Digestion Flashcards
T/F: Stimulatory substances released by excitatory efferent neurons within the enteric nervous system (ENS) include both acetylcholine and substance P.
True
T/F: The autonomic nervous system is comprised solely of sympathetic and parasympathetic branches.
FALSE!!
ANS has sympathetic, parasympathetic, AND enteric nervous system!
T/F: Sympathetic innervation of the gut wall exerts inhibitory actions at the post-ganglionic synapse through the release of norepinephrine.
True
T/F: A paracrine substance is carried through the circulation to distant sites of action.
FALSE!
T/F: Syncitial function of smooth muscle layers within the gastrointestinal tract is enabled by tight junctions.
FALSE!
Syncitial function is enabled by GAP JUNCTIONS!
Parasympathetic inputs to the gastrointestinal tract are carried by..
Vagus (CN X) and pelvic nerves
Paneth cells contribute to the gut epithelium’s role in defense against luminal pathogens by…
production and secretion of antimicrobial peptides
The avian crop has a function analogous to which region of many mammalian stomachs?
fundus
What is the function of the avian crop and the mammalian fundus?
storage
Gastrointestinal smooth muscle slow waves…..
are always present and result from pacemaker activity of interstitial cells of Cajal
In cattle, esophageal obstruction would result in metabolic acidosis through what scenario?
Net loss of HCO3- in saliva
NON-PATHOLOGICAL responses to serotonin release are:
- paracrine stimulation of enterocyte secretion
- increased motility
- regulation of enteric nervous system
This cell type secretes hydrochloric acid in the stomach?
parietal cell
What stimulates parietal cell hydrochloric acid secretion?
- histamine
- acetylcholine
- gastrin
Out of these 3 - histamine, acetylcholine, gastrin - which one has a bigger impact on parietal cells and can cause the release of the other two?
acetylcholine
Key functions of the GI system that help it do what it needs to (5)
- motility
- secretion
- digestion
- absorption
- storage/elimination
The key functions of the GI system are ________ (regulated/unregulated)
regulated
What is an additional function of the GI system not involved in the intake of nutrients?
protection from pathogens
Enzymatic digestion is for the breakdown of: (3)
- starches/sugars
- proteins
- fats
Carnivore GI systems are primarily _________ in nature
enzymatic
Omnivore GI systems are both _______ and __________ in nature
enzymatic and fermentative
Herbivore GI systems are primarily _________ in nature.
fermentative
The essential GI tract functions are under ________ and __________ control
intrinsic neural and endocrine control
“Autonomy of the GI system”
GI system is self-regulating
What enables the autonomy of the GI system? (4)
- innervation
- secreted factors (eg - hormones)
- immune control
- trophic effects
The peripheral Autonomic Nervous System is comprised of these 3 parts.
- parasympathetic
- sympathetic
- enteric
The _______________ INTRINSICALLY regulates the GI system.
Enteric Nervous System (ENS)
The ENS is modulated via inputs from EXTRINSIC _______ and __________ components
parasympathetic and sympathetic
This ENS-related plexus is located in the submucosal layer
Meissner’s plexus
This ENS-related plexus is located between the circular and longitudinal muscle layers.
Auerbach’s plexus
The _______ plexus, also known as the Meissner’s plexus, regulates secretions and local blood flow of the GI system.
Submucosal
The _______ plexus, also known as the Auerbach’s plexus, regulates muscle contraction and motility of the GI system.
