Exam 4- Digestion and Absorption

Question 1

Final breakdown of all food substances occurs where in the GI tract?

Answer 1

Small intestines

Question 2

Absorption involves what type of movement of digested products to the general circulation?

Answer 2

Transmural

Question 3

What is the 2 step breakdown of complex sugars?

Answer 3

Complex sugars –> (a-amylase) –> oligosacchariades –> simple sugars (monosaccharide)

Question 4

What enzymes break down 1:4 alpha linkages only?

Answer 4

Salivary and pancreatic amylase

Question 5

How are the majority of carbs ingested?

Answer 5

Complex polysaccharides

Question 6

Pancreatic amylase can’t handle what starch linkage?

Answer 6

1:6 linkage

Question 7

All oligosaccharides must be broken down into one of what 3 products to be absorbed?

Answer 7

Glucose, galactose, fructose

Question 8

What type of proteins are synthesized by epithelial cells and are needed for the membrane digestion of oligosaccharides?

Answer 8

Intrinsic membrane proteins

Question 9

What are the two main groups of the intrinsic membrane proteins?

Answer 9

Galactosidases and alpha glucosidases

Question 10

Lactase is what type of intrinsic membrane protein?

Answer 10

Galactosidase

Question 11

Sucrase, maltase, and alpha dextrinase are what type of intrinsic membrane proteins?

Answer 11

Alpha glucosidases

Question 12

The majority (80%) of ingested carbs are digested to what?

Answer 12

Glucose

Question 13

Glucose transport is primary or secondary active transport?

Answer 13

Secondary active (since plasma glucose concentration is high)

Question 14

What transporter is Na-dependent entry at the apical membrane and facilitates the movement of glucose and galactose into the cell?

Answer 14

SGLT-1 transporters

Question 15

What transporter on the basolateral membrane is involved with transport of glucose and galactose to the interstitium via facilitated diffusion?

Answer 15

GLUT2

Question 16

What transports fructose (w/o energy) on the apical membrane into the cell?

Answer 16

GLUT 5

Question 17

Most disorders of carbohydrate digestion and absorption are due to what?

Answer 17

Deficiencies that prevent breakdown of carbs to an absorbable form

Question 18

What breaks down lactose? What are the end products?

Answer 18

Lactose → glucose and galactose, via lactase

Question 19

What breaks down sucrose? What are the end products?

Answer 19

Sucrose → glucose and fructose, via sucrase

Question 20

What breaks down a-dextrins? What is the end product?

Answer 20

Alpha-dextrins → glucose, via maltase and alpha-dextrinase

Question 21

What breaks down maltotroise? What is the end product?

Answer 21

Maltotriose → glucose, via maltase, sucrase, alpha-dextrinase

Question 22

What breaks down maltose? What is the end product?

Answer 22

Maltose → glucose, via maltase, sucrase, alpha-dextrinase

Question 23

Unabsorbed carbs hold water osmotically and cause what clinical condition?

Answer 23

Osmotic diarrhea (lumen is isosmotic to interstitium)

Question 24

What are the 3 clincal sx of unabsorbed lactose?

Answer 24

Osmotic diarrhea, cramps, abd distension

Question 25

What is a potential consequence of long-term intestinal disease?

Answer 25

Lactase deficiency (membrane lactase dysconfigured)

Question 26

What is the primary enzyme in luminal digestion?

Answer 26

Amylase

Question 27

What are the products of protein digestion? (2)

Answer 27

Amino acids and oligopeptides

Question 28

Where are the proenzymes of protein digestion stored?

Answer 28

Pancreas

Question 29

What happens if the proenzymes of protein digestion become active before being released from the pancreas?

Answer 29

Pancreatitis

Question 30

What enzyme is required to activate the proenzymes of protein digestion?

Answer 30

H+ to activate pepsinogen to pepsin Enterokinase to activate trypsinogen to trypsin

Question 31

Proteins make up 20-35% of caloric intake with a significant amount coming from where?

Answer 31

Endogenous sources (desquamated cells and gastric secretions)

Question 32

The final breakdown of proteins occurs where?

Answer 32

Brush border via peptidases

Question 33

Amino acids are co-transported into the cell with what?

Answer 33

Sodium gradient via 2˚ active transport

Question 34

How are di and tripeptides co-transported in the cell?

Answer 34

Coupled w/ H+ transport via 2˚ active trasport

Question 35

In addition to peptidase breakdown in the brush border layer, how else are proteins digested? (2)

Answer 35

Amino acid carriers and endocytosis (neonates)

Question 36

Decreased protein absorption as a result of pancreatic insuffiency will lead to what?

