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GIGU > Digestion and Absorption in GI Tract > Flashcards

Digestion and Absorption in GI Tract Flashcards

1
Q

What is lactose intolerance?

A

Can’t digest dairy carbs

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2
Q

What is absent or deficient in lactose intolerance?

A

lactase in SI brush border

–>75% lactose unabsorbed

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3
Q

What is the pathology behind lactose intolerance?

A

lactose–>SCFAs and H+ gas–> acetate, butrate and propionate

These acids remain in lumen, holds in water and causes OSMOTIC diarrhea

–>ferments into methane and H+ gast

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4
Q

What are primary sugars in the human diet?

A

sucrose, lactose, starch

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5
Q

What are secondary sugars in the human diet?

A 
amylose
glycogen
ETOH
lactic acid
pyruvic acid
pectins
dextrines
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6
Q

Are there digestive enzymes for cellulose in the body?

A

NO

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7
Q

Where does the beginning process of starch breakdown occur?

A

mouth via salivary amylase

starch–>maltose and glucose polymers

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8
Q

Where does most of starch breakdown occur?

A

SI via pancreatic amylase

disaccharides, maltose, glucose polymers

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9
Q

What breaks down disaccharides into glucose, galactose and fructose?

A

brush border enterocytes

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10
Q

Maltose–>

A

glucose x2

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11
Q

Trehalose–>

A

glucose x2

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12
Q

Lactose–>

A

glucose and galactose

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13
Q

Sucrose–>

A

glucose and fructose

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14
Q

What transporters are on the luminal side of epithelial cells of SI?

A

SGLT1 (secondary active transport for glucose and galactose)

GLUT5 for fructose

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15
Q

What transporters are on the basolateral side of epithelial cells of SI?

A

Na/K ATPase–>sets concentration gradient

GLUT2 for fructose, glucose and galactose

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16
Q

How to test carb assimilation problems

A

Fasting, given D-xylose and collect urine for 5 hrs to check absorptive capacity of prox SI

–>absorbed via active Na cotransport and passive diffusion but not utilized

***breath tests also used

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17
Q

Define congenital trypsin absence

A

absence of trypsin and all pancreatic enzymes

–>trypsin activates other pancreatic enzymes

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18
Q

Define chronic pancreatitis

A

lack of proteases (trypsinogen) and pancreatic enzymes

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19
Q

Define cystinuria

A

Defect in transport of basic AA–>cysteine, lysine, arginine, ornithine

SLC3A1 and SLC7A9

–>aa in feces

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20
Q

Define Hartnup disease

A

Can’t absorb neutral AA

–>sx resemble pellagra/niacin deficiency

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21
Q

Define Cystic fibrosis

A

CFTR (Cl- channel on apical duct cell) mutations–>loss of bicarb secretion

–>chronic and acute pancreatitis

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22
Q

What can cystic fibrosis cause?

A

pancreatitis

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23
Q

Where is pepsin secreted?

A

stomach as pepsinogen, pH 2-3

–>not essential for protein breakdown (10-20%)

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24
Q

Where are most proteins broken down?

A

SI via pancreatic enzymes

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25
Q

What pancreatic enzymes break down protein in SI?

A

Trypsin, chymotrypsin, carboxypeptidase, elastase

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26
Q

Trypsin and chymotrypsin break down proteins into_______

A

small polypeptides

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27
Q

Carboxypeptidase breaks down proteins into __________

A

carboxyl ends of AA

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28
Q

What enzymes are secreted by SI to break down proteins?

A

aminopolypeptidase, dipeptidase

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29
Q

Where are aa, di and tripeptides absorbed?

A

enterocytes

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30
Q

What are pancreatic enzymes secreted as?

A

zymogens + by enterokinase trypsinogen or trypsin

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31
Q

On epithelial SI cells, are there separate co-transporters for each amino acid type?

32
Q

Do epithelial cells of SI only absorb AA?

A

no–> also absorb dipeptides, tripeptides and H+

33
Q

What is on the basolateral epithelial cell of SI to absorb AA?

A

Na/K ATPase maintains gradient

Separate facilitated diffusion for each amino acid type

34
Q

What are the difference between transporters on the apical and basolateral epithelial SI cells to absorb AA?

A

apical: co-transporters (Na)
basolateral: facilitated diffusion

35
Q

Caucasian women and people of European decent are more likely to develop ___

A

celiac disease

36
Q

Sx of celiac disease

A

Ab–>destroy SI villi and crypts

abd pain, N, V, steatorrhea, unexplained weight loss, constipation or diarrhea

37
Q

What sx do celiacs have r/t malabsorption?

A

tingling or numbness of hands and feet, itchy skin with rash, fatigue, seizures, easy bruising, bone fx

38
Q

What are celiacs deficient in d/t malabsorption?

A

folate, iron, calcium, vitamins A, B12 and D

39
Q

What is tropical sprue?

A

loss or decreased number of intestinal epithelial cells

–>unknown cause

40
Q

What does tropical sprue cause?

