digestive regulation Flashcards
regulation of GI function; describe intrinsic system
- In the GI wall
- Enteric nervous system
- Endocrine control
regulation of GI function; describe extrinsic system
- Outside wall of GI tract
- Influence intrinsic system
- Central nervous system
- Endocrine control
enteric nervous system is connected to, communicated w and receives feedback from the ___ and ____
SNS and PNS
is enteric nervous system capable of independent function from the remainder of the nervous system
yes; local reflex activity
what is enteric nervous system involved with in the regulation of digestive processes
Controls secretions of the GI organs
Controls peristalsis and some other movements
instrinsic system nerves and endocrine secretion
- nerves; enteric nervous system (ENS)
- endocrine secretions; secretin, gastrin, CCK, GIP, and Motilin
extrinisc system nerves and endocrine secretions
- nerves; vagus and splanchnic nerves
- endocrine secretions; aldosterone
what 3 neurons are included in the enteric nervous system (ENS)
1) sensory (afferent) neurons
2) interneurons
3) motor (efferent) neurons
in ENS, the sensory (afferent) neurons detect
chemical and mechanical conditions in the gut
in the ENS, motor (efferent) neurons control
peristalsis
in the ENS, interneurons
make the enteric nervous system capable of reflexes, and able to act as an integrating centre when there’s no CNS input
sensory neurons include mechanoreceptors; where are they and what do they do
- Within muscle layers
- sense Distension of gut (stretch, pressure)
sensory neurons include chemoreceptors; where are they and what do they do
- Mucosa
- sense chemical conditions in gut lumen (peptides, pH, etc)
ENS; where do interneurons travel within
travel long distances within the myenteric plexus (auerbach’s) and connect the myenteric and submucosal plexus (meissner’s)
Submucous plexus (Meissner plexus): where and what does it regulate
in submucosa → regulates fluid and electrolyte movement across the intestinal mucosa
Myenteric plexus (Auerbach plexus): where and what does it regulate
in muscularis propria between the longitudinal and circular layers of the smooth muscle in walls of the GI tract →
coordinates smooth muscle contractions involved in peristalsis
motor (efferent) neurons innervate what
smooth muscle within the gut wall and within arteries
Regulation of smooth muscle contractions occurs via
interneuronal connections.
The signal that efferent neurons that signal glands within the gut can be either
excitatory – stimulating movement or release of substances from glands ‐ or inhibitory
describe axon terminals in the ANS (what are they called, what do they allow for and what do they secrete)
often in bead‐like strings,
called varicosities
allow for a bigger, more wide‐spread activation of the target tissue, and allow more neurotransmitter to be released across that range of tissue
secrete neurotransmitters aka neurocrines, can be excitatory or inhibitory
Excitatory neurocrine transmitters are mainly _____, meaning they secrete ______
cholinergic
acetylcholine
- although also neuropeptides such as substance P which are also excitatory
inhibitory neurocrine transmitters are mainly
peptides
Vasoactive intestinal
peptide can be either excitatory or inhibitory, depending on the receptor on the target tissue. When it is released in the gut muscle, it has an ______ effect. However, when it’s released in the mucosal glands, it has an _____ effect.
inhibitory
stimulatory
how is the ENS an exception to the 2-neuron efferent innervation rule of the ANS
It might have 3 or more neurons
enteric nervous system accomplishes synaptic transmission by using more than ____ neurotransmitters including :
30
acetylcholine, dopamine, nitric oxide and serotonin
visceral reflexes
stimulus and response
stimulus
* Change in temperature
* Stretch of the GI tract
* Pain (irritation) in the viscera
* Change in blood gas composition
response
* Shivering, hair erection, sweating
* Sneezing, coughing
* Contraction of the GI tract
* Change in breathing pattern
where are endocrine cells found
in the epithelium of the GI tract
endocrine cells have a narrow apex; what does it do
samples lumen contents
endocrine cells have a broad base that secretes
regulatory peptides (true enodcrines, paracirnes, autocrines and neurocrines)
endocrine cells secrete regulatory peptides: some of these secreted peptides are true endocrine hormones
where do they travel and what are 2 examples
They travel through the
blood stream to affect other regions of the gut.
