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A Physiology > 6.5. Degradation and absorption of nutrients. Absorption of water, potassium and sodium. Absorption of iron and vitamin B12. > Flashcards

6.5. Degradation and absorption of nutrients. Absorption of water, potassium and sodium. Absorption of iron and vitamin B12. Flashcards

1
Q

I. Basics
1. What is the average daily intake of human body?

A

A. 8 - 10 L fluid
B. 300g - 500g carbohydrate/day
C. 40 - 100g proteins/day
D. 40 - 100g lipid/days
E. 50 - 100g fibers/ day

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2
Q

I. Basics
2. What is the definition of digestion?

A

cleavage of big molecules to smaller molecules (small intestine)

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3
Q

I. Basics
3. What is the definition of absorption?

A
  • The small molecules will be transported through the epithelial cell layers
  • The molecules can either enter to the blood or to the lymph
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4
Q

II. General mechanisms of digestion and absorption
1. What are the 4 general mechanisms of digestion?

A
  1. Luminal hydrolysis of polymer to monomer
  2. Brushborder hydrolysis of oligomer to monomer
  3. Intracellular hydrolysis
  4. Luminal hydrolysis followed by intracellular resynthesis
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5
Q

II. General mechanisms of digestion and absorption
2. What are the 2 ways that absorption can be happened?

A

Can be active or passive process

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6
Q

III. Phases of digestion and absorption
1. What are the 3 phases of digestion and absorption?

A
  1. Oral phase
  2. Gastric phase
  3. Small intestinal phase
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7
Q

III. Phases of digestion and absorption - ORAL PHASE
2A. What happen during digestion of oral phase?

A
  • Initiation of carbohydrate and lipid digestion
  • Amylase (initiation of starch digestion)
  • Lingual lipase (important in infants/young children: pancreatic tissue is not developed completely)
    +) use lipase for lipid degradation of the breast milk instead)
    => Can cleave triacylglycerol to glycerol + 3 fatty acids
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8
Q

III. Phases of digestion and absorption - ORAL PHASE
2B. What happen during absorption of oral phase?

A
  1. Absorption: (lipid-soluble substances can be absorbed in the oral cavity)
  2. Substances that can be absorbed:
    - Alcohol (ethanol)
    - Medicine (sublingual medicines -> nitrogen monoxide)
    - Nicotine (snus)
    - Dope, narcotics
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9
Q

III. Phases of digestion and absorption - GASTRIC PHASE
3A. What happen during digestion of gastric phase?

A
  1. Carbohydrate digestion until low pH destroys amylase
  2. Lipid digestion by gastric and lingual lipase
  3. Protein degradation (20% of total protein digestion)
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10
Q

III. Phases of digestion and absorption - GASTRIC PHASE
3B. What happen during absorption of gastric phase?

A
  1. Absorption is due to mucosa
  2. Substances that can be absorbed
    - Alcohol
    - Medicines, drugs (aspirin can inhibit the production of PGl2 -> harm gastric mucosa)
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11
Q

III. Phases of digestion and absorption - SMALL INTESTINAL PHASE
4A. What is the role of small intestine?

A

The small intestine is responsible for the vast majority of digestion and absorption processes.

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12
Q

III. Phases of digestion and absorption - SMALL INTESTINAL PHASE
4B. Why is surface area important in the intestinal mucosa?

A

The larger the relative surface increase, the larger the surface area (m2)

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13
Q

III. Phases of digestion and absorption - SMALL INTESTINAL PHASE
4C. Why is the longitudinal arrangement important in the small intestine?

A

We also have the longitudinal arrangement of the small intestine, which increases the surface area even further.
-> This explains why the enterocytes/epithelial cells that are involved in the absorption of nutrients are replaced every 2 to 3 days
=> because the food movement will continuously shed the epithelial cells = desquamation (shedding of dead epithelial cells)

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14
Q

III. Phases of digestion and absorption - SMALL INTESTINAL PHASE
4D. Identify Longitudinal section of the villus

A
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15
Q

III. Phases of digestion and absorption - SMALL INTESTINAL PHASE
4E. Identify Cross section of the villus

A
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16
Q

III. Phases of digestion and absorption - SMALL INTESTINAL PHASE
4F. What is the fate of the enterocytes that are involved in the absorption?

A

The enterocytes that are involved in the absorption of nutrients are replaced every 2 to 3 days.

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17
Q

III. Phases of digestion and absorption - SMALL INTESTINAL PHASE - Carbohydrates
5A. Which enzyme is the starch-digesting enzyme?

