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PHYS Exam 6 > GI 3- Small Intestine and Colon- Motility, Digestion, Absorption > Flashcards

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

1
Q

What are the functions of the small intestine?

A

secretion
digestion
absorption
motility

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2
Q

What is secreted in the duodenum?

A

CCK
secretin
GIP
HCO3-

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3
Q

What are the motility patterns in the duodenum?

A

MMC
segmentation
peristalsis

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4
Q

What is absorbed in the ileum (the last segement of small intestine)?

A

bile acids
vitamin B12

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5
Q

What is the purpose of the migrating motility complex in the small intestine?

A
  • sweeps intestines of undigested material
  • 1 every 90 minutes
  • motilin
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6
Q

When does the migrating motility complex happen in the small intestine?

A

fasting

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7
Q

What is the motility pattern of the small intestine during feeding?

A

➢ BER Slow waves in small intestine
➢ Interstitial Cells of Cajal
➢ 3-12 waves/min
➢ Controlled 1⁰ by ENS

  • two types (segmentation and peristalsis)
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8
Q

What stimulates the feeding motility patterns in the small intestine?

A
  • Distention of duodenum
  • Nutrient content of chyme
  • Gastroenteric Reflex – short feedback loop from stomach to small intestine
  • Hormones
    ✓ Stimulated by: CCK, Gastrin, Insulin, and Serotonin
    ✓ Inhibited by: secretin and glucagon
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9
Q

What hormones stimulate motility in the small intestine?

A

CCK
gastrin
insulin
serotonin

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10
Q

What hormones inhibit motility in the small intestine?

A

secretin
glucagon

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11
Q

What are the two patterns of motility during feeding?

A

segmentation
peristalsis

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12
Q

What does segmentation motility do in the small intestine?

A

➢ Mixing
- chyme with digestive enzymes
- emulsifies fats
- adjusts pH
- exposes mucosa to chyme

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13
Q

What does peristalsis do in the small intestine?

A

➢ Propel chyme through small intestine at a velocity of 1 cm/min.
➢ Spread chyme across mucosal surface as it enters from stomach
➢ Can begin anywhere in the small intestine
➢ Normally weak and die out after traveling only 3 – 5 cm
➢ 3 - 5 hours from pyloric valve to ileocecal valve

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14
Q

What does the duration of feeding pattern depend on?

A
  1. caloric content
  2. nutrient composition (fats>proteins>carbs)
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15
Q

Net rate of movement of any substance across the intestinal epithelium is influenced by:

A

➢ Surface area (east-west)
➢ Motility (north-south)

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16
Q

What are the substances presented for digestion/absorption in the small intestine?

A

➢Macronutrients – carbohydrate, protein, fat – Require “digestion”
➢Electrolytes – Na+, K+, Ca++, Mg++, Fe++, Cl-, PO4—
➢Water
➢Bile salts
➢Vitamins – fat soluble, water soluble
➢Drugs

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17
Q

What affects digestion in the small intestine?

A

➢ Motility
➢ Large surface area
➢ Appropriate pH
➢ Hydrolytic enzymes – carbohydrates, protein, fat
➢ Emulsifying factors – Fat

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18
Q

What affects absorption in the small intestine?

A

➢ Large surface area
➢ Specialized cells
➢ Specific transport mechanisms – carriers, pumps, pores
➢ Energy
➢ Blood or lymph flow

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19
Q

Most substances completely digested and absorbed in __________ small intestine

A

proximal (~25%)

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20
Q

What are the consequences of most substances being completely digested in the proximal small intestine?

A

↑ intake produces ↑ absorption, may produce ↑storage and obesity

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21
Q

Digestive enzymes in small intestine require a ______ pH to function

A

neutral

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22
Q

What allows for a neutral pH in the small intestine when H+ is coming from stomach?

A

Pancreatic HCO3-

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23
Q

What are the two sites for digestion of proteins and carbs?

