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GI > Fluid And Digestion > Flashcards

Fluid And Digestion Flashcards

1
Q

Amount of water in the GI tract

A

9L

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2
Q

What percentage of water in the gut comes from secretions

A

80%

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3
Q

Amount of water in GI tract from saliva

A

1.5 L

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4
Q

Amount of water in GI tract from gastric juices

A

2 L

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5
Q

Amount of water in GI tract from bile

A

0.5 L

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6
Q

Amount of water in GI tract from pancreatic juices

A

1.5 L

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7
Q

Amount of water in GI tract from intestinal secretions

A

1.5 L

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8
Q

Amount of water in GI tract from drinking water

A

2L

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9
Q

Water absorption in the stomach

A

Small amount
Small surface area and lacks solute absorbing mechanisms which create osmotic gradient

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10
Q

Where is majority of water reabsorbed in GI tract

A

Small intestine
8.5 L

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11
Q

Amount of water reabsorbed by small intestine

A

8.5 L

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12
Q

Amount of water reabsorbed by colon

A

400 ml

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13
Q

Amount of water excreted by faeces

A

100ml

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14
Q

How is small intestine adapted for water absorption

A

Epithelial membrane very permeable to water
Na+ is very abundant in chyme: actively transported into cells in ileum and Jejunum
Luminal membrane transport is variably coupled with glucose, amino acids and other substances

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15
Q

Na+ and small intestine

A

Na+ very abundant in chyme
Actively transported into cells in ileum and Jejunum

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16
Q

Colon and water reabsorption

A

Contents are iso-osmotic
Na+ actively pumped from the lumen and water follows osmotically
K+ reabsorbed by passive diffusion, rate determined by gradient
Cl- is reabsorbed in exchange for HCO3-, intestinal contents becomes more alkaline

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17
Q

Na+ and colon

A

Actively pumped from lumen and water follows osmotically

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18
Q

K+ and small intestine

A

Reabsorbed by passive diffusion
Rate determined by gradient

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19
Q

Cl- and colon

A

Cl- is reabsorbed in exchange for HCO3- - contents becomes more alkaline

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20
Q

How many stages of sodium absorption

A

2

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21
Q

1st stage of sodium absorption

A

Na/K ATPase on basolateral side of cell
Pumps Na+ out of the cell to create a low intracellular concentration of Na+

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22
Q

2nd stage of sodium absorption

A

Membrane transport protein
Glucose-sodium transporter uptakes from luminal side (apical side)
1 glucose: 2 Na+
Glucose moved out through GLUT2 protein

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23
Q

Glucose transporter in GI epithelial cells

A

GLUT2

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24
Q

Paracellular movement

A

Between cells

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25
Q

Number of Na+ moved via glucose-sodium transporter

A

2

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26
Q

Sodium secretion (and water)

A
  1. Na/K ATPase creates low intracellular concentration of Na+
  2. NKCC2 restores Na+ levels by pumping it into the cell along with K+ and 2Cl- ions
  3. K+ levels restored by a K+ channel
  4. Cl- ions excreted on the apical membrane into the gut lumen
  5. This is modulated by:
    -VIP increases cAMP to increase NKCC2 and Cl- channels
    - ACh increases intracellular Ca2+ to increase Cl- channels
  6. h2O follows the gradient of Cl-
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27
Q

VIP and sodium secretion

A

Increases cAMP to increase NKCC2 and Cl- channels

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28
Q

ACh and sodium secretion

A

Increased intracellular Ca2+ to increase Cl- channels

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29
Q

Water secretion follows gradient of which ion

A

Cl-

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30
Q

What does NKCC2 pump

A

1 Na+
1 K+
2 Cl-

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31
Q

Factors affecting absorption

A

Number and structure of enterocytes
Blood and lymph flow
Nutrient intake
GI motility

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32
Q

Factors affecting secretion

A

Irritants
Bile
Bacterial toxins
Neural and hormonal inputs to secretion and GI motility

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33
Q

Coeliac disease

A

1% of population suffer
Genetic component
Gluten- found in wheat, rye and barley
Villi become damaged
Digestion is impaired