A

Amylase

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18
Q

III. Phases of digestion and absorption - SMALL INTESTINAL PHASE - Carbohydrates
5B. Examples of plant and animal starches?

A
  • Plant starch amylopectin – branched polymer of glucose units
  • Plant starch amylose – linear α-1,4-linked polymer of glucose
  • Animal starch glycogen
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19
Q

III. Phases of digestion and absorption - SMALL INTESTINAL PHASE - Carbohydrates
5C What is amylopectin?

A

a water-insoluble polysaccharide and highly branched polymer of α-glucose units found in plants

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20
Q

III. Phases of digestion and absorption - SMALL INTESTINAL PHASE - Carbohydrates
5D. What is amylopectin?

A

a water-insoluble polysaccharide and highly branched polymer of α-glucose units found in plants

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21
Q

III. Phases of digestion and absorption - SMALL INTESTINAL PHASE - Carbohydrates
5E. What is amylopectin?

A

a water-insoluble polysaccharide and highly branched polymer of α-glucose units found in plants

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22
Q

III. Phases of digestion and absorption - SMALL INTESTINAL PHASE - Carbohydrates
5F. What is cellulose?

A

β-1,4-linked glucose polymer. Intestinal enzymes cannot hydrolyze β-glycosidic linkages
- remain undigested and contribute to dietary fiber (formation of feces)

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23
Q

III. Phases of digestion and absorption - SMALL INTESTINAL PHASE - Carbohydrates
5G. Example of disaccharides

A

Sucrose and lactose

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24
Q

III. Phases of digestion and absorption - SMALL INTESTINAL PHASE - Carbohydrates
5H. Example of monosaccharides

A

Glucose and fructose

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25
Q

III. Phases of digestion and absorption - SMALL INTESTINAL PHASE - Carbohydrates
6A. What are the 2 phases of carbohydrates digestion?

A
  1. Luminal digestion
  2. Cellular digestion
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26
Q

III. Phases of digestion and absorption - SMALL INTESTINAL PHASE - Carbohydrates
6B. How does luminal digestion occur?

A
  • During digestion of carbohydrates, they need to be digested until monosaccharide molecules, since those are the ones which can be absorbed
  • Salivary + pancreatic amylases break down the polysaccharides
    => α-amylase catalyzes the hydrolysis of the internal α-1,4 bonds, which gives us the end products: maltose, maltotriose and α-limit dextrins
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27
Q

III. Phases of digestion and absorption - SMALL INTESTINAL PHASE - Carbohydrates
6C. How does CELLULAR digestion occur?

A

Brush-border digestion: (apical membrane of epithelial cells)
- Oligosaccharidases are found on the brush border membrane, which will hydrolyze disaccharides into monosaccharides
1. Lactose -> LACTASE -> glucose + galactose
2. Sucrose -> SUCRASE -> glucose + fructose
3. Maltose + maltotriose -> MALTASE = GLYCOMYLASE = glucose
4. α-limit dextrin -> ISOMALTASE -> glucose

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28
Q

III. Phases of digestion and absorption - SMALL INTESTINAL PHASE - Carbohydrates
7A. What is the role of the α-amylase?

A

The α-amylase catalyzes the hydrolysis of the internal α-1,4 bonds
**They do NOT give MONOSACCHARIDES

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29
Q

III. Phases of digestion and absorption - SMALL INTESTINAL PHASE - Carbohydrates
7B. List 4 important Brushborder oligosaccharides

A
  1. Lactase
  2. Sucrase
  3. α-dextrinase (also called isomaltase)
  4. Glucoamylase (also called maltase)
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30
Q

III. Phases of digestion and absorption - SMALL INTESTINAL PHASE - Carbohydrates
7B1. What is the role of lactase?

A

splits lactose into glucose and galactose

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31
Q

III. Phases of digestion and absorption - SMALL INTESTINAL PHASE - Carbohydrates
7B2. What is the role of Sucrase?

A

splits sucrose into glucose and fructose

32
Q

III. Phases of digestion and absorption - SMALL INTESTINAL PHASE - Carbohydrates
7B3. What is the role of α-dextrinase?

A

α-dextrinase (also called isomaltase):
=> “debranches” the α-limit dextrins by cleaving the α-1,6 bonds at the branch points

33
Q

III. Phases of digestion and absorption - SMALL INTESTINAL PHASE - Carbohydrates
7B4. What is the role of Glucoamylase (also called maltase)?

A

Glucoamylase (also called maltase)
=> cleaves the terminal α-1,4 glycosidic bonds to break maltooligosaccharides down to glucose units.

