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GI Final - MSI Spring > Digestion and Absorption Process in GI tract > Flashcards

Digestion and Absorption Process in GI tract Flashcards

1
Q

What are the two main paths of nutrients, electrolytes and water from lumen to the blood?

A

cellular and paracellular

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2
Q

What are the two types of digestive activity ?

A

cavital (luminal) digestion: digestion from enzymes secreted by salivary glands, stomach, and pancreas

Membrane (contact) digestion: hydrolysis by enzymes synthesized by epithelial cells

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3
Q

The surface of the small intestine is arranged in longitudinal folds called…

A

folds of kerckring

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4
Q

Where are villi the longest in the small intestine?

A

duodenum

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5
Q

What are the functions of enterocytes? what are they susceptible to ?

A

they are epithelial cells that function in digestion, absorption and secretion
turnover rate: 3-6 days
Susceptible to irradiation and chemotherapy

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6
Q

What are the functions of goblet cells?

A

mucus-secreting cells that provide physical, chemical and immunologic protection

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7
Q

What is the function of paneth cells?

A

part of the mucosal defenses against infection

secrete agents that destroy bacteria or produce inflammatory responses

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8
Q

What mechanisms does the enterocyte used to control the flux of solutes and fluids between the lumen and blood?

A

pinocytosis: at base of microvilli (major mechanism of uptake of protein)
Passive diffusion: thru pores in cell membrane or intercellular spaces
Facilitated diffusion
active transport

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9
Q

What barriers must solute move across to get through enterocyte?

A 
unstirred layer of fluid
glycocalyx
apical membrane 
cytoplasm 
basolateral membrane
basement membrane 
wall of the blood capillary
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10
Q

The capacity of the intestine to adapt is key in several clinical scenarios including small bowel resection and bypass. When is adaptation limited?

A

If terminal ileum is resected, absorption of vit B112 and bile salts is abolished

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11
Q

In what form can carbs be absorbed?

A

only monosaccharides

glucose, galactose, and fructose

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12
Q

How is starch broken down?

A

amylase breaks it down to disaccharides then other enzymes like maltase and sucrase breaks it down to glucose

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13
Q

How is lactose and sucrose broken down?

A

Lactose by lactase to form glucose and galactose

sucrose by sucrase to form glucose and fructose

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14
Q

What transporters are on the lumenal side of epithelial cells that absorb carbs?

A

SGLT1: Symporter of Na and glucose/galactose - secondary active transport
GLUT 5: fructose - facilitated

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15
Q

What transporters are on the basolateral side of epithelial cells that help in the absorption of carbs?

A

Na/K ATPase

GLUT 2: does glucose, galactose, and fructose facilitated diffusion

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16
Q

What happens with lactose intolerance?

A

Brush-border lactase is deficient
Lactose remains in lumen and holds water, causes osmotic diarrhea
Fermented into methane and gas

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17
Q

what enzyme is released in the stomach to break down proteins?

A

pepsinogen

protein->amino acids and oligopeptides

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18
Q

What are the endopeptidases: break peptide bonds of nonterminal amino acid?

A

Pepsin, trypsin, chymotrypsin, elastase

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19
Q

What are the exopeptidases: break peptide bonds from end-pieces of terminal amino acids.?

A

Carboxypeptidase A

Carboxypeptidase B

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20
Q

What activates trypsinogen?

A

enteropeptidase in the brush border

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21
Q

What activates all endopeptidases and exopeptidases?

A

trypsin

22
Q

What are the absorbable forms of proteins?

A

A.a, dipeptide and tripeptide

23
Q

What transporters for a.a. can be found on the luminal side of Epithelial cells of the small intestine?

A

there are 4 separate cotransporters of Na/a.a.: one each for neutral, acidic, basic and imino aa.
Cotransporter for H/dipeptides/tripeptides
Na/H antiporter

24
Q

What transporters for a.a. can be found on the basolateral side of epithelial cells of the small intestine?

A

Na/K ATPase
There are 4 separate facilitated diffusion mechanisms: one each for neutral, acidic, basic, and imino aa.

Peptidase inside the cell can break down dipeptides and tripeptides or they can diffuse through membrane

25
Q

When do disorders of protein assimilation occur?

A

when there is a deficiency of pancreatic enzymes or a defect in transporters of the intestinal epithelial cells

  • chronic pancreatitis and cystic fibrosis: enzyme deficiency
  • trypsin absence
  • cystinuria
  • hartnup disease
26
Q

What is cystinuria?

A

defect in or absence of Na- amino acid cotransporters: transporter for di-basic amino acids is absent from small intestine and kidney
Genetic disorder
a.a. secreted in feces

27
Q

What is Hartnup disease?

A

inability to absorb neutral amino acids like tryptophan
Recessive genetic disorder
Symptoms similar to pellagra (deficiency of niacin)
Diarrhea, mood changes, neurologic problems, short, red rash, photosensitivity
Urine sample-high excretion of neutral aa and by-products (serotonin)

28
Q

What is CFTR?

