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BISC 438 > lectures 1-3: GI tract, digestion of carbs & proteins > Flashcards

lectures 1-3: GI tract, digestion of carbs & proteins Flashcards

1
Q

absorption

A

movement of nutrients across mucosal epithelial lining from lumen, into blood or lymph

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2
Q

oral cavity

A

mechanical digestion
saliva contains amylase, partial digestion of starch
bicarbonate and carbonic anhydrase in saliva neutralize acids

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3
Q

stomach

A

site of temporary food storage
secretes HCl, enzymes, zymogens
mixes food/digestive juices, producing chyme
regulates rate of chyme entry into small intenstine

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4
Q

canaliculi

A

channels in parietal cells of gastric pits that supply gastric HCl to lumen

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5
Q

gastric pits

A

in stomach, contain cell types that produce various secretions in digestion
parietal cells are the source of gastric HCl with channels calls canaliculi

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6
Q

gastric HCl secretion

A

disassociation of H2O: H+ ions, OH- combines with CO2 to make HCO3- (bicarbonate)
bicarbonate transported out of cell in exchange for Cl-

Cl- and K+ from cytoplasm to canaliculi
proton pumps exchange K+ for H+ from cytoplasm

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7
Q

mucosa

A

first layer of lumen
composed of 3 layers, including an epithelial layer that comes in direct contact with food particles. A second layer contains small blood & lymphatic vessels

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8
Q

small intestine function

A

location of most digestion and nutrient absorption
receives secretion from liver, gallbladder, pancreas

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9
Q

chief cells

A

in stomach, secrete pepsinogen, which is activated in acidic environment > pepsin

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10
Q

brunner glands

A

produce alkaline solution which brings chyme pH to optimal pH (neutral) for pancreatic digestive enzymes

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10
Q

HCl function

A

acidic environment activates pepsinogen into pepsin
acidic environment favors denaturing of proteins
denaturing proteins makes peptide bonds more accessible to proteolytic enzymes (ex. pepsin)

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11
Q

submucosa

A

connective tissue layer

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12
Q

monomers

A

only form that can be absorbed

linked by glycosidic bonds to form polysaccharides

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12
Q

parts of the GI tract (inside to outside)

A

lumen, mucosa, submucosa, muscularis externa, serosa or adventita

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13
Q

muscularis externa

A

2 or 3 layers of muscle, controls GI tract motility

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14
Q

carbohydrates

A

simple sugars to large polymers
cellulose is indigestible, aka dietary fiber (slows down absorption of sugar)

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15
Q

Serosa/Adentitia

A

Serosa is loose connective tissue, and an extension of peritoneal cavity
(which holds abdominal organs in place).
Adventitia is an outermost connective tissue layer
found in regions outside of the peritoneal cavity.

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16
Q

α-amylase

A

converts starch (amylose and amylopectin) into oligosaccharides
salivary and pancreas glands

cleaves α1,4 glycosidic bonds

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17
Q

pepsin

A

cleaves peptide bonds into smaller peptides

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18
Q

amylopectin

A

dietary polysaccharides more complex in structure
α1,4 and α1,6 glycosidic bonds

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19
Q

amylose

A

linear and unbranched form of starch, easier to digest
only α1,4 glycosidic

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20
Q

maltase-glucoamylase
sucrase-isomaltase

A

exoglucosidases / membrane-bound oligosaccharidases on enterocytes that cleave one glucose unit at a time

21
Q

sucrase

A

sucrose into glucose and fructose
cleaves α1,4 and α1,2B

22
Q

isomaltase

A

cleave α1,6 branch points of α-dextrins

23
Q

maltose structure

A

all α1,4 bonds

24
Q

lactose

A

sugar in milk
B1,4 linkages cleaved by lactase

25
Q

trehalose

A

dissacharide (2 glucose monomers) in bacteria, fungi, plants invertabrates

digested by trehalase, cleaves α1’1α’

26
Q

SGLT1

A

glucose/galactose transporter, intestine > enterocyte

transmembrane protein located on apical side of enterocytes, co-transports 2 Na+ with 1 sugar
high affinity for substrates (low Km) > transport at low conc

27
Q

GLUT2

A

glucose/galactose/fructose transporter, enterocyte > blood
low affinity, high capacity transporter
basolateral membrane of enterocyte

can aid through apical membrane when luminal glucose levels are high - glucose saturates SGLT1, high fructose intake, or activation of TasIR3/2 by natural/artificial sweeteners

restricted to basolateral w consumption of complex carbs & under fasting conditions

