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Gastroenterology > "Follow the Molecules" > Flashcards

"Follow the Molecules" Flashcards

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1
Q

Malabsorption

A

Impaired absorption of nutrients

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2
Q

Maldigestion

A

Impaired digestion of nutrients within the intestinal lumen or at the terminal digestive site of the brush border membrane of mucosal epithelial cells

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3
Q

What are the 3 steps required for normal nutrient absorption?

A
  1. Luminal processing
  2. Absorption into the intestinal mucosa
  3. Transport into the circulation
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4
Q

Global malabsorption

A

Dz a/w either diffuse mucosal involvement or a reduced absorption surface.

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5
Q

Partial or Isolated malabsorption

A

Dz that interferes w/the absorption of specific nutrients

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6
Q

A celiac sprue is an example of global or partial malabsorption? Why?

A

Global Malabsorption b/c diffuse mucosal dz can lead to impaired absorption of almost all nutrients

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7
Q

Pernicious anemia is an example of global or partial malabsorption? Why?

A

Partial Malabsorption b/c it is a dz that leads to defective cobalamin (vit B12) absorption

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8
Q

Where are most dietary lipids absorbed?

A

Prox 2/3 of Jejunum

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9
Q

What is Emulsion? Why?

A

The generation of a suspension of tiny fat droplets in water…triglycerides must be emulsified to expose a large surface area to lipolytic enzymes

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10
Q

Emulsification in the Upper GI tract

A

Mastication & Gastric Mixing…fat droplets released are coated w/ingested phospholipids

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11
Q

Emulsification in the Stomach

A

Lingual Lipase & Gastric Lipase begin fat hydrolysis

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12
Q

Emulsification in the Duodenum

A
  • Pancreatic Lipase breaksdown each triglyceride into a 2-monoglyceride & 2 fatty acids.
  • Phospholipids & Cholesterol are further hydrolyzed by phospholipase A2 & pancreatic cholesterol esterase
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13
Q

What 3 factors optimize the effect of pancreatic enzymes?

A
  1. Colipase - anchors lipase to triglycerides and prevents bile salts from deactivating lipase.
  2. Intraluminal pH ~6.5 - entry of gastric hydrogen ions stimulates the release of secretin which enhances pancreatic bicarbonate secretion raising the pH
  3. Bile Salts
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14
Q

Zollinger-Ellison Syndrome

A

A disease that substantially decreases duodenal pH, selectively inhibiting fat absorption.

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15
Q

Enterohepatic Circulation

A

Bile salts mix w/lipolytic products in the duodenum forming micelles or liposomes. In this form, 2-monoglycerides & fatty acids enter the unstirred water layer that lies adjacent to the enterocyte & are then absorbed across the apical cell membrane. Bile salts remain in the intestinal lumen and travel to the terminal ileum where they are actively reabsorbed, enter the portal circulation & then re-secreted as bile.

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16
Q

Dz or resection of >100cm of terminal ileum commonly results in…

A

Severe impairment of the enterohepatic circulation of bile salts resulting in fat malabsorption

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17
Q

Florid small bowel bacterial overgrowth commonly results in…

A

Deconjugation of bile acids resulting in fat malabsorption

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18
Q

What often accompanies atrophic gastritis or the use of PPI’s?

A

A mild form of bacterial overgrowth that does not lead to fat malabsorption. However, sustained use of PPI’s does interfere w/the absorption of vitamin B12.

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19
Q

Chronic Cholerrheic Diarrhea

A

Water secretion in the colon stimulated by bile acids not absorbed in the small intestine possibly from the loss of a shorter segment of the terminal ileum.

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20
Q

The absorption of fatty acids occurs by…

A
  1. Passive Diffusion

2. Protein-Mediated Transport Processes

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21
Q

What are the 3 proteins that transport fatty acids?

A

Fatty acid transport protein 4 (FATP4), CD36 & Caveolin-1

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22
Q

Explain the process fatty acids undergo w/in villus absorptive cells

A

Fatty acids are transported intracellularly to the smooth endoplasmic reticulum to be resynthesized into triglycerides. Chylomicrons are then formed by the aggregation of triglycerides, cholesterol esters, phospholipids & apoproteins. The chylomicrons bind to the basolateral membrane, transported to the intestinal lymphatics & enter general circulation

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23
Q

List the areas where disruption of physiological process would lead to fat malabsorption & steatorrhea

Study These Flashcards
A
  • Impaired production or activity of pancreatic lipase or colipase
  • Disorders of bile acid metabolism
  • Decrease in the absorptive surface area
  • Defective apoproteins necessary for the packaging of chylomicrons
  • abnormalities in lymphatic flow
24
Q

What are the most abundant digestible carbohydrates in the human diet?

