Term
| What is the difference between the function of the portal vein and hepatic veins? Where do each drain? |
|
Definition
Portal v - drains gut and delivers nutrient-rich, O2 poor blood to liver to get "cleaned"
hepatic v- 3 veins which drain O2 poor blood from the liver to the IVC |
|
|
Term
| what is the contribution of blood supply to the liver from the portal v and hepatic a? |
|
Definition
portal v - 75%
hepatic a - 25% |
|
|
Term
| describe the organization of a classic lobule |
|
Definition
| hexagonal shape with a draining central vein in the center and portal triads at each vertice |
|
|
Term
| what structures make up the portal triad? |
|
Definition
| portal vein, hepatic artery, bile duct |
|
|
Term
| describe the flow of bile and blood within a lobule |
|
Definition
| blood flows thru the sinusoids and drains into the central vein while bile flows in the opposite direction, thru canaliculi to the bile duct |
|
|
Term
| where are bile canaliculi located? |
|
Definition
| between adjacent hepatocytes, sealed off by tight junctions on either side |
|
|
Term
| which surface of a hepatocyte is the apical surface and which is the basolateral? |
|
Definition
apical - facing other hepatocytes (bile canaliculi located b/w apical faces of 2 adjacent hepatocytes)
basolateral - facing blood sinusoid and the space of Disse |
|
|
Term
| what are the major components of bile? |
|
Definition
water ~ 1 L/day
bile acids
phospholipids
cholesterol
bile pigments (bilirubin)
metabolites of drugs, hormones
HCO3- |
|
|
Term
| there are many different transporters in hepatocyte membranes to transport the various components of bile in and out of the cell. what regulates gene expression of these transporters? |
|
Definition
| bile salts, via Bile acid receptor/farnesoid X receptor (FXR) |
|
|
Term
| what types of cells line bile ducts? |
|
Definition
| cholangiocytes - columnar epithelial cells |
|
|
Term
| what kind of modifications of bile occur in the ducts? |
|
Definition
| movement of water (bile becomes isotonic); absorption of glucose and amino acids; secretion of HCO3- in response to secretin; secretion of IgA molecules |
|
|
Term
| what is the precursor of bile acid? |
|
Definition
|
|
Term
| what is the first and regulated step of bile acid synthesis? |
|
Definition
|
|
Term
| what is the difference b/w primary and secondary bile acids? |
|
Definition
| 7-dehydroxylation by gut bacteria cause bile acids to lose one -OH group |
|
|
Term
| how do bile acids in hepatocytes increase their solubility in water? |
|
Definition
| conjugation with glycine or taurine lowers their pKa, increase solubility |
|
|
Term
| what happens to bile acids above the critical micellar concentration (CMC)? |
|
Definition
| spontaneously self-associate into micelles with hydrophobic areas facing away from the aqueous environment |
|
|
Term
|
Definition
| in bile, micelles can associate with phospholipids and cholesterol, forming mixed micelles |
|
|
Term
| T/F: while stored in the gallbladder, bile is concentrated and becomes hypertonic. |
|
Definition
| F: bile IS concentrated 5-20 fold, but isotonicity is maintained b/c micelles have little osmotic activity |
|
|
Term
| what is CCK's effect on the gallbladder and the sphincter of Oddi? what is the mechanism for these responses? |
|
Definition
gallbladder - contraction due to CCK receptors on smooth muscle in gall bladder
sphincter - CCK activates inhibitory neurons that release VIP and NO |
|
|
Term
| what is the difference in mechanism b/w VIP and secretin receptors and Bombesin, CCK, and ACh receptors? (pancreas lecture) |
|
Definition
VIP, secretin - act via cAMP messenger
Bombesin, ACh, CCK - act via Ca2+ and calmodulin |
|
|
Term
| what are two bile acid modifications that increase their solubility? where do these modifications take place? |
|
Definition
conjugation with glycine or taurine in hepatocyte
deconjugation and dehydroxylation by bacteria in ileum and colon, producing secondary bile acids |
|
|
Term
| what happens to bile salts that are not excreted in feces? |
|
Definition
| Na+ dependent transporters on the sinusoidal membrane of the hepatocyte reabsorb 80-90% of bile salts that reach the liver via hepatic portal blood |
|
|
Term
|
Definition
| phosphatidylcholine - major form of phospholipid in bile |
|
|
Term
| what is the function of phospholipids in bile? |
|
Definition
| bile salts + phospholipids solubilize other lipids better than bile salts alone |
|
|
Term
| how is lecithin secreted into bile? |
|
Definition
|
|
Term
| what is the liver's source of cholesterol? |
|
Definition
| synthesizes cholesterol and takes it up from plasma lipoproteins |
|
|
Term
| what is the function of ABC5/8? |
|
Definition
| secretes free cholesterol into bile |
|
|
Term
| what makes urine yellow and poop brown? |
|
Definition
|
|
Term
|
Definition
| bile pigment derived from the breakdown of RBC's in the spleen |
|
|
Term
| what are some common hormone metabolites excreted in bile? |
|
Definition
| CONJUGATED thyroid and steroid hormones |
|
|
Term
which of the following proteins are synthesized by the liver:
albumin
fibrinogen
angiotensinogen
Apo D |
|
Definition
|
|
Term
| in order for bile salts to be recycled, they must be absorbed from the blood and secreted into the canaliculi. what transporters are used in these processes? |
|
Definition
basolateral: cotransport - Na+ and bile salts, use NTCP transport protein.