A
  • intraluminal (stage 1; pancreatic hydrolases)
  • mucosal surface (stage 2; brush border hydrolases)
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24
Q

What does intraluminal (stage 1) digestion result in?

A
  • yields di- and tripeptides, amino acids, maltose, maltotriose, α-limit dextrins, glucose
  • fat digestion (only in stage 1)
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25
Q

What does mucosal surface (stage 2) digestion result in?

A

End products: amino acids and di- and tripeptides, glucose, galactose, fructose.

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26
Q

Fats are digested intraluminal, mucosal surface, or both?

A

intraluminal (stage 1; pancreatic) only!

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27
Q

Starch and Glycogen digestion by __________________.
_____________________ produce
the monosaccharides

A

pancreatic amylase
Brush border hydrolases

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28
Q

What type of transport does glucose, galactose, and fructose use on the apical membrane?

A

glucose/galactose = active
fructose = passive

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29
Q

What type of transport does glucose, galactose, and fructose use on the basolateral membrane?

A

all passive

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30
Q

What begins protein breakdown?

A

pepsin in the stomach

  • important for collagen digestion
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31
Q

When is pepsin inactivated?

A

when it reaches the small intestine (basic pH)

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32
Q

Small peptides and amino acids produced by __________ in the small intestine.

A

Trypsin, Chymotrypsin, Carboxypolypeptidases, Elastase (stage 1 from pancreas)

33
Q

____________ produce amino acids in the small intestine

A

Brush border peptidases (stage 2)

34
Q

What type fo transporter is the peptide transporter 1 (PEPT1)?

A

secondary active symporter

35
Q

What is the pharmacological significance of PEPT1 (peptide transporter 1) in the small intestine?

A

Can be used for drug delivery

36
Q

What is the most abundant dietary fat?

A

triglycerides (TG)

37
Q

Digestion of fat requires emulsification via what…

A

bile salts
lecithin

38
Q

What begins the digestion of fat?

A

lingual lipase (stomach)

  • only 10% of fat digestion
39
Q

What does most of the fat digestion?

A

pancreatic lipase (stage 1) in small intestine

40
Q

The products of fat digestion are solubilized in what?

A

micelles

41
Q

What do micelles allow for?

A
  • Removes TG digestion products from fat globules so fat digestion can continue
  • Transports TG digestion products to brush border membrane
42
Q

Digestion of cholesterol esters by pancreatic _______________

A

cholesterol ester hydrolase

43
Q

Digestion of phospholipids by Pancreatic _____________

A

Phospholipase A2

44
Q

Micelle Formation and Breakdown
are in ____________

A

equilibrium

45
Q

Fatty acids and MonoGlycerides cross ___________ membrane via simple diffusion

A

apical

46
Q

In what organelle are TryGlycerides resynthesized?

A

smooth ER

47
Q

TG and other hydrophobic substances packaged into ____________

A

chylomicrons

48
Q

Chylomicrons are secreted across what membrane via exocytosis?

A

basolateral

  • enter lymphatic vessels (NOT blood)
49
Q

What is the job of surface cells in the small intestine?

A
  • Mature intestinal epithelial cells
  • Absorb Na+, Cl-, and H2O
50
Q

What is the job of crypt cells in the small intestine?

A
  • Found deep in the spaces between the circular folds
  • Immature intestinal epithelial cells
  • Produced by stem cells
  • Mature and migrate to surface
  • Secrete Na+, Cl-, and H2O
51
Q

Secretion crypt cells and absorption of surface cells create what?

A

➢ Provides flowing H2O for absorbing intestinal digestates
➢ Normally balance between Absorption and Secretion

52
Q

If the secretion from the crypt cells is not enough what occurs?

A

cystic fibrosis

53
Q

If the secretion from the crypt cells is too much what occurs?

A

infectious diarrhea

54
Q

What is the prandial state of surface cells in the small intestine?