34
Q

III. Phases of digestion and absorption - SMALL INTESTINAL PHASE - Carbohydrates
8. Explain Lactose intolerance

A
  • lack of lactase => cannot degrade lactose properly = lactose not cleaved fully
  • lactose will pass to the colon => acidic metabolites + gas are produced => diarrhea
35
Q

III. Phases of digestion and absorption - SMALL INTESTINAL PHASE - Carbohydrates
8A. How does the absorption of carbohydrates occur?

A

Monosaccharides are transported across the enterocytic PM through different proteins
- Primary active transport (Na+/K+-ATPase) will create the huge Na+-gradient, which drives the transport of the sugar against its concentration gradient
- SGLT1 (secondary active transporter) in the small intestine takes up glucose + galactose against their concentration gradient through brush-border => coupling transport to that of Na+
- Facilitated transport of fructose across the brush border membrane is mediated by GLUT5. (not an active mechanism)
- All three monosaccharides leave the cell at the basolateral membrane by facilitated transport via GLUT2.

36
Q

III. Phases of digestion and absorption - SMALL INTESTINAL PHASE - Carbohydrates
8B. Make a schematic drawing of the absorption of carbohydrates?

A
37
Q

III. Phases of digestion and absorption - SMALL INTESTINAL PHASE - Carbohydrates
8C. Make a schematic drawing of the absorption of carbohydrates WITH REHYDRATION THERAPY?

A
38
Q

III. Phases of digestion and absorption - SMALL INTESTINAL PHASE - Proteins
9. What is the amount of protein that human body absorbs daily?

A

Daily intake (40-100g) + 50g protein from desquamation (protein content of dead epithelial cells)

(End of digestion, we absorb back 97% of AAs + 3% from feces => essential AAs cannot be synthesized by the body, thus, must be obtained from the diet)

39
Q

III. Phases of digestion and absorption - SMALL INTESTINAL PHASE - Proteins
10A. Make a general scheme of protein digestion

A
40
Q

III. Phases of digestion and absorption - SMALL INTESTINAL PHASE - Proteins
10B. What are the 3 phases of protein digestion?

A
  1. Gastric digestion
  2. Luminal digestion
  3. Brush-border digestion
41
Q

III. Phases of digestion and absorption - SMALL INTESTINAL PHASE - Proteins
10C. What happen during gastric digestion of proteins?

A
  • 15-20% of proteins digested here
  • Proteins are hydrolyzed to smaller polypeptides by acidic pH of the stomach
  • Pepsinogen is auto-activated by a low pH => becomes pepsin (chief cells)
42
Q

III. Phases of digestion and absorption - SMALL INTESTINAL PHASE - Proteins
10D. What happen during luminal digestion of proteins?

A
  • In the small intestine, the pancreas secretes protease precursors, which are inactive in the pancreas until they are secreted into the small intestine
  • In the wall of the small intestine, enterokinases (peptidases) wait and cleave inactive trypsinogens into active trypsin’s
  • Trypsin will then go on and activate the protease
    precursors: (proelastase -> elastase and so on – check figure)
43
Q

III. Phases of digestion and absorption - SMALL INTESTINAL PHASE - Proteins
10E. What happen during Brush-border digestion of proteins?

A
  • The pancreatic proteases convert dietary proteins to oligopeptides
  • Brush-border peptidases then convert the oligopeptides to AAs and di-/tripeptides
  • The AAs are taken up across the brush-border membrane by several AA transporters, and di-/tripeptides are taken up by a H+-peptide symporter
44
Q

III. Phases of digestion and absorption - SMALL INTESTINAL PHASE - Proteins
11A1. How does absorption of amino acids occur?

A

Absorption of AAs: (like in proximal tubules)
- Secondary active process (Na+-coupled)
- Absorbed AAs are released from the cells via facilitated diffusion process
- 75% of AA uptake

45
Q

III. Phases of digestion and absorption - SMALL INTESTINAL PHASE - Proteins
11A2. Make a schematic drawing for the absorption of amino acids

A
46
Q

III. Phases of digestion and absorption - SMALL INTESTINAL PHASE - Proteins
11B. How does the absorption of di-/tripeptides occur?

A
  • Secondary active transport process (H+-coupled)
  • Di-/tripeptides are processed further in the cell =
    intracellular digestion (to AAs)
  • Via facilitated processes -> interstitium -> blood capillaries
  • 25% of AA-uptake
47
Q

III. Phases of digestion and absorption - SMALL INTESTINAL PHASE - Proteins
11C. How does the absorption of whole proteins occur?