canaliculi/apical: secreted via bile salt export protein (BSEP) |
|
|
Term
| which transporter moves phospholipids into the canaliculi? |
|
Definition
|
|
Term
| which protein transports bilirubin glucuronide into the canaliculi? |
|
Definition
|
|
Term
| which protein transports cholesterol into the into the canaliculi? |
|
Definition
|
|
Term
name the molecule transported by each protein below, found on the apical membrane of hepatocytes:
MRP2
MDR3
ABC 5/8
BSEP |
|
Definition
MRP2 - biliRubin glucuronide
MDR3 - phospholipiD
ABC 5/8 - cholesterol
BSEP - bile salts |
|
|
Term
| where do substances secreted into the canaliculi end up? |
|
Definition
| canaliculi drain into bile ducts and end up in the gallbladder or eventually in the gut (enters at 2nd part of duodenum via greater duodenal papilla) |
|
|
Term
| what important characteristic of bile acids allows them to sit at oil-water interfaces? |
|
Definition
| they are amphipathic, with hydrophobic and hydrophilic regions |
|
|
Term
[wk 1]
what stimulates CCK secretion?
what are its actions? |
|
Definition
presence of protein and/or fat in intestine
actions: 1. gallbladder contraction; 2. HCO3- pancreatic enzyme secretion; 3. inhibition of gastric emptying |
|
|
Term
| how are bile salt levels regulated? |
|
Definition
| bile salts in portal blood stimulate bile secretion and inhibit bile acid synthesis |
|
|
Term
| what is enterohepatic circulation? |
|
Definition
| it refers to the circulation of bile salts from liver to intestines back to liver due to mechanisms for reabsorption and re-secretion of bile salts |
|
|
Term
| is bilirubin conjugated or unconjugated in the plasma? in the canaliculi? |
|
Definition
plasma - unconjugated
canaliculi - conjugated (get conjugated in hepatocyte to make it more soluble in bile, then transported into canaliculi) |
|
|
Term
|
Definition
| exogenous organic compounds with no nutritive value or enzyme-cofactor function |
|
|
Term
| what is the liver's role in carbohydrate metabolism? |
|
Definition
gluconeogenesis, glycogenolysis: produce glucose
stores glucose as glycogen after meals |
|
|
Term
| what is the liver's role in protein metabolism? |
|
Definition
| can produce acetyl CoA and ketone bodies from a.a.'s and a-keto acids |
|
|
Term
| what is the liver's role in fat metabolism? |
|
Definition
take up chylomicron remnants and long chain fatty acids.
