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GI Final > 6 Digestion And Absorption In The GI Tract > Flashcards

6 Digestion And Absorption In The GI Tract Flashcards

1
Q

Two major routes for digestion

A

Cellular: from lumen through apical membrane, intracellular space of epithelial cells, and cross basolateral membrane into blood

Paracellular: between epithelial cells through lateral intracellular space through tight junctions

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2
Q

Tow types of digestive activity

A

Cavital (luminal): digestion resulting from the actions of enzymes secreted by the salivary glands, stomach, and pancreas

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

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3
Q

Intestinal mucosa is ideal for its fx of ____ because its lumen is arranged in longitudinal folds called ____.

What increases the surface area and what do they contain?

A

Absorption

Folds of Kerckring

Villi and microvilli; digestive enzymes

Have tight junctions

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4
Q

Cell types in the intestinal epithelium and fx

A

Enterocytes: epithelial cells; digestion, absorption, secretion; susceptible to irradiation and chemo

Goblet cells: mucus secreting; provide physical, chemical, and immunological protection

Paneth cells: mucosal defense; secrete agates that destroy bacteria or produce and inflammatory response

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5
Q

Three ways substances pass through enterocytes

A

Pinocytosis: at the base of the microvilli; mechanism for protein uptake

Passive diffusion: through pores in the cell membrane, between cells; channels on both membranes

Membrane transporters: facilitated diffusion; active transport (can be cotransporters)

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6
Q

Pathway (barriers) of solutes moving across the the enterocytes from lumen to blood

A

Unstirred layer of fluid

Glycocalyx

Apical membrane with microvilli

Cytoplasm of cell

Basolateral membrane

Basement membrane

Wall of blood capillary/lymphatic vessel

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7
Q

Terminal ileum resection abolishes ____ and _____ absorption

A

Bile salt and vitamin B12

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8
Q

Name the enzyme in carb assimilation in the SI:

Starch-> maltose->glucose

Lactose->glucose and galactose

Sucrose-> glucose and fructose

Trehalose-> glucose

A

Alpha amylase (pancreatic secretions); maltase

Lactase (brush border enzyme)

Sucrase (brush border enzyme)

Trehalase (brush border enzyme)

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9
Q

Monosaccharides are absorbed into the enterocytes through ____.

Transports glucose and galactose

Transports glucose, galactose, and fructose

Transports fructose

All powered by ____.

A

Transport proteins

SGLT1 (usages Na concentration gradient)

GLUT2

GLUT5

Na/K ATPase

***know what happens if you don’t have a transporter; ex: lack GLUT5, build up of fructose in lumen

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10
Q

Failure in the ability to digest carbs

Brush border ____ enzyme is deficient or absent

Lactose remains in the lumen; holds water causing ____.

A

Lactose intolerance

Lactase

Osmotic diarrhea

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11
Q

D-Xylose test

A

D-xylose is a monosaccharide

Give a set dose to the pt that is normally easily absorbed by passive diffusion

Measure levels to see the absorptive capacity of the proximal SI to absorb sugars

***tests for malabsorption, but doesn’t tell you which sugar is the problem

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12
Q

Main digestive enzymes in protein assimilation:

Pepsinogen (from chief cells)-> pepsin

Trypsinogen (from pancreas)-> trypsin

Trypsin converts enzymes to ____.

A

Low pH of stomach

Enterokinase (from brush border of SI)

Proteases

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13
Q

There are separate ____ and ____ for each AA type including neutral, acidic, basic, and imino crossing the enterocyte (brush border)

AA co-transporters use ____.

Dipeptides and tripeptides co-transporters use ____.

A

Co-transporters and diffusion mechanisms

Na+

H+ (not the best choice; pancreatic secretions should be secreting HCO3 to neutralize the H+)

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14
Q

Deficiency of pancreatic enzymes; lack a protease (like trypsinogen)

A

Chronic pancreatitis and cystic fibrosis

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15
Q

Absence of trypsin

Leads to what?

A

Congenital trypsin absence

Absence of all pancreatic enzymes because trypsin catalyze the hydrolysis of those enzymes

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16
Q

Defect or absence of Na/AA cotransporters

Di-basic AA transporter absent from SI and kidney because of an intestinal deficiency causing AA to be secreted in the feces…what AA are absent?

