conv to pepsin by HCL. Pepsin in stom cleaves pep bonds next to aromatic AA= oligo pep and AA to SI.
-panc rel prot eases as zymogen to prev pancreatitis. Trypsinogen activ by BB eneteropeptidases then activs others eg chyotrypsinogen. Trypsin cleaves bonds by pepsin AA.
Eneteropeptidases hydrol int pep bonds- trypsin, chymot, elastase. Exopeptidases hyd from C termin- carboxypeptidase.
-abs prot prods- AA and small peps abs, in ad prot not. BB enzs breakd oligo pep furth. AA activ and passive upt. Cotransp Na like gluc. Dipep and tri can be abs by mechs linked to active expulsion H+.
4/5 diff cotransp for diff types AA- neut, acid, basic, imino. Di/tripeps moved by H+ cotransp- in cell conv to AA by cytosol peptidases.
LO2 electrolyte/water upt.
-Na by AT out cell on basolat. Na diff to epith. Water foll into intracell sp.
osmot grad from all abs=upt water. Fluid abs is isosmot. SI abs more water than LI desp LI main job. Both have Na/K ATPase on basolat= grad for Na in. Apical mem- SI Na cotransp. LI Na channs- induced by aldosterone.
LO2 min upt
- Ca active transcell abs. Ent cell via facil diff Carr prot- Ca ATPase rem Ca from basolat=low intracell. Active proc occ proxim where less Ca avail, later more passive paracellul transp. Proc reqs vitD-allow calbindin to transf Ca through cell. stim by PTH.
- Fe mostly in haem. Gastric ac imp for abs. PPI= iron defic. Fe abs X a pic mem, binds apoferritin (moves X basolat). In circ bound to transferrin- sec by enterocs.
LO2 vit upt
-diff of facil diff. Water sol main abs by Na cotransp. Gluc, AA, vit.
Vit C/B. Vit B12 abs in termin ileum bound to IF from parietal. Lack= pernicious anaemia. B12 defic due to gastritis, termin ileum rem. B12 Essen for erythropoiesis.
LO4: desc patts motil in SI.
-int grad btw meals- int pacemakers higher freq proxim. Smooth musc contrac drives slow caudal prog, not static bact etc.
-segm foll meal- conts move back/ forth=mix and keep for abs. segm only mixes. Int grad means differential segm rates in adjoin section int= net caudal movem slow.
-peristal- contrac moves cont. in each sec int firing pacemaker (12x per min duod, 8 in termin ileum). Sends activ through nerve plexi=contrac smooth musc at intervals.
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LO5: desc func of LI. Desc motil of colon and rectum.
-some abs in LI=semi solid faeces. LI dig to haustra segms. As circ muscs more compl than longit which have been reduced to taenia coli.
Segm/haustral shuttling in proxim colon- agit/mix- keeps it in and allows most rem water abs fro faeces. Propels slow tow sigmoid.
Mass movem 1-3 per day. Can move cont rap from transv to rectum. Often trigg by eat (gastri-colic reflex). By coord peristal. Distens=urge deaf ate. Often at fixed times.
LO6: desc mech of defacation.
- rectum norm empty. Fill to 25%=urge.
Anal sphincter- int smooth musc, ext vol striated.
When urge- int sphincter reflex- PNS contr. Ext relax vol contr. Intra abdo press incr= expulsion.
Chyme
-chyme once conditioned- isotonic, neut, dig nearly compl. Chyme deliv to duod hypert, acidic, apart dig. Condit by osmot movem water in, hepat and bil sec HCO3 and enzs=isog sol prog slow through SI where abs occ.
