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The Alimentary Canal > Nutrient Digestion and Absorption > Flashcards

Nutrient Digestion and Absorption Flashcards

1
Q

What are the primary dietary constituents

A

Carbohydrates
Proteins
Fat
Vitamins
Water
Minerals

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2
Q

How many molecules are in a oligosaccharide?

A

3-9 molecules

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3
Q

How many molecules are in a polysaccharide?

A

10+ molecules

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4
Q

What are some carbohydrates?

A

Monosaccharides
Disaccharides
Oligosaccharides
Polysaccharides

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5
Q

What are the 3 main monosaccharides?

A

Glucose
Galactose
Fructose

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6
Q

What is the difference between alpha and beta glucose?

A

Structural isomers of glucose
The orientation of the OH group on C1 is different
Beta has OH group above ring
Alpha has OH group below ring

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7
Q

What is the differences and similarities between D-glucose and L-glucose?

A

Stereoisomers
In D-glucose the 3 hydroxyl groups are on right side with one hydrogen
In L-glucose, they are on left
D-glucose is mainly used and is narrower

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8
Q

What are the 3 disaccharides?

A

Maltose
Sucrose
Lactose

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9
Q

What is maltose made up of?

A

2 glucose molecules

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10
Q

What is sucrose made up of?

A

1 glucose and 1 fructose

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11
Q

What is lactose made up of?

A

1 galactose and 1 glucose

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12
Q

What are the breakdown products of monosaccharides?

A

Complex CHOs which are absorbed by small intestine

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13
Q

What bond is two monosaccharides bonded together by?

A

Glycosidic bond

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14
Q

What are disaccharides are broken down into?

A

Constituent monomers by brush border enzymes in the small intestine

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15
Q

Describe degradation of disaccharides?

A

Brush border enzymes break down them in small intestine
Degradation by lactase, maltase and sucrase

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16
Q

What are 3 main polysaccharides?

A

Starch
Cellulose
Glycogen

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17
Q

What is alpha-amylose?

A

Glucose linked in straight chains

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17
Q

What is amylopectin?

A

Glucose chains highly branched

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17
Q

Describe a starch

A

Plant storage form of glucose
Glucose monomers linked by alpha 1,4 glycosidic bonds - hydrolysed by amylases

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18
Q

Describe cellulose

A

Constituent of plant cell walls
Dietary fibre - requires bacteria (cellulase)
Unbranched, linear chain of glucose monomers linked by beta 1,4 glycosidic bonds

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19
Q

Describe glycogen

A

Animal storage form of glucose
Linked by alpha 1,4 glycosidic bonds

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20
Q

What is the differences of starch, cellulose and glycogen?

A

Starch and Glycogen have alpha bonds so can be hydrolysed by amylases in saliva and pancreas
Cellulose is beta bonds so requires bacteria/cellulase

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21
Q

What are some features of the small intestine?

A

Apical membrane
Microvilli
Tight junctional complex
Basolateral membrane

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22
Q

What is transcellular transport?

A

Hydrophobic molecules can transport through cell

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23
Q

What is vectoral transport?

A

Needs carriers and energy so is active directional transport

24
Q

What are some glucose transporters?

A

SGLT1 - need 2 Na and 1 glucose
GLUT2 - enables protein facilitated glucose movement across cell membranes
Works along with the Na/K pump to create electro chemical gradient

25
Q

Are glucose transporters passive or active?

A

Active

26
Q

What are some fructose transporters in small intestine?

A

GLUT5 - facilitated diffusion so passive as no fructose in blood but high glucose

27
Q

Describe proteins

A

Polymers of amino acids linked together by peptide bonds with variation in chain length
Small - 3 to 10 in length = peptides

28
Q

What are the enzymes which hydrolyse proteins and peptide bonds into amino acids?

