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Biochemistry Year 1 > Digestion and absorption > Flashcards

Digestion and absorption Flashcards

1
Q

What are the organs of the GI tract?

A

Mouth, salivary gland, stomach, pancreas, liver, gall bladder, small intestine, large intestine

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2
Q

What does the mouth do?

A

Mechanical digestion

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3
Q

What does the salivary gland do?

A

Secretes fluid and digestive enzymes

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4
Q

What does the stomach do?

A

Body of stomach secretes mucus, pepsinogen and HCl; antrum of stomach secretes mucus, pepsinogen and gastrin; stores large quantities of food until it can be accommodated in intestines; mixes food with gastic secretions to form a homogenous, acidic chyme; regulates rate of emptying chyme into duodenum; secretes intrinsic factor

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5
Q

What does HCl do within the stomach?

A

Activates pepsin from pepsinogen; kills many pathogens; denatures and breaks down food proteins so are more vulnerable to enzyme action; inactivates hormones of foreign origin; increases absorption of Fe and Ca

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6
Q

What does gastrin do?

A

Stimulates motility and HCl production

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7
Q

What is intrinsic factor necessary for?

A

Vitamin B12 absorption

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8
Q

What does the pancreas do?

A

Secretes NaHCO3 (to neutralise acidic content from stomach) and digestive enzymes

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9
Q

What does the liver do?

A

Secretes bile

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10
Q

What does the gall bladder do?

A

Temporarily stores bile; makes more concentrated

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11
Q

What do the small intestines do?

A

Absorb water, nutrients, and electrolytes

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12
Q

How does the small intestine have such a large SA?

A

Has folds of kreckring, villi, and microvilli; villi have folds in mucosal layer, microvilli, and brush border membrane of mucosal epithelial cells

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13
Q

What do the large intestines do?

A

Absorb small amount of water and electrolytes; contains large colony of bacteria which: metabolise fibre to SCFA, which can be absorbed by diffusion; and produce Vitamin K

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14
Q

How many litres of chyme enters the large intestines each day?

A

1.5l

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15
Q

What is peristalsis?

A

The contraction of adjacent segments of the GI tract in sequence

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16
Q

What are the enzymes involved in the digestion of carbs, and the reactions they catalyse?

A

Salivary amylase: starch –> dextrins and maltose. Pancreatic amylase: dextrins –> maltose. In small intestine:- lactase: lactose –> galactose + glucose; maltase: maltose –> glucose + glucose; sucrase: sucrose –> fructose + glucose

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17
Q

How are glucose and galactose absorbed?

A

Glucose and galactose through sodium-dependent glucose transporter 1 (SGLT1) into epithelial cell from intestinal lumen (process is facilitated diffusion with Na+); Na+ actively transported into blood; Na+ diffuses back into intestinal lumen; glucose and galactose through GLUT2 into blood

18
Q

How is fructose absorbed?

A

Fructose through GLUT5 into epithelial cell from intestinal lumen; fructose through GLUT2 into blood

19
Q

Why do sports drinks often have a mixture of fructose and glucose?

A

As they use different transporters, rate of absorption within the small intestine will be increased

20
Q

What are the enzymes involved in the digestion of proteins, and the reactions they catalyse?

A

In stomach, pepsin: proteins –> large peptides. In small intestine:- pancreatic enzymes (trypsin, chymotrypsin, proelastase): large peptides –> small peptides; brush border enzymes (aminopeptidase, dipeptidases): small peptides –> amino acids; pancreatic enzyme (carboxypeptidase): small peptides –> amino acids

21
Q

How is pepsin activated?

A

Chief cell in gastric pit releases pepsinogen; parietal cell in gastric pit releases HCl; HCl activates pepsinogen –> pepsin

22
Q

How are pancreatic proteases activated in the duodenum?

A

Membrane bound enterokinase activates trypsinogen –> trypsin; trypsin activates chymotrypsinogen –> chymotrypsin; chymotrypsin activates precarboxypeptidase –> carboxypeptidase

23
Q

How are proteins absorbed?