A
  • Both enterocytes and specialized M cells can
    take up intact proteins
  • Rarely (e.g. in the case of breast milk Ig) whole proteins will be phagocytosed directly into the cell and then directly into the interstitial side w/o digestion
  • Lysosomal proteases in the enterocytes degrade most (~90%) of the endocytosed proteins
  • Food allergy can occur due to absorption of intact protein (5-HT -> diarrhea)
48
Q

III. Phases of digestion and absorption - SMALL INTESTINAL PHASE - Lipids
12A. What is the amount of lipids that human body need daily?

A

Daily intake: 50-100g lipids/day + 10-12g desquamation (lipid content of enterocytes)

49
Q

III. Phases of digestion and absorption - SMALL INTESTINAL PHASE - Lipids
12B. Make a general scheme of fat digestion

A
50
Q

III. Phases of digestion and absorption - SMALL INTESTINAL PHASE - Lipids
12C. How does fat digestion occur?

A
  • There are many different types of lipids, thus, there are several different enzymes
    to deal with lipids
  • The pancreatic secretions contain lipase (for triacylglycerides), esterases (for cholesterol), and phospholipase A2 (for phospholipids), as well as colipase to aid lipase as it can only act on lipid droplet surfaces
  • Fats are emulsified with bile and general mixing, so that the pancreatic lipase enzyme can access the lipids and cleave them into fatty acids and 2-monoglycerides
51
Q

III. Phases of digestion and absorption - SMALL INTESTINAL PHASE - Lipids
12D. How does digestion of triglyceride occur?

A
52
Q

III. Phases of digestion and absorption - SMALL INTESTINAL PHASE - Lipids
12E. How does digestion of phospholipids occur?

A
53
Q

III. Phases of digestion and absorption - SMALL INTESTINAL PHASE - Lipids
12F. How does digestion of Cholesterol ester occur?

A
54
Q

III. Phases of digestion and absorption - SMALL INTESTINAL PHASE - Lipids
12G. What is the role of bile acids?

A

Bile acids emulsify dietary lipids

55
Q

III. Phases of digestion and absorption - SMALL INTESTINAL PHASE - Lipids
13. How does Breakdown of emulsion droplets to mixed micelle occur?

A
  • By the help of bile + GI-motility, we make smaller and smaller lipid droplets
  • The lipases can act on the surface of these droplets, and release the lipid molecules
    => those lipid molecules can be incorporated into the micelles, which are produced during the bile formation
56
Q

III. Phases of digestion and absorption - SMALL INTESTINAL PHASE - Lipids
14. Micellar transport of lipid breakdown products to the surface of the enterocyte
=> How does this occur?

A
  • The bile salts will form cylindrically shaped micelles with the mixed lipid digestion products and these will be transported to the surface of the enterocytes for further breakdown and absorption
  • This happens in an area near the surface epithelium called the ‘’acidic unstirred layer’’, which is a microclimate zone
    => due to the pH-change, the lipid molecules will dissolve out from the mixed micelle
    => the free fatty acid will diffuse through the later and be absorbed
57
Q

III. Phases of digestion and absorption - SMALL INTESTINAL PHASE - Lipids
15. How does absorption of lipid occur?

A
  1. Long-chain fatty acids and other products of lipid digestion are converted back to triaglycerols, phospholipids, and esters of cholesterol in the SER
  2. Fat droplets form in the SER
  3. Apolipoproteins are synthesized in the RER and then (except APO A-I) move to the SER, where they associate with lipid droplets.
    - APO A-I associates with chylomicrons in the Golgi apparatus
  4. Nascent chylomicrons and VLDLs arrive at the Golgi apparatus. Here, apolipropteins are glycosylated
  5. Vesicles carrying chylomicrons or VLDLs bud off from the Golgi apparatus -> move to and then fuse with the basolateral membrane in the transport vesicles => releasing chylomicrons or VLDLs
  6. Chylomicrons and VLDLs are passed to lymphatic capillaries to enter the lymph
  7. Glycerol, short-chain, and medium-chain fatty acids enter blood circulation
58
Q

III. Phases of digestion and absorption - SMALL INTESTINAL PHASE - Lipids
16. How does absorption of bile salts occur?

A
  • When the mixed micelles are emptied (all lipids absorbed), then we can take up bile acids/salts at the ileum (terminal part) -> active transport process
  • Bile salts are absorbed both by simple diffusion and by Na+-bile salt symporter
  • Conjugated bile salts are absorbed mainly by this symporter; unconjugated bile salts are absorbed by diffusion
59
Q

