Problem 1: The Digestive System

Question 1

What is Digestion?

Answer 1

the process of making food absorbable by mechanically and enzymatically breaking it down into simpler chemical compounds in the digestive tract.

Question 2

What is Absorption?

Answer 2

movement of small units from gut into blood system or lymphatic system for circulation

Question 3

Gastrointestinal tract: Mouth. Function? Enzymes?

Answer 3

a. When digestion begins
b. Chewing
c. Saliva which brings enzymes
i. salivary amylase → initiates the digestion of carbohydrates in the form of starches
ii. lingual lipase → fat digestion, released by cells at base of the tongue

Question 4

Gastrointestinal Tract: Oesophagus

Answer 4

a. moves food from mouth to your stomach

i. By peristalsis

Question 5

Gastrointestinal Tract: Stomach. Content? Function?

Answer 5

a. gastric juices: water,
hydrochloric acid ( = pH of 2 in stomach and helps digestion and unfolding of proteins in order to be able for enzymes to attack the proteins),
mucus,
pepsin (= enzyme which breaks down proteins smaller peptides),
gastric lipase (= used for digestion of lipids; hydrolyses triglycerides into fatty acids & glycerol),
gastrin,
intrinsic factor (= a protein for absorbing vitamin B12)
b. mixes food into liquid chyme
c. kills pathogenic bacteria that may have been ingested

Question 6

GI: Small Intestine. What is absorbed? Structure? Function?

Answer 6

a. digestion is completed for fats, protein, carbohydrates.
b. Structure
i. folding large surface area to maximize absorption of nutrients. Around 3x more SA
ii. Have structures called vili (villus) expand area 10x
1. Have blood and lymph vessels
iii. Around 1000 Hairlike structures called microvilli increasing SA 20x so 600x increased SA.
c. Consists of duodenum, jejunum, and ileum.
d. Majority of nutrients absorbed
e. 3 Meters long
i. Duodenum 25-30cm (most digestion, since digestives juices get secreted into here)
ii. Jejunum 120cm
iii. Ileum 150cm
f. Intestinal lining renewed every 2-5 days

Question 7

GI: Large Intestine. What is absorbed? Function? Structure?

Answer 7

a. absorbs water and electrolytes (= used for osmotic value; ions to help with muscle contraction), Sodium Chloride, potassium and vitamin K
b. gut microbiota
c. forms and stores feces
d. Structure
i. Cecum, colon, rectum and anal canal

Question 8

GI: Assisting Organs: Liver

Answer 8

i. produces bile which helps with digestion and absorption (for fats) EMULSIFIES
ii. small intestine cannot digest everything
iii. enterohepatic circulation (intestine - liver) = bile goes from liver to small intestine to gallbladder

Question 9

GI: Assisting Organs: Gallbladder

Answer 9

i. stores and concentrates bile from liver. During gallbladder storage of bile, it is concentrated 3-10 fold by removal of some water and electrolytes

Question 10

GI: Assisting Organs: Pancreas

Answer 10

i. secretes enzymes that affect absorption and digestion: amylase and trypsin
ii. Releases Hormones: (help with regulating metabolism and how nutrients are used in the body)
1. insulin → maintaining the same level of glucose in the blood
2. secretin → it releases bicarbonate (HCO3-) → used for pH: it neutralises the pH from the chyme/ bolus that comes from the stomach because their pH is 2 and that’s too low for enzymes to be able to work for digestion → makes the pH 6 in the first part of the small intestine (duodenum)

Question 11

GI: Rectum. Function

Answer 11

holds and releases feces via the anus

Question 12

What are the different physical movements associated with digestion?

Answer 12

Peristalsis
- longitudinal muscles and circular muscles contract
Segmentation
- same muscular movements but it breaks chyme in smaller parts + it mixes it with digestive juices → small intestine

Question 13

What are the different chemical breakdowns associated with digestion?

Answer 13

Enzymes – are large proteins that catalyse (speed up reaction) but are not altered in the process

• Hydrolysis – a reaction that breaks apart a compound through the addition of water
• Other fluids help
• Acid in stomach, bile, mucus

Question 14

4 Roads of Absorption: Passive diffusion

Answer 14

done through concentration gradient → particles move from high concentration to low concentration to create a concentration equilibrium
o only water, oxygen or alcohols can go through the membrane
o does not use energy

Question 15

4 Roads of Absorption: Facilitated Diffusion

Answer 15

Facilitated diffusion also requires no energy, but it involves a carrier, or protein molecule located on the outside of the cell membrane that binds the substance and carries it into the cell. The cotransporter can sometimes be electrolytes. fructose
o does not use energy

Question 16

4 Roads of Absorption: Active Transport

Answer 16

o goes against concentration gradient
o uses ATP
o minerals

Sodium bicarbonate is absorbed by active transport and glucose and amino acid co-transport.

Question 17

4 Roads of Absorption: Endocytosis

Answer 17

o when cell membrane surrounds the molecules and breaks them down
o absorption of fatty acids (cannot pass membrane)

Question 18

What is the role of the gut microbiome?

Answer 18

Gut bacteria breaks down non-digestible carbohydrates into short chain fatty acids, which feed the colon cell.

• Provides essential capacities for the fermentation of non-digestible substrates like dietary fibers and endogenous intestinal mucus.
• This fermentation supports the growth of specialist microbes that produce short chain fatty acids (SCFAs)
• control appetite
• extract energy from compounds that you otherwise cannot digest (can kill cancer cells)

Question 19

What is the difference between prebiotics and probiotics?

Answer 19

Pre = non living
- food for probiotics and help grow the probiotics
- how to increase: consuming non-digestible foods → fibres
- Low fiber intake reduces production of small chain fatty acids and shifts the gastrointestinal microbiota metabolism to use less favorable nutrients
Pro = living
- provide health benefits for the host (mutually beneficial relationship)
- most Bifidobacterium and Lactobacillus species
Synbiotics = combined pre and probiotics together