Fluid And Digestion Flashcards
1
Q
Amount of water in the GI tract
A
9L
2
Q
What percentage of water in the gut comes from secretions
A
80%
3
Q
Amount of water in GI tract from saliva
A
1.5 L
4
Q
Amount of water in GI tract from gastric juices
A
2 L
5
Q
Amount of water in GI tract from bile
A
0.5 L
6
Q
Amount of water in GI tract from pancreatic juices
A
1.5 L
7
Q
Amount of water in GI tract from intestinal secretions
A
1.5 L
8
Q
Amount of water in GI tract from drinking water
A
2L
9
Q
Water absorption in the stomach
A
Small amount
Small surface area and lacks solute absorbing mechanisms which create osmotic gradient
10
Q
Where is majority of water reabsorbed in GI tract
A
Small intestine
8.5 L
11
Q
Amount of water reabsorbed by small intestine
A
8.5 L
12
Q
Amount of water reabsorbed by colon
A
400 ml
13
Q
Amount of water excreted by faeces
A
100ml
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
15
Q
Na+ and small intestine
A
Na+ very abundant in chyme
Actively transported into cells in ileum and Jejunum
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
17
Q
Na+ and colon
A
Actively pumped from lumen and water follows osmotically
18
Q
K+ and small intestine
A
Reabsorbed by passive diffusion
Rate determined by gradient
19
Q
Cl- and colon
A
Cl- is reabsorbed in exchange for HCO3- - contents becomes more alkaline
20
Q
How many stages of sodium absorption
A
2
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+
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
23
Q
Glucose transporter in GI epithelial cells
A
GLUT2
24
Q
Paracellular movement
A
Between cells
25
Number of Na+ moved via glucose-sodium transporter
2
26
Sodium secretion (and water)
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-
27
VIP and sodium secretion
Increases cAMP to increase NKCC2 and Cl- channels
28
ACh and sodium secretion
Increased intracellular Ca2+ to increase Cl- channels
29
Water secretion follows gradient of which ion
Cl-
30
What does NKCC2 pump
1 Na+
1 K+
2 Cl-
31
Factors affecting absorption
Number and structure of enterocytes
Blood and lymph flow
Nutrient intake
GI motility
32
Factors affecting secretion
Irritants
Bile
Bacterial toxins
Neural and hormonal inputs to secretion and GI motility
33
Coeliac disease
1% of population suffer
Genetic component
Gluten- found in wheat, rye and barley
Villi become damaged
Digestion is impaired
34
Oral rehydration
High levels of Na+ and glucose
Aids absorption of electrolytes and thus water
35
Cholera
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
36
Which enzyme produces cAMP
Adenylate cyclase
37
Protein requirement for a healthy adult per day
40-50g
38
Number of essential amino acids
8
39
Number of amino acids
20
40
Function of peptides in diet
Supply essential amino acids and replace nitrogen which has been converted to urea
41
Which optical isomer of amino acids can the body use
L-isomers
42
Zwitterions
Have both negative and positive charge on same molecule
43
Stimulus of gastric acid production
Increased gastrin secretion
Histamine from ECL cells
Parasympathetic innervation(enteric and vagal)- ACh
44
Inhibition of gastric acid production
Intestinal hormones (GIP, VIP, somatostatin, secretin, glucagon)
Prostaglandins
45
Cell targets and actions of gastric acid
Activation of pepsinogen to pepsin
46
Production of H+ in parietal cells- 2 methods
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
47
Production of gastric acid
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
48
Source of K+ ions in stomach lumen
Food
Ions that have diffused back into the lumen through K+ channels
49
Increased secretion of HCl mechanism
Results from migration of H/K ATPase proteins to the apical membrane in vesicles
Removal of end products speeds up forward rate of reaction
50
Amount of stomach acid produced per day
2 L
51
pH of gastric acid
2
52
2 types of gastrin
G17
G34
(Number of amino acids)
53
