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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
What pancreatic enzymes break down protein in SI?
Trypsin, chymotrypsin, carboxypeptidase, elastase
26
Trypsin and chymotrypsin break down proteins into_______
small polypeptides
27
Carboxypeptidase breaks down proteins into __________
carboxyl ends of AA
28
What enzymes are secreted by SI to break down proteins?
aminopolypeptidase, dipeptidase
29
Where are aa, di and tripeptides absorbed?
enterocytes
30
What are pancreatic enzymes secreted as?
zymogens + by enterokinase trypsinogen or trypsin
31
On epithelial SI cells, are there separate co-transporters for each amino acid type?
yes
32
Do epithelial cells of SI only absorb AA?
no--> also absorb dipeptides, tripeptides and H+
33
What is on the basolateral epithelial cell of SI to absorb AA?
Na/K ATPase maintains gradient Separate facilitated diffusion for each amino acid type
34
What are the difference between transporters on the apical and basolateral epithelial SI cells to absorb AA?
apical: co-transporters (Na) basolateral: facilitated diffusion
35
Caucasian women and people of European decent are more likely to develop ___
celiac disease
36
Sx of celiac disease
Ab-->destroy SI villi and crypts abd pain, N, V, steatorrhea, unexplained weight loss, constipation or diarrhea
37
What sx do celiacs have r/t malabsorption?
tingling or numbness of hands and feet, itchy skin with rash, fatigue, seizures, easy bruising, bone fx
38
What are celiacs deficient in d/t malabsorption?
folate, iron, calcium, vitamins A, B12 and D
39
What is tropical sprue?
loss or decreased number of intestinal epithelial cells -->unknown cause
40
What does tropical sprue cause?
diarrhea, steatorrhea, cramps, N, weight loss, gas--->d/t impaired lipid absorption and reduced microvilli surface area TMT: tetracycline and folate 6 months
41
What are the luminal surface of SI arranged in longitudinal folds called?
folds of Kerkckring
42
What are the fxn of villi/microvilli?
increase surface area for absorption
43
Where are villi longest?
duodenum
44
What must be transversed by nutrients, water and electrolytes?
brush border -->site of activity of digestive enzymes
45
What are Paneth cells in intestines?
mucosal defense, secrete agents that destroy bacteria and produce inflammatory responses
46
What are the turnover rates of enterocytes?
3-6 days -->digestion, absorption, secretion -->susceptible to irradiation and chemotherapy
47
What is the major mechanism for uptake of protein?
pinocytosis at base of microvilli
48
How do substances cross into enterocytes?
pinocytosis (protein) passive diffusion facilitated diffusion active transport
49
What are the barriers from lumen, through enterocyte to blood?
``` Lumen Unstirred Layer Glycocalyx Microvilli Tight jxn and intracellular space of enterocyte Basement membrane Capillary ```
50
Lingual and gastric lipase act on ____ in _________
TAGs in stomach
51
What role does CCK play in fat digestion?
inhibits gastric emptying so can mix activates GB emptying
52
Where does most digestion of lipids occur?
SI
53
What is secreted into SI from the pancreas to complete fat digestion?
``` 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
What is the fxn of colipase?
activated by trypsin displaces bile salts by binding to pancreatic lipase-->digest lipids
55
ApoB on chylomicron fxn?
lipid absorption
56
Where do chylomicrons go once formed in intestinal cells?
lymphatics
57
What sx is universal with problems with fat digestion/absorption?
steatorrhea
58
Define pancreatitis in terms of enzyme dysfunction
trypsin become activated in pancreas and digests it -->impaired bicarb and enzyme secretions
59
Why is neutral duodenum pH so important?
lumen must be neutralized y bicarb-containing pancreatic secretions for fat digestion/absorption to occur
60
What can cause deficits in bile salts?
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
What detects SIBO?
breath test-->methane and H+
62
How are fat soluble vitamin absorbed?
A, D, E, K | same as lipids
63
How are vitamins B and C (water soluble) absorbed?
Na-dependent cotransporter except B12
64
What is vitamin B12 absorbed?
forms complexes with other proteins (R proteins secreted in salivary juices, IF and transcobalamin II)
65
What are the fxns of Vitamin B12
- cofactor in folate recycling and nerve myelination - DNA synthesis - H+ acceptor coenzyme
66
What is caused by failure of RBC maturation when vit B12 is deficient?
pernicious anemia -->also macrocytic and megaloblastic anemia
67
What can cause the stomach not to produce enough IF?
- 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
What surgical aspects can cause lack of vitamin b12 absorption?
-gastrectomy (loss parietal cells~IF) - gastric bypass - ->exclusion of stomach, duodenum and prox jejunum alters absorption of vitamin B12
69
What does calcium absorption depend on?
vitamin D -->absorbed across enterocytes and reab in kidneys
70
What binding protein is essential for absorption of calcium in the SI?
vitamin D-dependent calcium binding protein (calbindin D-28K)
71
What is absorbate of SI?
always ISOSOMITC -->solute and water absorption occur in proportion
72
What electrolytes does the jejunum primarily absorb?
sodium
73
What electrolytes does the ileum primarily absorb/secrete?
sodium secretes bicarb
74
What electrolytes does the colon primarily absorb/secrete?
sodium absorption potassium and secretion ****modulated by aldosterone
75
What causes excess chloride secretion in the colon?
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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