GI physiology and pathophysiology Flashcards
what is the GIT wall made of
- mucous membrane
- lamina propria
- muscularis mucosae
- submucosa
- muscularis externa
- serosa
- submucosal plexus
- myenteric plexus
what does the mucosa do
facilitates movement of food
what does the lamina propria and muscularis mucosae do
they are part of movement and motility
what does the submucosa do
its involved in secretion
what does the submucosal plexus do
its the first layer of the enteric nervous system and is involved in excretion
what does the myenteric plexus do
its part of motility
what are the stages of smooth muscle contraction
- intracellular Ca increases when Ca enters cell from extracellular fluid or sarcoplasmic reticulum
- Ca binds to calmodulin. it is a calcium binding messenger protein
- Ca calmodium complex activates myosin light chain kinase
- MLCK phosphorylates myosin light chains in myosin heads - increasing myosin ATPase activity
- phosphorylated myosin binds with acting forming cross bridges
- actin slide along myosin - contraction
what does the enteric nervous system do in the GIT
works independently of the CNS controlling local reflexes, changing motility or secretion
what do the sensory neurones of the ENS do
- monitor changes in luminal activity eg distension
- pH
- osmolarity
- levels of nutrients
what do efferent secretomotor neurons do in the ENS
- stimulate or inhibit effector cells, smooth muscle cells, epithelial cells that secrete or absorb fluid, electrolytes, submucosal blood vessels and enteric endocrine cells
what does parasympathetic modulation of the ENS do
promotes motility and secretion
what does sympathetic modulation of the ENS do
inhibits motility and secretion by contracting sphincerts
what does the myenteric plexus do
mainly controls GI motility
what does the submucosal plexus do
mainly controls GI secretion
what is peristalsis
an intrinsic local reflex that helps move food through the GI tract towards the anus
how does peristalsis work
muscle contractions behind the food bolus
what do excitatory neurones do in peristalsis
excitatory neurones behind the food bolus allow contractions of circular muscles by releasing ACH
what do inhibitory neurones do in peristalsis
allow for circular muscles to relax which is facilitated by nitric oxide and vasoactive intestinal peptide
what is Hirschsprung disease
- severe constipation with an absence of the ENS in the distal colon
- has a segment of increased tone, narrow lumen and devoid of propulsive activity
what is achalasia
- a failure of oesophageal peristalsis and relaxation of the lower oesophageal sphincter when swallowing
- come from loss of VIP and NO inhibitory interneuron and the excitatory neural tone dominates
what is the slow wave motility mechanism
- cyclical changes in membrane potential
- generated by pacemaker cells
- regulator of GIT motility
what is the role of segmentation and haustration in motility
- mix the contents of small and large intestine
- contracts circular muscle and pinches off different regions
what does the migration motor complexes do in motility mechanism
- cycle of electrical activity triggering motor activity in the fasting state
- clears the content of stomach before next meal
- mediated by ghrelin, motilin and vagus nerve
what is the role of mass movement in the motility mechanism
- enhanced rate of peristalsis
- triggered by gastrocolic and duodenoscopic reflexes
what is the hormone ghrelin
stimulate you to want to eat again
what is the hormone motilin
stimulates the movement of things out of your stomach to prepare the next food to enter
what does the gastroileal reflex do
stomach promotes the opening of the ileoceacal sphincter
what does the colonoileal reflex do
inhibits ileal emptying when the colon is streatched
what does the gastrocolic/ duodenocolic reflexes do
where food entering the stomach or duodenum promotes the motility of the colon
what does the enterogastric reflex do
distension of the small and large intestine inhibits stomach motility and secretion
what does intestinointestinal reflex do
over distension of one part of the intestine leads to relaxation of the rest of the intestine
what is the gastric accommodation reflex
allows the stomach to relax and increase compliance to accommodate food volume
what is the innervation of the gastric accommodation reflex
vagovagal reflex pathway, activate the inhibitory motor neurones
what is the function of the gastric accommodation reflex
- prevents pressure rising
- provides time to allow efficient mixing and break down of food
- allows stomach to be a temporary store
what are the stages of the gastric accommodation reflex
- food enters stomach
- sensory receptors detect distension and stretching of stomach walls
- volume and pressure information sent to brain stem via vagus nerve
- efferent vagal nerve signal to fundus and proximal stomach
- activation of inhibitory motor neurones and release of VIP and NO
- relaxation of smooth muscle cells in stomach wall
what is gastroparesis
delayed gastric emptying in the absence of stomach blockage. caused by vagal injury
what is emesis
the vomiting centre in the medulla oblongata from sensory and psychological inputs
what tiggers nausea and vomiting
chemoreceptor trigger zone in the area postrema allowing chemical changes in bloodstream to induce these feelings
what does the nucleus of the solitary tract do in vomiting
initiation and integration of reflexed
- also triggered by motion sickness
what are the stages of vomiting reflex
- stimuli from stomach/ pharynx
- visceral afferents
- chemoreceptor trigger zone
- vomiting centre
- vomiting reflex
how does the action of vomiting work
- wave of reverse peristalsis in the distal small intestine
- skeletal muscles contract to decrease thoracic pressure and increase abdominal pressure
- abdo wall and pyloric contraction, opens lower oesophageal sphincter
what is haematemesis
- vomiting blood either red clots of coffee grounds
- cause my upper GI bleed
what are the different types of small bowel obstructions
- extrinsic compression
- internal blockage of the lumen by abnormal material
- mural disease encroaching on the lumen
what are the symptoms of small bowel obstruction
- abdominal pain
- bloating
- severe constipation
- vomiting
what factors regulate gastric motility and emptying
- volume of chyme
- degree of fluidity
- presence of fat, acid, hypertonicity or distension
- emotion
- intense pain
how does volume of chyme affect gastric motility and emptying
increase volume stimulate motility and emptying
how does the degree of fluidity affect motility and emptying
increased fluidity allows more rapid emptying
how does fat, acid, hypertonicity or distension effect gastric motility and emptying
in the duodenum they inhibit further gastric motility and emptying until the duodenum has coped with factors already present
how does emotion and intense pain effect motility and emptying
- emotion can stimulate or inhibit
- intense pain will inhibit
what is the internal control of defication
- enteric muscle
- smooth muscle
- involuntary control
what is the external control of defecation
- skeletal muscle
- voluntary control
what does stretching the rectum cause
- increases peristalsis through the ENS
- increase regional peristalsis via spinal activation of PNS
- relax of internal anal sphincter
- contraction of external anal sphincter
what is the role of gastrocolic/ duodenocolic reflexes in defecation
- mass movement after meal
- mediated by vagus nerve following distension of stomach and duodenum
what is the role of the intrinsic reflex in defecation
- mediated by ENS in rectal wall
- faeces enter > distension > afferent signal through myenteric plexus > peristaltic waves > faeces to anus > internal anal sphincter relaxed