metabolizes fatty acids to acetyl CoA and acetoacetate
synthesizes and secretes VLDLs |
|
|
Term
| what is the liver's role in cholesterol metabolism? |
|
Definition
-synthesizes cholesterol from acetyl CoA
-utilizes cholesterol from bile salts
-excretes cholesterol in bile |
|
|
Term
| what are the main functions of the small intestine? |
|
Definition
digestion
absortion
secretion
motility |
|
|
Term
| what are 3 ways the small intestine increases its surface from a simple cylinder? |
|
Definition
1. circular folds
2. villi
3. microvilli |
|
|
Term
| where does the bulk of digestion take place within the small intestines? |
|
Definition
| upper part - duodenum, proximal jejunum |
|
|
Term
what is the average total daily intake of:
carbohydrates
protein
fat
cholesterol |
|
Definition
carbs - 200-300g
protein - 70-90g
fat - 100g
cholesterol - 1200-1700 mg |
|
|
Term
| what types of carbohydrates can be absorbed? |
|
Definition
|
|
Term
| how many phases are in carbohydrate digestion? what are the phases called? |
|
Definition
luminal phase - when food is in lumen of gut
brush border phase - when food is interacting with enzymes in the brush border (microvilli) of the intestines |
|
|
Term
| what are the luminal phase enzymes involved in carb digestion? what is their optimum pH? what are the end products of the luminal phase? |
|
Definition
pancreatic and salivary a-amylase
pH 7
cleave a-1,4 internal linkages only
end products: di- (maltose)and tri- saccharides (maltotriose) and small branched chain glucose polymers (a-limit dextrin) |
|
|
Term
| what are the brush border phase enzymes involved in carb digestion? what are the end products? |
|
Definition
sucrase-isomaltase, lactase, maltase
end products: monosaccharides (glucose, fructose, galactose)
**now can be absorbed |
|
|
Term
| how do glucose and galactose get absorbed from lumen into blood across the hepatocyte? |
|
Definition
apical/luminal side: SGLT1 transporter -co-transports Na+, glucose/galactose
basolatera/blood side: GLUT2 - facilitated diffusion of glucose/ galactose down concentration gradient |
|
|
Term
| how does fructose get absorbed from lumen into blood across the hepatocyte? |
|
Definition
lumen side: GLUT5 - facil diffusion
blood side: GLUT 2 - facil diffusion |
|
|
Term
| describe the overall driving force for glucose, galactose, fructose transport across intestinal epithelium |
|
Definition
| Na+/K+ ATPase on basolateral membrane keeps intracellular [Na+] low. So Na+ flows down its conc. gradient, pulling glucose/galactose with it thru SGLT1. Fructose diffuses down its conc. gradient thru GLUT5. Once in enterocyte, glucose, galatose, fructose diffuse out via GLUT2. |
|
|
Term
| what kinds of proteins can be absorbed? |
|
Definition
| di- and tri- peptides, via specific carriers |
|
|
Term
| what are the phases of protein digestion in the intestine? what happens in each phase? |
|
Definition
-luminal phase: hydrolysis of proteins by gastric (pepsin) and pancreatic proteases
-brush border phase: further digestion of large proteins to a.a., di- and tri- peptides |
|
|
Term
| how do the pancreatic enzymes in the luminal phase get activated? |
|
Definition
| in the enterocyte trypsinogen is cleaved by enterokinase and activated to trypsin. Trypsin then cleaves other pancreatic zymogens (chymotrypsin, elastase, carboxypeptidase a, carboxypeptidase b) |
|
|
Term
| what are the end products of the luminal phase of protein digestion? |
|
Definition
40% amino acids
60% small peptides |
|
|
Term
| what is that major di- and tri- peptide transporter on the luminal enterocyte membrane? how does it function? |
|
Definition
PepT1 - is a H+ linked electrogenic proton/peptide cotransporter
a Na+/H+ transporter pumps Na+ in and keeps intracellular H+ low (pumps it out). PepT1 carries H+ and a peptide back in |
|
|
Term
| what is the effect of the Na+/H+ in the luminal enterocyte membrane? |
|
Definition
