Digestive part 4 + 5 (BIOS 1310)

where is secretin produced?

enteroendocrine S cells of the duodenum

what are the effects of secretin?

inhibits gastric secretion and emptying, increases secretion of HCO3- rich fluid from the pancreatic duct cells, bile duct cells, and duodenal duct cells

what is the purpose of HCO3- in the duodenum?

neutralize pH

where is CCK (cholecystokinin) produced?

enteroendocrine I cells in duodenum

what is the stimulus for CCK prroduction?

partially digested food in the duodenum

what are the effects of CCK?

increase pancreatic acinar cells producing enzymes, gallbladder contraction, and relaxes the hepatopancreatic sphincter

what increases the surface area in the small intestine?

length, circular folds, villi, and microvilli

what is the purpose of the plicae circularis (circular folds)?

increase surface area and forces spiral movement of chyme to slow it down for better absorption

what is within villi?

capillaries/ lacteal

what are intestinal crypts?

between villi containing stem cells, enteroendocrine cells, and paneth cells

what are lacteals?

lymphatic capillaries that carry chyle (milky fluid of lymph + fat globules)

were are paneth cells?

at the bottom of an intestinal crypt

what do paneth cells secrete?

antimicrobials (lysozyme and defensisns), growth factors for stem cells

what is the life span of intestinal epithelial cells?

2-6 days

how many cells are shed daily in the intestine?

10^11 cells/ day

what cells are in microvilli?

enterocytes

what forms the brush border?

enterocytes

what enzymes are on the brush border?

maltase, lactase, sucrase (integral membrane proteins/ terminal enzymes)

what is contact digestion?

membranous phase using brush border enzymes + their matching transporters

what increases contact during the membraneous phase?

segmentation

what are examples of complex carbs?

starch, glycogen, and cellulose (indigestible)

what are the 2 kinds of starch?

amylose (spiral) and amylopectin (branched)

what enzymes do hydrolysis of starch?

salivary and pancreatic amylase

what are the products of the brush border enzymes?

monosaccharides

what are dual-activity enzymes?

brush border enzymes that have 1 protein but 2 active sites

what is corn syrup?

made from corn starch (amylase) including glucose, maltose, and oligosaccharides

what is high fructose corn syrup (HCFS)?

a sweeter version that uses glucose isomerase to convert glucose to fructose

what is the relative sweetness of carbs?

fructose (173)> sucrose (100)> glucose (74)

what is HFCS-55 used in?

soft drinks

what is HFCS-42 used in?

processed foods

what is the paracellular route of absorption in the small intestine?

pathway through semipermeable tight junctions

what is the transcellular route of absorption in the small intestine use?

secondary active transport and facilitated diffusion

how are glucose and galactose absorbed by the small intestine?

secondary active transport (symporters with Na+)

how is fructose absorbed by the small intestine?

facilitates diffusion (once in the cell most is converted to glucose)

where does reabsorbed glucose, fructose, and galactose go?

to the hepatic portal system

what flows through the paracellular route in the small intestine?

water and its dissolved solutes via osmosis

where does protein digestion begin?

stomach with pepsin

where is the propeptide cleaved off of zygomens?

duodenum

what 3 enzymes work in protein digestion to form oligopeptides in the small intestine?

trypsin, chymotrypsin, elastase

what enzyme does peptide bond hydrolysis in the small intestine?

carboxypeptidase

what are the brush border enzymes of protein digestion?

carboxypeptidase, aminopeptidase, dipeptidase

what is the function of the brush border enzymes in protein digestion?

break oligo-, tri-, and dipeptides down into individual AAs

how are AAs transported into the IEC?

Na+/ amino acid cotransorter/ symporter (secondary active transport)

how are AAs transported out of the IEC into the blood?

via amino acid transporters (facilitated diffusion)

what enzymes start lipid digestion?

lingual and gastric lipase

what action of the stomach makes lipids into smaller droplets?

mixing/ churning

what happens in the duodenum during lipid digestion?

lipid particles combine with bile micelles

what do micelles do?

collect more lipids

which enzyme inserts into micelle?

pancreatic lipase

what does not need digested?

cholesterol

how does the small intestine absorb fat?

micelles contact enterocyte membrane, simple and facilitated diffusion take place

when are carrier proteins needed for fat absorption?

fatty acids and cholesterol

what happens once monoglycerides and FFAs enter the enterocytes?

converted back into triglycerides

once the enterocyte reforms triglycerides, what happens?

they are repackaged into chylomicrons (coated with phospholipids and proteins in the Golgi)

after fats are packed into chylomicrons what happens?

exocytosis out of enterocyte and absorbed by the lacteal

what can the stomach absorb?

alcohol and some drugs

what is the primary site of absorption?

small intestine before ileum

what does the ileum reabsorb?

bile salts and vitamin B12

how are water and electrolytes reabsorbed?

osmosis (small intestine absorbs most)

what is intestinal flora?

microbes/ mainly bacteria within the large intestine

how many more microbes than human cells?

10x

what is the role of intestinal flora?

ferment some indigestible carbs

what do intestinal flora produce?

gases and short-chain fatty acids

what is an example of gases produces by intestinal flora?

CH4, CO2, dimethyl sulfide (farts)

what is an example of SCFAs produced by intestinal flora and why are they important?

acetic, propionic, and butyric acids: calories for colonocytes and have anti-inflammatory proliferative effects

what type of symbiosis do intestinal flora have?

mutualism

what vitamins do intestine flora produce?

vitamin B and K

how does intestinal flora aid in immunity?

communicate with immune cells for tolerance, and act as a barrier

what digestion takes place in the large intestine?

breakdown by bacteria only

what does the large intestine absorb?

bacterial products (SCFAs and vit B + K), water, and electrolytes

what does the colon do?

compacts waste

what does the rectum do?

stores wastes