28
Q

GLUT5

A

fructose transporter, intestine > enterocyte
apical side of enterocyte
lower affinity, higher Km

29
Q

glucoamylase

A

a1,4 in oligos 2-9 units

30
Q

Tas receptor

A

G-protein-coupled receptors in taste buds that combine to function as a “sweet” receptor

activated by sugar and sugar substitutes

activates GLP2 which activates GLUT2 translocation
sweet goes to Tas > GLUT2 goes to apical

insulin returns GLUT2

31
Q

endogenous protein

A

protein from own body, saliva, gastric juice, pancreatic enzymes, sloughed intestinal cells

31
Q

6 phases of protein digestion

A

1) gastric hydrolysis of peptide linkages
2) digestion into smaller peptides by pancreatic proteases
3) Hydrolysis of peptide linkages into oligopeptides by apical membrane peptidases.
4) Digestion of di/tripeptides by cytoplasmic peptidases in enterocytes.
5) Metabolism of some amino acids in enterocyte.
6) Transport amino acids across basolateral membrane into interstitial fluid, where they subsequently enter the blood stream.

32
Q

cholecystokinin (CCK)

A

stimulates secretion of enzymes and zymogens in the pancreas

activation: polypeptides/AAs enter lumen of the proximal small intestine and stimulate mucosal enterocytes to release CCK into blood

33
Q

serine protease

A

Endopeptidases (substrate specificity varies)

Characterized by serine residue at its active site, as part of serine/histidine/aspartate catalytic triad.

The serine residue is a nucleophile, and initiates the reaction by donating electrons.

34
Q

major zymogens

A

trypsinogen-1 and 2, proelastase, chymotrypsinogen, procarboxypeptidase A and B.

Two classes of pancreatic enzymes: serine proteases and carboxypeptidases

35
Q

carboxypeptidase

A

cleaves AAs from the C-terminus of peptide substrates
carboxypeptiddase A & B, secreted by pancreas, are metalloenzymes requiring Zn2+ in the active site

36
Q

pancreatic zymogen activation

A

catalyzed by enteropeptidase (serine protease), cleaves amino terminal peptide from trypsinogen 1 and 2 > active trypsin
trypsin activates other zymogens

37
Q

how does our body detect AAs in our body?

A

taste receptors detect presence of various molecules within the body
fatty acids and AAs in chyme > release of CCK, zymogens, protein digestion

38
Q

pancreatic enzymes are active at …

A

a neutral pH
bicarbonate neutralizes pH in chyme

39
Q

product of pancreatic enzyme digests

A

amino acids and peptides 2-8 AAs in length

40
Q

brush border enzymes

A

exopeptidases which hydrolyze oligopeptides (products of pancreatic digestion), membrane bound dimers (one subunit anchors to membrane, other hydrolyzes)

41
Q

glutamine

A

primary fuel source for enterocytes

42
Q

amino acid transporters

A

AAs can be taken up by enterocytes
transport across membranes by secondary active transport and facilitated mechanisms

43
Q

food matrix

A

nutrient/non-nutrient components of food and their relationships with each other
ex: plant cell wall precent pancreatic proteases from digesting proteins embedded in cell wall, lunasin has protease inhibitors

44
Q

protein digestibility

A

determined by measuring amount of food nitrogen in terminal ileum and comparing it to total food nitrogen
(measuring in feces would factor in bacterial metabolism, whereas ileum measures nitrogen before bacteria metabolizes AAs)

45
Q

enterocytes

A

intestinal absorptive cells, epithelial cells lining intestines

46
Q

protein digestion in the colon

A

bacterial enzymes metabolize undigested amino acids/peptides > ammonia, amines, other nitrogenous compounds > feces and urine

47
Q

maltase

A

a(1,4) in starch oligos and maltose disaccharides

48
Q

lactase

A

cleaves B1,4 linkage of lactose

49
Q

cascade activation of pancreatic enzymes

A

1) fatty acids and AAs in chyme stimulate CCK release
2) pancreas releases lipase, amylase, proteolytic enzymes, bicarbonate (to neutralize)
3) enteropeptidase cleaves trypsinogen to form active trypsin
4) trypsin activates other zymogens
5) pancreatic enzymes hydrolyze many peptide bonds > product is AAs and peptide 2-8 AAs in length

50
Q

Why should we measure food nitrogen content in the ileum, instead of measuring it in feces?

A

fecal nitrogen includes endogenous sources, bacteria, other non-dietary sources

BISC 438 (28 decks)

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