examples of this include gastrin and somatostatin.
endocrine cells secrete regulatory peptides: some of these secreted peptides are paracrines
where do they travel and what are 2 examples
- Diffuse locally through extracellular fluid
(ECF) - Somatostatin, peptide YY
endocrine cells secrete regulatory peptides: some of these secreted peptides are autocrines
modify or regulate functions of same cell
endocrine cells secrete regulatory peptides: some of these secreted peptides are neurocrines
what are these released by
enteric neurons
GASTRIN
production
actions
release stimulus
production: distal stomach
actions:
primary: stimulates stomach HCl
secondary: stomach motility, trophic effect on stomach epithelium
release stimulus:
- Distension of stomach antrum
- Vagal stimulation
- Protein in stomach
- High gastric pH
SECRETIN
production
actions
release stimulus
production: duodenum
actions:
primary: stimulates pancreatic HCO3- secretions
secondary: stimulates billary HCO3- secretion
release stimulus
H+ in duodenum
cholecystokinin (CCK)
production
actions
release stimulus
production: SI, most in duodenum
actions:
primary; stimulates pancreatic enzyme secretion
secondary: inhibits gastric emptying
release stimulus: proteins and fats in SI
gastric inhibitory polypeptide (GIP)
production
actions
release stimulus
production: duodenum, upper jejunum
actions:
primary: inhibits gastric motility and secretions
secondary: stimulates insulin (if sufficient glucose present)
release stimulus
CHO and fat in SI
motilin
production
actions
release stimulus
production: duodenum, jejunum
actions
primary: increases gut motility between meals
secondary: regulate tone lower esophageal sphincter
release stimulus: ACh
major gastrointestinal hormones (5)
- gastrin
- secretin
- cholecystokinin (CCK)
- gastric inhibitory polypeptide (GIP)
- motilin
gastrin feedback loop
- Stomach fills with food
- Buffering occurs → increase pH + Protein in stomach
- Gastrin released
- Increased HCl production
- Decrease pH → decreases Gastrin release
Intrinsic system (Enteric Nervous System) influenced by
extrinsic system
autonomic nervous system includes
- Parasympathetic (stimulates)
- Sympathetic (inhibitory)
Parasympathetic Nervous System: ganglion location
Ganglion is close to target organ
Parasympathetic Nervous System: Preganglionic fibres synapse on
cell bodies of enteric nervous system
Parasympathetic Nervous System: postganlionic fiber is short or long
short
(so long myelinated preganglionic nerve)
sympathetic nervous ganglia location
close to spinal cord in thorax and abdomen
autonomic nervous system: brief recap
The efferent nerves are a 2 nerve
system. They have a pre‐ and a post‐ganglionic nerve, which synapse in a ganglion. In the parasympathetic nervous system, this ganglion is close to the target organ. In fact, they synapse on the cell bodies of the enteric nervous system, in the myenteric or submucosal plexus. So it has a long myelinated preganglionic nerve, with the ganglion sitting close to the target organ. This preganglionic nerve releases acetylcholine. The acetylcholine goes across the synaptic cleft and binds to a nicotinic type 2 receptor. From here, that stimulates the post‐ganglionic nerve, which is also cholinergic. So this postganglionic nerve also releases acetylcholine into the synaptic cleft. Now, this acetylcholine can bind to a number of different types of muscarinic receptors, types 1, 2 and 3. This are G‐protein coupled receptors. So when they get stimulated, they stimulate a signal transduction pathway
symapthetic nervous system: is postganglionic fibre long or short
long
(short preganglionic fibre, which is myelinated, with the cell body in the spinal cord.)
sympathetic nervous system recap
Then we’ve got the sympathetic nervous system. You have your first, short
preganglionic fibre, which is myelinated, with the cell body in the spinal cord. When it
gets to the autonomic ganglia, there’s a synapse. This ganglia is sitting close to the spinal cord in the thorax and abdomen. This presynaptic nerve releases acetylcholine, which diffuses across the synaptic cleft and binds to a nicotinic type 2 receptor. These particular receptors also allow for ions to travel through and will stimulate the longer postganglionic nerve, which goes all the way to the effector tissue. In the GI tract, this postganglionic nerve releases noradrenaline, or norepinephrine. Some post‐ganglionic fibres synapse on the cell bodies of the enteric nervous system, other synapse directly on GI muscles and glands. Sympathetic stimulation in the GI tract usually has an inhibitory effect.
