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GI Exam #2 > Digestion And Absorption Of The GI Tract > Flashcards

Digestion And Absorption Of The GI Tract Flashcards

1
Q

Cellular movement vs. paracellular movement

A

Cellular movement occurs through the apical membrane into the cell and out the basso lateral membrane to the blood.
Paracellular movement occurs between cells (think tight junctions, etc.)

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2
Q

Carbohydrate enzymes released in saliva (1)

A

Amylase

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3
Q

Carbohydrate enzymes released in the stomach

A

None

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4
Q

Carbohydrate enzymes released in the pancreas (1)

A

Amylase

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5
Q 
Carbohydrate enzymes released in the intestinal mucosa (5)
S
M
L
T
Alpha
A 
Sucrose
Maltese
Lactase
Trehalase
A-dextrinase
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6
Q

Protein enzymes release in saliva

A

None

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7
Q

Protein enzyme released in the stomach (1)

A

Pepsin

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8
Q 
Protein enzymes released in the pancreas 
T
C
C
E
A

Trypsin
Chymotrypsin
Carboxypeptidase
Elastase

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9
Q

Protein enzymes released by the intestinal mucosa
A
D
E

A

Amino-oligopeptidase
Dipeptidase
Enterokinase

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10
Q

Lipid enzymes released in saliva (1)

A

Lingual lipase

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11
Q

Lipid enzyme released in the stomach (1)

A

Gastric lipase

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12
Q

Lipid enzyme released in the pancreas
L
P
C

A

Lipase-colipase
Phospholipase A2
Cholesterol ester hydrolase

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13
Q

Lipid enzymes of the intestinal mucosa

A

None

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14
Q

Cavital (luminal) digestion vs membrane (contact) digestion

A

Capital is from the enzymes secreted by organs.

Membrane is from enzymes released by epithelial cells.

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15
Q

Where are villi the longest?

A

Duodenum

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16
Q

Microvillar surface is the same as:

A

Brush border

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17
Q

Enterocyte features (4)

A

Epithelial cells
Digestion, absorption, secretion, etc.
Cells replaced every 3-6 days.
Susceptible to irradiation and chemo.

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18
Q

Paneth cells

A

Defends against infection. Produce Abx.

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19
Q

3 cell types of intestinal epithelium `

A

Enterocytes
Goblet cells
Paneth cells

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20
Q

What control the flux of salutes and fluid between lumen and blood?

A

Enterocyte membrane

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21
Q

How does the enterocyte membrane control the flux? (4)

A

Pinocytosis (major way)
Passive diffusion thru pores
Facilitated diffusion
Active transport

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22
Q

What barriers must nutrients traverse from lumen to blood? (7)

A 
Unstirred Fluid
glycocalyx
Apical membrane
Cytoplasm
Basolateral membrane
Basement membrane
Capillary wall
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23
Q

What happens if ileum is resected?

A

Cannot absorb vit B12 and bile salts.

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24
Q

What kind of sugars can be absorbed by enterocytes?

A

Monosaccharides - glu, gal, fru.

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25
Q

How can glu/gal get across the luminal membrane?

What kind of transport?

A

SGLT1. Symport w/ Na+.

Seondary active transport.

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26
Q

How can fru get across the luminal side of the enterocyte?

A

GLUT 5 tranporter. Uniporter.

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27
Q

How do glu, gal, fru get across the basolateral membrane into the blood?

A

GLUT 2 transporter. Uniporter.

Paired w/ Na/K.

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28
Q

Lactose intolerance

A

No lacttase in brush border.
Undigested lactose holds water and causes osmotic diarrhea.
Can ferment into methane and H gas to lead to gas.

29
Q

What enzyme causes the conversion of trypsinogen to trypsin in the SI?

A

Enterokinase

30
Q

What enzyme catalyzes all other zymogens in the SI?

A

Trypsin

31
Q

Explain autocatalysis and trypsin

A

Trypsin activated by enterokinase. Trypsin then goes on to convert trypsinogen to trypsin.

32
Q

AAs are transported across the luminal membrane via:

What is unique about transport of AAs?

A

Symport w/ Na+.

All kinds of AAs are transported differently (Neutral, basic, acidic, etc).

33
Q

How do AAs get across the basolateral side?

A

Uniporter of AAs paired w/ Na/K

34
Q

What is the process of dipeptides/tripeptides from the lumen to the blood?

A

Symport paired w/ H+. Peptidase converts them to AAs which use the AA uniport.

35
Q

Chronic pancreatitis and cystic fibrosis are caused by:

A

Deficiency of pancreatic enzymes

36
Q

Cystinuria

A

Defect in the Na/AA transporter for dibasic AAs (Cys, Lys, Arg, Orn) and is not available in the SI and kidney.

37
Q

What happens to the undigested AAs in Cystinuria?

A

Cys builds up urine and can form stones.