| creates a region of high [H+] in the brush border - "unstirred layer" with pH 6; creates H+ gradient to "power" the H+, peptide cotransport thru PepT1 |
|
|
Term
| what happens to peptides once inside the enterocyte? |
|
Definition
| further digestion to a.a.'s by intracellular peptidases |
|
|
Term
| how do breakdown products of protein get into the blood? what other substances exit the cell in the same manner? |
|
Definition
-a.a.'s exit via basolateral a.a. transporters
-peptides can also exit via transporters; peptide like drugs (ACE inhibitors, etc) are also transported |
|
|
Term
| what genetic defects might affect protein absorption? name 2 diseases of protein absorption |
|
Definition
altered expression or function of a.a. or peptide transport proteins
-cystinuria: increased excretion of cation a.a.'s and cystine cause renal stones
-Hartnup - impaired absorption of neutral a.a.'s. resulting in niacin deficiency (synth. from Tryptophan, a neutral a.a. |
|
|
Term
| do patients with cystinuria or Hartnup's disease show symptoms of protein deficiency? why? |
|
Definition
| usually no, due to absorption of di- and tri- peptides |
|
|
Term
| what are the physical and chemical processes that occurs in the gastric phase of lipid digestion? |
|
Definition
physical: breakdown and emulsification of proteins and phospholipids to small lipid particles
chemical: breakdown by gastric lipase and in newborns, by lipase from milk |
|
|
Term
| what is gastric lipases optimum pH and its end products? |
|
Definition
pH 4-5
breakdowns triglycerides to make diglycerides and free fatty acids |
|
|
Term
| what are the 3 enzymes for lipid digestion and where do they act? what is the role of colipase? |
|
Definition
intestinal lipid digestion occurs by pancreatic lipases in lumen
-pancreatic lipase: specific for 1, 3 fatty acids in triglyceride
-cholesterol esterase: cleaves a variety of ester bonds
-phospholipase A2: cleaves lecithin to lysolecithin (good emulsifying agent)
-colipase: anchors lipase to the fat droplet |
|
|
Term
| what is the optimum pH for the intestinal lipases? what does it suggest about the conditions needed for their activity? |
|
Definition
pancreatic lipase, cholesterol esterase, phopholipase A2 all have pH optimum of 6-7
-depend on gastric acid neutralization to be effective |
|
|
Term
| how do digestion products of the lipases interact with bile acis? |
|
Definition
| digestion products (free fatty acids (FFA), monoglycerides, glycerol) and bile acids form mixed micelles and diffuse thru unstirred layer to the brush border |
|
|
Term
| how do FFA and glycerol in mixed micelles get absorbed? |
|
Definition
| fatty acids are in equilibrium b/w being in micelle and being free. FFA can get taken into cell via fatty acid transport protein |
|
|
Term
what happens to FFA's once absorbed?
what happen to bile salts? |
|
Definition
FFA are bound to intracellular fatty acid binding protein (FABP). Resynthesis of triglycerides occurs in enterocytes and they are packaged into chylomicrons.
-bile salts travel to terminal ileum where they get reabsorbed |
|
|
Term
| which digestion products of lipids require transport by micelle and which can freely diffuse w/o micelle solubilization? |
|
Definition
monoglycerides, long chain fatty acids need to be incorporated into micelles
glycerol, short- and medium- chain fatty acids can diffuse thru unstirred layer without micelle solubilization |
|
|
Term
what is a chylomicron?
what is the eventual fate of a chylomicron? |
|
Definition
| lipid digestion products are re-synthesized into triglycerides and packaged into chylomicrons. These are released by exocytosis and taken into lacteals (terminal lymph vessels in intestine) |
|
|
Term
| what is the role of Apo proteins in chylomicrons transport? |
|
Definition
Apo B-48, Apo A-1 and A-4 form coats for chylomicron secretion and aid in their uptake and metabolism by peripheral tissues.
