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Block D - Digestion and Metabolism > Physiology -- Intestinal Absorptive and Secretory Processes > Flashcards

Physiology -- Intestinal Absorptive and Secretory Processes Flashcards

(105 cards)

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1
Q

4 enzymes that break down proteins to small peptides

A
  • Pepsin
  • Trypsin
  • Chymotrypsin
  • Carboxypeptidase
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2
Q

Location of Brunner’s glands

A

Duodenum submucosa

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3
Q

Contents of Brunner’s glands

A
  • No digestive enzymes
  • Lots of HCO3-
  • Mucin
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4
Q

Location of goblet cells

A

Throughout the small intestine

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5
Q

Secretions of goblet cells

A

Mucin

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6
Q

Characterization of intestinal mucosa

A

Crypts and villi

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7
Q

Location of complete digestion and absorption in terms of the small intestine

A

Villi

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8
Q

Location of secretion in terms of small intestine

A

Crypt

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9
Q

Rate of cell shedding at the tip of the villus

A

100 x 106 cells/min

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10
Q

Location of villus enzymatic activity

A

Brush border

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11
Q

Secretions from crypt cells and volume produced

A

No digestive enzymes

Succus entericus (3L per day)

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12
Q

Ionic composition of succus entericus

A

Isotonic:

  • Na+
  • K+
  • Cl-
  • HCO3-
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13
Q

pH of succus entericus secretions

A

~7.5 - 9

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14
Q

What is located in the lumen of the SI crypts?

A

Cotransporter protein transporting Na+ and Cl-

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15
Q

Describe the function of the cotransporter of the crypts

A
  • Na+ brought out of cell by Na+-K+-ATPase
  • Na+ cotransported with Cl- into cell
  • Cl - secreted out of the other end of the cell through Ca++ dependent cAMP
  • Na+ also flows between cells
  • Water follows osmotic gradient
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16
Q

Effect of vibrio cholerae bacterium

A

Enterotoxic effect: bind to receptors on apical membrane –> stimulate adenylate cyclase –> increase cAMP = maximally stimulates intestinal secretion

Net result = overwhelms the absorptive capacity of SI and colon (need rapid rehydration)

Also, cAMP decreases absorption of neutral NaCl in villi

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17
Q

Describe the regulation of succus entericus secretions

A

Poorly understood interactions of ENS, ANS, gut peptides (gastrin, VIP) acting in paracrine/endocrine fashion

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18
Q

Effect of prostaglandins and histamine on succus entericus secretion

A

Increase secretion

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19
Q

Effect on somatostatin on succus entericus secretion

A

Inhibition of secretion

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20
Q

Function of villi

A
  • Synthesize enzymes (retained in brush border)
  • Absorb nutrients and fluids
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21
Q

6 enzyme types synthesized by the intestinal villi

A
  • Enterokinase
  • Amylase
  • Lipase
  • Aminopeptidases
  • Dipeptidases
  • Disaccharases
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22
Q

4 disaccharases synthesized by the intestinal villi

A
  • Sucrase
  • Maltase
  • Isomaltase
  • Lactase
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23
Q