A

Cystinuria

Cysteine, lysine, arginine, ornithine

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17
Q

Cannot absorb neutral AA

Symptoms resemble pellagra caused by a ____ deficiency

A

Hartnup disease

Niacin/vitamin B3

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18
Q

Sucrose, lactose, or glucose are are absorbed as glucose by _____.

A

Brush border enzymes

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19
Q

Proteins break down into substances that are more easily absorbed

Where?

Polypeptides broken down in ___.

A

Dipeptides, tripeptides, and AA

Mostly in SI

Stomach

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20
Q

Why is trypsinogen activated in the SI?

A

It is secreted by the pancreas; if it is activated in the pancreas, trypsinogen would be converted to trypsin and would begin to activate enzymes that would destroy the pancreas

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21
Q

Mutation of CFTR receptor

CFTR normally regulates the Cl channel on the apical membrane of ductal cells

Pancreatic problems: can’t absorb Cl so can’t secrete HCO3

Leads to pancreatitis

A

Cystic fibrosis

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22
Q

Lipids are ____, therefore must be solubilized in order to be transported

A

Insoluble

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23
Q

Enzymes of lipid assimilation:

Triglyceride->monoglyceride & 2 FA

Cholesterol ester->cholesterol & FA

Phospholipid-> lysolecithin & FA

A

Lingual, gastric, and pancreatic lipases

Cholesterol ester hydrolase

Phospholipase A2

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24
Q

What lipases initiate digestion of lipids in the stomach?

How?

A

Lingual and gastric lipases

Break down lipids into small droplets that are emulsified in the stomach by dietary proteins (no bile acids in stomach)

25
Q

What role does CCK play in lipid assimilation?

When is it secreted?

Fx?

A

Allows more time for proper lipid digestion

Secreted when lipids first appear in the SI

Slows the rate of gastric emptying (more mixing)

Activates gallbladder secretions

26
Q

What pancreatic enzymes are secreted into the SI to complete lipid digestion?

A

Pancreatic lipase

Colipase

Cholesterol ester hydrolase

Phospholipase A2

27
Q

Enzymes activated by trypsin

A

Colipase

Phospholipase A2

28
Q

Lipid digestion begins in the mouth with a ____ but most takes place in the ____.

A

Lingual lipase

SI

29
Q

Catalyzes the production of cholesterol; hydrolyzes triglycerides to glycerol

A

Cholesterol ester hydrolase

30
Q

Proenzyme activated by trypsin; displaces bile salts by binding to pancreatic lipase (pushes bile salts off fat droplets so lipase can do its job)

A

Coliapse

31
Q

Proenzyme activated by trypsin

A

Phospholipase A2

32
Q

Secreted as an active enzyme; inactivated by bile salts without pancreatic lipase

A

Pancreatic lipase

33
Q

Five steps in lipid assimilation to make a chylomicron

A

Solubilization by micelles (packaging using bile salts)

Diffusion of micellar content across apical membrane

Re-esterification (put lipids back together; goes on continuously)

Chylomicron formation (packaged fat that leaves the cell)

Exocytosis of chylomicrons

34
Q

Steps where lipid assimilation can go wrong

All of it can result in ____.

A

Pancreatic enzyme secretion

Bile acid secretion

Emulsification

Micelle formation

Diffusion of lipids into intestinal epithelial cells

Chylomicron formation

Transfer of chylomicrons into lymph

STEATORRHEA

35
Q

Failure to secrete proper amounts of pancreatic enzymes

A

Pancreatic insufficiency

36
Q

Gastrin-secreting tumor of the pancreas

Increased H+ secretion by gastric parietal cells

Overload of acid into duodenum

A

Zollinger-Ellison syndrome

(Improper acidity of duodenum because pancreas not working so can’t secrete HCO3; build up of H+; lipase can’t work in an acidic environment)

37
Q

Impaired HCO3 and enzyme secretion

A

Pancreatitis

38
Q

Bacteria deconjugate bile salts, impairing ____ formation.

Severe bacterial overgrowth damages the intestinal ____.

Two main causes are too little gastric secretion and SI dysmotility

A

Micelle

Mucosa

Small intestinal bacterial overgrowth (SIBO)

39
Q

What interferes with the formation of micelles in the SI?

