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Question 1

Objective:

Review anatomy, function and regulation of gastro-intestinal system (GIT)

Question 2

Objective:
Understand the digestion and absorption of nutrients in different parts of the GIT

Question 3

Objective:
Describe the absorption pathways of hydrophilic (water-soluble) and hydrophobic (fat soluble) nutrients and how they are transported via the vascular and lymphatic systems

Question 4

Role of mouth in digestion?

Answer 4

Ingesting food
Chewing food
Saliva released has amylase; breaks down starches

Question 5

Role esophagus in digestion?

Answer 5

Esophageal sphincter:
1) Allows passes from mouth to esophagus and from esophagus to stomach
2) Prevents back flow from stomach up the esophagus

Question 6

Role of stomach

Answer 6

• Acids and enzymes mix with food
• Turns the food into a paste for easier digestion (liquid mass called “the chime”
• The chime then goes into small intestine (duodenum first)

Question 7

Phyloric sphincter

Answer 7

Allows the chime to go from stomach –> duodenum
- prevents back flow from duodenum –> stomach

Question 8

Role of small intestine

Answer 8

Enzymes are secreted from pancreas that break down energy-yielding macronutrients and macronutrients into their singular form (primed for digestion)

Question 9

Role of Pancreas

Answer 9

Makes the enzymes that help break down the energy-yeilding nutrients in small intestine.

Question 10

Role of Bile

Answer 10

produced in Liver
stored in galbladder
released in small intestine for liquid digestion

Question 11

Role of Large Intestine

Answer 11

reabsorption of minerals, nutrients and water

Question 12

Role of Rectum

Answer 12

Elimination!

Question 13

Role of intestinal folds and villi

Answer 13

in small intestine
has peaks and valleys
help absorb nutrients

Has lacteal (tip of lymphatic vessel)
Arteries move blood towards the tip (capillaries) and veins move blood away

Also has lymphatic vessel going in and out to the tip of the capilaries

Question 14

Role of small intestine Microvilli

Answer 14

For absorption; they have “transporters” for nutrients

Also have digestive enzymes to break down any remaining molecules into their simplest form (for absorption)

Question 15

Peanut Butter Sandwich example: What’s the role of each organ for digestion?

Answer 15

Mouth:
- chewing and swallowing of “bolus” (little digestion)
- CHO/Starch: salivary amylase
- Fibre: seed coat crushed by teeth

Stomach:
- collecting and churning (some digestion)
- CHO/Starch: bolus mixed with gastric juice, inactivation of amylase
- Protein: denaturation (uncoil) b/c of acid + gastric protease (breaks down proteins –> peptides)
- Lipid: mixed with gastric juice and separates into water / lipid phase
-lipid phase stays longer (floats to the top); water goes straight into duodenum

Small intestine
- Digesting and absorbing
- Sugars: absoption
- Starch: pancreatic and intestinal sell surface (Brush-boarder membrane;BBM) enzymes = simple sugars (monosaccharides)
- Lipid (TG) - bile (emulsifies fat) + pancreatic lipase breaks lipid –> glycerol + fatty acids (absorbed)
- Protein: pancreatic proteases = amino acids absorbed
- Vitamins/Minerals: absorbtion

Large intestine:
- reabsorbing and eliminating
- Fluid/Minerals: absorbed
- Fibre: bacterial fermentation products absorbed / unfermented fibres –> decal bulk; binds cholesterol and minerals to poo and excreted
- Lipids: Bile and cholesterol excreted

Question 16

How are nutrients absorbed in the intestine?
(3 ways)

Answer 16

Water & simple lipids: simple diffusion (high –> low conc. via phospholipid bi-layer)

Water-soluble, hydrophilic vitamins: facilitated diffusion (carrier flips from lumen to intrasite)

Glucose & Amino Acids: active transport (requires energy, carrier flips from lumen to intrasite)

*“Lumen” is outside the cell

Question 17

Describe how: water-soluble (hydrophilic) nutrients enter the body?

Answer 17

From the small intestine –> Capiliaries (tips of villi) –> Hepatic Portal Vein –> Liver –> rest of the body

Question 18

Describe how: fat-soluble (lipophilic) nutrients enter the body?

Answer 18

i.e. cholesterol, phospholipids, fatty-acids, and glycerol

Packaged into “chylomicrons (CM)” in enterocyte –> CM enters lymphatic vessels –> lymph circulation (thoracic duct collects lymph and enter circulation via left subclavian vein; just above the heart) –> directly to vascular circulation (supplies tissues); bypasses the liver (may uptake by liver post bypass
)

Question 19

Describe Endocrine Regulation of Digestion and Absorption.
(6 ways)

Answer 19

under self-regulating or negative-feedback mechanisms

When food bolus enters stomach:
Gastrin – G-gastrin cells maintain pH 1.5 –> HCl release from parental cells in stomach

When chyme enters duodenum:
Secretin – S-cells in Cryps of Lieberkuhn –> Targets pancreas to release neutralizing HCO3 + digestive enzymes (don’t want to burn duodenum)

When lipids enter duodenum:
CCK – Cholecystokinin; I-cells in duodenum –> Targets gall bladder to release bile, and the liver to synthesize bile

When lipids or protein enters duodenum:
CCK – Targets pancreas to release HCO3 + digestive enzymes, and slows GI mobility (good for digestion)

When glucose enters duodenum:
**Gastric-inhibitory peptide – GI-Peptide, K-cells in duodenum/jejunum –> Targets Beta-cells pancreas –> insulin secretion (important for glucose transport and absorption)

When nutrients enter ileum:
Glucagon-like peptide 1 – GL-Peptide-1, L-cells in ileum –> Targets Beta-cells pancreas –> insulin secretion (increase glucose uptake) –> surpasses glucagon secretion from Alpha-cells pancreas