Control of the digestive system Flashcards
What is found within the gut walls that is part of the intrinsic control systems?
enteric nervous system and gut hormones
what is part of the extrinsic control systems?
outside of the gut:
vagus and pelvic nerve (parasympathetic)
splanchnic nerves (sympathetic)
Aldosterone
what are the two plexuses of the enteric nervous system?
submucosal plexus
myenteric plexus
fight or flight –>
digestive system inhibited
what are vagal nerve fibres responsible for?
innervating the abdominal viscera (stomach)
carrying signals from the taste buds (to determine what animal eats)
projecting from the CNS to parasympathetic ganglia near organs and to the pharynx (the afferents and efferents)
what does the splanchnic nerve do?
carries signals to the CNS regarding presence of pathologies
result of painful stimuli?
evokes sympathetic repsonses in GI tract results in inhibition of gut motility and increased glandular secretions
what is aldosterone?
it is a steroid hormones
where is aldosterone secreted from? and when?
secreted by adrenal cortex following stimulation by:
low sodium
angiotensin
andrenocorticotrophic hormone
high potassium
what does aldosterone do?
it stimulates sodium and water reabsorption from gut and salivary glands
what is vomiting?
an active reflex
what is invovled in vomiting?
chemoreceptors trigger zone, vafal afferent system, vestibular system and CNS
What happens to ensure airway protection from vomiting?
epiglottis closes off laryngeal opening
soft palate elevates to seal off nasopharynx
what does the mecahnisms allow?
portect the airway from aspiration odf stomach contents in the animal
what else happens ot ensure the path from oesophagus to mouth is ready?
the larynx elevates and straightens out oesophagus
what is vomiting controlled by?
by the vomit centre in thje brainstem
what are the four ways that vomitting can be induced by naturally?
intiated at GI level
initiated outside GI tract
Initiated by irritation of the gastric epithelium e.g. pain and anxiety
or by partially digested food
what kind of process is regurgitation?
passive process
ileus?
no movement, no contraction of the stomach
what type of organ is the gut?w
an immune organ
why is the gut an immune organ?
the intestinal mucosa is exposed to microorganisms (e.g. contaminated food/toxins) and antigens
what type of cells reside in the gut mucosa?
immune cells
Describe the first way that defence occurs by the gut?
Cells respond to antigenic stimulation by synthesising antibodies and recruiting killer cells
Describe the second way that the gut defends itself?
Cells secrete inflammatory mediators (eg PG, cytokines, histamine) which interact directly with the ENS and GI endocrine/paracrine cell
what are the anatomical causes of regurgitation?
megaoesophagus, hiatal hernia
what are the functional causes of regurgitation?
ileus (no movement)
gastric reflux
apart from anatomical and functional causes, what else causes regurgitation?
foreign bodies in upper GI tract
what happens during regurgitation?
undigested content moves back up the oesophagus
what is regurgitation?
the incapacity of oesophagus to empty content into stomach
When vomiting is initiated at GI level, how does this happen?
sensory cells (mechanoreceptors) with nerve endings in the pharynx
tension receptors and chemoreceptors in the gastric/duodenal mucosa
when vomiting is initiated outside GI tract, what happens?
chemoreceptors trigger zone (closed to 3rd ventricle) afferent input to vomit centre: drugs, toxins inflammatory mediators in blood
Constant stimulatioh of the semicircular canals afferent input to vomit
what is vomiting controlled by?
the brainstem
contraction of which muscles does vomiting involved?
contraction of striated muscles and other structures outside the GI tract
What 5 things have to happen in order for vomiting to take place?
Relaxation of muscles and closing of pylorus
Contraction of abdominal muscles
Expansion of chest while glottis closed
Opening of upper oesophageal sphincter
Antiperistaltic motility in duodenum
What muscles need to relax in order for vomiting to take place?
stomach and lower oesophageal sphincter
why do abdominal muscles need to contract to allow vomiting to take place?
to increase the pressure in the abdominal cavity
why does the chest need to expand while the glottis is closed in order for vomiting to occur?
need to lower intrathoracic pressure on oesophagus
Vomiting requires high/low intraabdominal pressure?
high
how is high intraabdominal pressure achieved?
diaphragm squeezes the stomach, raising pressure inside
simultaneous contraction of abdominal oblique muscles further squeezes stomach
high abdominal pressure plus what two other things results in vomiting?
high abdominal pressure as well as low thoracic pressure and open oesophagus
How is low intrathoracic pressure achieved to allow vomiting?