III. Phases of digestion and absorption - SMALL INTESTINAL PHASE - IONS
17. How does absorption of ions occur?

A
  • Nutrient-coupled Na+-absorption occurs
    throughout the small intestine
  • Primary mechanisms for postprandial Na+-
    absorption are glucose/AA-coupled absorption, which occur only in the villous epithelial cells
    -> mediated by SGLT1 and Na+-AA cotransporters (2nd active transport)
  • Also have Na+-absorption in the distal colon via ENaC (upregulated by aldosterone)
60
Q

III. Phases of digestion and absorption - SMALL INTESTINAL PHASE - calcium
18A. How does absorption of calcium occur?

A

passive paracellularly, or active transport

61
Q

III. Phases of digestion and absorption - SMALL INTESTINAL PHASE - calcium
18B. Making a schematic diagram of calcium absorption

A
62
Q

III. Phases of digestion and absorption - SMALL INTESTINAL PHASE - calcium
18C. What is the average daily intake and absorption of calcium?

A

1/ The average daily intake: ~ 1 g.
2/ The average daily absorption ~ 0.4 g (mostly from duodenum and jejunum)
(passive paracellularly, or active transport)

63
Q

III. Phases of digestion and absorption - SMALL INTESTINAL PHASE
19A. What is the amount of iron in the entire pool in body?

A

~ 4g

64
Q

III. Phases of digestion and absorption - SMALL INTESTINAL PHASE
19B. What is The average daily loss of iron?

A

~ 0,1mg (iron loss ↑ in women)

65
Q

III. Phases of digestion and absorption - SMALL INTESTINAL PHASE
19C. How does absorption of iron occur?

A

1/ Heme iron: absorbed intact by enterocytes
2/ inorganic way: Fe2+ only (divalent metal transport)

66
Q

III. Phases of digestion and absorption - SMALL INTESTINAL PHASE
20A. How does the absorption of water occur?

A
  • Absorption of water is purely passive process, driving force: osmotic gradient
  • Either transcellular or paracellular
    ~80-85% from jejunum and ileum ~15-20% from colon
67
Q

III. Phases of digestion and absorption - SMALL INTESTINAL PHASE
20B. What is the Overall fluid balance in the gastrointestinal tract?

A

~ 2 L of water is ingested / day ~ 7 L of various secretions enter the GI tract / day

Of this total of 9 L:
~ 8.5 L is absorbed in the small intestine.
~ 0.5 L is passed on to the colon, (absorbs 80% to 90% of the
water presented to it)

68
Q

III. Phases of digestion and absorption - SMALL INTESTINAL PHASE
21. How does the absorption of vitamins occur?

A

1) The fat-soluble vitamins include: A, D, E, K
- Mostly passive absorption
-> diffused to epithelial cells

2) The water-soluble vitamins include: C, B1, B2, B6, B12, Niacin, Biotin, Folic acid
- Mostly absorbed by Na+-dependent transport

69
Q

III. Phases of digestion and absorption - SMALL INTESTINAL PHASE
22A. How is Cobalamin (B12) synthesized?

A

itamin B12 (cobalamin, CBL) is synthesized only by microorganisms using animal products (meat,fish,eggs).

(B12 deficiency causes anemia)

70
Q

III. Phases of digestion and absorption - SMALL INTESTINAL PHASE
22B. How does absorption of Cobalamin (B12) occur?

A

1) Cobalamin is bound to protein in food
2) The acidic pH + pepsin release cobalamin from dietary proteins
3) Salivary + gastric glands secrete haptocorin (R-protein), which binds to cobalamin
4) Gastric parietal cells secrete intrinsic factor (IF)
5) The pancreas secretes proteases + HCO3- (alkaline secretion)
6) CBL is released from haptocorin (R-protein), which binds to cobalamin and the CBL-IF complex forms
7) Ileal enterocytes absorb the
CBL-IF complex -> B12 is bound to specific carrier proteins in the bloodstream after absorption

71
Q

III. Phases of digestion and absorption
23. What happen during the colonic phase?

A
  1. Na+ + water can be absorbed in the large intestine + some drugs
  2. Of the ~8,5 L/day presented to the small intestine, the small intestine removes ~6,5 L/day, delivering ~2 L/day to the colon.
  3. The large intestine removes ~1,9 L/day, leaving ~0,1 L/day in the feces.
72
Q

IV. Sites of nutrient absorption
1. What are the sites of nutrient absorption of carbohydrates, proteins and lipids?

A
73
Q

IV. Sites of nutrient absorption
2. What are the sites of nutrient absorption of calcium, iron and folate?

A
74
Q

IV. Sites of nutrient absorption
3. What are the sites of nutrient absorption of bile acids?

A
75
Q

IV. Sites of nutrient absorption
4. What are the sites of nutrient absorption of cobalamin?

A

A Physiology (88 decks)

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