Answer 36

Malnutrition

Question 37

Pancreatic insufficiency will have what effect on the amount of trypsin that reaches the intestines?

Answer 37

Decreased/insufficienct amounts of trypsin

Question 38

What condition is a congential defect in transport of neutral amino acids?

Answer 38

Hartnup disease (absorption of di- and tripeptides ok)

Question 39

In what condition is the transporter for dibasic amino acids absent from the gut and kidney resulting in the loss of dibasic amino acids in urine and feces?

Answer 39

Cystinuria

Question 40

What motion is required for the digestion of fats due to their insolubility and tendency to coalesce?

Answer 40

Churning and bile emulsification

Question 41

What are the 4 key events in fat digestion?

Answer 41

Secretion of bile and lipases, emulsification of fats by bile, enzymatic hydrolysis of ester linkages, solubilizing digestion products within micelles for delivery to enterocytes

Question 42

What enzyme is primary responsible for the digestion of fats?

Answer 42

Pancreatic lipase (lingual lipase plays small role)

Question 43

Pancreatic lipase requires assistance from what other enzyme?

Answer 43

Colipase (prevents bile salt inhibition of this enzyme)

Question 44

What eznymes removes fatty acid moiety from cholesterol, vitamins A, D, E, and glycerides and can remove all three ester linkages?

Answer 44

Cholesterol ester hydrolase

Question 45

What enzyme hydrolyzes phospholipids at 2 position in fat digestion?

Answer 45

Phospholipase A2

Question 46

Products of fat digestion are removed quickly by the formation of what?

Answer 46

Micelles

Question 47

Once triglycerides are broken down, they combine with bile acids to form micelles. How is the micelle absorbed?

Answer 47

Diffuse across the unstirred layer to the mucosal surface of the apical membrane of the enterocyte where it breaka down and its contents absorbed by simple diffusion

Question 48

What are the components of a micelle? (breaken down into these components for simple diffusion) (4)

Answer 48

Long-chain FFA, 2-MG, phospholipids, cholesterol

Question 49

How much of ingested fat is removed by the small intestine?

Answer 49

95%

Question 50

What happens to the components of micelles once they pass into the enterocyte via simple diffusion?

Answer 50

Reassemble TG and phospholipids

Question 51

What structure has a TG and cholesterol core is surrounded by phospholipids and apoproteins?

Answer 51

Chylomicron

Question 52

How does a chylomiron re-enter blood circulation? (3 steps)

Answer 52

Exocytosed and enters lacteal → lacteal transports chylomicron into general lymph → into blood stream

Question 53

Chylomicrons carry triglycerides to what tissues? (3)

Answer 53

Adipose tissue, skeletal muscle, cardiac muscle

Question 54

What makes up the majority of a chylomicron?

Answer 54

Triglycerides (\> cholesterol, PLs, apoproteins)

Question 55

Zollinger Ellison syndrome results in abnormal lipid digestion or lipid absorption?

Answer 55

Lipid digestion

Question 56

What syndrome causes dysfunctional lipolysis as a result of a gastrin secreting tumor in duodenum or pancreas that creates an acidic small intestine and dysfunctional pancreatic lipase?

Answer 56

Zollinger Ellison syndrome

Question 57

What rare disease causes steatorrhea due to abnormal lipid absorption caused by generalized lymphatic dystrophy?

Answer 57

Whipple's disease

Question 58

Whipple's disease results in abnormal lipid digestion or lipid absorption?

Answer 58

Lipid absorption

Question 59

What enzymes are produced in the pancreas? (8)

Answer 59

Amylase, trypsin, chymotrypsin, carboxypeptidase, elastase, lipase-colipase, phospholipase A, cholesterol esterase nonspecific lipase

Question 60

What enzymes are produced in the brush border? (8)

Answer 60

Enterokinase, disaccharidases, maltase, sucrase, lactase, peptidases, aminooligopeptidase, dipeptidase

Question 61

What dictates the vitamin absorption mechanism?

Answer 61

Solubility

Question 62

What are the fat soluble vitamins? (4)

Answer 62

A, D, E, K

Question 63

What are the water soluble vitamins? (8)

Answer 63

B1, B2, B6, B12, C, biotin, folate, pantothenic acid

Question 64

How are fat soluble vitamins solubilized/ transported and how do they enter circulation?

Answer 64

Micelles, chylomicrons

Question 65

How are most water soluble vitamins absorbed?

Answer 65

Via Na+ dependent co-transport (exception is B12)

Question 66

How is vitamin B12 absorbed?

Answer 66

Binds to gastric intrinsic factors which protects it from digestion, then absorbed in ileum

Question 67

What is the main MOA for calcium reuptake in the intestines?