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34
Q

Oral rehydration

A

High levels of Na+ and glucose
Aids absorption of electrolytes and thus water

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35
Q

Cholera

A

Vibrio Cholerae
Transmitted through contaminated water
Toxin released from bacteria
Binds to interstitial cells
Stimulates adenylate cyclase to produce more cAMP and increase expression of Cl- channels
Dramatic efflux of ions and water - 15-20 L/day
Watery diarrhoea

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36
Q

Which enzyme produces cAMP

A

Adenylate cyclase

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37
Q

Protein requirement for a healthy adult per day

A

40-50g

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38
Q

Number of essential amino acids

A

8

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39
Q

Number of amino acids

A

20

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40
Q

Function of peptides in diet

A

Supply essential amino acids and replace nitrogen which has been converted to urea

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41
Q

Which optical isomer of amino acids can the body use

A

L-isomers

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42
Q

Zwitterions

A

Have both negative and positive charge on same molecule

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43
Q

Stimulus of gastric acid production

A

Increased gastrin secretion
Histamine from ECL cells
Parasympathetic innervation(enteric and vagal)- ACh

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44
Q

Inhibition of gastric acid production

A

Intestinal hormones (GIP, VIP, somatostatin, secretin, glucagon)
Prostaglandins

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45
Q

Cell targets and actions of gastric acid

A

Activation of pepsinogen to pepsin

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46
Q

Production of H+ in parietal cells- 2 methods

A
  1. H2O in parietal cells dissociates into OH- and H+
  2. CO2 and H2O create HCO3- and H+ via carbonic anhydrase
    Method 2 preferred to prevent buildup of OH- — OH- levels kept low by re-association with H+ ions
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47
Q

Production of gastric acid

A

H+ ions pumped into stomach lumen by H/K ATPase pumps
HCO3- is secreted into the capillary in exchange for Cl-
Cl- ions diffuse into the lumen through Cl- channels
In the lumen H+ and Cl- react to form HCl

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48
Q

Source of K+ ions in stomach lumen

A

Food
Ions that have diffused back into the lumen through K+ channels

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49
Q

Increased secretion of HCl mechanism

A

Results from migration of H/K ATPase proteins to the apical membrane in vesicles
Removal of end products speeds up forward rate of reaction

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50
Q

Amount of stomach acid produced per day

A

2 L

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51
Q

pH of gastric acid

A

2

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52
Q

2 types of gastrin

A

G17
G34
(Number of amino acids)

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53
Q

Which is the active form of gastrin

A

G17

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54
Q

In between feeding which form of gastrin is released in a larger quantity

A

G34

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55
Q

What secreted gastrin

A

G cells

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56
Q

Stimulus of G cells

A

Amino acids/peptides in stomach lumen
Distension of stomach
Activation of enteric nervous system
Neural- vagus nerve from hindbrain (Cephalic reflex)

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57
Q

Inhibition of G cells

A

Decreased pH

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58
Q

Cell targets and actions of gastrin

A

Parietal cells —> HCl release
ECL cells —> histamine release —> parietal cells —> HCl release
Whole stomach —> trophic effect (walls grow in size and number of cells)

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59
Q

Which cells secrete pepsinogen

A

Chief cells from stomach body

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60
Q

What activates pepsinogen to form pepsin

61
Q

Stimulus of pepsinogen release

A

Parasympathetic nerve activity (vagus)
Enteric nerve activity

62
Q

Inhibition of pepsin

A

Pepsin is inhibited by HCO3- which irreversibly inactivates it

63
Q

At what pH is pepsin most effective

64
Q

What percentage of protein digestion does pepsin account for

65
Q

Mechanism of pepsin

A

Breaks down collagen
Increases surface area of molecules for more efficient digestion

66
Q

pH in duodenal cap

67
Q

pH in duodenum (excluding duodenal cap)

68
Q

Endopeptidases

A

Split polypeptides internal bonds

69
Q

Examples of endopeptidases

A

Trypsin
Chymotrypsin
Elastase

70
Q

Exopeptidases

A

Cleaves amino acids off ends of polypeptides

71
Q

What activates trypsinogen—> trypsin

A

Enterokinase

72
Q

Examples of exopeptidases

A

Carboxyl dipeptidases
Amino pepridases of the microvilli border

73
Q

3 locations for peptide digestion

A

Intestinal lumen
Brush border
Intracellular

74
Q

What activates most peptidases

75
Q

Absorption of amino acids

A

Amino acids are absorbed through facilitated diffusion and cotransport
Na?K ATPase creates a Na+ gradient
Amino acids absorbed alongside Na+