A

➢ Electrogenic
➢ Anions and water follow

55
Q

What is the post-prandial state of surface cells in the small intestine?

A

➢ Electroneutral
➢ H2O follows

56
Q

What is happens during secretion in the crypt cells?

A

➢ Electrogenic
➢ Na+ and H2O follows

57
Q

What do cholera and E. coli infections produce that lead to diarrhea?

A

produce enterotoxins that increase cAMP

58
Q

What doe enterotoxins do?

A

↑ [cAMP]

➢ cAMP activates Cl- secretion via CFTR into gut lumen: massive diarrhea.

59
Q

What is the oral rehydration theory?

A

drink water, sugar, and salt to cause the sodium-glucose cotransport to pull water back through basolateral side into the blood

60
Q

Enterotoxins do not affect ___________ cotransport.

A

sodium-glucose

61
Q

What happens to vitamin B12 absorption in the stomach?

A

➢ Binds to the R-binding protein
➢ Stabilizes B12 in acidic environment
➢ Intrinsic factor secreted by gastric parietal cells cannot interact with B12 at low pH

62
Q

What happens to vitamin B12 absorption in the duodenum?

A

➢ Proteases digest R-binding protein
➢ B12 binds to intrinsic factor (pH
neutral)

63
Q

What happens to vitamin B12 absorption in the ileum?

A

➢ Intrinsic factor/Vit B12 binds to IFCR and taken into cells via receptor-mediated endocytosis

64
Q

What happens to vitamin B12 absorption inside the cell?

A

➢ Intrinsic factor degraded
➢ B12 binds to TCII
➢ Complex crosses BL via exocytosis

65
Q

What can vitamin B12 bind to intrinsic factor?

A

when the pH is neutral
- small intestine

66
Q

What can cause maldigestion?

A

➢ Pancreatic “insufficiency”
➢ Liver disease
➢ Biliary obstruction

67
Q

What can cause malabsorption?

A

➢Achlorhydria (no acid in stomach)
➢Short bowel
➢Mucosal disease (i.e. Celiac Disease – autoimmune destruction of intestinal cells)
➢Lactose intolerance

68
Q

What does the first half of the colon do?

A

Absorbing Colon
➢ Absorption of water and electrolytes from chyme to form solid feces

69
Q

What does the second half of the colon do?

A

Storage Colon
➢ Storage of Fecal matter until it can be expelled

70
Q

Takes _____ hours to move contents from ileocecal valve to anus

A

8-15 hours

71
Q

Poor motility in the colon causes…

A

greater absorption and hard feces (constipation)

72
Q

Excess motility in the colon causes…

A

less absorption and diarrhea (loose feces)

73
Q

What do haustrations (mixing movements) in the colon do?

A

➢ Fecal material slowly dug into and rolled over
➢ All fecal material gradually exposed to mucosal surface
➢ Facilitates absorption of water and dissolved substances
➢ Movement of material from cecum through ascending colon

74
Q

What do mass movements (propulsive movements) do?

A

➢ 1-3x each day
➢ Transverse to Sigmoid
➢ Occurs throughout colon for 10 min.
➢ Force feces into rectum
➢ Gastrocolic and Duodenocolic Reflexes
➢ Irritation can stimulate

75
Q

What is the role of colon bacteria?

A

➢Slow motility promotes growth
➢ Ileocecal valve keeps bacteria in colon
➢ Ferment undigested carbs to short-chain fatty acids
➢ Produce Vitamin K
➢ Increase resistance of the intestinal mucosa to colonization with pathogenic microorganism
➢ Produce Flatus

76
Q

What nerve controls the external anal sphincter?

A

pudendal nerve
- skeletal motor nerve from conscious cortex

77
Q

What controls the internal anal sphincter?

A

parasympathetic nerves (pelvic nerves)

78
Q

What are the sensory receptors on the rectum for?

A

afferent nerve fibers
- sense stretch in rectum

PHYS Exam 6 (4 decks)

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