Answer 67

Upregulation of calcium binding protein (CaBP = rate limiting) present in enterocytes

Question 68

Ca passivley enters the enterocyte and is transported via what to the basolateral membrane?

Answer 68

CaBP (binding protein)

Question 69

What are the 2 mechanisms for movement of calcium on the basolateral membrane of the intestines?

Answer 69

Ca-ATPase (active) and NaCa exchanger (passive)

Question 70

Does PTH have a direct effect on Ca absorption in the enterocyte?

Answer 70

No

Question 71

What is calcium absorption regulated by?

Answer 71

PTH and vitamin D

Question 72

How much iron is ingested vs absorbed?

Answer 72

Amount ingested \>\> amount absorbed

Question 73

What promotes intestinal absorption and solubilization of iron?

Answer 73

Gastric acid (reduces Fe3+ to Fe2+)

Question 74

What binding protein is required for plasma transport of iron?

Answer 74

Transferrin

Question 75

What is the preferred form of iron within the body?

Answer 75

Ferrous (Fe2+)

Question 76

What is the intracellular storage depot for iron that allows for the release of iron in a controlled fashion?

Answer 76

Ferritin (iron binding protein)

Question 77

When is ferritin lost?

Answer 77

When enterocyte is sloughed off

Question 78

What is the single biggest source of ingested and secreted fluids?

Answer 78

Pancreatic juice and bile (diet contributes ~2/10 L)

Question 79

What is the primary site of water and electrolyte absorption?

Answer 79

Small intestine (then colon)

Question 80

What organ is impermeable to water?

Answer 80

Stomach

Question 81

What is the driving force for water movement?

Answer 81

Solute transport (Na)

Question 82

What is the 1st site for Na+ absorption?

Answer 82

Small intestine (mechanism similar to proximal tubule, Na/H exchagner maintained by Na-K-ATPase)

Question 83

What part of the intestines has a net reabsorbtion of Na and HCO3 (+sugar, and AA)?

Answer 83

Jejunum

Question 84

What are the effects of Na+/H+ exchange in the jejunum? (2)

Answer 84

Acidifies lumen and neutralizes lumenal HCO3-

Question 85

What drives paracellular Cl- absorption?

Answer 85

Voltage gradient

Question 86

What portion of the intestines does the following occur: Both H+ and HCO3 are secreted into the lumen (resulting in NO pH change) to drive transport of Na and Ca in the cell

Answer 86

Ileum

Question 87

What is the net reabsorption activity of the ileum?

Answer 87

Recovery of sodium and chloride (+ sugar and amino acids)

Question 88

What transporters contribute to chloride being reabsorbed into cells in the ileum? (2)

Answer 88

Apical chloride-HCO3 antiporter and Na/H exchanger

Question 89

Passive Na and K channels in the apical membrane of the colon responsible for what?

Answer 89

Na absorption (into the cell) and K secretion (into the lumen of the colon)

Question 90

ENaC is induced by what in the colon?

Answer 90

Aldosterone

Question 91

What is K secretion dependent on in the colon?

Answer 91

"Flow dependent"

Question 92

What is the effect of diarrhea on the colon?

Answer 92

Increase K+ loss due to increased flow of chyme through the colon

Question 93

Diarrhea is often associated with loss of what 3 things?

Answer 93

Fluid, HCO3- (causes metabolic acidosis), loss of K+ (hypokalemia)

Question 94

Diarrhea will result in electrolyte imbalances that manifest as what?

Answer 94

Metabolic acidosis and hypokalemia

Question 95

What is the result of decreased/ impaired surface area of the small intestine? (ex Crohns)

Answer 95

Diarrhea

Question 96

What is the result of osmotic diuresis due to unreabsorbable osmolytes? (ex. lactase enzyme deficiency)

Answer 96

Diarrhea

Question 97

What is a common cause of secretory diarrhea?

Answer 97

Cholera

Question 98

What can occur if chloride secretion in the colon is increased?

Answer 98

Secretory diarrhea

Question 99

What is the MOA for cholera? (4 steps)

Answer 99

1. Cholera toxin binds to apical membrane of crypt cells 2. Irreversible activation of adenylate cyclase 3. Increased cAMP production/ activity which opens Cl- channels 4. Increased secretion of Cl- on the apical membrane

Question 100

What is the treatment for secretory diarrhea?

Answer 100

Oral rehydration therapy (and control presence of vibrio cholerae)

Question 101

What maintains the Na and Cl concentration gradients within the epithelials cells of the colon?

Answer 101

NaKCC1 transporter (Na, K, 2 Cl) maintained by Na/K-ATPase