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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
Q

whats luminal digestion?

A

Initial digestion involving enzymes secreted into lumen

26
Q

what enzymes are involved in luminal digestion?

A

Salivary glands - amylase
Stomach - pepsin
Small intestine - trypsin, chymotrypsin, lipase and
amylase (from pancreas)

27
Q

whats contact digestion (in SI)?

A

Digestion completed by enzymes produced by enterocytes (absorptive cell)

These enzymes attached to brush border of enterocytes

28
Q

what is the site of contact digestion?

A

Brush border microvilli (mucus granules, microvilli form brush border, enterocyte-absorptive cell)

29
Q

Chemical digestion of CARBOHYDRATES

whats the LUMINAL digestion of carbs?

A

Use Salivary and pancreatic amylase

Polysaccharides converted to disaccharides

30
Q

Chemical digestion of CARBOHYDRATES

whats the CONTACT digestion of carbs?

A

Disaccharidases
Sucrase, lactase and maltase
Bound to brush border of SI

to Convert disaccharides to monosaccharides

31
Q

Chemical digestion of PROTEINS

whats does the LUMINAL digestion of proteins involve?

A

Pepsin in stomach
Trypsin, chymotrypsin
- Secreted by pancreas
- Operate in small intestine

32
Q

Chemical digestion of PROTEINS

what is LUMINAL digestion of proteins?

A

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
Q

Chemical digestion of PROTEINS

what is CONTACT digestion of proteins?

A

Involves peptidases
- Attached to brush border of SI

Many types

Convert polypeptides to individual amino acids

34
Q

Chemical digestion of lipids

where does digestion occur?

A

intestinal lumen

NO contact digestion

35
Q

Digestive enzymes dissolved in luminal fluid

A

Protein and sugars (soluble in water)

Fats (insoluble in water) - requires more complex process

36
Q

what are the stages of Chemical digestion of LIPIDS?

A

Emulsification
Stabilisation
Hydrolysis (digestion)
Formation of micelles

37
Q

whats Emulsification of LIPIDS?

A

Motility separates large fat droplets down into smaller droplets (0.5 - 1.0 μm)
- forms an EMULSION

increase SA for digestion

38
Q

where does Emulsification of LIPIDS occur?

A

Stomach - retropulsion

SI - segmentation

39
Q

whats Stabilisation of LIPIDS?

A

use lecithin and bile salts

  • secrete in bile
  • stabilise emulsion droplets
  • allow formation of smaller droplets

Increase SA for digestion even further

40
Q

where does Stabilisation of LIPIDS occur?

A

SI

41
Q

what does Hydrolysis of LIPIDS involve?

A

lipase and colipase (cofactor) - Both secreted by the pancreas

42
Q

where does Hydrolysis of LIPIDS occur?

A

lumen of SI at the surface of emulsion droplets

NO contact digestion at microvilli

43
Q

whats Hydrolysis of LIPIDS?

A

Co-lipase anchors lipase to surface of emulsion droplet

Lipase converts triglycerides to: Monoglyceride and Free fatty acids

44
Q

whats the formation of micelles?

A

Products of fat digestion are insoluble in water. Monoglyceride and Long chain fatty acids.

Kept in solution through the formation of micelles

45
Q

whats micelles?

A

Small droplets (4 - 6 nm diameter)

Consist of 20 - 30 molecules

  • Bile salts/lecithin
  • Amphipathic compounds
  • Fatty acids
  • Monoglycerides
46
Q

what do 20-30 molecules do micelles consist of?

A

Bile salts/lecithin
- Amphipathic compounds
Fatty acids
Monoglycerides

47
Q

what do Carbohydrates, Proteins, Lipids get digested to (smallest size)?

A

Monosaccharides
Amino acids
Micelles

HUBS192 (36 decks)

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