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Physiology > GI 3 Small Intestine and Colon: Motility, Digestion and Absorption > Flashcards

GI 3 Small Intestine and Colon: Motility, Digestion and Absorption Flashcards

1
Q

what is the valve that separates the stomach and the duodenum

A

pyloric valve

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2
Q

what is the valve that separates the ileum and the colon

A

ileocecal valve

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2
Q

what is the valve that separates the ileum and the colon

A

ileocecal valve

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3
Q

what are the segments of the small intestine in order

A

duodenum -> jejunum -> ileum

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4
Q

where does most secretion occur in the small intestine

A

duodenum

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5
Q

where does mot digestion occur in the small intestine

A

duodenum

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6
Q

where does most absorption occur in the small intestine

A

duodenum

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7
Q

what does the duodenum secrete

A

CCK
secretin
- GIP
HCO3-

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8
Q

what does the ileum secrete

A

PYY and HCO3-

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9
Q

where does the smallest amount of digestion and absorption occur

A

ileum

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10
Q

what does the dudoenum absorb

A

Fe

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11
Q

what does the ileum absorb

A

bile acids and vitamin B12

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12
Q

what are the motility patterns that occur in the duodenum

A

MMC
segmentation
peristalsis

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13
Q

describe the fasting pattern of motility in the small intestin

A

MMC
- uses motilin to sweep intestines of undigested material
- one every 90 minutes

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14
Q

describe the feeding pattern of motility in the small intestine and the primary control

A

-BER slow waves
- interstitial cells of cajal
- 3-12 waves per minute
- primary control is ENS

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15
Q

what are the stimuli of the feeding pattern of motility in the small intestine

A

-distension of duodenum
-nutrient content of chyme
- gastroenteric reflex
- hormones

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16
Q

what is the gastroenteric reflex

A

short feedback loop from stomach to small intestine

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17
Q

what hormones stimulate the feeding pattern motility in small intestine? inhibit?

A

-stimulate: CCK, gastrin, insulin, serotonin
- inhibit: secretin, glucagon

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18
Q

what are the 2 patterns of motility in the feeding pattern of the small intestine

A

segmentation and peristalsis

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19
Q

what happens in segmentation

A
  • mixing of chyme with digestive enzymes to emuslify fats, adjust pH, and expose mucosa to chyme
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20
Q

describe peristalsis in the small intestine

A

-propels chyme through small intestine at a rate of 1cm/min
- spreads chyme across mucosal surfaces as it enters from stomach
-can begin anywhere in small intestine
-normally weak and dies out after 3-5 cm

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21
Q

how long does it take to pass food from pyloric valve to the ileocecal valve

A

3-5 horus

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22
Q

what does the duration of feeding pattern depend on

A

-caloric content of the meal
- nutrient composition of the meal
- proteins > fats > carbs

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23
Q

what is the net rate of movement of any substance across the intestinal epithelium influenced by

A

-surfacea rea
-motility

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24
Q

what is the east-west vector and what is it influenced by

A
  • absorption
  • influenced by SA
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25
Q

what is the north south vector and what is it influenced by

A
  • how rapidly food moves from mouth to anus
  • influenced by motility
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26
Q

what are the substances presented for digestion and/or absorption

A
  • macronutrients
  • electrolyes: Na+, K+, Ca2+, Mg2+, Fe2+, Cl-, PO4-
  • water
  • bile salts
    -vitamins
    -drugs
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27
Q

what are the factors that influence digestion

A
  • motility
  • surface area
  • pH
  • hydrolytic enzymes for carbs, protein and fat
  • emulsifying factors for fat
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28
Q

what are the factors that influence absorption

A
  • SA
  • specialized cells
    -specific transport mechanisms - carriers, pumps, pores
  • energy
  • blood or lymph flow
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29
Q

what percentage of substances are completely digested and absorbed in the proximal small intestine and what is the exception

A

25% except dietary fat

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30
Q

what are the consequences of increased intake

A

increased absorption may produce increase storage and obesity

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31
Q

what is the gastric bypass surgery

A

diversion of chyme to distal small intestine

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32
Q

what pH do luminal enzymes in the small intestine require to function

A

neutral pH

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33
Q

what contributes to the pH of the small intestine

A
  • H+ from the stomach
  • bile HCO3-
    -pancreatic HCO3-
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34
Q

what concentration of HCO3- does maximal stimulation of pancreas produce

A

145 mEq/L

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35
Q

where does most bicarbonate come from

A

the pancreas

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36
Q

what are the two sites for digestion of protein and carbohydrates

A

-intraluminal (stage I - pancreatic hydrolases)
- mucosal surfaces (Stage II - brush border hydrolases)

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37
Q

what does intraluminal digestion yield

A

di- and tripeptides, amino acids, maltose, maltotriose, alpha limit dextrins, glucose

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38
Q

where is fat digestion completed

A

in the lumen

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39
Q

what are the end products of mucosal surface digestion

A

amino acids, di- and tripeptides, glucose, galactose and frutose

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40
Q

what is the typical intake of carbohydrates in american diet and what percentage of the daily caloric intake does it make up

