Digestion And Absorption 4: Large Intestine

Question 0

What is the definition of fibre? Explain

Answer 0

Carbohydrates that enter the large intestine
Carbohydrates that are not digested and absorbed in the small intestine can act as fermantive substrates in the large intestine.
Eg resistant starch, non-starch polysaccharides and oligosaccharides

Question 1

What is fermentation, were dies it occur, what does it produce?
What are the products used for?

Answer 1

Microbial fermentation is the action of digestion in the large intestine.
End products of fermentation are:
-volatile fatty acids (short chain fatty acids)
-microbial protein

VFA production can provide big contribution to energy in herbivores.

Question 2

Components of food that act as fibre
Non-starch polysaccharides
2 types

Answer 2

1. Insoluble non-starch polysaccharides
   - found in cell wall
   - not soluble in solution
   - ferment relatively slowly
   - fermentation produces energy via VFA
   - sources include fibrous foods (such as bran, mature pasture and hay)
2. Soluble NSP
   - soluble
   - bind cellulose and hemicellulose together In the plant cell wall
   - rapidly fermentable in rumen (yields VFA)
   - rapidly ferment in the LI, even in omnivores and carnivors
   - dietary sources include fibrous foods as well as cereal grains (oats, barley), legumes (lupins) and fruit
   - good for humans

Question 3

Components of food that act as fibre

2. Resistant starch

Answer 3

• starch that is resistant to digestion in the small intestine and therefore passes into the large intestine
• readily fermentable in the large intestine
• cooking increases starch digestibility in SI by converting resistant starch into into digestible starch

Dietary sources include:

• starchy uncooked foods like potato
• whole cereal grain

Question 4

Components of food that act as fibre

3. Oligosaccharides

Answer 4

-smaller polysaccharides (8-10 units)
-readily fermented in the large intestine (produce VFA)
Eg legumes
Insulin eg artichokes
Lactose eg milk

Question 5

Describe the metabolism of protein in the large intestine

Answer 5

Proteins (especially plant proteins) can be incompletely Digested in the SI and then enter the LI and act as substrates for fermentation.
-endogenous protein can also act as substrates for microbes in the LI (endogenous protein is derived from cell turnover, intestinal secretions, abrasions in small intestine)
-fermentation of protein by microbes in the LI doesn’t benefit the animal. Microbial protein (micro flora) is not digested by the host and passes into the faeces and lost.
-some vitamins held in the microbial cells may be absorbed by the host
-fermentation of protein in the LI can result in production of secondary metabolites (amino acids that aren’t deaminated)
Eg tyrosine (secondary metabolites= creosol, phenol) and tryptophan (secondary metabolites = indole and skatole)
-microbes in the large intestine can help reduce the accumulation of secondary metabolites
-the accumulation can be reduced by fermentable fibre by supporting microbial growth

Question 6

Name and talk about some of the disease and health issues associated with fermentation in the large intestine

Answer 6

Rapid fermentation in the LI can lead to diarrhoea. Rapid is caused by:

• malabsorption of nutrients in the SI
• excess rapidly fermentable material passing into LI (positive effects on humans)

1. Malabsorption in SI:
   A) lactose intolerance- lactase deficiency. Lactose enters the large intestine and is rapidly fermented to VFA, lactate and gas
   B) pancreatic insufficiency
   -poor production of digestive enzymes result in malabsorption of food in SI, so there’s increased substrates entering LI that are fermented to VFA, lactate and gas➡ osmotic diarrhoea
   C) infection of small intestine:
   -caused by bacterial growth, parasites
   -reduced efficiency for digestion/ absorption in SI, undigested food and microbes pass into LI ⬆ fermentation

Question 7

Name and talk about some of the disease and health issues associated with fermentation in the large intestine
2. Rapid fermentation in LI

Answer 7

• high levels of resistant starch in the diet
• poor starch digestion in SI
  
  • rapid intro to high starch diet
• high levels of oligosaccharides In the diet

Question 8

What are the positive effects of fibre for humans?

Answer 8

1. Prevention of constipation
   - soluble and insoluble fibre in the diet modifies faecies bulk and texture
2. Prevention if diverticulitis
   - increased bulk and softening of digests reduces intra luminal pressure
3. Prevention of haemorrhoids
   - reduced constipation ; stool softening reduces straining
4. Prevention/ reduced risk of colon cancer
   - reduced transit time, increased bulk and reduce carcinogens concentration (eg bile acids)
   - butyrate
5. Reduces LDL (bad) cholesterol
   - can aid in cholesterol control
6. Improves glycemic control
   - slows digestion of carbs, and release of glucose into bloodstream-useful in diabetics and for weight loss
   - associated with glycemic index of foods