76
Q

Absorption of peptides

A

Co-transport with H+

77
Q

Where does protein digestion start

78
Q

Zymogen of elastase

A

Proelastase

79
Q

Zymogen of colipase

A

Procolipase

80
Q

What percentage of carbohydrate calories are ingested

81
Q

What percentage of carbohydrate calories ingested come from starch

82
Q

What percentage of carbohydrate calories ingested come from sucrose

83
Q

What percentage of carbohydrate calories ingested come from lactose

84
Q

What percentage of carbohydrate calories ingested come from maltose

85
Q

Monosaccharides examples

A

Glucose
Fructose
Galactose

86
Q

Oligosaccharides

A

Several sugar molecules

87
Q

Which optical isomer of sugars can be used by the body

88
Q

Sucrose

A

Glucose and fructose

89
Q

Glycogen

A

Principle dietary polysaccharide
From animal sources
Polymer of glucose molecules
Joined by Alpha 1-4 glycosidic linkages and some chain branching Alpha 1-6 glycosidic linkages

90
Q

Starch

A

Majority alpha 1-4 glycosidic linkages
Some chain branching but much less than glycogen

91
Q

Lactose

A

Forms beta linkage: OH groups lie above the plane of the molecule
Requires its own enzyme to break it down

92
Q

Cellulose

A

Only has beta 1-4 glycosidic linkages

93
Q

Starch is first degraded by…

A

Ptyalin (Alpha amylase in saliva)

94
Q

Optimal pH of ptyalin

95
Q

Where does carbohydrate digestion start

96
Q

Which glands secrete ptyalin

A

Parotid and submandibular glands

97
Q

End products of starch break down

A

Maltose
Maltotriose
Larger polymers of glucose
Alpha-limit dextrins (branched polymers with around 8 units)

98
Q

Alpha-limit dextrins

A

Branched polymers with around 8 units

99
Q

Where does further digestion of oligosaccharides occur

A

Microvilli membrane

100
Q

Enzymes on microvilli membrane for digestion of oligosaccharides

A

Maltase
Sucrase
Lactase
Alpha-limit dextrinase

101
Q

What percentage of starch digestion is the duodenum responsible for

102
Q

Which hormone is responsible for signalling starch digestion in duodenum

103
Q

What gland secretes Alpha amylase into duodenum

104
Q

What stimulates duodenal digestion of starch

A

Arrival of chyme in duodenum

105
Q

What does pancreatic alpha amylase catalyse

A

Break down of alpha 1-4 linkages

106
Q

What does pancreatic alpha amylase not catalyse

A

Break down of:
Alpha 1-6 linkages
Alpha 1-4 linkages next to branch points
Terminal alpha 1-4 linkages

107
Q

Where are monosaccharides absorbed

A

Brush border membrane

108
Q

Which monosaccharides require active transport for absorption

A

Glucose
Galatose

109
Q

Absorption of glucose and galactose

A

Low Na+ concentration created intracellularly
Monosaccharides co-transported with Na+ (SGLT)

110
Q

Which co-transporter is used for Na+ and glucose or galactose

111
Q

Absorption of fructose

A

Facilitated diffusion (GLUT)

112
Q

Which protein is responsible for facilitated diffusion of monosaccharides

113
Q

Movement of monosaccharides from cell to blood

A

Facilitated diffusion via GLUT on basolateral membrane
Diffuse through capillary pores into hepatic portal veins

114
Q

Most carbohydrates are digested and absorbed in the first…….. of the small intestine

115
Q

What occurs when monosaccharides enter the liver

A

Converted to glucose

116
Q

What does the creation of alpha-glycerol phosphate require

A

Dihydroxyacetone phosphate which is reduced during glycolysis

117
Q

Two fates of glucose in the liver

A

Stored as glycogen
Converted to alpha-glycerol phosphate and fatty acids

118
Q

Pathway of glucose to stored triglycerides

A

Glucose
Fatty acids and alpha-glycerol phosphate
Triglycerides and fatty acids
VLDLs and LDLs
Adipocytes capillaries
Triglycerides released
Triglycerides stored