38
Q

Hartnup disease

A

Cannot absorb neutral AAs.

Can cause pellegra, diarrhea, mood prblems photosensitivity, uncoordinated movements, etc.

39
Q

Urine from a pt w/ Hartnups will have an increase in what?

A

Trypophan and its byproduct, serotonin.

40
Q

What happens in CF in the pancreas?

A

CFTR channel is mutated –> build up of HCO3- in the ductal cell. Pancreas cannot secrete enzymes properly –> pancreatitis.

41
Q

Breakdown of TAGs leads to (3)

A

Monoglyceride and 2 FAs

42
Q

Breakdown of cholesterol ester leads to (2)

A

Cholesterol and FA

43
Q

Breakdown of phospholipids leads to (2)

A

Lysolecithin and FA

44
Q

Which enzymes begin lipid digestion in the stomach?

A

Lingual and gastric lipase.

45
Q

Overview of lipid digestion in the stomach

A

Lipids broken down into small droplets which are emulsified in stomach by dietary proteins (no bile in stomach).
CCK is released which slows gastric emptying.

46
Q

Where does most lipid digestion occur?

A

SI

47
Q

Overview of SI digestion of lipids (2)

A

Bile salts emulsify lipids further..

Pancreatic enzymes secreted into SI to complete digestion.

48
Q

Pancreatic lipase is inactivated by:

A

Bile salts

49
Q

Colipase function

A

Displaces pancreatic lipase allowing bile to work.

50
Q

How are products of lipid digestion solubilized?

A

In mixed micelles

51
Q

5 steps of lipid processing in the SI

A
  1. Solubilization by micelles.
  2. Diffusion of micellar content across apical memb.
  3. Reesterification
  4. Chylomicron formation
  5. Exocytosis of chylomicron to lymph
52
Q

Loss of ApoB can lead to:

A

Abetalipoproteinemia –> inhibits absorption of dietary lipids.

53
Q

What is considered “critical” for the integrity of pancreatic enzyme function?

A

Fine regulation of the acidity of the duodenum.

It needs to be neutralized by HCO3- due to the low pH coming from the stomach.

54
Q

Zollinger-ellison syndrome

A

Gastrin secreting tumor in the pancreas.

Leads to increased H+ secretion by gastric parietal cells –> acid overload in duodenum.

55
Q

Pancreatitis

A

Impaired HCO3- and enzyme secretions

56
Q

What can cause deficiency in bile salts?

A

Ileal resection –> poor recirculation of bile salts –> less bile salts avail.
SIBO –> bacteria overgrowth causes deconjugation of bile salts which impairs micelle formation. It also damages bacterial ovegrowth in the intestinal mucosa.

57
Q

What can cause SIBO (2)?

A

Decreased gastric acid secretion.

Poor SI motility.

58
Q

Tropical sprue features

What is it treated with?

A

Intestinal infection –> decreased intestinal epithelial cells –> reduced microvillar surface.
This severely impairs lipid absorption because the surface area is decreased.

Tetracycline and folate for 6 mo.

59
Q

Celiac sprue

A 
Autoimmune d/o.
ABs against gliadin (gluten component).
Leads to destruction of SI villi and hyperplasia of intestinal crypts.
Poorly absorbs folate, Ca, Fe, vitamins.
Managed w/ gluten-free diet.
60
Q

Fat soluble vitamins undergo what mechanism of absorption?

A

Same as lipids.

61
Q

How are water soluble vitamins absorbed? (B1, B2, B3, B12, C)

A

Na-dependent cotransport in the SI.

62
Q

Vitamin B12 (cobalamin) forms complexes with what proteins to be absorbed? (3)

A

R proteins
IF
Transcobalamin II

63
Q

Functions of cobalamin (vit B12)

A

Coenzyme for reducing ribonucleotides (DNA replication).
Cofactor for folate synthesis and nerve myelination.
Improtant for DNA synthesis in RBCs.

64
Q

2 disruptions in absorption of vitamin B12 (surgical disruptions)

A 
Gastrectomy (loss of parietal cells --> no IF)
Gastric bypass (exclusion of stomach, duodenum, and proximal jejunum alters absorption of vit B12)
65
Q

2 Main causes of pernicious anemia

A

Atrophic gastritis - chronic inflammation of stomach mucosa –> loss of parietal cells.
Autoimmune metaplastic atrophic gastritis - immune system attacks IF or gastric parietal cells.

66
Q

Inadequate Ca absorption can cause (2)

A

Rickets

Osteomalacia

67
Q

Ca is absorbed in which 2 places?

A

Intestines and kidneys (lesser extent)

68
Q

Iron reabsorption

A

Liver secretes apotransferrin –> enters duodenum.
Apotransferrin binds w/ free iron and Hb –> transferrin.
Transferrin allows iron to be absorbed.

GI Exam #2 (9 decks)

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