exam 3 pt 1

Question 1

`describe the anatomy of the GI tract & contributions of each component to the digestion of food.

Answer 1

• oral cavity & pharynx: teeth, tongue, saliva, glands, soft palate (mechanical & chemical digestion, swallowing)
• esophagus: bounded by upper & lower esophageal sphincter (prevents acid reflex)
• stomach: food bolus to chyme, mechanical digestion
• small intestine: duodenum (absorption begins), jejunum (most nutrients absorbed), ileum (empties into large intestine)
• large intestine: from ilium to anus (absorbs water & electrolytes, microbial fermentation, formation/storage of feces)

Question 2

what characteristic is unique to the stomach? what are other examples of maximizes surface area in GI tract?

Answer 2

• stomach has rugae (folds in the stomach), increases surface area, & flatten out when stomach is distended
• small intestine (jejunum & ileum) has large, circular folds (plicae circulares)

Question 3

what are the 3 sections of the small intestine? what is unique to each section?

Answer 3

• duodenum: begins absorption of nutrients
• jejunum: most nutrients absorbed & plicae circulares
• ileum: less prominent plicae circulares & empties into cecum

Question 4

what enzymes are present in the small intestine? what are they use for, & what is the mechanism for each?

Answer 4

• digestive enzymes
• brush border enzymes: peptidases, glucosidases, galactosidase

Question 5

what are the primary functions of the large intestine? liver? gallbladder?

Answer 5

• large intestine: absorption of water & electrolytes, microbial fermentation, formation/storage of feces
• liver: processes blood from digestive tract & produces bile
• gallbladder: stores bile

Question 6

what are the main functions/products of the pancreas? what key digestive processes are these involved in?

Answer 6

• endocrine: secretion of hormones
• exocrine: secretion of digestive enzymes
• neutralize the HCl from the stomach

Question 7

what are the exocrine pancreas enzymes? what reactions do these catalyze?

Answer 7

• amylase: the hydrolysis of starch to sugar
• lipase: hydrolysis reaction
• nucleases: breakdown RNA

Question 8

what are the 4 cell types in the pancreas? what do they do?

Answer 8

• 70-80% B cells synthesize & secrete insulin
• 15-20% a cells synthesize & secrete glucagon
• 5% g cells synthesize & secrete somatostatin
• cells that secrete pancreatic polypeptide

Question 9

what are the key cells contributing to digestion throughout the GI tract? (stomach, small & large intestine)

Answer 9

• stomach: mucoid, parietal, chief, enteroendocrine cells
• small & large intestine: goblet & absorptive (enterocytes) cells

Question 10

what type of membrane is found in the GI tract? Hoe do nutrients move through these membranes?

Answer 10

semi-permeable membrane: nutrients move through diffusion (from high to low concentration)

Question 11

what is secondary active transport? what are some examples?

Answer 11

cotransport of an ion; dependent on ionic gradient &/ electrical potentials across the membrane
ex: sodium glucose pump, glucose symporter SGLT1

Question 12

where is amylase secreted for carbohydrate digestion? what bonds does it cleave? what are the produces?

Answer 12

amylase is secreted from the salivary & pancreas exocrine glands
- cleaves the internal a(1,4) glycosidic bonds
- produces glucose polymers of different lengths

Question 13

what enzymes are present at the brush border membrane for the digestion of carbohydrates? what are the substrates & products?

Answer 13

• maltase (maltose): glucose & glucose
• sucrase (sucrose): glucose & fructose
• lactase (lactose): galactose & glucose

Question 14

how are carbs transported into the enterocytes?

Answer 14

• carbs are digested to glucose, fructose, & galactose before small intestine absorption
• enterocytes absorption is mediated by Na(+)- glucose cotransporter SGLT1

Question 15

where does the digestion of proteins begin?

Answer 15

stomach - gastric phase

Question 16

what enzymes digest proteins in the stomach? know characteristics of each.

Answer 16

pepsins (endopeptidase): hydrolyze peptide bonds within the polypeptide
- peptide bonds that involve the carboxyl groups of tyrosine, phenylalanine, tryptophan
- no peptide bonds that involving proline

Question 17

how does the digestion of proteins take place in the small intestine? list the sequence of events/substrates/enzymes/products that ultimately yield individual amino acids.

Answer 17

in the small intestine where trypsin and chymotrypsin released by the pancreas act on the proteins and break them down into dipeptides, tripeptides, and amino acid units

Question 18

describe absorption & the final steps of digestion for oligopeptide.

Answer 18

completed in the small intestine with brush border & pancreatic enzymes; they split the oligopeptides into amino acids dipeptides & tripeptides

Question 19

how are amino acids absorbed? what are the different apical & basolateral amino acid transporters? what amino acids do they transport?

Answer 19

some amino acids are metabolized in the enterocytes
different genes encode apical vs. basolateral transporters
- lumen to chyme vs. cytosol to circulation
glutamine, glutamate, aspartate, arginine (amino acids transported)

Question 20

describe lipid digestion.

Answer 20

begins in the oral cavity through exposure to lingual lipase, then to the stomach through gastric & lingual enzymes