Location of paneth cells

A

Base of crypts

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24
Q

2 substances secreted by paneth cells

A

Lysozymes

Defensins

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25
Function of paneth cell secretions
Possible importance in protecting mucosa against bacteria
26
Contents of SI lamina propria
Lymphocytes and plasma cells
27
Role of SI lamina propria contents
Secretion of Ig = important in mucosal immune system
28
Volume of colonic secretions
Small
29
pH of colonic secretions
Alkaline
30
Composition of colonic secretions
* [HCO3-] = 100 - 150 mEq/L * [K+] = 100 - 150 mEq/L
31
Protein included in colonic secretions
Mucin
32
Characteristic feature of colonic secretions
Bacterial activity NO DIGESTIVE ENZYMES
33
Approximate daily input and output of solids
Input = 500 g Output = 50 g
34
Approximate daily water input and output
Input = 2000 mL Output = 200 mL
35
Approximate composition of solid output
* 30% bacteria * 30% undigested fiber * 10 - 20% lipids * 10 - 20% inorganic matter
36
Volume of fluid produced by salivary glands
1500 mL
37
Sources of fluids input to the GI
* Oral intake * Salivary glands * Stomach * Bile * Pancreas * Intestine
38
Volume of stomach fluids produced daily
2500 mL
39
Volume of bile produced daily
500 mL
40
Volume of pancreatic fluid produced daily
1500 mL
41
Volume of intestinal fluids produced daily
1000 mL
42
Approximate volume of fluid that must be absorbed daily
9000 mL
43
Location of fluid absorption in GI
Duodenum Colon
44
Approximate daily fluid absorbed from duodenum
7000 mL
45
Approximate daily fluid absorbed by colon
1800 mL
46
Describe the composition of proteins released into the lumen of the GIT
* 50g as enzymes * 30g as cells * Total = 30g
47
Fate of amino acids derived from digested proteins
Go to the amino acid pool
48
2 characteristics of sites of exchange
* Very large surface area * Intimate contact with blood vessels
49
What part of the GI tract is absolutely essential to life?
Intactness of at least part of the small intestine (i.e. colon cannot take over nutrient absorption)
50
Response of small intestine to resection
* Hypertrophy * Hyperplasia i.e. increase + of villus cells and increaase height of villi to increase absorptive capacity by up to 5x
51
4 trophic factors for SI
* Luminal nutrients * Hormones (G, CCK, glucagon, etc) * Local neural factors * Growth factors (epidermal, PGs, insulin-like, etc)
52
What promotes the integrity of the GIT
Normal utilization (i.e. regular eating)
53
Consequence of parental feeding (i.e. no stimulation of the gut) on GIT
Intestinal mass decreases
54
Dscribe the process of diarrhea
55
Describe the state of blood flow during a meal
50 - 100% increase, most of which is shunted to the mucosa to maximize absorption
56
Rate of postprandial blood flow to the intestine
1 - 2 L/min
57
Lympho flow to intestine
1 - 2 mL/min
58
4 mechanisms for vasodilatoin
* Metabolites * Bradykinin * NANC neurons (VIP? NO? etc) * Hormones
59
Describe the blood flow through the layers of the intestinal walls
High density of cells in the mucosa = high blood flow
60
Describe the changes in surface area from duodenum to ileum
Gradual decrease in: * Diameter * Thickness of wall * Number of folds * Number of villi * Size and shape of villli
61
Where is the efficiency of nutrient absorption greatest?
Proximal SI
62
Describe the relative surface area of small intestinal sections
50% of total SI surface area is the in proximal 25% of the SI
63
Describe the permeability of the SI sections
* More permeable tight junctions * Apical membranes are leakier
64
4 reasons why the efficiency of absorption is greatest in the proximal SI
* Greater surface area * More permeable * Greater concentration gradients * Brush border enzymes and transporters are denser in proximal SI
65
Major area of Iron and Ca++ absorption in SI
Duodenum
66
Major area of carbohydrate absorption in SI
Whole SI but decreasing distally, notably mid-jejunum
67
Major area of proteins, lipids, salt and water in SI
Whole SI but decreasing distally
68
Major area of vitamin B12 absorption in SI
Ileum
69
Major area of bile acid absorption in SI
Slight absorption throughout the whole SI with gradual increase through duodenum to jejunum, but marked increase at ileum
70
5 methods of absorption in SI
* Simple diffusion * Facilitated diffusion * Active transport * Pinocytosis * Osmosis
71
Percentage of carbohydrates absorbed
99%
72
Percentage of fat absorbed
95%
73