A

Within the small intestine. Amino acids are absorbed directly into epithelial cell with help of Na+; dipeptides absorbed into epithelial cell with help of H+; dipeptides –> amino acids by cytoplasmic peptidases; amino acids diffuse into capillary

24
Q

How are amino acids utilised in protein turnover?

A

Dietary protein digested; broken down into amino acids; aa’s to liver; processed and stored; aa’s taken to muscle to build muscle/ be used used in signalling processes; aa’s transported to other places within body that need protein for different cellular turnover

25
Q

What are the enzymes involved in the digestion of lipids, and the reactions they catalyse?

A

Saliva and stomach hold lipase: hydrolyse TGs (slow process b/c TGs are not water soluble, which is where lipase is found. Duodenum:- pancreatic lipase: hydrolyses TGs –> liberates LCFAs. Small intestine:- bile salts from gall bladder: emulsify lipid droplet –> emulsion droplets; bile salts and pancreatic lipase: emulsion droplets –> monoglycerides + FFAs

26
Q

What is a micelle?

A

A ball with FFAs and MGs (hydrophobic core) surrounded by bile salts (hydrophilic side outwards)

27
Q

How are lipids absorbed?

A

In small intestine. Micelles –> MGs + FFAs at edge of epithelial cell; MGs and FFAs diffuse into epithelial cell; water-based environment causes MGs and FFAs to be repackaged at ER –> TGs; TGs within lipoproteins –> chylomicrons; chylomicrons diffuse into lympthatic system; MCFAs diffuse into blood stream, coated with albumin

28
Q

Which is absorbed more quickly, carbs or fats?

A

Carbs (within 30-60 minutes). Fats involve more complex processes

29
Q

Where are fats taken to if the body is exercising?

A

To muscles; if are not exercising, stored in adipose tissue

30
Q

What occurs if there are too many fats to store (spillover)?

A

Fats taken to liver, where they are recycles to be used later if needed

31
Q

How are fat soluble vitamins absorbed?

A

Absorbed along with FFAs; diffuse into epithelial cell of small intestine; aid formation of chlyomicrons; diffuse into lympthatic system

32
Q

Where are vitamins mostly absorbed?

A

Jejunum and ileum, mostly by diffusion

33
Q

How are water soluble vitamins absorbed when at low concentrations?

A

Active transport. Vitamin B1 and and C involve Na+ dependent active processes. Vitamin B12 requires formation of complex with intrinsic factor; complex binds with specific receptor; complex undergoes endocytosis and is engulfed into epithelial cell

34
Q

Where are coenzymes, such as B vitamines, cleaved from their enzymes?

A

In small intestine

35
Q

What is the absorption of minerals like?

A

They aren’t very well absorbed: 35% Ca, 20-30% Mg, 14-41% Zn

36
Q

How is Na absorbed?

A

By active transport; much more Na is secreted back into intestinal lumen than kept within body, so need to have high reabsorption

37
Q

2-4 hours before an event, what is the recommended ingestion of fluids and foods?

A

5-7ml/kg of BW; salt snack and small meals may help; increase fluids if urine is dark/ no urine

38
Q

During an event, what is the recommended ingestion of fluids and foods?

A

Sufficient fluid to limit body mass loss to <2% (0.4-0.8l/hr); limit excessive electrolyte imbalance; if >1hr, consider CHO addition; if >2hrs/ salty sweater, add Na

39
Q

<12 hours after an event, what is the recommended ingestion of fluids and foods?

A

1.5l/kg of BM loss; Na

40
Q

How do water and carbs impact each other?

A

Increased concentration of carbs decreases % of max delivery of H2O

41
Q

How does Na impact water and carbs?

A

Increased Na increases absorption of water and CHO

42
Q

How does Na increase water absorption?

A

Na is actively absorbed, increasing water potential gradient and pulling water into epithelial cell by osmosis

Biochemistry Year 1 (23 decks)

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