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Physiology > GI 3 > Flashcards

GI 3 Flashcards

1
Q

Fasting pattern (4)

A

Migrating Motility Complex
Motilin
Sweep intestines of undigested material
One every 90 minutes

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2
Q

Feeding Pattern (4)

A

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

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3
Q

feeding pattern

Stimuli (4)

A

Distention of duodenum
Nutrient content of chyme
Gastroenteric Reflex – short feedback loop from stomach to small intestine
Hormones

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4
Q

Hormones
Stimulated by: (4)
Inhibited by: (2)

A

CCK, Gastrin, Insulin, and Serotonin

secretin and glucagon

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5
Q

Two patterns of Motility

A
  1. Segmentation

2. Peristalsis

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6
Q
  1. Segmentation (4)
A

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

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7
Q
  1. Peristalsis (5)

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

A 
stomach
1
small intestine
3 – 5 cm
3 - 5
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8
Q

Duration of feeding pattern depends on: (2)

A

Caloric content of meal

Nutrient composition of meal

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9
Q

Nutrient composition of meal (2)

A

Carb > Protein > Fats

Ex. 450 kcal nutrient mixed meal will disrupt MMC for ≈ 3 hours

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10
Q

Net rate of movement of any substance across the intestinal epithelium is influenced by: (2)

A

Surface area

Motility

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11
Q

Substances Presented for Digestion and/or Absorption (6)

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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12
Q

Factors influencing Digestion (5)

A 
Motility
Large surface area
Appropriate pH
Hydrolytic enzymes
-carbohydrates, protein, fat
Emulsifying factors
-Fat
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13
Q

Factors influencing Absorption (5)

A 
Large surface area
Specialized cells
Specific transport mechanisms – carriers, pumps, pores
Energy
Blood or lymph flow
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14
Q

Most substances completely digested and absorbed in

A

proximal (~25%) small intestine.

-Dietary fat is the (potential) exception

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15
Q

This has consequences: (3)

A

↑intake produces ↑absorption, may produce ↑storage and obesity.
Diversion of chyme to distal gut is one treatment for obesity

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16
Q

Digestive enzymes in small intestine require a — pH to function

A

neutral

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17
Q

Pancreatic HCO3-

-Maximal stimulus of pancreas produces

A

pancreatic juice with [HCO3- ] of 145 mEq/L (5x plasma [])

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18
Q

Two Sites for Digestion of Protein and Carbohydrate

A
  1. Intraluminal (Stage I – pancreatic hydrolases):

2. Mucosal surface (Stage II – brush border hydrolases):

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19
Q
  1. Intraluminal (Stage I – pancreatic hydrolases): (2)
A

yields di- and tripeptides, amino acids, maltose, maltotriose, α-limit dextrins, glucose;
Fat digestion completed in lumen.

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20
Q
  1. Mucosal surface (Stage II – brush border hydrolases): (1)
A

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

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21
Q

Typical American diet includes ≈ — carbs

A

250 – 300 g/day

≈ ½ Daily Caloric Intake

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22
Q

Polysaccharides/Disaccharides (2)

A

Need to be broken down into building blocks (Glucose, Fructose, and Galactose) before it can be absorbed.
Fiber (Cellulose) cannot be digested and is lost in feces

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23
Q

Carbohydrate Digestion

Begins in mouth when food exposed to

A

salivary amylase

Not significant
Enzyme inactivated by acidic gastric juice

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24
Q

Carbohydrate Digestion
>95% digested in small intestine by (2)
Brush border hydrolases produce the

A

Starch and Glycogen digestion by pancreatic amylase

monosaccharides

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25
Q

Typical American diet includes ≈ — protein

A

60 – 90 g/day
1/6 average daily caloric intake/day
≈50 g endogenous protein added

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26
Q

≈50 g endogenous protein added (3)

A

protein added to lumen in form of mucus and enzymes
Disintegration of epithelial cells
Polypeptides must be digested into small peptides or Amino Acids

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27
Q

Digestion

Begins in stomach by pepsin (3)

A

10-20% total protein digestion
Important for collagen digestion
Enzyme inactivated by basic pH in Small Intestine

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28
Q

80-90% digested in small intestine by:
Small peptides and amino acids produced by (4)
Brush border peptidases produce —

A

Trypsin, Chymotrypsin, Carboxypolypeptidases, Elastase

amino acids

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29
Q

Peptide Transporter 1 (PEPT1)

Pharmacological Significance –

A

Extremely broad substrate availability

Can be used for drug delivery

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30
Q

Typical American diet includes ≈ — fats

A

70 – 100 g/day

≈ 1/3 Daily Caloric Intake

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31
Q

Most abundant dietary fats =

A

triglycerides (TG)

32
Q

Most abundant dietary fats = triglycerides (TG)

Smaller amounts of (3)

A

cholesterol, cholesterol esters, and phospholipids

33
Q

Digestion of fat requires emulsification (2)

A

Bile Salts

Lecithin (phospholipid)

34
Q

fat digestion reduces the

A

interfacial surface tension of fat

35
Q

Agitation of the fat (Segmentation), breaks the fat globule down into smaller fragments, increasing

A

surface area for digestion.

