Week 2 Digestion

Question 1

Digestion: Mouth

Answer 1

Chewing and starch digestion
> Mastication muscles: buccinator (cut), masseter, temporalis, and TMJ capsule
> Macerate (small particles of food –> increase SA) –> carb digestion with amylase (Acid labile) –> mucus lubricate/protect GI tract cells –> antimicrobial (lysozyme digesting bacterial cell wall)
> Taste Receptors on taste buds: Sweet (Sugars, glycine), Salty (NaCl), Sour (Acids), Bitter (Salicin, PTC), Umami (L-glutamate) and *carbonation (sema7A and sema3A vesicles; <100 mM Na attracts us to food, >300 mM activates sour and bitter receptors + aversion
> Olfaction (Taste/flavor):

Question 2

Digestion: Esophagus (10 in)

Answer 2

Bolus delivery:
> Secretes water and mucus
> Peristalsis: entry via voluntary upper esophageal sphincter, and ends in cardiac lower esophageal sphincter to prevent acidic backflow

Question 3

Digestion: Stomach (2-3 hours)

Function only

Answer 3

1. Solubilizes and digests food to acid chyme
   > Pepsinogen (pepsin precursor, protease) and mucus
   > HCl: denatures amylase protein, hydrolyzes carbs, dissolves Ca2+ minerals, kills microbes and self-cleavage –> pepsin
   > Alcohol is primary nutrient (20%); minor water amount

Question 4

Digestion: Stomach

Layers/structure

Answer 4

1. Gastric pits: acid and pepsinogen release
2. Parietal cells: HCl
   > Cl from blood to parietal cells and HCO3 to blood
   > Parietal cells break down H2CO3 –> HCO3 and H+ –> proton pumps and Cl channels ship HCl to lumen
3. Chief cells: pepsinogen source (activated by acid to pepsin)
4. Surface Mucous Cells: mucus release protects stomach lining from acid, protease and inflammation from antigens

Question 5

Digestion: Intestines (motility)

General

Answer 5

1. Tract Wall: Mucosa, submucosa, muscle and serosa
   > Circular folds in wall: villi project into intestine + microvilli on absorptive cells –> increase SA 600x; crypt surrounded by lacteal and epithelial cells (thick outer yellow layer is circular and longitudinal muscles pushing chyme through intestinal tracts
2. Infant stomach:
   > Raw honey + clostridium botulinum –> muscle paralysis toxin –> no botulism poisoning
   > Eating solid food too early can increase diabetes risk (4-6 months is best switch time)
3. Compartmentalization
   > Pyloric sphincter: control stomach content into SI
   > Hepatopancreatic sphincter: control bile/pan juice into SI
   > Ileocecal valve: prevent LI content from reentering SI
   > Anal sphincter: prevent defecation until nature calls

Question 6

Digestion: SI (3-10 hours; 3m)

Answer 6

Final digestion and nutrient absorption
> Duodenum (10 in): NaHCO3 release from pancreas to neutralize HCl
> Jejunum (4); ileum (5)
> Enzymes: bile, lipase, protease (chymotrypsin and trypsin), glycosidase, amylase for nutrient breakdown for absorption
> 70-90% water (1’ nutrient) and 80% alcohol
> Regeneration very 3-5 days (if not villi are destroyed and no nutrient absorption –> diarrhea)

Question 7

Digestion: LI/colon (72 hours)

Answer 7

Water and mineral absorption
> Absorbs Na/K, solidifies mass, secretes animal connective tissue, supports microbiome (Vitamin K and biotin), ferment undigested material
> 100 trillion microbial cells
> Some FA absorption
> Water 10-30% total

Question 8

Accessory Organs

Answer 8

1. Hepatic Portal Vein: gut –> liver; immediate glucose processing and toxin protection
2. Lymphatic System: fat delivery to blood stream
3. Salivary glands: mucus, amylase and lysozyme
4. Liver: bile production and glycogen/lipid storage, detoxification (CytP450)
5. Gall Bladder: Bile storage and release to pancreatic duct
6. Pancreas: NaHCO3 (neutralize) and Enzyme mix with bile and delivered to duodenum
7. Bile Salts (Detergent for lipid uptake): glycoholic and taurocholic acids (Red Bull)

Question 9

Regulation of Digestion

Answer 9

1. Nervous System: Control saliva, swallowing and gastric secretions
2. GI self-regulation: factors released that affect digestion functions (hormones)

Question 10

Bayliss and Starling:

Answer 10

HCl in intestinal lumen –> pancreatic secretion of PEPTIDE HORMONES
> Gastrin (stomach/duodenum) in response to food –> HCl and pepsinogen release –> gastric and intestinal motility
> Cholecystokinin (CCK) in SI in response to dietary fat in chyme –> pancreatic enzymes and bile release from GB
> Secretin in SI in response to acidic chyme during digestion –> pancreatic bicarbonate release

Question 11

Push and Pull of Metabolism

Answer 11

1. Anabolism: 
> Glucose + Glucose + ATP --> Glycogen
> Glycerol + FA + ATP --> Triglycerides
> AA + AA + ATP --> protein
2. Catabolism: opposite
3. ATP: high energy phosphate bonds (Energy used in A; energy released in C)

Question 12

Roux En Y Procedure

Answer 12

Create stomach pouch out of a small part of stomach –> attach directly to SI (byass most of stomach and duodenum)