recall that Apo proteins are synthesized in the liver |
|
|
Term
| what are sources of cholesterol? |
|
Definition
| diet, bile, shed mucosal cells (small amt) |
|
|
Term
| what kind of digestive processes must cholesterol undergo for absorption? |
|
Definition
| dietary cholesterol is sometimes esterified, must be hydrolyzed by cholesterol esterase |
|
|
Term
| what accounts for the selective absorption of cholesterol vs. plant sterols across the brush border? |
|
Definition
| two ABC transporters pump plant sterols out of cells into lumen; other ABC transporters transport cholesterol in (mechanism not well understood) |
|
|
Term
| what is the fate of cholesterol after absorption into the enterocyte? |
|
Definition
| esterification by acyl coA cholesterol acetyltransferase (ACAT) in ER and incorporated into chylomicrons |
|
|
Term
| what happens to cholesterol in chylomicron remnants after passage thru the lymph? |
|
Definition
| chylomicron remnants are taken up by liver, cholesterol is excreted into bile or secreted into plasma as VLDL or HDLs |
|
|
Term
| what is the relationship b/w Ca2+ absorption and Vit D3? |
|
Definition
| 1,25(OH)2-D3 binds to nuclear vit D receptor and regulated gene transcription of the proteins needed for transcellular Ca2+ absorption. |
|
|
Term
| what are the two types of Ca2+ absorption? which are vit D3 dependent? |
|
Definition
paracellular - thru tight junctions, vit D independent
transcellular - thru enterocyte, vit D dependent |
|
|
Term
| where in gut is transcellular Ca2+ absorption most active? what are the proteins involved in absorption? |
|
Definition
-most active in duodenum
-brush border transport channel: CaT1
-inside enterocyte: calbindin (Ca2+ binding protein) binds and transports Ca2+
-basolateral: PMCA1, Ca2+ ATPase |
|
|
Term
| how is 1,25(OH)2-D3 made? where is it made? |
|
Definition
| 1. Skin: vit D3 made by acting on 7-dehydrocholesterol; 2. Liver: hydroxylation on 25 position; 3. Kidney: hydroxylation on 1 position (regulated by parathyroid hormone) |
|
|
Term
| what substances are primarily absorbed in the stomach? |
|
Definition
-lipophilic molecules (ethanol)
-weak acids (aspirin, gets protonated in acidic environment and diffuses across mucosa - link to pharm: ion-trapping) |
|
|
Term
| what substances are primarily absorbed in the duodenum and proximal jejunum? |
|
Definition
| iron, calcium, fat, sugars, amino acids |
|
|
Term
| what substances are primarily absorbed in the terminal jejunum? |
|
Definition
|
|
Term
| what substances are primarily absorbed in the ileum? |
|
Definition
bile salts
vit B12 (remember Vit B12 is bound to intrinsic factor in the stomach and carried thru intestines, finally absorbed in terminal ileum) |
|
|
Term
| what substances are primarily absorbed in the colon? |
|
Definition
short chain fatty acids from fermentation of indigestible carbs (i.e. fiber, etc.)
water, Na+ Cl- |
|
|
Term
| how does water absorption occur in the duodenum? |
|
Definition
| via leaky tight junctions; water rushes into lateral intercellular spaces, making fluid isotonic. it then drains into capillaries and lymph |
|
|
Term
| what are the 2 primary countertranporters involved in ion uptake in the intestine? what is their net effect? |
|
Definition
Na+/H+ countertransport
Cl-/HCO3- countertransport
net: NaCl absorption and H+, HCO3- secretion |
|
|
Term
| what are the 3 regions of the GI tract that secrete HCO3-? |
|
Definition
| bile duct cells (cholangiocytes); pancreatic duct cells; duodenum (from Brunner's glands) |
|
|
Term
| which cells of the small intestine are mostly involved in secretion, and which are involved in absorption? |
|
Definition
secretion: crypt cells
absorption: villus cells |
|
|
Term
| what is the method of Cl- secretion in the crypt cells of the small intestine? what regulates it? |
|
Definition
| Na+/Cl- cotransport via basal side; Cl- transport out on apical side via CFTR chloride channel. channel is regulated (activated) by cAMP |
|
|
Term
| how do bacterial endotoxins (cholera) cause diarrhea? |
|
Definition
| activates adenylcyclase, makes cAMP, overstimulates secretions |
|
|
Term
what is the frequency of slow waves in the:
stomach
duodenum
ileum |
|
Definition
3 wave/mins
12 waves/ min
9 waves/min |
|
|
Term
| what determines whether or not a slow wave in intestinal smooth muscle causes a contraction? |
|
Definition
| whether it surpasses the electrical threshold and stimulates action potentials |
|
|
Term
| what is the sources of slow waves in the intestine? how can these cells be identified? |
|
Definition
| interstitial cells of cajal (ICC cells). have spontaneous electrical activity, and are couples to smooth muscle cells via gap junctions. identified by presence of cKit receptor |
|
|
Term
| what are kinds of motility patterns of the small intestine occur during the absorptive? |
|
Definition
