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

Digestion and Absorption Process in GI tract Flashcards

(52 cards)

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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?

22
Q

What are the absorbable forms of proteins?

Study These Flashcards
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?

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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?

Study These Flashcards
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
When do disorders of protein assimilation occur?
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
What is cystinuria?
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
What is Hartnup disease?
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
What is CFTR?
a regulated anion channel that is located at the apical surface of the duct cell that transports Cl ions
29
What is one of the first organs to fail in cystic fibrosis? Why?
pancreas Loss of bicarb secretion (Cl/HCO3 antiporter) ability to flush active enzymes out of duct loss Recurrent acute and chronic pancreatitis
30
What breaks down lipids in the stomach and small intestine?
lipases
31
How must lipids be processed to be absorbed?
lipids need to be solubilized in micelles and transported to apical membrane of intestinal epithelial cells for absorption
32
Describe the intial digestion of lipids in the stomach?
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
What allows for sufficient time for lipids to get digested properly?
CCK, slows rate of gastric emptying | released when lipids
34
What happens to pancreatic lipase once it enters the small intestine? When does it become efficient?
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
What is colipase and phospholipase A2 activated by?
trypsin
36
What is the role of cholesterole ester hydrolase?
catalyze the production of cholesterol | hydrolyzes TG to produce glycerol
37
What is the optimal pH for pancreatic lipase?
6
38
How are lipids processed in epithelial cell of the small intestine? What can an abnormality in any of these steps result in?
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
Chol + FFA = ? MG + FFA = ? LysoPL + FFA = ? And where do these reactions occur?
Chol E TG PL Epithelial cell of small intestine
40
What leads to abetalipoproteinemia? Why?
No ApO B because there will be no absoprtion of dietary lipids
41
What is pancreatic insufficiency?
failure to secrete adequate amounts of pancreatic enzymes
42
What can cause deficiencies of bile salts?
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
What causes SIBO?
Decrease gastric acid secretion and small intestine dysmotility can cause an overgrowth of bacteria
44
What is tropical sprue? What is the treatment?
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
What is non-tropical sprue? Most common with what race and sex?
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
What are the fat-soluble vitamins? how are the absorbed?
A, D, E, K | same mechanism as lipids
47
What are the water-soluble vitamins? How are they absorbed?
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
What does cobalamin form a complex with in order to be absorbed?
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
What surgeries can disrupt the absorption of vit B12?
Gastrectomy: loss of parietal cells | Gastric bypass: exclusion of stomach, duodenum and proximal jejunum alters absorption
50
What is vitamin B12 anemia called? What are common causes?
pernicious anemia 1. atrophic gastritis: loss of parietal cells with chronic inflammation 2. Autoimmune response against IF or gastric parietal cells
51
What does sunlight change 7-dehydrocholesterol into?
Cholecalciferol - vitamin D3
52
What is needed to increase Gut Ca absorption, bone calcification and bone resorption?
1,25 Dihydroxy-D3

GI Final - MSI Spring (11 decks)

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