Motility and Secretion I

Interstitial Cells of Cajal

• part muscle and part fibroblast

• Network of gap junctions between them and onto smooth muscle

• Function: pacemakers of gut

• can be modified by CNS

slow waves, which are regular, are generated by?

• can the slow waves by themselves cause contraction?

• Interstitial Cells of Cajal

• No

• you need action potential superimposed

GI motor neurons: can be ? use?

• excitatory and inhibitory

• Use axonal varicosities

  • allows for dispersion of NT over large area

Exctitatory NT in GI

ACh and Substance P

Inhibitor NT in GI

VIP and NO

motor neurons can also cause?

secretion

which neurons dominate?

Inhibitor

The physiological ileus is?

lack of contraction

Periastalsis

• Pulsive movement that allows you to move contents along

  • propulsive segment

    • Relaxation of long, and contraction of circular muscle

  • Receiving Segment

    • Contraction of long, relaxation of circular

Power propulsion

long distance peristalsis

Synaptic gating

Forms gates to prevent power propulsion from creating long distance travels: uses inhibitory signals

• long distance can create diarrhea and vomiting

Sphincters

• smooth muscle valves

• Normally closed

• Inhibitory motor neurons control:

  • active = open

  • inactive = closed

Esophageal sphincters

• upper: 2/3 is striated muscle: no AIR

• lower 1/3 is smooth muscle

as you move out of the duct, does osmalarity increase or decrease?

Osmolarity decreases as you move out

serous cells

secrete amylase or pytalin (breaks down carbs and starch), stored in zygomen granules

myoepithelial cells

squeeze to cause contraction of saliva

Regulation of secretions in mouth

• PSNS → kallkrein enzyme that makes bradykinin

  • bradykinin increases capillary permeability and vasodilates, which causes secretion into secretory duct

Saliva functions: digestion

• salivary amylase (pytalin): digests some carbs

• Lingual lipase: breaks down some fat

Besides digestion, other 5 functions of saliva

• Lubrication

  • Mucins: glycoproteins that contribute most of the viscosity to saliva (helps with swallowing)

• Neutralization of acid: (HCO3- bicarbonate), old treatment for ulcer

• Solvent action: allows for taste (dissolves)

• Aids in speech

• Water balance: prevents dry mouth

rugae

stomach: folds that allow stomach to expand/flatten when it fils with food

Functional regions of stomach

• reservoir: storage, tonic contractions

• Antral pump: digestion: phasic contractions

contents of food as they leave stomach

Chyme

Motility of stomach

• Gastric action potential (slow wave)

  • Rapid upstroke = depolarizing phase = leading contraction

  • Plateau phase = trailing contraction

• Gastric Retropulsion: as waves of contraction sweep down stomach and head towards pyloric sphincter, intitial wave will close sphincter, but plataeu phase willl cause food particles to be pushed back up into stomach

Gastric action potential and contractile cycle starts in ?

midcorpus

glands of stomach

• Cardiac: mucous cells

  • mucous cells secrete protective mucuous

• Pyloric glands: contain G cells

  • G cells: secrete gastrin

• Oxyntic glands

  • Mucuous cells: secrete mucous

  • Parietal cells: secrete intrinsic factor

  • Chief cells: secrete pepsinogen

Hcl secretion regulation

“alkaline tide”

• AcH (vagal stim), gastric, histamine: cause intracellular Ca2+ → gastric hydrogen ion pump → Hcl secretion

cephalic phase

• first: just in the head: thoughts, smell, taste, chewing, swallowing

  • Hcl and pepsinogen secretion

gastric phase

• food in stomach

• Protein, stretching of stomach

• increases HCl, pepsinogen, gastrin secretion

Intestinal phase

• chyme starts reaching duodenum

• decrease Hcl, pepsinogen secretion

• increase secretion of enterogastrones (inhibits gastric activity)

Function of gastric juice

• digestion:

  • store pepsinogen as it is safe

  • Slow movement to active form (hcl activates) fast to convert back

• Bacteriocidal action: low pH kills most bacteria in stomach

• supplies intrinsic factor = needed for B12 absorption

mucus layer

thick layer, loaded with bicarbonate that neutralizes gasric juice before reaches cells

pernicisous abnemia

lack of Vit B12

Trichobezoar

• foreign object in stomach made of hair