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| 1 |
regions of the small intestine
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duodenum (25 cm), jejunum (2.5 m), ileum (3.5 m)
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| 2 |
levels of folding in the small intestine to increase surface area
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primary folds (3x)secondary finger-like projections (10x)tertiary level (20x)
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primary folds
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involving the entire mucosa and some submucosa, they begin in the distal duodenum, are tallest...
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| 4 |
plicae circularis
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permanent primary folds that run mostly circumferentially
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| 5 |
secondary finger-like projections
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villi composed of epithelium and lamina propria that project into the GI lumen w/ crypts b/w...
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tertiary level of folding
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microvilli on the apical plasma membrane of columnar absorptive epithelial cells to increase...
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| 7 |
microvilli
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aka brush border, striated borderactin microfilament core that continues down into filaments...
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| 8 |
enterocyte structure and function
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aka columnar absorptive cellsapical microvilli bound laterally by junctional complexes regulating...
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goblet cells structure and function
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unicellular mucus-secreting glands interspersed b/w enterocytes and increase in number along...
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| 10 |
paneth cell structure and function
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pyramidal exocrine cells found at the base of crypts w/ abundant basal RERsecretes lysozymes...
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| 11 |
enteroendocrine cell function
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secretion of 5-HT, secretin, CCK, pancreozymin, GIP, somatostatin, histamine, etc
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| 12 |
M (microfold) cells
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antigen transporting cells over lymphoid follicles (ie Peyer's patch) to phagocytose luminal...
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| 13 |
intermediate cells
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undifferentiated/differentiating cells lining the lower half of the crypts that can form goblet...
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| 14 |
lamina propria
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CT under the epithelium whose vasculature is essential to remove hepatic portal digestion products
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| 15 |
lacteals
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central lymphatics in the villi
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| 16 |
submucosal Brunner's glands
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mucus-secreting glands only in the duodenum whose alkaline pH neutralizes that acid chyme to...
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| 17 |
function of the myenteric plexus in the small intestine
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segmentation for mixing and peristalsis for forward propulsion of materials
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| 18 |
outer most layer of the small intestine
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serosa (except for the adventitia around the retroperitoneal portion of the duodenum) often...
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| 19 |
location for alkaline secretions of the liver and pancreas to enter the duodenum
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duodenal papilla
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| 20 |
secretions of the small intestine
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Brunner glands secrete mucous to protect the duodenal wallCrypts of Lieberkuhn secrete mucus...
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| 21 |
form of most dietary carbohydrates
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starch, sucrose, and lactose
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| 22 |
compostiion of starch
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20% amylose (straight chain alpha 1,4 linked glucose)80% amylopectin (branch chain polymer...
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| 23 |
undigestible carbohydrates
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cellulose and dietary fiber
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| 24 |
how does carbohydrate digestion begin?
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salivary alpha-amylase is secreted in the mouth, but has limited exposure to food b/c it is...
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| 25 |
sources of protein
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exogenousendogenous (30-50%) - from hydrolytic enzymes and glycoproteins in secretions and...
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| 26 |
carbohydrate, protein, and fat intake and percentage of the diet
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carbs: 250-800 g/day, 50-60%protein: 75-100 g/day, 10-20%fat: 12-160 g/day, 30-40%
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| 27 |
what determines fatty acid water solubility?
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length of the fatty acid chain**most of the diet contains water-insoluble long chain FA
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| 28 |
acylglycerol
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a FA attached to a glycerol
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| 29 |
triglyceride
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three FAs attached to a glycerol, which is more than 90% of dietary lipids
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| 30 |
cholesterol derivatives
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steroids and bile acids
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| 31 |
what enzyme is responsible for lipid digestion in the mouth?
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lipid lipases
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| 32 |
mechanical digestion of lipids in the small intestine
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fat is emulsified into small droplets by bile salts, lecithin, and intestinal contractions...
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| 33 |
major brush border carbohydratases
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maltase, sucrase, lactase, and alpha-limit dextrinase (isomaltase)
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| 34 |
what is the rate-limiting step of absorption of monosaccharides?
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entry of monosaccharides into the cell
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| 35 |
carbohydrate products absorbed by the enterocyte
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only monosaccharides, which are glucose, galactose, and fructose
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| 36 |
how is fructose absorbed by the small intestine?
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moves down its conc gradient via the GLUT5 transporter and is converted to glucose and lactic...
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| 37 |
how are glucose and galactose absorbed by the small intestine?
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originally conc in lumen is greater and transport is downhill; as more is transported, process...
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| 38 |
what happens to glucose and galactose after they are absorbed by the small intestine
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exit cell via GLUT2 (facilitated diffusion) and passive diffusion into the capillaries of the...
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| 39 |
at what point in the GI tract are all carbohydrates normally absorbed?
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mid-jejunum
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| 40 |
where does protein digestion begin and where is most of it done?
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begins in the stomach w/ pepsinmost is done in the duodenum and jejunum by proteolytic enzymes...
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| 41 |
after pancreatic digestion, how are proteins digested?
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enterocyte peptidases producing dipeptides, tripeptides, and free AA
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| 42 |
what is the rate limiting step in the absorption of AA?
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transport of AA
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| 43 |
how are AA absorbed?
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by the jejunum, most AA have been absorbed by in the form of di and tripeptides via Na+ dependent...
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| 44 |
digestion of triglycerides
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procolipase converted to colipase by trypsin --> binds pancreatic lipase --> open lipase active...
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function of colipase in the presence of bile salts and lipase
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binds the triglyceride at the oil water interface and to lipase so that lipase can work w/o...
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| 46 |
how fast is triglyceride hydrolysis?
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rapid due to the excess amount of pancreatic lipase compared to the amount of fat present
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| 47 |
digestion of phospholipids
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prophospholipase A2 -->phospholipase A2 --> cleaves the FA from the phospholipid in the presence...
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| 48 |
digestion of cholesterol
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pancreatic cholesterol esterase cleaves the FA from the dietary cholesterol ester to yield...
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| 49 |
critical concentration
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the concentration of bile salts at which the bile salts begin to form simple micelles, which...
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| 50 |
mixed micelles
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bile salts around the exterior, monoglycerides and lysophosphatides w/ polar ends facing the...
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| 51 |
function of mixed micelles
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facilitate the movement of fat-soluble substances through the aqueous chyme
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| 52 |
layers mixed micelles must pass through to deliver fats to enterocytes
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unstirred water layer (including mucous coat) and the lipid membrane barrier
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| 53 |
rate limiting step in lipid absorption
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migration of micelles to the microvilli surface
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| 54 |
re-esterification
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process of reconstitution of lipid products into fat after they enter the sER of enterocytes
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| 55 |
structure of chylomicron
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core of triglycerides (reconstituted lipids) and cholesterol surrounded by a phospholipid coat
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| 56 |
molecule responsible for exocytosis of chylomicrons
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beta-lipoprotein
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| 57 |
pathway of chylomicrons from intestines
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enter lacteals to lymphatic circulation --> thoracic duct --> subclavian vein
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| 58 |
location of most lipid absorption
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duodenum
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| 59 |
molecule bound to B12 in the plasma
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transcobalamin
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| 60 |
fat soluble vitamins
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A, D, E, K
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| 61 |
method of absorption of water soluble vitamins
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facilitated or passive diffusion or carrier-mediated transport
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