Study These Flashcards
A

Starch, sucrose, lactose

25
Can cellulose be digested in the small intestinal lumen?
No! they are fermented in the colon
26
Dietary starch is made up of what 2 polysaccharides?
Amylose & Amylopectin
27
Breakdown of Dietary Starch
Salivary & pancreatic amylase digest starch producing oligo- & disaccharides (such as, maltotriose & maltose). These products are then further degraded at the microvillus membrane by brush border enzymes, hydrolyzing both digested & indigested oligo- & disaccharides into monosaccharides. Monosaccharides are then absorbed by either active or passive transport
28
List the possible reasons for impaired absorption of carbohydrates
- Deficiency in pancreatic amylase - Reduced disaccharidase activity in the small intestinal epithelium - Decreased absorptive intestinal surface area.
29
What is Primary Carbohydrate Malabsorption? What are 2 Deficiency examples?
- Single functional elements of carbohydrate digestion or absorption are missing. - Congenital Lactase Deficiency & Sucrase-Isomaltase Deficiency
30
What is Secondary Carbohydrate Malabsorption? What disease is an example?
- Reduced intestinal absorptive area from a disease | - Celiac Disease
31
What happens to carbohydrates that are not digested/absorbed in the small intestine?
They undergo degradation & bacterial fermentation in the colon. Producing short-chain fatty acids (butyrate, propionate, acetate, lactate), carbon dioxide, hydrogen, & methane.
32
Excessive bacterial fermentation in pt's w/carbohydrate malabsorption causes?
Acidic stools, abdominal distention & flatulence
33
What is the preferred energy source for colonic epithelial cells?
Short-chain fatty acids efficiently absorbed from the colon.
34
Why can breath tests by used to look for malabsorption of a particular carbohydrate?
Fermentation of unabsorbed carbohydrates produces hydrogen & methane that is excrete through the lungs.
35
Where does protein absorption begin? & by what enzyme?
Stomach by the action of gastric pepsins (pepsinogen 1 & 2) which are activated at a low pH
36
Can pt's w/achlorhydric still digest proteins?
Yes = lost control of gastric emptying
37
Amino acids released by gastric digestion stimulate the release of what enzyme?
Cholecystokinin (CCK) from duodenal & jejunal endocrine epithelial cells.
38
Explain pancreatic enzyme digestion
In the duodenum, active pancreatic proteases digest proteins producing amino acids, dipeptides & tripeptides.
39
Explain amino acid absorption
In the small intestine, amino acids, dipepetides & tripeptides are absorbed through sodium-dependent amino acid co-transporters at the brush border. This step is passive & also secondary active transport w/the energy indirectly provided by a sodium-potassium ATPase pump.
40
Activation of pancreatic enzymes
Enterokinase is released from duodenal microvillus by bile salts. Enterokinase converts trypsinogen to trypsin. Trypsin catalyzes pancreatic protesases to their active form.
41
Impaired digestion & absorption of dietary protein from impaired pancreatic protease secretion/activity occurs in what 2 disease examples?
Chronic pancreatitis & Cystic fibrosis
42
What are 2 possible consequences of protein malabsorption?
Hypoalbuminemia & Protein malnutrition
43
Carotenoids are absorbed by?
Passive diffusion
44
Folate & Calcium are absorbed by?
Active transport
45
Fat-soluble vitamins (A, D, E & K) require solubilization in what type of phase for absorption?
Mixed Micellar
46
What is the predominant site for the absorption of most vitamins & minerals?
Prox half of small intestine
47
What are two exceptions for the site of absorption of vitamins?
Vitamin B12 & Magnesium
48
How is vitamin B12 absorbed?
Specific ileal receptor that recognizes B12-intrinsic factor complex
49
Ileal dz or resection >100cm is a/w a high risk of what vitamin deficiency?
Vitamin B12 Deficiency
50
Where is magnesium absorbed?
Distal intestines including the colon
51
Pt's w/Distal small intestinal & Colonic dz are susceptible to...
Hypomagnesium
52
What happens to vitamins & minerals in pt's w/untreated fat malabsorption?
Excess fatty acids in the intestinal lumen bind divalent cations (calcium & magnesium) creating "soaps" & causing losses of these minerals.
53
Clinically significant deficiencies of cation minerals are common in untreated fat malabsorption and create a high risk for...
Metabolic Bone Disease
54
The problem of calcium depletion in untreated fat malabsorption is magnified if what other deficiency is present?
Vitamin D Deficiency
55
Magnesium is required for the secretion & peripheral action of what hormone?
Parathyroid Hormone
56
What can occur in responsive to magnesium replacement in a pt w/fat malabsorption?
Refractory Hypocalcemia
57
What stimulates the secretion of pancreatic lipase & colipase?
High levels of free fatty acids in chyme

Gastroenterology (1 decks)

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