A

250-300 g/day
~50% daily caloric intake

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41
Q

what do polysachharides and disaccharides need to be broken down into before it can be absorbed

A

glucose fructose and galacose

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42
Q

what happens with fiber digeestion

A

fiber cannot be digested and is lost in feces

43
Q

where does carbohydrate digestion begin

A

in the mouth with salivary amylase but not significant

44
Q

what is salivary amylase inactivated by

A

acid gastric juice

45
Q

what percentage of carbohydrate digestion is done by the small intestine

A

95%

46
Q

describe carbohydrate digestion in the small intestine

A
  • starch and glycogen digestion by pancreatic amylase
  • then brush border hydrolases produce the monsaccharides such as lactose, maltose and sucrose
47
Q

describe the mechanism of carbohydrate digestion and absorption

A
  • pancreatic amylase converts polysaccharides into maltose and then brush border enzymes convert into monosaccharides in the lumen
  • frustose is transported passively across apical membrane and passively across BL membrane or converted into glucose
  • glucose and galactose are transported actively across apical membrane with Na+
  • glucose and galactose passively move across BL membrane into ISF
48
Q

why is some fructose converted into glucose and galactose in the intestinal epithelial cell

A

glucose and galactose are absorbed faster than fructose

49
Q

what is the typical protein intake daily in the american diet and what fraction of daily caloric intake does it make up

A
  • 60-90 g/day
    -1/6 average daily caloric intake
50
Q

how much endogenous protein is added daily

A

about 50 g

51
Q

protein is added to the lumen in the form of what

A

mucus and enzymes

52
Q

what must polypeptides be digested into before absorption

A

small peptides or amino acids

53
Q

where does protein digestion begin

A

in the stomach by pepsin

54
Q

what is pepsin important for

A

collagen digestion

55
Q

what is pepsin inactivated by

A

basic pH in small intestine

56
Q

what percentage of total protein digestion does the stomach do

A

10-20%

57
Q

how much protein is digested by the small intestine

A

80-90%

58
Q

what are small peptides and amino acids in the small intestine produced by as a result of protein break down

A

trypsin, chymotrypsin, carboxypolypeptidases, elastase
- brush border peptidases produce amino acids

59
Q

describe the mechanism of protein digestion across an intestinal epithelial cell

A
  • pancreatic proteases and peptidases convert proteins into small peptides and amino acids
    -amino acids move with Na+ across the apical membrane and facilitate diffusion across BL membrane
  • small peptides move across apical membrane with H+ and are converted into amino acids by peptidases
60
Q

what transporter is responsible for movement of small peptidases across the apical membrane and what makes it special

A

peptide transporter 1 (PEPT1)
- no specificity
- can be used for drug delivery

61
Q

what is the average fat consumption in the american diet daily and what percentage of daily calories does it account for

A
  • 70-100g/day
  • about 30%
62
Q

what is the most abundant dietary fat and what are the other sources of dietary fat

A

-most abundant: triglycerides
- others: cholesterol, cholesterol esters, and phospholipids

63
Q

what does fat emulsification for digestion

A

bile salts and lecithin

64
Q

what do emulsifiers do

A
  • reduce the interfacial surface tension of fat
  • breaks down the fat globule down into smaller fragments, increasing the surface area for digestion
65
Q

where does fat digestion begin, what enzyme, and what percentage of total fat digestion does it account for

A
  • in the stomach by lingual lipase
  • less than 10%
66
Q

what enzyme does fat digestion in the small intestine

A

pancreatic lipase

67
Q

how long does it take for pancreatic lipase to digest all TG it can reach

A

less than 1 minute

68
Q

what does pancreatic lipase produce

A

fatty acid and monoglyceride

69
Q

what are fat digestion products packaged into

A

micelles

70
Q

what is the importance of micelles

A
  • removes TG digestion products from fat globules so fat digestion can continue
  • transports TG digestion products to brush border membrane
71
Q

what are cholesterol esters digested by

A

cholesterol ester hydrolase

72
Q

what are phospholipids digested by

A

pancreatic phospholipase A2

73
Q

describe the mechanism of fat absorption across an intestinal cell

A

-FA and MG cross apical membrane by simple diffusion
- FA and MG move into smooth ER to keep [FA] and [MG] low in cell and maintain the gradient for their diffusion into the cell
- fat soluble vitamins. phospholipids and cholesterol esters absorbed by same mechanism
- TG and other hydrophobic substances are packaged into chylomicrons and secreted across BL membrane via exocytosis
- chylomicrons enter lymphatic vessels via lacteals and are transported to systemic circulation

