6 Digestion And Absorption In The GI Tract

Question 1

Two major routes for digestion

Answer 1

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

Question 2

Tow types of digestive activity

Answer 2

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

Question 3

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?

Answer 3

Absorption

Folds of Kerckring

Villi and microvilli; digestive enzymes

Have tight junctions

Question 4

Cell types in the intestinal epithelium and fx

Answer 4

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

Question 5

Three ways substances pass through enterocytes

Answer 5

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)

Question 6

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

Answer 6

Unstirred layer of fluid

Glycocalyx

Apical membrane with microvilli

Cytoplasm of cell

Basolateral membrane

Basement membrane

Wall of blood capillary/lymphatic vessel

Question 7

Terminal ileum resection abolishes ____ and _____ absorption

Answer 7

Bile salt and vitamin B12

Question 8

Name the enzyme in carb assimilation in the SI:

Starch-> maltose->glucose

Lactose->glucose and galactose

Sucrose-> glucose and fructose

Trehalose-> glucose

Answer 8

Alpha amylase (pancreatic secretions); maltase

Lactase (brush border enzyme)

Sucrase (brush border enzyme)

Trehalase (brush border enzyme)

Question 9

Monosaccharides are absorbed into the enterocytes through ____.

Transports glucose and galactose

Transports glucose, galactose, and fructose

Transports fructose

All powered by ____.

Answer 9

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

Question 10

Failure in the ability to digest carbs

Brush border ____ enzyme is deficient or absent

Lactose remains in the lumen; holds water causing ____.

Answer 10

Lactose intolerance

Lactase

Osmotic diarrhea

Question 11

D-Xylose test

Answer 11

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

Question 12

Main digestive enzymes in protein assimilation:

Pepsinogen (from chief cells)-> pepsin

Trypsinogen (from pancreas)-> trypsin

Trypsin converts enzymes to ____.

Answer 12

Low pH of stomach

Enterokinase (from brush border of SI)

Proteases

Question 13

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 ____.

Answer 13

Co-transporters and diffusion mechanisms

Na+

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

Question 14

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

Answer 14

Chronic pancreatitis and cystic fibrosis

Question 15

Absence of trypsin

Leads to what?

Answer 15

Congenital trypsin absence

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

Question 16

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?

Answer 16

Cystinuria

Cysteine, lysine, arginine, ornithine

Question 17

Cannot absorb neutral AA

Symptoms resemble pellagra caused by a ____ deficiency

Answer 17

Hartnup disease

Niacin/vitamin B3

Question 18

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

Answer 18

Brush border enzymes

Question 19

Proteins break down into substances that are more easily absorbed

Where?

Polypeptides broken down in ___.

Answer 19

Dipeptides, tripeptides, and AA

Mostly in SI

Stomach

Question 20

Why is trypsinogen activated in the SI?

Answer 20

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

Question 21

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

Answer 21

Cystic fibrosis

Question 22

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

Answer 22

Insoluble

Question 23

Enzymes of lipid assimilation:

Triglyceride->monoglyceride & 2 FA

Cholesterol ester->cholesterol & FA

Phospholipid-> lysolecithin & FA

Answer 23

Lingual, gastric, and pancreatic lipases

Cholesterol ester hydrolase

Phospholipase A2

Question 24

What lipases initiate digestion of lipids in the stomach?

How?

Answer 24

Lingual and gastric lipases

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

Question 25

What role does CCK play in lipid assimilation? When is it secreted? Fx?

Answer 25

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

Question 26

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

Answer 26

Pancreatic lipase Colipase Cholesterol ester hydrolase Phospholipase A2

Question 27

Enzymes activated by trypsin

Answer 27

Colipase Phospholipase A2

Question 28

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

Answer 28

Lingual lipase SI

Question 29

Catalyzes the production of cholesterol; hydrolyzes triglycerides to glycerol

Answer 29

Cholesterol ester hydrolase

Question 30

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

Answer 30

Coliapse

Question 31

Proenzyme activated by trypsin

Answer 31

Phospholipase A2

Question 32

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

Answer 32

Pancreatic lipase

Question 33

Five steps in lipid assimilation to make a chylomicron

Answer 33

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

Question 34

Steps where lipid assimilation can go wrong All of it can result in ____.

Answer 34

Pancreatic enzyme secretion Bile acid secretion Emulsification Micelle formation Diffusion of lipids into intestinal epithelial cells Chylomicron formation Transfer of chylomicrons into lymph STEATORRHEA

Question 35

Failure to secrete proper amounts of pancreatic enzymes

Answer 35

Pancreatic insufficiency

Question 36

Gastrin-secreting tumor of the pancreas Increased H+ secretion by gastric parietal cells Overload of acid into duodenum

Answer 36

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)

Question 37

Impaired HCO3 and enzyme secretion

Answer 37

Pancreatitis

Question 38

Bacteria deconjugate bile salts, impairing ____ formation. Severe bacterial overgrowth damages the intestinal ____. Two main causes are too little gastric secretion and SI dysmotility

Answer 38

Micelle Mucosa Small intestinal bacterial overgrowth (SIBO)

Question 39

What interferes with the formation of micelles in the SI?

Answer 39

Deficiency of bile salts Ileal resection Small intestinal bacterial overgrowth (SIBO)

Question 40

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

Answer 40

Ileal resection

Question 41

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?

Answer 41

Tropical Sprue Tetracycline, folate

Question 42

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?

Answer 42

Celiac Sprue Gluten-free diet

Question 43

Forms of gut microbacteria: Type of fiber (inulin) Bacteria/microorganisms contacting foods Others

Answer 43

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

Question 44

What type of vitamins have the same absorption mechanisms as lipids? What type are absorbed by Na dependent cotransport

Answer 44

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

Question 45

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

Answer 45

R proteins (secreted in salivary juices) Intrinsic factor Transcobalamin

Question 46

Functions of vitamin B12

Answer 46

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

Question 47

Deficiency in vitamin B12 causes _____ of the large nerve fibers of the spinal cord Important in ____ synthesis in RBC

Answer 47

Demyelination DNA

Question 48

Failure of RBC maturation when vitamin B12 is deficient

Answer 48

Pernicious anemia | Macrocytic and megaloblastic are other vitamin B12 deficiency disorders

Question 49

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

Answer 49

Intrinsic factor and R protein Intrinsic factor receptors

Question 50

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 ____.

Answer 50

Vitamin B12 Intrinsic factor

Question 51

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

Answer 51

Atrophic gastritis Autoimmune metaplastic atrophic gastritis

Question 52

Chronic inflammation of the stomach mucosa that leads to loss of parietal cells ...................... Immune system attaches intrinsic factor protein or gastric parietal cells

Answer 52

Atrophic gastritis Autoimmune metaplastic atrophic gastritis

Question 53

Deficiency in vitamin D absorption caused by what? Vitamin D is a ____ vitamin.

Answer 53

Inadequate calcium absorption Rickets (children) Osteomalacia (adults/can add vitamin D to Ca) Fat soluble (malabsorption of fat, can have vitamin D deficiency)

Question 54

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.

Answer 54

Apotransferrin Hemoglobin Transferrin

Question 55

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

Answer 55

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

Question 56

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

Answer 56

Sugars, peptides, AA, Ca, water, electrolytes

Question 57

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

Answer 57

Bile acids, vitamin B12, water, electrolytes

Question 58

What nutrients are being absorbed in the colon?

Answer 58

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