Which is the active form of gastrin
G17
54
In between feeding which form of gastrin is released in a larger quantity
G34
55
What secreted gastrin
G cells
56
Stimulus of G cells
Amino acids/peptides in stomach lumen
Distension of stomach
Activation of enteric nervous system
Neural- vagus nerve from hindbrain (Cephalic reflex)
57
Inhibition of G cells
Decreased pH
58
Cell targets and actions of gastrin
Parietal cells —> HCl release
ECL cells —> histamine release —> parietal cells —> HCl release
Whole stomach —> trophic effect (walls grow in size and number of cells)
59
Which cells secrete pepsinogen
Chief cells from stomach body
60
What activates pepsinogen to form pepsin
HCl
61
Stimulus of pepsinogen release
Parasympathetic nerve activity (vagus)
Enteric nerve activity
62
Inhibition of pepsin
Pepsin is inhibited by HCO3- which irreversibly inactivates it
63
At what pH is pepsin most effective
1.6-3.2
64
What percentage of protein digestion does pepsin account for
20%
65
Mechanism of pepsin
Breaks down collagen
Increases surface area of molecules for more efficient digestion
66
pH in duodenal cap
2-4
67
pH in duodenum (excluding duodenal cap)
6.5
68
Endopeptidases
Split polypeptides internal bonds
69
Examples of endopeptidases
Trypsin
Chymotrypsin
Elastase
70
Exopeptidases
Cleaves amino acids off ends of polypeptides
71
What activates trypsinogen—> trypsin
Enterokinase
72
Examples of exopeptidases
Carboxyl dipeptidases
Amino pepridases of the microvilli border
73
3 locations for peptide digestion
Intestinal lumen
Brush border
Intracellular
74
What activates most peptidases
Trypsin
75
Absorption of amino acids
Amino acids are absorbed through facilitated diffusion and cotransport
Na?K ATPase creates a Na+ gradient
Amino acids absorbed alongside Na+
76
Absorption of peptides
Co-transport with H+
77
Where does protein digestion start
Stomach
78
Zymogen of elastase
Proelastase
79
Zymogen of colipase
Procolipase
80
What percentage of carbohydrate calories are ingested
50%
81
What percentage of carbohydrate calories ingested come from starch
50%
82
What percentage of carbohydrate calories ingested come from sucrose
30%
83
What percentage of carbohydrate calories ingested come from lactose
6%
84
What percentage of carbohydrate calories ingested come from maltose
1-2%
85
Monosaccharides examples
Glucose
Fructose
Galactose
86
Oligosaccharides
Several sugar molecules
87
Which optical isomer of sugars can be used by the body
D-isomers
88
Sucrose
Glucose and fructose
89
Glycogen
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
Starch
Majority alpha 1-4 glycosidic linkages
Some chain branching but much less than glycogen
91
Lactose
Forms beta linkage: OH groups lie above the plane of the molecule
Requires its own enzyme to break it down
92
Cellulose
Only has beta 1-4 glycosidic linkages
93
Starch is first degraded by…
Ptyalin (Alpha amylase in saliva)
94
Optimal pH of ptyalin
6.7-7.5
95
Where does carbohydrate digestion start
Mouth
96
Which glands secrete ptyalin
Parotid and submandibular glands
97
End products of starch break down
Maltose
Maltotriose
Larger polymers of glucose
Alpha-limit dextrins (branched polymers with around 8 units)
98
Alpha-limit dextrins
Branched polymers with around 8 units
99
Where does further digestion of oligosaccharides occur
Microvilli membrane
100
Enzymes on microvilli membrane for digestion of oligosaccharides
Maltase
Sucrase
Lactase
Alpha-limit dextrinase
101
What percentage of starch digestion is the duodenum responsible for
95%
102
Which hormone is responsible for signalling starch digestion in duodenum
CCK
103
What gland secretes Alpha amylase into duodenum
Pancreas
104
What stimulates duodenal digestion of starch
Arrival of chyme in duodenum
105
What does pancreatic alpha amylase catalyse
Break down of alpha 1-4 linkages
106
What does pancreatic alpha amylase not catalyse
Break down of:
Alpha 1-6 linkages