the diaphragm sharply and strongly contracts and moves caudally
this lowers the pressure in the thorax
low thoracic pressure opens the lower oesophageal sphincter
What does distension of the stomach lead to? (in terms of regulating muscle contractions)
There is an increase in activity of stretch-sensitive sensory cells leading to both an increase in gastrin and an increase in contraction of smooth muscle cells which results in an increase in empyting the stomach
what does peptides in the stomach result in? (to do with regulating muscle contractions)
peptides in stomach results in an increase of gastrin which results in an increase in contraction of smooth muscle cells which results in an increase in emptying the stomach
give an example of when and how the splanchnic nerve would carry signals to the CNS regarding presence of pathologies:
overdistension of gut wall > inflammation > presence of noxious substances in lumen
what does the presence of noxious substances in the lumen present as?
presents as colic or pain
what is involved in extrinsic control (outside of the gut)?
the vagus and splanchnic nerves
aldosterone (hormonal control)
zona glomerulosa of adrenal cortex (adrenal gl.)
sodium conservation (kidney, salivary gl, colon)
what are the five gut hormones?
gastrin, secretin, CCK, GIP, motilin
what does CCK stand for?
cholecystokinn
what GIP stand for?
gastric inhibitory polypeptide
where is gastrin produced?
the distal stomach
where is secretin produced?
mainly duodenum
where is CCK produced?
mainly duodenum
where is GIP produced?
proximal small intestine
where is motilin produced?
duodenum
what is the release stimuli for gastrin?
protein
what is the release stimuli for secretin?
H+ in the small intestine
what is the release stimuli for CCK?
fat and protein
what is the release stimuli for GIP?
fat and glucose
what is the release stimuli for motilin?
ACh
what are the major effects of gastrin?
stimulates acid (HCl) secretion
stimulates growth of mucosa
what are the major effects of secretin?
stimulates secretion of HCO3- in pancreas
what are the major effects of CCK?
stimulates production and secretion of pancreatic enzymes
causes gall bladder contractions
what are the major effects of GIP?
stimulates insulin production
inhibits HCl production and gastric emptying
what are the major effects of motilin?
regulation of MMC (migrating motor complex) during fasting
what are the five characteristics of gut hormones?
they: must be secreted by one cell in the gut and affect another cell
must be transported in the blood (endocrine)
release must be stimulated by food
secretion does not have to be controlled by neurones
A synthetic version of it must be able to mimic the natural hormone
meaning of endocrine?
hormones secreted near blood vessels
meaning of paracrine?
substances secreted in interstitial space (locally by diffusion)
meaning of enterochromaffin?
serotonin (muscle excitatory) & chemoreceptors
what are the hormones of the intrinsic system secreted by?
specialised epithelial cells: endocrine, paracrine and enterochromaffin
what type of function does the hormonal control of the intrinsic system have?
regulatory function not digestive
what is involved in the hormonal control of intrinsic system?
gut peptides and gut hormines
what nerve fibre does a signal go down which leads to the inhibition of digestive action when a fight or flight response is stimulated in an animal?
the preganglionic and postganglionic sympathetic nerve fibre
the majority of the reflexes coordinated by the secretion and muscle contraction involved in gut neuronal regulation exert what?
they exert a stimulatory influence using acetylcholine as a transmitter
certain reflex arcs release what other kind of neurotransmitters? And why is this important?
they release inhibitory neurotransmitters - this is important for relaxation of sphincters (facilitating emptying of that portion of the tract
what are the sensory neurones involved in gut neuronal regulation affected by?
affected by changes in content (via chemoreceptors within gut mucosa) and by changes in distension of wall (via mechanoreceptors within gut muscular layers)
what are the two types of motor neurones involved in gut neuronal regulation?
they can either be inhibitory or stimulatory
Which three neurones are involved in the gut neuronal regulation?
sensory neurons
motor neurons
interneurons
which neuron in the gut neuronal regulation is afferent?
sensory neurons
which neuron in the gut neuronal regulation is efferent?
motor neurons
what are the motor neurons in the gut neuronal regulation connected to?
either: smooth muscle cells or epithelial (secretory) cells that produce digestive juices or hormones
how do plexuses communicate with each other?
via interneurons
what are interneurons?
shorter neurones
how do plexuses communicate with the CNS?
via vagal and splanchnic nerves
What do the neurons within each plexus form synapses with?
each other
smooth muscle cells or glandular cells for contractions/secretions
neurons in the other plexus
what nervous system does the intrinsic control use?
the enteric nervous system
how many plexuses make up the enteric nervous system?
two
what are the two plexuses that the enteric nervous system contains?
the submucosal plexus and the myenteric plexus
what do the guts ‘own’?????????????????
the CNS
WHAT DOES THIS EVEN MEAN
what are the two types of control of the gut?
neural and hormonal
what are the gastrointestinal tract motor and secretory functions controlled by?
the gastrointestinal nervous system and the gastrointestinal endocrine system
what is the the gastrointestinal nervous system and the gastrointestinal endocrine system controlled by?
the CNS
