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AEU (CLB) > Digestion And Absorption > Flashcards

Digestion And Absorption Flashcards

1
Q

What is the definition of digestion?

A

The mechanical, chemical and microbial breakdown of large, insoluble food molecules into simple absorbable compounds.

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2
Q

What is the definition of absorption?

A

The process by which these simple compounds are taken across the intestinal membrane into the blood

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3
Q

What is the basic function of alpha amylases?

A

Alpha amylases catalyse the hydrolysis of starch into sugars

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4
Q

What is the optimum pH of salivary alpha amylase?

A

6.6-6.8

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5
Q

What is the function of salivary alpha amylase?

A

To START carbohydrate suggestion and act on starch

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6
Q

Where is pancreatic alpha amylase secreted from?

A

Secreted from the exocrine pancreas

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7
Q

What is pancreatic alpha amylase secreted from?

A

Secreted from the exocrine pancreas

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8
Q

What is the function of pancreatic alpha amylase?

A

To END carbohydrate digestion and act on complex carbohydrates.

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9
Q

How do alpha amylases work?

A

They attack alpha-1,4 glycosidic bonds in the middle of a CHO chain.

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10
Q

What are the 2 phases of carbohydrate digestion?

A

1) Luminal phase
2) Membranous phase

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11
Q

What happens during the luminal phase of carbohydrate digestion?

A
  • Starch and glycogen are degraded into compounds containing 2-9 glucose units
  • Remember that the products of luminal degradation cannot be absorbed by epithelial cells.
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12
Q

What happens during the membranous phase of carbohydrate digestion?

A

Di, tri and aligosacchrides broken down into monosaccharides by enzymes bound to the apical membrane of epithelial cells.

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13
Q

Where does the luminal phase of carbohydrate digestion occur?

A

Luminal phase happens mostly in the duodenum as this is where the ducts of the pancreas empty

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14
Q

What are enterocytes?

A

Columnar epithelial cells found at the surface of the villi

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15
Q

What 3 types of vessel can be found within each of the individual villi

A

Artery, vein, lymphatic vessel

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16
Q

What is the life span for an enterocyte?

A

2-3 days; when they die they will either be passed out with faeces/ degraded and reabsorbed

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17
Q

What are the 4 different mechanisms for absorption?

A
  • Passive diffusion
  • Facilitated diffusion
  • Active transport
  • Endocytosis
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18
Q

What are the products of carbohydrate digestion?

A

Glucose, fructose and galactose

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19
Q

How is fructose absorbed?

A

Fructose absorbed by carrier mediated (facilitated diffusion)

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20
Q

How is glucose transported from the lumen of the GI tract into the blood?

A
  • Glucose and sodium are cotransported together from the lumen into the intestinal cell
  • The concentration of sodium and glucose is higher inside the cell than in the blood
  • Glucose is moved into the blood via facilitated diffusion
  • Sodium pumps into the blood and potassium is pumped out of the blood (needs energy)
21
Q

What acs as a competitive inhibitor for glucose?

A

Galactose (can also be inhibited by glucose analogues)

22
Q

What is the general function of proteases?

A

Proteases break down proteins and polypeptides

23
Q

How do proteases work?

A

They cause cleavage of the peptide bonds by hydrolysis

24
Q

What are zymogens?

A

Zymogens are inactive precursors of proteases

25
Q

What are the two groups of gastrointestinal proteases?

A
  • Endopeptidases (these attack and cleave in the middle of amino acid chains)
  • Exopeptidases (these split off amino acids from the end of the chain)
26
Q

Where are endopeptidases and exopeptidases produced?

A
  • Endopeptidases are secreted by the stomach and the pancreas
  • Exopeptidases are secreted by the pancreas and the glands of the small intestine
27
Q

What are pepsins?

A

Pepsins are gastric proteases

28
Q

What is the function of pepsin and where is it produced?

A
  • Pepsin is alive at a low pH (<3)
  • Pepsin attacks all proteins (except mucin and keratin)
  • Pepsin is made from pepsinogen which is secreted by chief cells
29
Q

What is secreted simultaneously with pepsinogen?

A

H+ (secreted by parietal cells)

30
Q

How is HCl secreted by parietal cells?

A

By carrier mediated active transport from the parietal cell into the lumen

31
Q

Why is HCl needed?

A
  • HCl activates pepsinogen to make activated pepsinogen
  • Activated pepsinogen loses 44 amino acids from its chain to make pepsin
32
Q

How does pepsin make a positive feedback loop?

A

When pepsin is made, it stimulates more activated pepsinogen to become pepsin.

33
Q

What are the 3 endopeptidases produced by the pancreas?

A
  • Trypsinogen (trypsin)
  • Chymotrypsinogen (chymotrypsin)
  • Pro-elastase (elastase)
34
Q

Why do pancreatic endopeptidases have an alkaline optimum pH?

A

Because carbonate HCO3- ions are also secreted from the pancreas

35
Q

What are the two types of pancreatic Exopeptidase?

A
  • Carboxypeptidases (split amino acids from the carboxy terminal)
  • Aminopeptidases (split amino acids from the N terminal)
36
Q

Complete the sentence;
Proteases are both stores and secreted as ….

A

Zymogens

37
Q

What is the function of lipases?

A

Lipases digest fats by remaining fatty acids from triglycerides

38
Q

Where is lingual lipase active?

A

In the mouth and stomach

39
Q

Where is pancreatic lipase active?

A

In the small intestine (requires phospholipids and bile acids for activation)

40
Q

When is bile released?

A

In response to CCK

41
Q

What happens to bile after it has been used?

A

5% is excreted in faeces, 95% returns to the liver via enterohepatic circulation

42
Q

What does a micelle look like?

A
  • Small, spherical structures with hydrophilic heads on the outside and hydrophobic tails on the inside
43
Q

What does gastric lipase do?

A

Acts on fat droplets to start breaking them down into smaller droplets

44
Q

After pancreatic lipase had bound to the fat droplet, what else much be involved for fat digestion to start?

A

Colipase

45
Q

What happens once fatty acids and monoglycerides diffuse into micelles

A

They merge with the brush borders and are absorbed into the enterocytes

46
Q

How are chylomicrons formed?

A

Triacylglycerol is conjugated with proteins and phospholipids to form chylomicrons

47
Q

What else happens to T.A.G after the formation of chylomicrons?

A

Some of the TAG is broken down and fatty acids released into tissues

48
Q

How are vitamins and minerals absorbed into the small intestine?

A

By passive diffusion, carrier-mediated transport and active transport.

49
Q

Where does the absorption of water occur?

A

In the small and large intestine

AEU (CLB) (11 decks)

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