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Physiology II > GI: Digestion and Absorption > Flashcards

GI: Digestion and Absorption Flashcards

1
Q

Enzymes for digestion are excreted from… (3)

A

salivary glands
gastric chief cells
exocrine pancreas

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2
Q

final breakdown of all substances occurs wehre?

A

small intestine

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3
Q

What are the two major steps of CHO digestion?

A

complex sugar to oligosaccharide (1:6 link)

oligosaccharaide to monosaccharide (1:4 link)

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4
Q

What percent of ingested CHOs are complex?

A

60% (glycogen, amylose, amylopectins)

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5
Q

both salivary and pancreatic alpha-amylase break what bond on CHOs?

A

1:4 alpha bonds

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6
Q

Luminal digestion of partially converted starch by pancreatic amylase results in what 5 products?

A

lactose, alpha-dextrin, maltotriose, maltose, sucrose

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7
Q

Membrane digestion of CHO results in what three products?

A

glucose, galactose, fructose

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8
Q

Lactose is broken down to _____ via…

A

glucose + galactose via lactase

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9
Q

alpha-dextrins are broken down to ______ via…

A

glucose via maltase + alpha-dextrinase

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10
Q

What 3 enzymes convert maltotriose and maltose to glucose?

A

maltase, sucrase, alpha-dextrinase

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11
Q

Sucrose is converted to ________ via…

A

glucose + fructose via sucrase

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12
Q

Disaccharidases/oligosaccharidases are what type of proteins?

A

intrinsic membrane proteins

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13
Q

Where are disaccharidases/oligosaccharidases synthesized?

A

epithelial cells

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14
Q

What are the two types of disaccharidases/oligosaccharidases

A

galactosidases (lactase)

alpha-glucosidases (sucrase, maltase, alpha dextrinase)

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15
Q

What brings fructose in from the lumen to the small intestinal epithelial cell?

A

GLUT5

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16
Q

What percent of ingested CHO are digested to glucose?

A

80%

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17
Q

Glucose transport occurs via…

A

secondary active transport due to high plasma glucose

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18
Q

This is a sodium dependent channel on the apical membrane responsible for glucose/galactose uptake.

A

SGLT1

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19
Q

SGLT-1 uses the sodium gradient to transport what two substances from the lumen to the epithelial ICF?

A

glucose and galactose

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20
Q

This channel on the basolateral surfaces transports glucose and galactose via facilitated diffusion…

A

GLUT2

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21
Q

Does the intestinal epithelial cell have a sodium-potassium ATPase?

A

yes

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22
Q

Most disorders of CHO absorption/digestion have what pathophysiology?

A

enzyme deficiency prevent breakdown to absorbable form

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23
Q

disorders of CHO digestion result in what?

A

osmotic diarrhea

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24
Q

This is a congenital enzyme deficiency that may not be evident until later in life. It is present in about 50% of the population.