sympathetic action on smooth muscle walls
parasympathetic
relaxes
contracts
sympathetic action on smooth muscle sphincters
parasympathetic
contracts
relaxes
sympathetic and parasympathetic saliva secretion
increase
increase
parasympathetic action on gastric acid secretion
increases
parasympathetic action on pancreatic secretion
increase
extrinsic: endocrine effects:
aldosterone secreted in response to
- Low BP
- Low sodium
- High potassium
- Factors occurring outside of GI tract
main effects or aldosterone are in _____ but also has effects in GIT
kidney
______ is the main
mineralocorticoid steroid hormone produced by the adrenal gland
aldosterone
what does aldosterone stimulate
sodium and water reabsorption from the gut and salivary glands in exchange for potassium ions
gut-associated lymphoid tissue: GI tract has many immune cells such as
phagocytes and lymphocytes
gut-associated lymphoid tissue: Mucosa exposed to numerous
microorganisms and antigens
normmal immune response
- Production of antibodies
- Recruitment of killer cells
- Sensitised lymphocytes can secrete cytokines
cytokines influence intrinsic nervous and endocrine systems, give examples
- Increase motility and secretions
- Diarrhoea
- Dilute offending antigen
- “Flush” toxins from lumen
regulatory peptides have a trophic effect : so when food intake increases, amount of regulatory proteins released in GI tract increases (like gastrin)
this triggers hypertrophy of hut mucosa: what does this mean?
the amount of food that can be digested and absorbed increases
in summary: GIT has its own independent intrinsic enteric nervous system that contains
receptors, sensory neurons, interneurons and motor neurons
GIT has intrinsic endocrine system and main hormones include
gastrin, secretin, CCK, GIP and motilin
gastrin, secretin, CCK, GIP and motilin, these hormones are part of what system
intrinsic endocrine system of GIT
Which of the following statements regarding regulation of GI function is INCORRECT?
A.
The intrinsic system is comprised of 2 components, both of which are located within the wall of the GI tract. This system includes nerves, the enteric nervous system, as well as endocrine secretions such as secretin.
B.
The extrinsic system is comprised of 2 components, both of which are located outside the wall of the GI tract, and influence the intrinsic system. Extrinsic influence from the autonomic nervous system includes both afferent and efferent nerves. Extrinsic hormonal control is provided through the actions of gastrin.
C.
The extrinsic system is comprised of 2 components, both of which are located outside the wall of the GI tract, and influence the intrinsic system. Extrinsic influence from the autonomic nervous system includes both afferent and efferent nerves. Extrinsic hormonal control is provided through the actions of aldosterone.
D.
Gastrointestinal function is regulated by both intrinsic and extrinsic systems.
B.
The extrinsic system is comprised of 2 components, both of which are located outside the wall of the GI tract, and influence the intrinsic system. Extrinsic influence from the autonomic nervous system includes both afferent and efferent nerves. Extrinsic hormonal control is provided through the actions of gastrin.
Interneurons in the enteric nervous system travel within the myenteric plexus. What does the myenteric plexus co-ordinate?
Peristalsis
Which of the following is NOT a component of the enteric nervous system?
A.
Submucosal plexus
B.
Myenteric plexus
C.
Chemoreceptors in the GI tract
D.
Vagus nerve
D. Vagus nerve
Which of the following cell types found in the epithelium of the GI tract are part of the intrisic endocrine system?
Enterochromaffin cells
Which of the following hormones stimulates the parietal cells in the stomach to release hydrochloric acid?
Gastrin
Which of the following hormones stimulates pancreatic enzyme secretion, and is released when proteins and fats are present in the small intestine?
Cholecystokinin
Which neurotransmitter is released by the preganglionic fibre of the parasympathetic nervous system, when it synapses on a cell body of the enteric nervous system, in the myenteric or submucosal plexus?
Acetylcholine
Which of the following hormones is involved in the extrinsic endocrine control of the GI tract?
Aldosterone