Myenteric
ENS neurons have axonal __________ and _________, leading to further branching than the normal “garden variety’’ of neurons.
collaterals and varicosities
Excitatory efferent outputs - glands
secretion
Excitatory efferent outputs - muscle layers
contraction
Inhibitory efferent outputs - glands
No secretion
Inhibitory efferent outputs - muscle layers
relaxation
Sensory afferent inputs - chemoreceptor
luminal chemical conditions
Sensory afferent inputs - mechanoreceptors
distension within muscle layers
Parasympathetic can also be thought of as “___________”
rest and digest
Sympathetic can also be thought of as “__________”
fight or flight
Parasym. modulation of the ENS (4)
- vagus (CN X)
- pelvic nerve
- pre-ganglionic
- acetylcholine (cholinergic)
Is parasym. modulation of the ENS stimulatory or inhibitory?
stimulatory
Sympath. modulation of the ENS (3)
- splanchnic nerve
- primarily post-ganglionic
- norepinephtine (AKA noradrenaline - so adrenergic)
Is sympath. modulation of the ENS stimulatory or inhibitory?
inhibitory
Can the inhibitory nature of the sympathetic nervous system override the parasym. influence on the ENS?
YES!
GI self-regulatory hormones (5)
- CCK
- secretin
- GIP
- gastrin
- motilin
GI self-regulatory neurocrine secretions (5)
- acetylcholine
- NO (nitric oxide)
- substance P
- VIP (vasoactive intestinal peptide)
- serotonin
GI self-regulatory paracrine secretions (3)
- histamine
- somatostatin
- serotonin
GI self-regulatory candidate hormones (3)
- enteroglucagon
- pancreatic polypeptide
- peptide YY
What stimulates the release of gastrin?
- peptides
- amino acids
Major action of gastrin?
increase parietal cell HCl secretion
What stimulates the release of secretin?
- acid
- fat
- protein
Major action of secretin
- increases HCO3- secretion
- decreases HCl secretion
What cells produce gastrin? Where?
- G cells
- in duodenum and possibly pancreas
What cells produce secretin? Where?
- duodenal S cells
- in the duodenum and jejunum
What cells produce CCK? Where?
- I cells
- in small intestine and enteric neurons
What cells produce GIP? Where?
- K cells
- in the duodenum and jejunum
What cells produce motilin? Where?
- M cells
- in the duodenum and jejunum
What stimulates the release of CCK?
fats and proteins
Major action of CCK?
- increase pancreatic enzyme and insulin secretion
- increase bile secretion
- satiety factor
What hormone produced in the gut is the satiety factor?
CCK
What is the release stimulus for GIP?
fats and glucose
Major action of GIP?
- decrease gastric secretions
- increase insulin secretions
What stimulates the release of motilin?
- increase in duodenal pH
- acetylcholine
Major action of motilin?
antral and duodenal MMC, phase III induction during digestion
What does “CCK” stand for?
cholecystokinin
What does “GIP” stand for?
gastric inhibitory peptide
-OR-
glucose-dependent insulinotropic peptide
Substances that signal via the paracrine pathway? (4)
- somatostatin
- peptide YY
- serotonin (AKA 5-hydroxytryptamine (5-HT))
- histamine
Specialized epithelial cells present in the GI tract that the majority of these cells produce serotonin
enterochromaffin cells
Functions of serotonin?
Stimulates:
- enteric nervous system
- vagal afferents
- enterocyte secretion
- blood flow
Gastrin increases growth of __________
gastric mucosa
Enteroglucagon and cholecytokinin increase growth of _____________
intestinal mucosa
The muscle layers of the gut wall facilitate these 4 things
- propulsion
- retention
- physical breakdown of food
- particle mixing and circulation
The relationship between the propulsive movement and the transit time is ____________
inversely related
What is a syncytium?
multinucleated mass of protoplasm such as a striated muscle fiber
In which direction do the slow waves of the GI smooth muscle propagate?
oral to aboral
T/F: Slow waves require neural input
FALSE!
They are myogenic
Pacemaker cells for GI motility?
Interstitial cells of Cajal (ICC)
What are ICC?