| absorptive: local contractions to mix up chyme; contractions of muscularis mucosa cause villi to contract, mixing the unstirred layer and compressing lacteals. Near end of absorptive phase, short peristallic movements propel food aborally |
|
|
Term
| what kind of reflex loops are active in carrying out peristalsis (starting with distention as the stimulus)? |
|
Definition
| distension is sensed by mechanoreceptors-> passed to cells UPstream that release activating neurotransmitters (ACh, substance P); passed to cells DOWNstream that release inhibitory neurotransmitters (VIP). net result: contraction upstream of bolus, relaxation downstream |
|
|
Term
| what is the predominant motility pattern in the interdigestive/postabsorptive phase? |
|
Definition
| migrating motility complex (MMC) - wave of motion that starts in gastric antrum and sweeps indigestible material and bacteria out of the small intestine |
|
|
Term
| what is role of motilin in the MMC? what inhibits the MMC? |
|
Definition
-initiation of MMC occurs when motilin levels are at their peak
-when food enters the small intestine the MMC is inhibited |
|
|
Term
| if you swallow a foreign object (i.e. a dime), how will it get out of your GI tract? |
|
Definition
| the MMC will sweep it thru your intestine and facilitate its excretion |
|
|
Term
| how does the autonomic system regulate small intestinal motility? |
|
Definition
| excitatory and inhibitory neurotransmitters modulate slow wave amplitude and determine whether electrical threshold is reached and action potentions (i.e. contractions) are generated |
|
|
Term
| what is the response of the ileocecal sphincter to distension of the ileum or cecum? |
|
Definition
| increased pressure/distension of the cecum or ileum causes relaxation of the sphincter; utilizes reflex circuits of the myenteric plexus |
|
|
Term
| what is the response to the anal sphincters to rectal distention? what type of muscle is each sphincter made of? what causes these responses? |
|
Definition
increased pressure in the rectum causes relaxation of the internal anal sphincter (smooth muscle); contractions of external sphincter (skeletal muscle).
-acts via myenteric reflexes |
|
|
Term
| what is the pathology of Hirschprungs disease? |
|
Definition
| denervation of part of the myenteric plexus of the colon (usually exerts inhibitory influence), so colon gets distended --> congenital megacolon |
|
|
Term
| why is the composition of gases in the stomach and intestines different? |
|
Definition
| in stomach acid kills most bacteria; gas composition is similar to that of air. in intestines, gut bacteria produce gases and alter composition |
|
|
Term
| what are some of the roles of intestinal bacteria? |
|
Definition
| fermentation of indigestible carbohydrates, metabolize bile acids, synthesize vit K |
|
|
Term
| what are the main ions absorbed in the colon? |
|
Definition
Na+ and Cl-
this results in absorption of water |
|
|
Term
| what is the main route of Na+ and Cl- absorption in the proximal colon? |
|
Definition
same as intestinal mechanism:
Na+/H+ countertransport and HCO3-/Cl- countertransport are coupled |
|
|
Term
| what role does the cecum have in breakdown of indigestible carbohydrates (i.e. fiber)? how are the digestion products absorbed? |
|
Definition
undigested carbohydrates in the cecum get broken down to short chain fatty acids
-absorption is facilitated by Na+/H+ exchange |
|
|
Term
| what is main route of Na+ absorption in distal colon? what regulates this? |
|
Definition
Na+ moves into cell, down its electrochemical gradient, thru sodium channels
-aldosterone regulates number of channels; aldo release increases number |
|
|
Term
| how does Na+ that is transported into the cells of the colon get across the basolateral membrane? |
|
Definition
|
|
Term
| what is the colon's role in maintaining K+ levels? |
|
Definition
| colon can absorb or secrete K+ as needed |
|
|
Term
| what is the likely pathway for water absorption in the colon? why? |
|
Definition
| transcellular (not paracellular) thru aquaporins because it has tight epithelia |
|
|
Term
| how can you distinguish between small intestinal disease and colon disease in a person with diarrhea? |
|
Definition
| if you have usual amount of water (1.5L/day) entering colon, most likely colon disease (are getting net secretion from colon rather than absorption). greater than usual flow into ileocecal junction suggests small intestinal disease |
|
|
Term
| in which part of the gut would you find the following enzymes: maltase, sucrase, isomaltase, lactase? |
|
Definition
|
|
Term
| which organ produces the following enzymes: amylase, trypsin, chymotrypsin, carboxypeptidase, elastase, lipase, phospholipase A2, cholesterol esterase? |
|
Definition
| pancreas - gets released into duodenum |
|
|
Term
| what are two parts of the GI tract that contain skeletal muscle? |
|
Definition
upper 1/3 of esophagus
external anal sphincter |
|
|
Term
does the colon mucosa have crypts?
does it have villi? |
|
Definition
|
|