A

lactase deficiency

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25
Lactase deficiency prevents lactose digestion leading to...
osmotic diarrhea, abdominal distension
26
Proteins are ____% of caloric intake.
20-35%
27
A significant amount of protein comes from...
desquamated cells and gastric secretion
28
What catalyzes the conversion of trypsinogen to trypsin?
enteropeptidases
29
Gastric proteases (pepsins) are secreted from...
chief cells
30
Pancreatic enzymes from the _____ cells are activated in the ______
acinar cells small intestine
31
What are the products of protein digestion?
amino acids and oligopeptides
32
Trypsin catalyzes the conversion of...
proenzymes to active enzymes
33
Protein digestion begins in the stomach where protein is converted to ______ and _____ via...
AAs and oligopeptides via pepsin
34
In the small intestine, what 5 enzymes break proteins down to oligopeptides, amino acids, dipeptides and tripeptides?
trypsin, chymotrypsin, elastase, carboxypeptidase A and B
35
oligopeptides/large peptides that remain in the lumen after enzyme digestion can be further digested by peptidases at the ______ to be transported into the cell.
brush border
36
Protein transport is similar to glucose in that it is ______ transport coupled to...
secondary active coupled to sodium
37
Amino acids are transported from the lumen to the epithelial cell via...
sodium/AA cotransport
38
dipeptides and tripeptides are transported to the epithelial cell via...
H+ cotransport
39
What are the four protein cotransporters?
neutral AAs dibasic AAs dicarboxylic AAs imino/proline
40
Within the epithelial cell in the small intestine, what breaks dipeptides and tripeptides to amino acids for passage to blood?
intra cellular peptidases
41
T/F: Amino acid transporters specific for the class of amino acid...
True
42
What 3 diseases of protein digestion have the following characteristics? - insufficient trypsin in intestin - decreased protein absorption leading to malnutrition
pancreatic insufficiency/chronic pancreatitis/CF
43
What disease of protein digestion has the following characteristics? - congenital defect in neutral AA transport - di and tripeptide absorption remains normal
hartnup disease
44
What disease of protein digestion has the following characteristics? - absent dibasic AA transporter (for cystine, lysine, arginine) absent from guy and kidney - dibasic AAs lost in urine and feces
Cystinuria
45
What three factors make fat digestion difficult?
hydrophobic non water soluble enzymes require churning/bile emulsification
46
What are 4 key events in fat digestion?
secretion emulsification hydrolysis solubilizing
47
What must be secreted to digest fat?
bile and lipases
48
What bonds must be hydrolyzed in fat digestion?
ester linkages
49
lipid digestion products must be solubilized within____ to be delivered to enterocytes
micelles
50
Which lipid digestion enzyme? convert TGs to monoglyceride + 2 FFAs breaks FFAs off the 1,3 positions
pancreatic lipase
51
What prevents bile salt inhibition of pancreatic lipase?
colipase
52
What catalyzes the conversion of 2 monoglyceride to glycerol + 1 FFA?
cholesterolester hydrolase
53
cholesterol ester hydrolase can remove all three ester linkages, and removes fatty acids from what substances? (3)
cholesterol esters vitamins A/D/E glycerides
54
What can hydrolyze phospholipids at the 2 position?
phospholipase A2
55
products of fat digestion are quickly moved where with what substances?
bile acid micelles with lysophospholipid and cholesterol
56
The micelle breaks down and products diffuse where?
apical surface of enterocyte
57
Long-chain FFAs, 2-MG, phospholipids and cholesterol are absorbed into the enterocyte via...
simple diffusion
58
Micelles diffuse through what layer to the mucosal surface?
unstirred layer
59
what percent of ingested fat is removed by the small intestine?
95%
60
Once inside the enterocyte, what is the fate of micelle components?
lipid reassembly
61
What pathway of lipid reassembly? 2 monoglycerides + Fatty Acyl CoA → TGs
Monoglyceride acylation pathway
62
What pathway of lipid reassembly? glycolysis → P-Glycerol or diOH-AcetoneP → Alpha-GlycerolP → TGs
Phosphatidic Acid Pathway
63
What large molecule has a core of TGs and cholesterol surrounded by phospholipids and apoproteins?
chylomicrons
64
By what transport mechanism do chylomicrons leave enterocytes, and what do they enter?
exocytosis, enter lymph lacteals
65
What is the composition of chylomicrons?
84% TGs, 8% phospholipids, 6% cholesterol, 2% apoproteins
66
What abnormality of lipid digestion/absorption has the following characteristics? - gastrin secreting tumor - acidic small intestine - dysfunctional pancreatic lipase
abnormal digestion: Zollinger-Ellison Syndrome
67
What abnormality of lipid digestion/absorption has the following characteristics? - generalized lymphatic dystrophy - steatorrhea - rare, macrophages in jejunal lamina
Abnormal absorption: Whipple's Disease
68
What are the fat-soluble vitamins?
A, D, E, K
69
Fat soluble vitamins are processed in the same manner as dietary lipids, meaning they are transported in the lumen via _____ and enter circulation via...
transport micelles circulation via chylomicrons
70
Water soluble vitamins are most often absorbed via...
sodium dependent co-transport
71
B12 binds to _______ which protects it from digestion, allowing it to be absorbed where?
intrinsic factor, absorbed in ileum
72
Calcium absorption occurs where via...?
brush border via facilitated diffusion
73
What causes expression of the calcium binding protein (intracellular calcium shuttle)?
Vit. D3
74
What transporters are present on the basolateral membrane to allow calcium to enter circulation?
Calcium-ATPase Sodium-Calcium Exchanger
75
the amount of iron ingested is greater or less than the amount absorbed?
much greater (low absorption)
76
Gastric acid promotes intestinal absorption and solubilization of iron via what process?
reduce from Fe3+ (ferric) to Fe2+ (ferrous)
77
What is the plasma transporter for iron?
transferrin
78
What is the intracellular storage depot for iron?
ferritin
79
1.5-2.5 L of water is ingested per day. How much is secreted into the gut lumen by the GI tract?
7L
80
What percent of water is lost in feces?
2%
81
Is the stomach permeable to water?
no
82
reabsorption of water has what osmolarity
isosmotic
83
Water follows solute out of the basolateral membrane. So what transporters increase water absorption?
sodium cotransport of amino acids and sugars
84
What is the primary site for sodium absorption in the small intestine?
jejunum
85
What channels are present on the apical membrane of jejunal epithelial cells?
NHE, Sodium-Glucose/AA channels
86
What channels are present on the basolateral membrane of jejunal epithelial cells?
Bicarb Channel, AA/Glucose Channles, Sodium-Potassium ATPase
87
In the jejunum, is there a net secretion or net absorption of sodium bicarb?
absorption
88
Describe the mechanism of Cl- absorption in the jejunum?
voltage driven paracellular absorption
89
What transporters are present on the ilieal apical membrane?
NHE, Sodium-Glucose/AA channels Cl-/HCO3 exchanger
90
What transporters are present on the ilieal basolateral membrane?
Sodium-Potassium ATPase Sugar/AA channels Cl- channel
91
In the jejunum, there is a net reabsorption of NaHCO3. What is reabsorbed in the ileum?
NaCl
92
What is secreted into the lumen of ileal epithelial cells? What effect does this have on acid/base status?
H+ and HCO3- secretion, no change to acid/base
93
What channels are present on the apical membrane of colon epithelial cells?
ENaC (in) and K (out)
94
What stimulates ENaC channels on the apical membrane of colon epithelial cells?
Aldosterone
95
What regulates the rate of potassium secretion in the colon?
flow
96
What are three clinical effects of diarrhea?
Loss of fluid, bicarb, potassium
97
What are three major causes of diarrhea?
decreases surface area for absorption osmotic diarrhea excessive secretion (cholera)
98
Crypt cells have what channel on the basolateral surface that brings in chloride?
NKCC1
99
Cholera toxin stimulates secretion of Cl- out of what channel, via increased production of _______ via...
CFTR channel increases cAMP production via irreversible adenylyl cyclase activation
100
How does water and sodium follow chloride in cholera?
paracellular
101
What is an example of secretory diarrhea?
cholera
102
how do you treat cholera?
oral rehydration therapy

Physiology II (28 decks)

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