A

Proteases and peptidases

29
Q

Describe the breakdown of a protein

A

Endopeptidases break down the middle of chain into 2 smaller peptides
Aminopeptidase and Carboxypeptidases then further break down

30
Q

Describe transport of amino acid across membrane

A

Through SAAT1
Facilitated transport along by the Na/K pump

31
Q

Describe transport of di and tripeptides across membrane

A

NHE3 - exchanger
PepT1 is a c-transporter
Works along with Na/K pump and other pumps to go across into blood

32
Q

What is the acid microclimate?

A

pH less than 6 near brush border - microvilli
pH more than 7 further into small intestine
Affects the absorption of weak electrolytes

33
Q

Where does fat digestion take place and by what enzyme?

A

Small intestine by pancreatic lipase

34
Q

What form is fat most commonly ingested as?

A

Triacylglycerol

35
Q

What is triacylglycerol broken down into by lipase?

A

Monoglyceride and 2 fatty acids

36
Q

Describe triacylglycerols

A

Present as large lipid droplets which are insoluble in water so lipase works on surface of droplet making slow digestion

37
Q

What is the process of emulsification?

A

Dividing large lipid droplets into smaller droplets which increases surface area and accessibility for lipase action

38
Q

What does emulsification require?

A

Mechanical disruption of large lipid droplets into small droplets
Emulsifying agent - stops small reforming to large droplets

39
Q

What are some emulsifying agents?

A

Bile salts + phospholipids secreted in bile
Amphipathic molecules

40
Q

Explain amphipathic molecules as emulsifying agents

A

Non polar portions associate with non-polar interior of lipid droplet
Polar portions exposed at water surface so repel other small lipid droplets

41
Q

What is absorption enchased by formation of?

A

Micelles - smaller than emulsion droplets

42
Q

What does a micelle consist of?

A

Bile salt + monoglycerides + fatty acids + phospholipids

43
Q

Describe the structure of micelles

A

Polar at micelle surface then non-polar form core
Hydrophobic fatty acids and monoacylglycerols in interior
Bile salts on exterior

44
Q

What does micelle breakdown cause?

A

Releases small amounts of free fatty acids and monoglycerides into solution causing diffusion across plasma membrane

45
Q

What is the purpose of dynamic equilibrium between fatty acids and monoglycerides in solution and micelles?

A

Retains most of fat digestion products in solution while constantly replenishing supply of free molecules for absorption

46
Q

What happens when fatty acids and monoglycerides enter the smooth endoplasmic reticulum (sER)?

A

Reformed into triacylglycerol by enzymes in sER after entering epithelial cells

47
Q

When inside cells what is triacylglycerol coated in?

A

Amphipathic protein

48
Q

Explain triacylglycerol leaving epithelial cell

A

Transported in vesicles formed in sER membrane - processed in golgi apparatus and exocytosed at serosal membrane

49
Q

What are extracellular fat droplets called?

A

Chylomicrons

50
Q

Where do chylomicrons pass into?

A

Lacteals between endothelial cells - cant pass through capillary basement membrane

51
Q

What is the difference between fat-soluble and water-soluble vitamins?

A

Fat soluble follow fat absorption paths
Water soluble absorbed by passive diffusion or carrier mediated

52
Q

What does B12 deficiency lead to?

A

Pernicious anaemia - failure of red blood cell maturation

53
Q

How is Vitamin B12 absorbed?

A

Binds to intrinsic factor in stomach to form complex
then absorbed via specific transport in distal ileum

54
Q

How is iron absorbed?

A

Across brush border membrane via DMT1 into duodenal enterocytes
Either binds to ferritin or unbound

55
Q

What happens to iron bound to ferritin?

A

Protein iron complex - intracellular iron store

56
Q

What happens to iron that is unbound?

A

Transported across serosal membrane into blood and binds to transferrin

57
Q

What does hyperaemia cause?

A

Increased ferritin level so more iron bound in enterocytes

58
Q

What does anaemia cause?

A

Decreased ferratin levels and more iron released to blood

The Alimentary Canal (33 decks)

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