Gastrointestinal Physiology: Digestion Flashcards

1
Q

What are the 3 main nutrients that undergo chemical digetion?

A

Carbohydrates, lipids and proteins

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2
Q

These are made up of long chains of glucose joined by alpha 1-4 glycosidic bonds.

A

Starch and glycogen

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3
Q

What are the 3 disaccharides?

A

Sucrose, lactose and maltose

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4
Q

Why are lipids not essential to our bodies?

A

Because we can produce them endogenously so no need for them to be in our diet

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5
Q

What are some of the properties of lipids in our body? (3)

A
  • slow gastric emptying
  • source of energy
  • fat soluble vitamins A, D, E and K
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6
Q

What is the main component of lipids?

A

Triglycerides

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7
Q

This reduces the size of nutrients to allow them to be absorbed.

A

Chemical digestion

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8
Q

Where does chemical digestion occur? And what does it use to break down the food particles?

A

Chemical digestion occurs at the surface of food particles.

It uses digestive enzymes secreted by SI and pancreas to break the food down

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9
Q

This breaks up food and increases surface area available for chemical digestion. Usually occurs at the mouth.

A

Mechanical digestion

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10
Q

These are highly specific extracellular organic catalysts that are responsible for breaking down food particles during chemical digestion.

A

Digestive enzymes

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11
Q

What is the optimal pH for each of these enzymes:

a) salivary enzymes
b) gastric enzymes
c) small intestinal enzymes

A

a) alkaline
b) acidic
c) alkaline

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12
Q

What does it mean by digestive enzymes being highly specific?

A

Different enzymes bind to different substrates

  • amylase => starch
  • proteases => proteins
  • lipase => lipids
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13
Q

What are the 2 stages of chemical digestion?

A

Luminal digestion and contact digestion

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14
Q

This is the initial digestion which involves enzymes secreted into the lumen.

Additional question: this can occur at 3 different organs in the GI tract, what are those 3 and what enzymes specifically carryout this type of digestion?

A

Luminal digestion

Luminal digestion occurs in the stomach, the small intestine and the mouth. The enzymes in the stomach are usually pepsin, small intestine: pancreatic enzymes (pancreatic amylase, trypsin, chymotrypsin etc., and in the mouth: salivary amylase

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15
Q

This is the type of digestion which occurs in the small intestine. It involves enzymes produced by enterocytes which are attached to the brush border of the enterocytes.

A

Contact digestion (via microvilli brush border enzymes)

Remember: these enzymes are produced by the epithelial cells (enterocytes) of the small intestine. Segmentation helps contact digestion occur.

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16
Q

How are carbohydrates chemically digested?
- what are they broken down into
- where do they get broken down into
- what enzymes are responsible for breaking them down

A

Carbohydrate digestion occurs in two stages.

Luminal digestion occurs in the mouth and the small intestine
- luminal digestion breaks polysaccharides into oligosaccharides and disaccharides using salivary amylase and pancreatic enzymes

Contact digestion occurs in the small intestine
- contact digestion breaks disaccharides and breaks them down into monosaccharides using brushborder disaccharidases (carbohydrate enzymes)

17
Q

Where is the pancreatic amylase found?

A

in the small intestine; it is a pancreatic enzyme not a brushborder enzyme.

18
Q

How are proteins chemically digested?
- what are they broken down into
- where do they get broken down into
- what enzymes are responsible for breaking them down

A

Luminal digestion occurs in the stomach and the small intestine
- luminal digestion breaks proteins down into polypeptides using pepsin in stomach, and trypsin, chymotrypsin, and carboxypeptidase in the small intestine

Contact digestion occurs in the small intestine
- contact digestion breaks proteins into indvidual amino acids using peptidases (which are attached to the brush border)

19
Q

Where is carboxypeptidase made?

A

In the pancreas, secreted by the pancreas into SI

20
Q

How are lipids chemically digested?
- what are they broken down into
- where do they get broken down into
- what enzymes are responsible for breaking them down

A

Lipids only undergo luminal digestion in the small intestine using pancreatic lipase as the main enzyme (lingual and gastric lipase also play minor roles)

21
Q

Why do lipids have a more complex process of digestion?

A

Because the digestive enzymes are soluble in aqueous solutions, but lipids are not.

  • so need to convert lipids into a water soluble form so it can be broken down by water soluble enzymes
22
Q

What are the 4 stages of lipid digestion?

A

1) emulsification
2) stabilisation
3) digestion (hydrolysis)
4) formation of micelles

23
Q

This is the process where lipids are converted into small droplets. These droplets increase surface area for digestion.

A

Emulsification

24
Q

Where does emulsification of lipids occur? and what motility patterns are associated with it in these areas?

A

Stomach - retropulsion

Small intestine - segmentation

25
Q

Where does stabilisation of lipids occur? what is responsible for stabilisation and where is it secreted from?

A

Stabilisation occurs in the small intestine

Bile salts stabilise lipid droplets

Bile is secreted from the liver and concentrated in the gallbladder

26
Q

This is the process where the lipid droplets are reduced in size by bile salts in the small intestine. These also further increase surface area for digestion.

A

Stabilisation

27
Q

Where does hydrolysis of lipids occur?

A

In the small intestine at surface of emulsion droplets.

28
Q

What are the 3 main enzymes involved in hydrolysing lipids into monoglycerides and fatty acids?

A

Pancreatic lipase, lingual and gastric lipase and colipases as well (these anchor lipases to the triglyceride surface)

29
Q

This is the process where products of fat/lipid digestion are packaged into small droplets of about 20-30 molecules which allow it to be kept in solution.

A

Formation of micelles/

30
Q

What are micelles composed of?

A

Bile salts, fatty acids and monoglycerides

31
Q

What are the 2 products of fat/lipid digestion?

A

Monoglycerides and fatty acids