Percentage of protein absorbed
92%
74
Absorptive capacity for H2O
18 L
75
Absorptive capacity for glucose
3600 g
76
Absorptive capacity for amino acids
600 g
77
Absorptive capacity for fat
700 g
78
4 factors in absorption
* Adequate form of absorption * Adequate surface for absorption * Adequate rate of transit * Specific co-factors and transporters (for facilitated diffusion and active transport)
79
Describe carbohydrate absorption from its initial state to the SI
80
4 causes of carbohydrate malabsorption
* Sever pancreatic insufficiency * Selective deficiency of Brush Border disaccharases (or transporters) * Impaired enterocyte function (i.e. celiac disease) * Loss of mucosal surface
81
Describe how proteins are absorbed through the small intestine
82
Describe how fats are digested and absorbed through the SI
83
8 things to consider when analyzing malabsorption
* Number of nutrients (single or multiple?) * Enzyme deficiencies (single or multiple?) * Enzymes NOT activated? * Enzymes inactivated? * Co-factors absent? * Co-factors ineffective? * Surface area inadequate? * Transporter abnormalities? * Too rapid transit?
84
What is water absorption largely secondary to?
Na+ absorption
85
2 pathways of water absorption
* Transcellular * Paracellular
86
What is critical to Na+ absorption?
* Na+/K= ATPase in the basolateral membrane * Favors Na+ entry into the cell and then into intercellular spaces
87
Describe the mechanism for Na+ absorption in the distal colon alone
Electrogenic absorption * Occurs as a result of the pump actively extruding Na+ from cell to interstitial spaces * Lowers intracellular Na+ concentration * Makes the interior of the cell electronegative to lumen (favors entry of Na+ into cell)
88
Describe the mechanism for Na+ absorption in the jejunum and ileum
Glucose (or other non-electrolyte solute) stimulated absorption; Na+ movement across the brush border by either: * Carrier-mediated solute-coupled transport or * Passive, secondary to solvent drag denerated by the active transport of glucose
89
Describe the mechanism of Na+ absorption i nthe jejunum and distal colon
Neutral Cl- dependent absorption; coupled Na+/Cl- co-transport driven by the basolateral Na+ pump
90
Describe the mechanism of Na+ absorption in the ileum and proximal colon
Neutral Na+/Cl- absorption by dual ion exchange * (Na+/H+ and Cl-/HCO3-) or countertransport controlled by intracellular pH restricting HCO3- and H+ available for exchange
91
In cholera, what mechanisms of Na+ absorption are non-functional
* A = Electrogenic absorption * C = Neutral Cl- dependent absorption * D = Neutral Na+/Cl- absorption by dual ion exchange
92
In cholera. which mechanism of Na+ absorption is functional?
B = glucose (or other non-electrolyte solute) stimulated absorption
93
Treatment for cholera
Oral replacement to reverse dehyrdation
94
Compare the permeability and efficiency of the SI versus the colon in terms of water absorption
* SI is more permeable but less efficient * Colon is less permeable but more efficient
95
Describe the normal flow of water through the colon in a healthy individual
96
Describe the flow of water through two variations of small intestinal disease
B = high ileocecal flow but compensatory colonic absorption = same stool H2O as normal (no diarrhea) C = high ileocecal flow, compensatory absorption is maximized = increase H2O in stool (diarrhea)
97
Describe the flow of water through a diseased colon
D = normal ileocecal flow, but absorptive capacity of colon is REVERSED so that water actually ENTERS the colon instead of being absorbed FROM it --\> high H2O in stool = diarrhea
98
Define diarrhea
Loss of fluid and solutes in excess of 500 mL/day
99
5 mechanism-defined causes of diarrhea
* Absorptive defect * Non-absorbable osmotic effect * Secretory defect * Motility defect * Excessive intake??
100
How do absorptive defects cause diarrhea?
Decrease in absorptive surface
101
How do non-absorbable osmotic effects cause diarrhea?
Through non-absorbable osmotic agents
102
How do secetory defects cause diarrhea?
* Mechanism of cholera enterotoxin (can be applied to all of this kind of defect) * Decreased electroneural NaCl absorption
103
How do motility defects cause diarrhea
Decrease contractile activity and decreased resistance
104
Definition of acute diarrhea
Diarrhea for less than 14 days
105
Definition of chronic diarrhea
Diarrhea for \>30 days

Block D - Digestion and Metabolism (29 decks)

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