Control Of Alimentary Tract Flashcards
How does the innervation of the parasympathetic nervous system affect the gut?
Stimulates digestive activity
Stimulates gall bladder
Relaxes the rectum
How does innervation of sympathetic nervous system affect the gut?
Inhibits digestive activity Stimulates glucose release from the liver Inhibits salivation Relaxes bladder Contracts the rectum
Gut has its own “brain”
It’s called…
Enteric nervous system
Where are 2 muscles involved in peristalsis?
circular and longitudinal muscles
Where are circular muscles found?
found close to lumen
Where are longitudinal muscles found?
on outer surface
What are innervates GI tract?
innervated by intrinsic neurons of the enteric nervous system and by axons of extrinsic parasympathetic, sympathetic and visceral afferent neurons
Relaxation of fundus (reservoir) is mediated by reflexes and can be differentiated into 3 stages
- Receptive
- Adaptive
- Feedback
What is mechanism of fundus relaxation/storage?
relaxation is mediated by NANC
also controlled by reflex chains involving release of NA
when stomach is ready to receive food, NA is released from sympathetic nerve fibres which helps stomach to relax
Is pyloric sphincter often contracted or relaxed?
often relaxed but closes upon arrival of peristaltic wave
What is function of pyloric sphincter?
acts as sieve, larger particles are pushed back to antrum to be further digested
sieving effect: viscous + solid matter are retained in stomach
What causes opening of pyloric sphincter?
repulsion of chyme causes the opening -> small partially digested material is squirted through pyloric sphincter into duodenum
What are types of control in GI?
Endocrine, paracrine, neural (vago-vagal reflex, enteric or local reflex) and metabolic (type of food eaten)
Describe the difference in the structure of fundus + antrum? how do these differences help with their function?
Fundus -> has thinner muscle layer so it is able able to expand to allow accommodation to occur
Antrum -> large, thick muscle layer so is able to provide grinding action
When is gastrin secreted?
can be secrete because there’s distension of stomach or we have seen food
What does distension of stomach initiate?
neuronal stimulation that promotes gastrin releasing peptide which acts on G cells that release hormone gastrin
What are the effects of gastrin? (gastrin mediated effects)
gastrin travels in circulation
it can promote histamine secretion from enterochromaffin like cell (ECL) -> histamine binds to its receptors on surface of parietal cells. Parietal cells then secrete HCl
gastrin can also promote ACH release
What is difference between endocrine and paracrine?
hormones (endocrine) go to target tissues via BLOOD + paracrine agents go via interstitial fluid
What is paracrine control?
Gastrin can cause hypersecretion of acid
Somatostatin is only released when there is hypersecretion of acid
What is vago-vagal reflex?
describes type of reflex in which both afferent (sensory) + efferent (motor) axons are in vagus nerve trunk
describes reflex control of responses to gut stimuli via NTS + DMVN
the pathway of vago-vagal reflex is via…..
brainstem (medulla)
When is vago-vagal reflex active?
Active during receptive relaxation of stomach in response to swallowing -> reflex goes from stomach to brain + back to stomach -> active relaxation of smooth muscles of stomach. it promotes motility + acid secretion
What is NTS?
main site of termination of vagal afferents
What is DMVN?
main site of origin of vagal efferents (motor) supplying the gut
Describe the vago-vagal reflex pathway?
vagal afferents get sent to NTS -> vagal efferents will send motor reflexes down
Ach is released pre-ganglionically and post-ganglionically -> causes motility + acid secretion
What are 2 nerve fibres intrinsic to gut? What are their functions?
Myenteric plexus (auerbach's plexus) -> motor function for motility Submucosal plexus (Meissner's plexus) -> intestinal secretions
What are the neurotransmitters involved of enteric nervous system?
Ach, NO, NA, 5-HT, GABA + ATP
Where are myenteric plexus and submucosal plexus found?
found in wall of colon
What do the 2 plexuses receive?
receive inputs from both SNS + PNS
Parasympathetic activity ->increase contraction of proximal colon
Sympathetic activity -> decrease colonic movement
What is colo-colonic reflex?
is when you taken in food + its in stomach, food starts to get digested, food particles tend to promote movement aborally (lower end of gut) -> food starts to move down
What is myenteric plexus?
most prominent plexus
cholinergic innervation -> increases gastric motility + secretion
adrenergic stimulation -> decreases gastric motility + secretion
What is metabolic control?
types of food eaten
rate of emptying is dependant upon material’s ability to be absorbed:
- carbohydrates emptied quickly into duodenum
-proteins - slow emptying
-fatty foods - even slower
-fatty acids in duodenum -> decrease in gastric emptying by increasing contractility of pyloric sphincter
What is peristalsis?
- wave of propulsive contractions that move contents of gut towards anus
What is difference in peristalsis in large intestine and small intestine?
slower in large intestine compared to small intestine