119
Q

What hydrolyses triglycerides to monoglycerides and fatty acids

A

Lipoprotein lipase

120
Q

Where is lipoprotein lipase found

A

Blood facing surface of capillary endothelial cells, especially in adipose tissue

121
Q

Average daily lipid uptake

122
Q

3 main fatty acids

A

Palmitic acid
Stearic acid
Oleic acid

123
Q

Where does fat digestion start

124
Q

What initially breaks down large fatty molecules

A

Lipase
Cholesterol esterase
Phospholipase A

125
Q

3 types of lipase

A

Lingual
Gastric
Pancreatic

126
Q

Where does lipid digestion predominantly occur

A

Small intestine

127
Q

Mechanism of lipase

A

Splits bonds between 1st and 3rd carbons and their fatty acids
Forms monoglycerides and 2 free fatty acid chains

128
Q

Droplet formation

A

Lipids are insoluble so aggregate into droplets in upper portion of the stomach
Emulsified into smaller droplets 1mm in diameter

129
Q

Droplet formation requires

A

Mechanical disruption : provided by GI tract motility
Emulsifying agents: provided by phospholipids in food and bile salts in duodenum

130
Q

What are bile salts synthesised from

A

Cholesterol

131
Q

How do bile salts work

A

Non-polar ends associate with non-polar interiors of lipid droplets
Has an affinity for both fat and water so bring the 2 together leaving polar regions exposed to water
Repel other lipid droplets which have been emulsified preventing reaggregation

132
Q

Function of colipase

A

Bind the lipid droplet and lipase together creating micelles
Emulsifying agents impairs accessibility of lipase

133
Q

Which gland secretes colipase

134
Q

Constituents of micelles

A

Bile salts
Fat soluble vitamins (A, D, K, E)
Cholesterol
Fatty acids
Monoglycerides
Phospholipids

135
Q

Size of lipid droplets

A

1 mm in diameter

136
Q

Size of micelles

A

4-7 nm in diameter

137
Q

Where is bile reabsorbed

138
Q

What percentage of bile is excreted

139
Q

How many times a day is bile recycled

140
Q

Absorption of fats

A
  1. Bile salts from liver coat fat droplets
  2. Pancreatic lipase and colipase break down fats into monoglycerides and fatty acids stored in micelles
  3. Monoglycerides and fatty acids move out of micelles and enter cells by diffusion
    Cholesterol is transported into cells
  4. In sER triglycerides are resynthesised
  5. Absorbed fats combine with cholesterol and proteins in Golgi apparatus to form Chylomicrons or VLDL particles
  6. Exocytosed into lymphatic system via a lacteal
141
Q

Systemic handling of fats

A

Chylomicrons enter lacteals into lymphatic system
Lymph eventually drains into systemic veins
Once in blood circulation fatty acids are released by lipoprotein lipase
Fatty acids diffuse into adipocytes to combine with alpha-glycerol phosphate

142
Q

Why don’t Chylomicrons enter capillaries

A

Cannot diffuse through basement membrane

143
Q

Why can Chylomicrons enter lacteals

A

Have larger pores than capillaries

144
Q

How is alpha-glycerol phosphate produced

A

Glycolysis

145
Q

Why is glucose essential for triglyceride synthesis in adipocytes

A

Do not contain the enzyme to phosphorylate glycerol to alpha-glycerol

146
Q

How is glycerol produced

A

From dihydroxyacetone phosphate

147
Q

3 main sources of fatty acids for triglyceride synthesis

A
  1. Glucose that enters adipose tissue is broken down
  2. Glucose used in the liver to form VLDL triglycerides which are transported int the blood and taken up by adipocytes
  3. Ingested triglycerides transported in the blood in Chylomicrons and taken up by adipocytes
148
Q

Trace elements occur in a normal human diet. Which of the following metals is an example of a trace?

149
Q

67 year old woman has had her gastric antrum removed as treatment for chronic gastric ulcers. Her niece is worried that she won’t be able to digest her food properly. Which statement regarding carbohydrate digestion and absorption is correct?

A

Glucose is passively absorbed through a membrane transporter

GI (12 decks)

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