Lecture 3- Simple Digestive System w/o Caecum

Question 1

Digestibility

Answer 1

○ Does the host organism have the enzymes necessary to digest CHO
Digestible CHO vs. non-digestible CHO (fibre)

Question 2

Solubility

Answer 2

Is CHO soluble in the aqueous environment of the digestive tract

Question 3

Fermentability

Answer 3

Do gut bacteria have the enzyme necessary to break down CHO?

Question 4

Simple System Without Caecum:

Answer 4

• Monogastric
• Non-functional caecum
• Suited for a nutrient dense, low fibre diet
i.e. human, pigs, cats, dogs

Question 5

Gastrointestinal (GI) tract

Answer 5

• Gastrointestinal (GI) tract =/= digestive system

Digestive system refers to GI tracts and organs in the periphery as well (liver, pancreas, gall bladder…etc)

Question 6

Oral Cavity:

Answer 6

• Food is chewed (mechanical breakdown)
• Food mixed, enzymes in saliva begin to break down food
○ Alpha amylase breaks down digestible starches
Lingual lipase breaks down fats

Question 7

Stomach:

Answer 7

• Volume of 50 mL when empty, 1- 1.5 L when full
• Takes 2-6 hours for gastric emptying to occur
• pH of stomach is acidic (~2, favours protein digestion)
• Food becomes “chyme”
○ Mix of food, digestive juices
• Gastric glands secrete gastric juice
Releases water, electrolytes, HCl enzymes (require HCl to become activated to break down proteins)

Question 8

Small Intestine:

Answer 8

• Main site for nutrient digestion and absorption
○ Different nutrients absorbed in different regions of the small intestine
• Surface area ~ 30 m2
• Intestinal motility controlled by longitudinal and circular muscles
• Chyme acidity neutralized by pancreatic juice
○ Need to neutralize chyme in small intestine because enzymes here function at neutral pH, not acidic pH)
• Food digested by pancreatic juice and bile acids
○ Pancreatic juice includes digestive enzymes, bicarbonate (neutralizes chyme)
Bile acids from gall bladder solubulize fats

Question 9

Large Intestine/ Colon:

Answer 9

• Site of fermentation of non digestible carbohydrates via gut bacteria
○ Produces short chain fatty acids (SCFA), which are known known as volatile fatty acids (VFA)
§ Contributes to energy intake, but to a lesser degree (mainly used by bacteria for energy rather than going to the host)
• Some vitamins are produced by bacteria
Site of water absorption

Question 10

Surface Area of Small Intestine:

Answer 10

• Kerckring folds
	• Villi and crypts
		○ Located on kerckring folds
		○ Villi and crypts have different functions, allows for specificity in absorption
			§ Villi increases surface area
Crypts located between villi (glands)
	• Microvilli
		○ Located on each villi cell
Further increases surface area 

Diagram

Question 11

Nutrient Transport Mechanisms:

Answer 11

• Nutrients transported from intestine into blood stream in 3 different ways
○ Diffusion (passive transport)
○ Facilitated diffusion (passive transport)
○ Active transport
• Which transport mechanism is used depends on the nutrient’s
○ Solubility
○ Concentration gradient
Molecular size

Question 12

Fermentation in the Large Intestine:

Answer 12

• High number of bacteria in the large intestine compared to the stomach (neutral pH in large intestine)
○ 102-1012 bacteria/ gram of content (region specific)
○ 500-1000 species identified per person in the gut (different species, but similar core functions)
○ 1000:1 anaerobic to aerobic bacteria ratio
• Bacteria very important for fermentation of non digestible CHO
Generates lactate and SCFA