4/5- salivary glands + GI motility

3 phases of digestion

1. cephalic (reflex): prior to food entry, salivary glands major component

2. gastric: arrival of food into stomach

3. intestinal: arrival of food into duodenum

how is the cephalic phase triggered

thought, site, sound, smell of food → parasympathetic outflow → salivation, gastric + pancreatic secretion, release of bile into GI tract

liver releases 1 L of bile that is completely absorbed by what

ileum of small intestine

which CN is responsible for parasympathetic outflow in the cephalic phase

CN 7 + 9

5 positive regulators (stimulators) of saliva production

1. thought of food

2. smell of food

3. sight of food

4. act of chewing

5. nausea

4 negative regulators (decrease) of saliva production

1. dehydration

2. sleep

3. fear

4. anticholinergic drugs

T/F: positive regulators of saliva production can cause a 10x increase in saliva

true

6 causes of xerostomia

1. meds like anticholinergics

2. nerve damage

3. autoimmune destruction (Sjogrens)

4. infection (HIV)

5. radiation

6. severe dehydration

4 consequences of xerostomia

1. dental caries + disease

2. infections like thrush

3. difficulty speaking + swallowing

4. decreased taste

3 functions of bicarbonate (HCO₃^-) secretion in the GI tract

1. buffering pH

2. neutralizing gastric acid + provide optimal pH for digestive enzymes in duodenum

3. solubilizes macromolecules (mucin, bile acids)

3 sources of bicarbonate

1. plasma

2. carbonic anhydrase (CA): converts H₂O + CO₂ → H⁺ + HCO₃^-

3. GI lumen

what 4 things secreted in saliva by acinar cells

1. alpha-amylase: begins carbohydrate digestion + inactivated by low pH

2. lipase: beings lipid digestion by converting triglycerides → fatty acids + monoglycerides

3. mucin: involved in bolus formation + swallowing

4. extracellular fluid: similar ionic composition to plasma

pH must be ___ in order for alpha-amylase + lipase to be active

neutral

what cells in salivary glands modify the ion content of saliva by absorption + secretion

ductal cells

T/F: most salivary ductal cells do not express aquaporin (water) channels in their apical membrane + are impermeable to water

true

saliva is hyper or hypotonic

hypotonic, so that it aids the detection of salt in the diet

what’s responsible for the hypotonic saliva that enters the mouth

lack of aquaporin channels (AQP) in the apical membrane of most ductal cells

describe parasympathetic stimulation of salivary glands

increased secretion of fluid + ions from the acinar + ductal cells

describe sympathetic stimulation of salivary glands

increased fluid, ion, protein secretion but a minor contributor to increase in fluid volume

T/F: GI hormones play a role in salivary secretion regulation

false

which major salivary gland contributes the most saliva during no stimulation (fasted state)

1. submandibular gland: 69%

2. parotid gland: 26%

3. sublingual gland: 5%

which major salivary gland contributes the most saliva during stimulation (started eating something)

1. parotid gland: 69%

2. submandibular gland: 26%

3. sublingual gland: 5%

what’s the most common disorder of salivary glands

stones (sialoliths)

7 sphincters of the GI

1. upper esophageal (UES)

2. lower esophageal (LES)

3. pyloric

4. oddi

5. ileocecal

6. internal anal

7. external anal

which sphincter malfunctions in GERD

lower esophageal (LES)

where does the smooth muscle that continues through the GI tract start

lower 1/3 of esophagus

what happens during swallowing

1. pharynx constricts

2. UES opens

3. LES + proximal stomach relax

what is movement of the bolus as it goes down the esophageal body

primary peristalsis

what happens if there’s some food leftover in the esophagus

secondary peristalsis

esophageal peristalsis is caused by

sequential contraction of circular muscles of muscularis propria, mediated by acetylcholine

describe neurotransmitter mechanism of esophageal peristalsis

nitrergic inhibition: NO acts as an inhibitor to relax the smooth muscle as the bolus is traveling down

what’s achalasia

loss of nitrergic neurons (neurons that release NO) in distal esophagus → constriction of LES → pt has difficulty swallowing

which stimulates the enteric nervous system (ENS): sympathetic or parasympathetic nervous system

parasympathetic

how does the parasympathetic nervous system stimulate the ENS

via dorsal motor nucleus of CN X using ACh

how does the sympathetic nervous system inhibit the ENS

via sympathetic nerves using norepinephrine

2 distinct features of smooth muscles

1. dense bodies: point of attachment for myofilaments

2. gap junctions: electrically link sheets of muscle cells to contract as 1 unit

5 things that can modulate smooth muscle of the GI

1. autonomic nervous system neurotransmitters

2. hormones

3. intrinsic properties that produce spontaneous electrical activity

4. changes in local chemical composition

5. stretch (distention)

what happens first during GI tract perstalsis: contraction or relaxation

relaxation, then followed by contraction

distinguish the 2 branches of CN X for esophageal innervation

1. nucleus ambiguus → striated muscle in upper esophagus

2. dorsal motor nucleus → smooth muscle in lower esophagus

2 positive regulators of esophageal smooth muscle

1. acetylcholine (ACh)

2. substance P (SP)

2 negative regulators of esophageal smooth muscle

1. nitric oxide (NO)

2. vasoactive intestinal peptide (VIP)

what’s the valve between the small + large intestine

ileocecal valve (ICV)

2 primary functions of the ileocecal valve (ICV)

1. control flow between small + large intestine

2. prevent bacteria from large intestine contaminating small intestine

excessive motility of the large intestine results in

less fluid absorption + diarrhea/loose stool

2 main types of movement in the large intestine

1. haustral contractions

2. mass movements

where do the primary movements of the large intestine occur

ascending + transverse colon

differentiate between haustral contractions vs. mass movements

1. haustral contractions: occur every 30 min + last ~1 min, stimulated by stretch when food fills haustra

2. mass movements: long, slow, powerful that move over the colon 3/4x a day usually after meals, stimulated by gastrin release when food arrives in stomach