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HUBS192 > Lecture 26 GI Physio Digestion > Flashcards

Lecture 26 GI Physio Digestion Flashcards

1
Q

Chemical Digestion

The chemical hydrolysis of food is caused by?

A

Enzymes secreted

Enzymes attached to enterocytes of small intestine (brush border enzymes)

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2
Q

what are enzymes secreted by?

A

salivary glands
chief cells of stomach
acinar cells of the pancreas

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3
Q

what are the Main nutrients that undergo chemical digestion?

A

Carbohydrates (sugars)
Proteins
Lipids (fats)

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4
Q

whats carbohydrates?

A

Important source of energy

Consist of chains of monosaccharides (eg Glucose)

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5
Q

whats the Average amount of carbs ingested?

A

250 - 800 g/day in typical western diet

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6
Q

whats the composition of ingested carbs?

A

starch and glycogen
Cellulose
disaccharides
monosaccharides

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7
Q

whats starch and glycogen?

A

Main carbs in diet
Storage polysaccharides

Long chains of glucose - a1-4 glycosidic bonds

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8
Q

whats cellulose?

A

large amount in diet

cant digest
Structural polysaccharide in plants
b1-4 glycosidic bonds

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9
Q

whats ingest disaccharides?

A

Sucrose
Lactose
Maltose

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10
Q

whats ingest monosaccharide?

A

limited amount

Glucose

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11
Q

how much proteins do we ingest?

A

70-100 g/day in our food

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12
Q

what does the intestine also have to digest an equivalent amount of?

A

endogenous proteins such as enzymes, immunoglobulins

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13
Q

whats proteins required for?

A

amino acids
20 amino acids
Approximately 10 essential in diet

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14
Q

whats Ingested proteins?

A

Long chains of amino acids

Linked by peptide bond

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15
Q

how much lipids do we consume?

A

100 - 150 g/day.

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16
Q

what do lipids consist mainly of?

A

triglycerides

Contains fat soluble vitamins

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17
Q

what are Triglycerides?

A

Glycerol backbone with 3 fatty acids attached by ester bonds.

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18
Q

whats fatty acids variable chain length

short chain
medium chain
long chain

A

< 6 C
6-12 C
12-24 C

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19
Q

what size are ingest nutrients (same size even after digestion) and what size are absorb nutrients (to get them across epithelium into body)?

A

Large complex molecules (carbs, proteins, lipids)

Small molecules

20
Q

what does chemical digestion do?

A

reduce nutrients to size that allows them to cross the epithelial lining of GI tract

21
Q

what does chemical digestion need?

A

digestive enzymes

22
Q

whats digestive enzymes?

A

Are extracellular
Are organic catalysts
Function optimally at a specific pH
Are specific

23
Q

what does it mean that digestive enzymes are specific?

A

Will only act on a specific substrate
Require different enzymes for different substrates

E.g. proteases, lipase, amylase

24
Q

what 2 processes occurs in chemical digestion?

A

Luminal digestion

Contact digestion

25
whats luminal digestion?
Initial digestion involving enzymes secreted into lumen
26
what enzymes are involved in luminal digestion?
Salivary glands - amylase Stomach - pepsin Small intestine - trypsin, chymotrypsin, lipase and amylase (from pancreas)
27
whats contact digestion (in SI)?
Digestion completed by enzymes produced by enterocytes (absorptive cell) These enzymes attached to brush border of enterocytes
28
what is the site of contact digestion?
Brush border microvilli (mucus granules, microvilli form brush border, enterocyte-absorptive cell)
29
Chemical digestion of CARBOHYDRATES whats the LUMINAL digestion of carbs?
Use Salivary and pancreatic amylase Polysaccharides converted to disaccharides
30
Chemical digestion of CARBOHYDRATES whats the CONTACT digestion of carbs?
Disaccharidases Sucrase, lactase and maltase Bound to brush border of SI to Convert disaccharides to monosaccharides
31
Chemical digestion of PROTEINS whats does the LUMINAL digestion of proteins involve?
Pepsin in stomach Trypsin, chymotrypsin - Secreted by pancreas - Operate in small intestine
32
Chemical digestion of PROTEINS what is LUMINAL digestion of proteins?
Convert proteins into polypeptides and proteoses Lumen of stomach and SI ``` use: Pepsin in stomach Trypsin, chymotrypsin - Secreted by pancreas - Operate in small intestine ```
33
Chemical digestion of PROTEINS what is CONTACT digestion of proteins?
Involves peptidases - Attached to brush border of SI Many types Convert polypeptides to individual amino acids
34
Chemical digestion of lipids where does digestion occur?
intestinal lumen | NO contact digestion
35
Digestive enzymes dissolved in luminal fluid
Protein and sugars (soluble in water) Fats (insoluble in water) - requires more complex process
36
what are the stages of Chemical digestion of LIPIDS?
Emulsification Stabilisation Hydrolysis (digestion) Formation of micelles
37
whats Emulsification of LIPIDS?
Motility separates large fat droplets down into smaller droplets (0.5 - 1.0 μm) - forms an EMULSION increase SA for digestion
38
where does Emulsification of LIPIDS occur?
Stomach - retropulsion | SI - segmentation
39
whats Stabilisation of LIPIDS?
use lecithin and bile salts - secrete in bile - stabilise emulsion droplets - allow formation of smaller droplets Increase SA for digestion even further
40
where does Stabilisation of LIPIDS occur?
SI
41
what does Hydrolysis of LIPIDS involve?
lipase and colipase (cofactor) - Both secreted by the pancreas
42
where does Hydrolysis of LIPIDS occur?
lumen of SI at the surface of emulsion droplets NO contact digestion at microvilli
43
whats Hydrolysis of LIPIDS?
Co-lipase anchors lipase to surface of emulsion droplet Lipase converts triglycerides to: Monoglyceride and Free fatty acids
44
whats the formation of micelles?
Products of fat digestion are insoluble in water. Monoglyceride and Long chain fatty acids. Kept in solution through the formation of micelles
45
whats micelles?
Small droplets (4 - 6 nm diameter) Consist of 20 - 30 molecules - Bile salts/lecithin - Amphipathic compounds - Fatty acids - Monoglycerides
46
what do 20-30 molecules do micelles consist of?
Bile salts/lecithin - Amphipathic compounds Fatty acids Monoglycerides
47
what do Carbohydrates, Proteins, Lipids get digested to (smallest size)?
Monosaccharides Amino acids Micelles

HUBS192 (36 decks)

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