74
Q

what are the fat soluble vitamins

A

A,D,E, and K

75
Q

what are surface cells are what do they do

A
  • mature intestinal epithelial cells
    -absorb Na+, Cl- and H2O
76
Q

what are crypt cells and what do they do

A
  • immature intestinal epithelial cells
    -secrete Na+, Cl-, and H2O
77
Q

what are crypt cells produced by

A

stem cells

78
Q

where does fluid produced by crypt cells go and what does this fluid do

A
  • flows to surface cells to be reabsorbed
  • H2O flow allows for absorbing intestinal digestates
79
Q

what is the disorder not enough Cl- secretion

A

cystic fibrosis

80
Q

what is the disorder of too much Cl- secretion

A

infectious diarrhea

81
Q

describe the surface cells during the prandial state

A

-electrogenic
-glucose and Na+ move together across the apical membrane into the cell
- glucose diffuses passively across the BL membrane
- Na+ is moved into the ISF across the BL membrane by the Na+ K+ ATPase
- Na+ causes water to move across BL membrane into ISF and then Cl- to follow

82
Q

describe the surface cells during the post prandial state

A

-electroneutral
- Cl- moves into the cell while HCO3- moves out into the lumen across the apical membrane
- Na+ moves into the cell while H+ moves out into the lumen across the apical membrane
- Cl- moves into the ISF via the K+ Cl- symporter
- Na+ moves into the ISF via the Na+ K+ ATPase
- water follows these ions into the ISF

83
Q

how much sodium is secreted into the lumen per day? how much is ingested? how much is absorbed

A

-secreted: 30g/day
- 5-8g/day ingested
- more than 95% absorbed

84
Q

describe the Na+, Cl-, and H2O secretion by crypt cells

A
  • Cl- enters the cell in the apical membrane with K+ and Na+ and moves across the cell to be pumped out across the BL membrane by the CTFR channel
  • Na+ and water will follow
  • Na+ and K+ are pumped back out across apical membrane
  • electrogenic
85
Q

what increases Cl- secretion

A

anything that increases cAMP

86
Q

how do cholera and E coli infections affect Cl- secretion

A

-they produce enterotoxins that increase cAMP
- cAMP activated Cl- secretion into the lumen causing massive diarrhea
- up to 20L produced a day

87
Q

describe vitamin B12 absorption in the stomach, duodenum, ileum, and inside cells

A
  • stomach: binds to R binding protein which stabilizes B12 in the acidic environment. IF secreted by parietal cells cannot interact with B12 at low pH
  • in duodenum: proteases digest R binding protein and B12 binds to IF
  • in ileum: IF binds to IFCR and taken into cells via receptor mediated endocytosis
  • in cells: IF degraded, B12 binds to TCII, complex cross BL via exocytosis and enters hepatic portal blood
88
Q

what water soluble vitamins are transported? what are they cotransported with? and where is this completed

A
  • thiamin, riboflavin, niacin, pyridoxine, panthothenate, biotin, and ascorbic acid
  • cotransported with Na+
  • completed in upper small intestine
89
Q

what other substances are actively absorbed

A
  • Ca2+
    -PO4-
  • Mg2+
  • Fe2+
  • bile salts
90
Q

what is the absorbing function of the colon and how much is absorbed

A

-absorbing function in the proximal 1/2
-absorption of water and electrolytes from chyme to form solid feces
- about 1.4 L/day

91
Q

what is the storage function of the colon and how long can it be stored

A

-storage function in the distal 1/2
- storage of fecal matter until it can be expelled

92
Q

how long does it take to move contents from ileocecal valve to anus

A

8-15 hours

93
Q

what does poor motility in the colon cause

A

greater absorption and hard feces in transverse colon causing constipation

94
Q

how does diverticulitis happen

A

forms when too much pressure is in colon and little sacs pop out and fill with fecal matter and get infected

95
Q

describe mixing movements of the colon called haustrations

A
  • fecal material slowly dug into and rolled over
  • all fecal matter exposed to mucosal surface
  • facilitates absorption of water and dissolved substances
    -movement of material from cecum through ascending colon
96
Q

describe propulsive movements called mass movements in the colon and how often they occur

A
  • 1-3x per day
  • transverse to sigmoid
    -occurs throughout colon for 10 minutes
    -forces feces into rectum
97
Q

what stimulate mass movements

A

gastrocolic and duodenocolic reflexes and irritation

98
Q

what does slow motility in the colon promote with bacteria

A

bacterial growth

99
Q

what keeps the bacteria in the colon

A

the ileocecal valve

100
Q

what do colon bacteria do

A
  • ferment undigested carbohydrates to short chain fatty acids that are soluble and easily absorbed for nutrient salvage
  • produce vitamin K
  • increase resistance of the intestinal mucosa to colonization with pathogenic microorganism
  • produce flatus
101
Q

describe the defectation reflex

A
  • afferent nerve fibers cause parasympathetic fibers to relax internal anal sphincter and the descending and sigmoid colon
    -sympathetic nerve fibers cause contraction of external anal sphincter and cause defecation
102
Q

the rectum is empty until ____

A

mass movement

103
Q

what stimulates movement of luminal contents into colon

A

-pressure and chemical irritation relax sphincter and excite peristalsis
- fluidity of contents promotes emptying into the colon

104
Q

what inhibits movement of luminal contents into the colon

A

pressure or chemical irritation in cecum inhibits peristalsis of ileum and excites sphincter to contract

Physiology (41 decks)

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