A

Deficiency of bile salts

Ileal resection

Small intestinal bacterial overgrowth (SIBO)

40
Q

Total bile salt pool is reduced because of loss of enterohepatic recirculating of bile salts

A

Ileal resection

41
Q

Reduced microvilli surface area

Lipid absorption impaired due to loss of microvilli (steatorrhea)

Nutritional deficiencies of folate and a vitamin B12

Diarrhea

What do you treat with?

A

Tropical Sprue

Tetracycline, folate

42
Q

Autoimmune disorder leading to destruction of SI villi and hyperplasia of intestinal crypts

Malabsorption related to deficiencies in folate, iron, calcium, vitamins A,B12,D

Symptoms of malabsorption like numbness, tingling of extremities

Treatment?

A

Celiac Sprue

Gluten-free diet

43
Q

Forms of gut microbacteria:

Type of fiber (inulin)

Bacteria/microorganisms contacting foods

Others

A

Prebiotics

Probiotics

Live bacterial therapeutics
Roux-en-Y gastric bypass
Fecal microbiota transplant

44
Q

What type of vitamins have the same absorption mechanisms as lipids?

What type are absorbed by Na dependent cotransport

A

Fat-soluble (if pt had steatorrhea, they are not absorbing lipids…also not absorbing fat-soluble vitamins)
A,D,E,K

Water-soluble: B,C

45
Q

Vitamin B12 is a ____ vitamin that forms complexes with other proteins to be absorbed like ____.

A

R proteins (secreted in salivary juices)

Intrinsic factor

Transcobalamin

46
Q

Functions of vitamin B12

A

Performs several metabolic functions-hydrogen acceptor coenzyme

Acts as a coenzyme for reducing ribonucleotides to deoxyribonucleotides-replication of genes

Co-factor in folate coenzyme recycling and nerve myelination

47
Q

Deficiency in vitamin B12 causes _____ of the large nerve fibers of the spinal cord

Important in ____ synthesis in RBC

A

Demyelination

DNA

48
Q

Failure of RBC maturation when vitamin B12 is deficient

A

Pernicious anemia

Macrocytic and megaloblastic are other vitamin B12 deficiency disorders

49
Q

In vitamin B12 absorption, ____ and _____ have to get in the right place and get absorbed

____ bind to the vitamin B12 and pull it along

A

Intrinsic factor and R protein

Intrinsic factor receptors

50
Q

In gastric bypass, exclusion of the stomach, duodenum, and proximal jejunum alters the absorption of ____.

Gastrectomy causes the loss of parietal cells, the source of ____.

A

Vitamin B12

Intrinsic factor

51
Q

What causes the stomach to not produce enough intrinsic factor, leading to pernicious anemia?

A

Atrophic gastritis

Autoimmune metaplastic atrophic gastritis

52
Q

Chronic inflammation of the stomach mucosa that leads to loss of parietal cells

………………….

Immune system attaches intrinsic factor protein or gastric parietal cells

A

Atrophic gastritis

Autoimmune metaplastic atrophic gastritis

53
Q

Deficiency in vitamin D absorption caused by what?

Vitamin D is a ____ vitamin.

A

Inadequate calcium absorption

Rickets (children)

Osteomalacia (adults/can add vitamin D to Ca)

Fat soluble (malabsorption of fat, can have vitamin D deficiency)

54
Q

Iron absorption occurs when the liver secretes ____ into bile ->enters duodenum->binds with free iron and ____ forming transferrin.

_____binds to receptors on membranes of intestinal epithelial cells, absorbed into cells by pinocytosis and later released.

A

Apotransferrin

Hemoglobin

Transferrin

55
Q

What nutrients are absorbed in the proximal SI (duodenum)?

A

Fat, sugars, peptides, AA, iron, folate, Ca, water, electrolytes

56
Q

What nutrients are absorbed in the middle SI (jejunum)?

A

Sugars, peptides, AA, Ca, water, electrolytes

57
Q

What nutrients are absorbed in the distal SI (ileum)?

A

Bile acids, vitamin B12, water, electrolytes

58
Q

What nutrients are being absorbed in the colon?

A

Water, electrolytes, medium-chain triglycerides, MCTs, Ca, AA

GI Final (11 decks)

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