monogastric stomach Flashcards
stomach
initiates digestion with low pH, enzymatic activity, and physical constrictions
pyloric sphincter
smooth muscle valve enabling chyme entry into duodenum
what are the three major interlinked control mechanisms of the GI tract
- hormonal (endocrine)
- paracrine
- neural
CNS influence on the GI tract is ___
indirect via the ENS and GI endocrine systems
the innervation of the GI tract consits of two interacting components:
- extrinsic (autonomic CNS)
- intrinsic (enteric nervous system)
what type of innervation consists of the two subdivisions of the autonomic nervous system
extrinsic
what are the two subdivision of the autonomic nervous system
parasympathetic and sympathetic
both have important sensory (afferent) component
what type of nervous system can act independently of extrinsic neural innervation
the intrinsic - enteric nervous system
what are the two systems of ganglia that the ENS is arranged into
submucosal and myenteric plexuses
what is the major function of the GI tract
absorption
the GI control systems operate to provide an ____ for absorption
optimal environment
what are the two regulatory processes of the GI
motility and secretions
what is the neural control of the GI
- extrinsic from CNS: autonomic nervous system (parasympathetic and sympathetic)
- intrinsic: enteric nervous system
what is the chemical control of the GI
- endocrine secretions
- paracrine secretions
- neurocrine secretions
what is the myogenic control of the GI
muscle contraction via interstitial cells of Cajal
sympathetic innervation of the ENS is ____
postganglionic
mesenteric ganglia
parasympathetic innervation of the ENS is ____
preganglionic
vagus nerve and pelvic nerves
sympathetic innervation is inhibitory or stimulatory and what does it use
inhibitory and using peptide neurocrines
shuts off digestion
parasympathetic innervation is inhibitory or stimulatory and uses what
stimulatory and uses cholinergic - acetylecholine neurotransmitter
plexuses
places where nerves branch and rejoin
ganglia
bunches of nerve cell bodies (soma)
myenteric plexus
- ganglia between circular and longitudinal muscle
- extensive interneuronal connections
muscle contractions
submucosal plexus
- ganglia in submucosal layer
- interneuronal connections limited within plexus
local action - local mucus secretions
parasympathetic
- rest and digest
- blood pressure decrease, decreased energy usage, slower heart rate
- active digestion
where do the parasympathetic neurons synapse with
ENS neurons
sympathetic
- fight or flight
- blood pressure increases, heart rate increases
digestion slows down
where do sympathetic neurons synapse
- some directly affect target cells
- other synapse with ENS neurons
is there a synapse between enteric neurons and target cells
no; axons end in varicosities
what do varicosities release
neurocrine affecting nearby muscle and glandular cells
what is afferent signaling
sensory signaling to CNS and ENS
what is efferent signaling
motor signaling from the CNS & ENS
monogastric stomach is primarily a ____ stomach
glandular stomach
what are the glandular regions
- cardiac
- fundic
- pyloric
where are pseudo stratified and stratified columnar epithelium in the GI
in ducts of secretory glands throughout
where is stratified squamous epithelium in the GI
lips to cardiac stomach and anal canal
where is simple columnar epithelium in the GI
glandular stomach on
what is homogenizes and processes food function of the glandular stomach
- chemically via enzymes and acids secreted by the mucosa
- mechanically via muscular churning of the stomach wall
where does the epithelium change in the stomach
stratified squamous in the esophagus (nonglandular) to simple columnar (glandular)
the stomach is lined by longitudinal folds called
rugae
disappear when stomach distends
what do the mucus cells in epithelium secrete
protective gel layer: gastric mucosal barrier
what are the two functions of the gastric mucosal barrier
- protect stomach lining from auto-digestion
- protect stomach from abrasion with food
what do cardiac glands secrete
alkaline mucus
what do gastric (fundic) glands secrete
mucus, HCL, and pepsinogen
what do pyloric glands secrete
mucus/lysozyme and produce Gastrin
where are the gastric (fundic) glands located
fundus/body
what type of cells are in the neck of the gastric glands
mucous cells and stem cells
what type of cells are in the body of the gastric glands
- mucous cells
- chief cells
- parietal cells
- stem cells
- enteroendocrine cells
what do chief cells produce
pepsinogen
what do parietal cells produce
HCl
what do enteroendocrine cells produce
gastric hormones
what do mucous cells produce
mucins
what does the mucus blanket (gastric mucosal barrier) do
- traps bicarbonate ions (HCO3)
- the alkalinity of which offsets the acids secreted by the gastric gland and keeps the pH immediately around the epithelium at 7.0
enteroendocrine cells are ____
monohormonal
enteroendocrine cells produce hormones that contents are released into the lamina propria and act …
- locally
- enter the bloodstream and affect target cells
what are two important types of enteroendocrine cells and what do they produce
- G cells - gastrin (produce HCl - pro-digestion)
- D cells - somatostatin (suppresses gastrin)
where is gastrin produced
stomach region
distal stomach
where is cholecystokinin (CCK) produced
GI region
duodenum to ileum
where is gastric inhibitory polypeptide (GIP) produced
GI region
duodenum and upper jejunum
parietal cells - cytoplasm, produce, and how are they stimulated
- eosinophilic cytoplasm
- produce HCL
- stimulated to produce HCL by enteroendocrine hormone gastrin
chief cells - cytoplasm, produce
- basophilic cytoplasm
- proenzyme pepsinogen
when pepsinogen is released into the stomach it interacts with _ to form _
HCl; pepsin
what nervous systems does the enterogastric reflex involve
CNS and ENS, endo/paracrine signals
what type of fibers of the vagus nerve recieve stimuli in the duodenum
afferent
what are the types of stimuli that the duodenum recieves
enterogastric reflex
pH, fat, osmolarity
what do these stimuli block
enterogastric reflex
block Vagus-induced stomach emptying
what is released from endocrine cells in the duodenum
enterogastric reflex
CCK (cholecystokinin) and secretin into the bloodstream
what does CCK respond to
fat
what does secretin respond to
low pH
what do CCK and secretin do
suppress gastric emptying
how are H+ ions secreted and generated
- secreted from parietal cells
- generated from the dissociated of carbonic acid (H2CO3)
- this leaves behind one bicarbonate ion (HCO3-) per H+
the carbonic acid utilized in H+ generation is a product of
carbonic anhydrase; which combines H2O and CO2
exists in high concentrations in gastric mucosa
what happens in disease states where gastric secretions are not able to enter the intestine, or are lost via vomiting
blood pH can rise to dangerous levels
during the cephalic phase of digestion (anticipation-prior to food entry) which nerve is stimulated
vagal cholinergic nerves
(parasympathetic, stimulatory, Ach)
what does acidification of the gastric antrum stimulate
the release of somatostatin from D cells
what does somatostatin from D cells inhibit
gastrin release and thus acid secretion
what does vagal Ach inhibit
somatostatin release
pepsinogen is released as a __
proenzyme (zymogen) from chief cells by exocytosis
what does hydrochloric acid do to pepsinogen molecules
reversibly acivates them
what is pepsinogen cleaved into
pepsin
proventriculus
- glandular
- oxynticopeptic cells secrete both pepsinogen and HCL
ventriculus (gizzard)
- nonglandular
- grinding ingesta - grit