- modified smooth muscle cells
- found between smooth muscle layers and scattered amongst smooth muscle cells
____________ input enables action potentials in the GI tract
parasympathetic
Excitatory neurohormonal substances _______ the resting membrane potential, which __________ the likelihood for contraction and increases contraction and motility.
depolarize; increases
Inhibitory neurohormonal substances __________ the resting membrane potential, which _______ the likelihood for contraction.
hyperpolarize; decreases
Ingestion of food involves what 3 types of motion
- prehension (grasping)
- mastication (chewing)
- deglutition (swallowing)
T/F: The ingestion of food involves highly coordinated activities
True
Sensory nerves for prehension?
- Olfactory (CN I)
- Optic (CN II)
- Trigeminal (CN V)
Motor nerves for prehension?
- Trigeminal (CN V)
- Facial (CN VII)
- Glossopharyngeal (CN IX)
Importance of mastication?
- reduce particle size
- adds moisture to food
- adds salivary amylase to food
- prepares food for swallowing
Pushing the food bolus to the back of the pharynx is ____________, but this triggers local sensory nerve endings that initiate the ___________ of swallowing reflex.
voluntary; involuntary phase
The longitudinal and circular muscles of the esophagus relax and constrict _________ each other
opposite
The proximal portion of the stomach, the fundus, functions as a storage region. How does it accommodate ingesta?
By adaptive relaxation
How does the adaptive relaxation of the fundus occur?
- parasym. influence by CN X
- NOT mediated by ACh
- possibly via vasoactive intestinal peptide (VIP)
The ________, which is the distal part of the stomach, _______ ingesta and _________ it to the SI.
antrum; grinds; presents
Muscular activity of the antrum is increased by __________________ input
parasym. (ACh)
GI hormones that stimulate gastric motility
- gastrin
- motilin
GI hormones that inhibit gastric motility
- CCK
- Inhibin
- Gastric inhibitory peptide (GIP)
Two types of motility during the digestive phase in the small intestine
- propulsive
- non-propulsive
Non-propulsive motility has a ________ action
mixing
Propulsive motility is in which direction?
aboral
When is the ileocecal valve open?
during peristalsis
General functions of the colon
- water and electrolyte absorption
- fermenation of unabsorbed organic matter
- storage of feces
T/F: Pacemaker regions of the colon can move to regions in which mixing is required.
True
Carnivores have colonic pacemarkers located where?
near the juncture between transverse and descending colon segments
Where is the horse’s colonic pacemaker located?
near the pelvic flexure
Functions of saliva? (4)
- lubrication
- bactericidal
- digestion
- cooling
T/F: The initial salivary secretion is isotonic and is modified as it travels through the salivary gland.
True
Three types of salivary glands?
- serous
- mixed serous/mucous
- mucous
Salivary __________ cells secrete and isotonic fluid that contains both Cl- and HCO3-.
serous acinar
Salivary _________ cells reabsorb Na+ and Cl- but not H2O
ductal
The final saliva is _________ relative to plasma
hypotonic
In ruminants, conditions that impede salivation result in _______
acidosis
Parasympathetic stimulation of salivary glands
- CN VII
- CN IX - cholinergic receptors
Sympathetic stimulation of salivary glands
beta receptors
Is there endocrine regulation of salivary glands?
NO!
unusual; quite unique
Function of surface epithelial cells?
- secrete thick mucus and HCO3-
- protective function
Function of mucous neck cells?
- secrete thin mucus
- cell division
Function of parietal cells?
- HCl secretion
- intrinsic factor secretion (req. for vit. B12 absorption)
Function of chief cells?
pepsinogen secretion
Glands in the cardia of the stomach
- secrete only mucus
- alkaline
- protective function
The antrum of the stomach has what cells?
- D cells
- G cells
- chief cells
- NO parietal cells!!
______ and _________ lead to a histamine release, which then increases parietal cell HCl secretion
Gastrin and ACh
As food is digested and acid is neutralized, the drive for pancreatic secretion ___________.
decreases
In species lacking a gallbladder, such as the horse and rat, bile is released _________
continuously