Alpha 1-4 linkages next to branch points
Terminal alpha 1-4 linkages
107
Where are monosaccharides absorbed
Brush border membrane
108
Which monosaccharides require active transport for absorption
Glucose
Galatose
109
Absorption of glucose and galactose
Low Na+ concentration created intracellularly
Monosaccharides co-transported with Na+ (SGLT)
110
Which co-transporter is used for Na+ and glucose or galactose
SGLT
111
Absorption of fructose
Facilitated diffusion (GLUT)
112
Which protein is responsible for facilitated diffusion of monosaccharides
GLUT
113
Movement of monosaccharides from cell to blood
Facilitated diffusion via GLUT on basolateral membrane
Diffuse through capillary pores into hepatic portal veins
114
Most carbohydrates are digested and absorbed in the first…….. of the small intestine
20%
115
What occurs when monosaccharides enter the liver
Converted to glucose
116
What does the creation of alpha-glycerol phosphate require
Dihydroxyacetone phosphate which is reduced during glycolysis
117
Two fates of glucose in the liver
Stored as glycogen
Converted to alpha-glycerol phosphate and fatty acids
118
Pathway of glucose to stored triglycerides
Glucose
Fatty acids and alpha-glycerol phosphate
Triglycerides and fatty acids
VLDLs and LDLs
Adipocytes capillaries
Triglycerides released
Triglycerides stored
119
What hydrolyses triglycerides to monoglycerides and fatty acids
Lipoprotein lipase
120
Where is lipoprotein lipase found
Blood facing surface of capillary endothelial cells, especially in adipose tissue
121
Average daily lipid uptake
70-100 g
122
3 main fatty acids
Palmitic acid
Stearic acid
Oleic acid
123
Where does fat digestion start
Mouth
124
What initially breaks down large fatty molecules
Lipase
Cholesterol esterase
Phospholipase A
125
3 types of lipase
Lingual
Gastric
Pancreatic
126
Where does lipid digestion predominantly occur
Small intestine
127
Mechanism of lipase
Splits bonds between 1st and 3rd carbons and their fatty acids
Forms monoglycerides and 2 free fatty acid chains
128
Droplet formation
Lipids are insoluble so aggregate into droplets in upper portion of the stomach
Emulsified into smaller droplets 1mm in diameter
129
Droplet formation requires
Mechanical disruption : provided by GI tract motility
Emulsifying agents: provided by phospholipids in food and bile salts in duodenum
130
What are bile salts synthesised from
Cholesterol
131
How do bile salts work
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
Function of colipase
Bind the lipid droplet and lipase together creating micelles
Emulsifying agents impairs accessibility of lipase
133
Which gland secretes colipase
Pancreas
134
Constituents of micelles
Bile salts
Fat soluble vitamins (A, D, K, E)
Cholesterol
Fatty acids
Monoglycerides
Phospholipids
135
Size of lipid droplets
1 mm in diameter
136
Size of micelles
4-7 nm in diameter
137
Where is bile reabsorbed
Ileum
138
What percentage of bile is excreted
3%
139
How many times a day is bile recycled
8
140
Absorption of fats
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
Systemic handling of fats
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
Why don’t Chylomicrons enter capillaries
Cannot diffuse through basement membrane
143
Why can Chylomicrons enter lacteals
Have larger pores than capillaries
144
How is alpha-glycerol phosphate produced
Glycolysis
145
Why is glucose essential for triglyceride synthesis in adipocytes
Do not contain the enzyme to phosphorylate glycerol to alpha-glycerol
146
How is glycerol produced
From dihydroxyacetone phosphate
147
3 main sources of fatty acids for triglyceride synthesis
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
Trace elements occur in a normal human diet. Which of the following metals is an example of a trace?
Manganese
149
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?
Glucose is passively absorbed through a membrane transporter