A

a regulated anion channel that is located at the apical surface of the duct cell that transports Cl ions

29
Q

What is one of the first organs to fail in cystic fibrosis? Why?

A

pancreas
Loss of bicarb secretion (Cl/HCO3 antiporter)
ability to flush active enzymes out of duct loss
Recurrent acute and chronic pancreatitis

30
Q

What breaks down lipids in the stomach and small intestine?

A

lipases

31
Q

How must lipids be processed to be absorbed?

A

lipids need to be solubilized in micelles and transported to apical membrane of intestinal epithelial cells for absorption

32
Q

Describe the intial digestion of lipids in the stomach?

A

lingual and gastric lipases
10% of TG hydrolyzed to glycerol and FA
Broken down to small droplets
droplets emulsified in stomach by dietary proteins (NO BILE IN STOMACH)

33
Q

What allows for sufficient time for lipids to get digested properly?

A

CCK, slows rate of gastric emptying

released when lipids

34
Q

What happens to pancreatic lipase once it enters the small intestine? When does it become efficient?

A

Pancreatic lipase secreted as active enzyme is inactivated by bile salts

Colipase binds to pancreatic lipase to make it more efficient to break down TG into free fatty acids and 2 monoglyceride

35
Q

What is colipase and phospholipase A2 activated by?

A

trypsin

36
Q

What is the role of cholesterole ester hydrolase?

A

catalyze the production of cholesterol

hydrolyzes TG to produce glycerol

37
Q

What is the optimal pH for pancreatic lipase?

A

6

38
Q

How are lipids processed in epithelial cell of the small intestine? What can an abnormality in any of these steps result in?

A

Pancreatic enzyme secretion and bile acid secretion -> emulsification->micelle formation

  1. solubilization by micelles
  2. diffusion of micellar content across apical memb.
  3. reesterification
  4. chylomicron formation
  5. exocytosis of chylomicron into lymph

Steatorrhea

39
Q

Chol + FFA = ?
MG + FFA = ?
LysoPL + FFA = ?
And where do these reactions occur?

A

Chol E
TG
PL
Epithelial cell of small intestine

40
Q

What leads to abetalipoproteinemia? Why?

A

No ApO B because there will be no absoprtion of dietary lipids

41
Q

What is pancreatic insufficiency?

A

failure to secrete adequate amounts of pancreatic enzymes

42
Q

What can cause deficiencies of bile salts?

A

Ileal resection interrupts the enterohepatic circulation of bile salts which makes the total bile salt pool reduced

Small intestinal bacterial overgrowth can cause bile salts to decojugate

both causes failure of micelle formation and subsquent fat malabsorption

43
Q

What causes SIBO?

A

Decrease gastric acid secretion and small intestine dysmotility can cause an overgrowth of bacteria

44
Q

What is tropical sprue? What is the treatment?

A

reduction in the # of intestinal epithelial cells which in turn reduces the microvillar surface area
Cause: unknown
Steatorrhea, nutritional deficiencies (folate and vit B12)
cramps, nausea, weight loss,

Tx: tetracycline and folate for 6 mo.

45
Q

What is non-tropical sprue? Most common with what race and sex?

A

celiac sprue
autoimmune disorder
hereditary compoent
Abs against gluten lead to destruction of villi in small intestine and hyperplasia of intestinal crypts
Malapsorption: vit B12, folate, iron, Ca, Vit D and Vit A

Caucasians and european ancestry
Women

46
Q

What are the fat-soluble vitamins? how are the absorbed?

A

A, D, E, K

same mechanism as lipids

47
Q

What are the water-soluble vitamins? How are they absorbed?

A

B1, B2, B3, B12, C, biotin, folic acid, nicotinic acid and panthothenic acid
Most absorbed via Na-dependent cotransport in small bowel
B12 (cobalamin): forms complexes with other proteins to be absorbed

48
Q

What does cobalamin form a complex with in order to be absorbed?

A

R proteins: secreted in salivary juices
- Remains complex until in duodenum and pancreatic proteases
Intrinsic factor: secreted by gastric parietal cells
- Carries through IF receptor in distal ileum
Trnascobalamin II: carries from mucosa into blood

49
Q

What surgeries can disrupt the absorption of vit B12?

A

Gastrectomy: loss of parietal cells

Gastric bypass: exclusion of stomach, duodenum and proximal jejunum alters absorption

50
Q

What is vitamin B12 anemia called? What are common causes?

A

pernicious anemia

  1. atrophic gastritis: loss of parietal cells with chronic inflammation
  2. Autoimmune response against IF or gastric parietal cells
51
Q

What does sunlight change 7-dehydrocholesterol into?

A

Cholecalciferol - vitamin D3

52
Q

What is needed to increase Gut Ca absorption, bone calcification and bone resorption?

A

1,25 Dihydroxy-D3

GI Final - MSI Spring (11 decks)

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