36
Q

Fat Digestion

Begins in

A

stomach
lingual lipase
< 10% (Insignificant)

37
Q

> 90 % in Small Intestine of Fat Digestion (4)

A

Pancreatic lipase (and Colipase)
Enormous quantities secreted
Digests all TG it can reach in < 1 min.
Produces fatty acid (FA) (X2) and mono-glyceride (MG).

38
Q

Digestion products solubilized in micelles
Removes
Transports

A

TG digestion products from fat globules so fat digestion can continue

TG digestion products to brush border membrane

39
Q

Fat Digestion of: (3)
Cholesterol esters by
Phospholipids by

A

pancreatic cholesterol ester hydrolase
Pancreatic Phospholipase A2
Packaged into micelles with TG digestion products

40
Q

Micelle Formation and Breakdown are in —

A

equilibrium

41
Q

FA and MG cross apical membrane via

A

simple diffusion

42
Q

In smooth ER, — resynthesized

A

TG

43
Q

In smooth ER, TG resynthesized
Keeps (2) low inside cell
Maintains gradient for (2)

A

[FA] and [MG]

simple diffusion and absorption

44
Q

(3) absorbed by same mechanism

A

Fat-soluble vitamins (A, D, E, K),
phospholipids, and
cholesterol esters

45
Q

TG and other hydrophobic substances packaged into chylomicrons and secreted across

A

BL membrane via exocytosis

46
Q

Chylomicrons enter lymphatic vessels via

A

the lacteals and are transported to systemic veins and enters circulation

47
Q

Surface Cells (2)

A

Mature intestinal epithelial cells

Absorb Na+, Cl-, and H2O

48
Q

Crypt Cells (5)

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
49
Q

Fluid secreted by Crypt cells flow to surface cells where —

A

reabsorbed

50
Q

Provides flowing H2O for

A

absorbing intestinal digestates

51
Q

Normally balance between (2)

A

Absorption and Secretion

52
Q

Significance of secretion:
Not enough:
Too much:

A

cystic fibrosis

infectious diarrhea

53
Q

Prandial State (2)

A

Electrogenic

Anions and water follow

54
Q

Post –Prandial (2)

A

Electroneutral

H2O follows

55
Q

Sodium in GI Lumen (3)

A

30g/day secreted into lumen
5-8g/day ingested
Normally >95.5% absorbed

56
Q

(2) infections are major cause of death in undeveloped countries.

A

Cholera and E. coli

57
Q

Cholera and E. coli infections are major cause of death in undeveloped countries.
Both produce enterotoxins that

A

↑ [cAMP]i.

58
Q

cAMP activates Cl- secretion via CFTR into gut lumen:

A

massive diarrhea.

59
Q

Up to –L/day of diarrhea can be produced

A

20

60
Q 
Vitamin B12 (Cobalamin) Absorption
In stomach  (3)
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

61
Q 
Vitamin B12 (Cobalamin) Absorption
In Duodenum (2)
A

Proteases digest R-binding protein

B12 binds to intrinsic factor (pH neutral)

62
Q 
Vitamin B12 (Cobalamin) Absorption
In Ileum (1)
A

Intrinsic factor binds to IFCR and taken into cells via receptor-mediated endocytosis

63
Q 
Vitamin B12 (Cobalamin) Absorption
Inside cells (3)
A

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

64
Q

Absorption of Water Soluble Vitamins

Thiamin, riboflavin, niacin, pyridoxine, pantothenate, biotin, and ascorbic acid: (2)

A

Cotransport with Na+

Completed in upper small intestine.

65
Q

Other Actively Absorbed Substances (4)

A

Ca++, PO4—
Mg++
Fe++
Bile salts

66
Q 
Function
Absorbing Colon (3)
A

Proximal ½
Absorption of water and electrolytes from chyme to form solid feces
≈ 1.4 L/day

67
Q 
Function
Storage Colon (2)
A

Distal ½

Storage of Fecal matter until it can be expelled

68
Q

Takes – hours to move contents from ileocecal valve to anus

A

8-15

69
Q

Mixing Movements “Haustrations” (4)

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

70
Q

Propulsive Movements “Mass Movements” (6)

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
71
Q

– different bacterial species (# bacteria in colon > # cells in human body)

A

1500

72
Q

Slow motility promotes —

A

growth

73
Q

– valve keeps bacteria in colon

A

Ileocecal

74
Q

Ferment undigested carbohydrates to short-chain fatty acids: (3)

A

Soluble and easily absorbed.
Nutrient salvage
Evidence obesity associated with biasing microbes to species efficient at nutrient salvage

75
Q

Colon Bacteria

Produce

A

Vitamin K (vital since amount in diet not sufficient)

76
Q

Colon Bacteria

Increase resistance of the intestinal mucosa to colonization with ]

A

pathogenic microorganism

77
Q

Colon Bacteria

Produce —

A

Flatus

Physiology (53 decks)

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