A

diarrhea, steatorrhea, cramps, N, weight loss, gas—>d/t impaired lipid absorption and reduced microvilli surface area

TMT: tetracycline and folate 6 months

41
Q

What are the luminal surface of SI arranged in longitudinal folds called?

A

folds of Kerkckring

42
Q

What are the fxn of villi/microvilli?

A

increase surface area for absorption

43
Q

Where are villi longest?

44
Q

What must be transversed by nutrients, water and electrolytes?

A

brush border

–>site of activity of digestive enzymes

45
Q

What are Paneth cells in intestines?

A

mucosal defense, secrete agents that destroy bacteria and produce inflammatory responses

46
Q

What are the turnover rates of enterocytes?

A

3-6 days

–>digestion, absorption, secretion

–>susceptible to irradiation and chemotherapy

47
Q

What is the major mechanism for uptake of protein?

A

pinocytosis at base of microvilli

48
Q

How do substances cross into enterocytes?

A

pinocytosis (protein)
passive diffusion
facilitated diffusion
active transport

49
Q

What are the barriers from lumen, through enterocyte to blood?

A 
Lumen
Unstirred Layer
Glycocalyx
Microvilli
Tight jxn and intracellular space of enterocyte
Basement membrane
Capillary
50
Q

Lingual and gastric lipase act on ____ in _________

A

TAGs in stomach

51
Q

What role does CCK play in fat digestion?

A

inhibits gastric emptying so can mix

activates GB emptying

52
Q

Where does most digestion of lipids occur?

53
Q

What is secreted into SI from the pancreas to complete fat digestion?

A 
pancreatic lipase (already active on secretion)
-->inactivated by bile salts if it doesn't attach to colipase

cholesterol ester hydrolase (already active)
–>catalyzes production of free cholesterol, hydrolyzes triglycerides to glycerol

phospholipase A2
–>proenzyme that will be activated by trypsin

54
Q

What is the fxn of colipase?

A

activated by trypsin

displaces bile salts by binding to pancreatic lipase–>digest lipids

55
Q

ApoB on chylomicron fxn?

A

lipid absorption

56
Q

Where do chylomicrons go once formed in intestinal cells?

A

lymphatics

57
Q

What sx is universal with problems with fat digestion/absorption?

A

steatorrhea

58
Q

Define pancreatitis in terms of enzyme dysfunction

A

trypsin become activated in pancreas and digests it

–>impaired bicarb and enzyme secretions

59
Q

Why is neutral duodenum pH so important?

A

lumen must be neutralized y bicarb-containing pancreatic secretions for fat digestion/absorption to occur

60
Q

What can cause deficits in bile salts?

A

ileal resection d/t lost place of absorption

SIBO
–>bacteria deconjugate bile salts so they can’t form micelles
too little gastric secretion or SI dysmotility

61
Q

What detects SIBO?

A

breath test–>methane and H+

62
Q

How are fat soluble vitamin absorbed?

A

A, D, E, K

same as lipids

63
Q

How are vitamins B and C (water soluble) absorbed?

A

Na-dependent cotransporter except B12

64
Q

What is vitamin B12 absorbed?

A

forms complexes with other proteins (R proteins secreted in salivary juices, IF and transcobalamin II)

65
Q

What are the fxns of Vitamin B12

A
  • cofactor in folate recycling and nerve myelination
  • DNA synthesis
  • H+ acceptor coenzyme
66
Q

What is caused by failure of RBC maturation when vit B12 is deficient?

A

pernicious anemia

–>also macrocytic and megaloblastic anemia

67
Q

What can cause the stomach not to produce enough IF?

A
  • atrophic gastritis
  • –>chronic inflammation leads to loss of parietal cells
  • autoimmune metaplastic atrophic gastritis
  • ->immune system attacks IF protein or parietal cells in stomach
68
Q

What surgical aspects can cause lack of vitamin b12 absorption?

A

-gastrectomy (loss parietal cells~IF)

  • gastric bypass
  • ->exclusion of stomach, duodenum and prox jejunum alters absorption of vitamin B12
69
Q

What does calcium absorption depend on?

A

vitamin D

–>absorbed across enterocytes and reab in kidneys

70
Q

What binding protein is essential for absorption of calcium in the SI?

A

vitamin D-dependent calcium binding protein (calbindin D-28K)

71
Q

What is absorbate of SI?

A

always ISOSOMITC

–>solute and water absorption occur in proportion

72
Q

What electrolytes does the jejunum primarily absorb?

73
Q

What electrolytes does the ileum primarily absorb/secrete?

A

sodium

secretes bicarb

74
Q

What electrolytes does the colon primarily absorb/secrete?

A

sodium absorption

potassium and secretion

**modulated by aldosterone

75
Q

What causes excess chloride secretion in the colon?

A

cholera toxin

–>induces cAMP that increases Cl secretion along with sodium and water

***secretory diarrhea d/t malabsorption

GIGU (37 decks)

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