Absorption and Digestion definitions

Question 1

define folds of kerckring

Answer 1

surface of small intestine that is increased via longitudinal folds => villi project from these folds

Question 2

define enterocytes

Answer 2

surface of villus is layer of columnar epithelial cells=> principal digestive and absorptive cells of small bowel

Question 3

define goblet cells

Answer 3

cells that secrete mucus that are interspersed bw enterocytes

Question 4

define microvilli

Answer 4

apical surface of enterocyte covered by hundreds tiny processes

Question 5

define brush border

Answer 5

microvillous surface to increase exposure to luminal contents to enterocyte membrane

Question 6

define crypts

Answer 6

tube like projections down into surface at base of each villus

Question 7

define paneth cells

Answer 7

cells at bottom of crypts that may regulate microbiota in gut

Question 8

What happens as the enterocyte matures?

Answer 8

progresses toward villous tip => digestion and absorption increase due to enzyme increase, better transport processes and membrane carriers differentiate

Question 9

villous cells may differentiate into enteroendocrine cells that have what function?

Answer 9

synthesis and release of secretin and CCK

Question 10

small bowel rates of cell division and turnover are influenced by what?

Answer 10

luminal contents (nutrients, growth factors) and GI hormones => increased cell loss increases cell turnover and repair of damaged mucosa

Question 11

Define digestion

Answer 11

chemical breakdown of ingested food into absorbable molecules and is due to enzymes secreted into lumen or bound to apical membranes of enterocyte

Question 12

2 types of digestion

Answer 12

luminal (cavital) digestion;

membrane (contact) digestion

Question 13

define luminal digestion

Answer 13

takes place in GI tract via enzymes of salivary glands, stomach and pancreas

Question 14

define membrane digestion

Answer 14

carried out by hydrolytic enzymes synthesized by enterocyte that are inserted into brush border as parts of microvilli membrane

Question 15

Why must enterocytes continuously secrete hydrolytic enzymes?

Answer 15

replace those that are broken down or lost into the lumen

Question 16

Digestive enzymes of salivary glands

Answer 16

amylase;

lingual lipase

Question 17

digestive enzymes of stomach

Answer 17

pepsin

Question 18

digestive enzymes of pancreas

Answer 18

amylase; trypsin; chymotrypsin; carboxypeptidase; elastase; lipase-colipase; phospholipase A2; cholesterol esterase (nonspecific)

Question 19

digestive enzymes of intestinal mucosa

Answer 19

enterokinase; Disaccharidases (sucrase, maltase, trehalase, a-dextrinase); Peptidases (amino-oligopeptidase, dipeptidase)

Question 20

define steatorrhea

Answer 20

malabsorption of fat causing dietary fat in stool from decrease in minimum of 80% lipase secretion

Question 21

When is digestion and absorption completed?

Answer 21

before the ingesta enters the ileum

Question 22

Do disaccharidases change levels throughout live?

Answer 22

no; present at birth with same level during adulthood

Question 23

what causes a shift in the pancreatic enzymatic secretions?

Answer 23

enzymes shift in response to chronic changes in diet => adaptation

Question 24

If a person substitutes protein in a significant amount over carbohydrates, what enzymes will change?

Answer 24

decrease in amylase; increase in proteases

Question 25

what enzyme(s) are increased during a high fat diet?

Answer 25

lipases

Question 26

What controls the changes in enzyme secretion?

Answer 26

enzyme synthesis via feedback regulation of CCK, secretin, and insulin on mRNAs for enzymes

Question 27

define absorption

Answer 27

movement of nutrients, water, electrolytes through the epithelium into blood and lymph

Question 28

define secretion

Answer 28

movement of water, electrolytes from blood and lymph in opposite direction

Question 29

Absorptive pathway consists of 8 barriers. Name them

Answer 29

1) unstirred layer of water crossed by diffusion
2) glycocalyx
3) apical membrane of cell
4) cytoplasm of enterocyte
5) basolateral cell membrane
6) intercellular space
7) basement membrane
8) wall of capillary or lymph vessel

Question 30

what is glycocalyx

Answer 30

filamentous glycoprotein surface coat

Question 31

what is significant about the apical membrane of cell?

Answer 31

contains protein carriers for specific transport of nutrients

Question 32

How is blood supplied to each villus?

Answer 32

one or more central arterioles that form capillary network beneath absorbing cells

Question 33

describe blood flow w/in absorptive pathway

Answer 33

ascends centrally and descends peripherally => absorbed substances enter descending network to drain into portal vein

Question 34

define lacteal

Answer 34

found in each villus and is a central lymphatic vessel

Question 35

what is significant about the lacteals?

Answer 35

products of fat digestion enter lacteals and blood via Left thoracic duct

Question 36

How does simple diffusion take place?

Answer 36

pores of membrane or lipid domain of membrane => controlled by [ ] and electrical gradient of molecule

Question 37

What must be used to push substances against their gradient?

Answer 37

active transport

Question 38

how is active transport generally accomplished?

Answer 38

secondary to using Na+ gradient from Na/K ATPase in the basolateral membrane

Question 39

define facilitated diffusion

Answer 39

membrane transport carriers w/ concentration gradient and no energy use

Question 40

define pinocytosis

Answer 40

large molecule transportation as plasma membrane invaginates around it

Question 41

where does pinocytosis typically occur?

Answer 41

base of microvilli

Question 42

define paracellular transport

Answer 42

movement of water and small electrolytes through tight junctions directly into intercellular spaces

Question 43

How does the absorptive capacity for most nutrients change?

Answer 43

greater proximally and decreases distally

Question 44

What would occur if ileum is removed?

Answer 44

vit B12 and bile salts would not be absorbed leading to steatorrhea

Question 45

why does steatorrhea occur if ileum is lost?

Answer 45

liver cannot synthesize sufficient new bile acids to replace those lost for fat digestion and absorption

Question 46

What are the primary membrane digestive enzymes?

Answer 46

disaccharidases (sucrase, maltase, trehalase, a-dextrinase);

peptidases (amino-oligopeptidases, dipeptidases)