Regulation of GI tract Flashcards
- What type of cells does that GI tract have lots of that monitor what si going on. What are some examples of these?
a. Sensory cells
b. Wall stretch, nutrient conc, metabolite conc, osmolarity, pH, irritation of mucous membrane
- What does stimulation of sensory cells in the GI initiate
a. Reflex coordination of smooth muscle and hormones
- How does the CNS play a part in GI
a. Sight and smell of food
b. Regulation of appetite
- What are digestion processes regulated and coordinated by?
a. Regulated = negative feedback mechanisms
b. Coordinated = neural and hormonal regulation
- What is special about the GI nervous system
a. It has its “own” one – ENTERIC = only GI
b. Sensory and motor nerve cells within the wall of the GI that can act completely independently to the CNS and peripheral
c. 2 nerve plexus that synapse with each other:
sensory cells that respond to content of the lumen and degree of wall stretch
Motor cells that stimulate smooth muscle cells (motility) and epithelial cells (secretion of digestive juices or hormones)
- What types of reflex arcs are there in the GI
a. Short reflex arcs = enteric nervous system as only in small part of body = very local
b. Long reflex arcs = autonomic nervous system = coordinate activity between different organs within the GI. Sympathetic halts digestion, parasympathetic promotes digestion
What are the complex reflex arcs in the enteric nervous system
- consist of simple reflex arcs that are connected by interneurones which mean the nerve impulse is propagates wider
In the enteric nervous system what are most reflexes and what transmitter
- most reflexes are stimulatory
- Main transmitter = acetylcholine
- other inhibitory transmitters which usually act on spincters to relax them e.g. gastro-duodenal junction and ileo-colic junction
What nervous system is occurring for GI function
When the parasympathetic nervous system overrides the symapthetic. Dont want to be in a fight or flight
What are the ganglions like for para nervous system GI
PARASYMPATHETIC:
- Long pre ganglionic fibres that run in vagus (cranial nerve) = cholinergic
- Short post ganglionic fibres embedded within the wall of GI tract. Ach to stimulate secretion and motility
What are the ganglions like for sympathetic nervous system GI
Sympathetic overrides para = digestion shut down.
- roughly equal length pre and post ganglionics, 2. separate areas where synapse = discrete ganglia
- out of spinal cord = pre ganglionics which run to a ganglion, synapse with post ganglionic in that ganglion
- post ganglionic fibres run along arteries to organ of innervation
- Pre ganglion = cholergic
- post ganglion = adrenergic = noradrenaline neurotransmitter to inhibit secretion and motility, and decrease blood supply to GI tract
What influences the autonomic nervous system of the GI
- sight, smell, taste of food
What are entero-enteric reflexes?
give e.
- coordinate activity between different parts of the GI tract
- e.g. mastication stimulates release of saliva, gastric juice, pancreatic juice and bile
e. g. stretching of stomach relaxes ileo-colic sphincter to allow food to move out of small intestine in preparation for food moving into small intestine from stomach. = gastro-colic = empty of colon in prep for food to pass down
What role does gastrin have on GI
- Produces
- Stimulation
- Effect
- P = caudal stomach
- Stimulated by break down products of protein so presence of peptides, amino acids, acetylcholine
- Effect: stimulates HCL secretion, growth of gastric/ intestinal mucosa
What role does secretin have on GI
- Produces
- Stimulation
- Effect
- P = Mainly duodenum
- Stimulation = HCL
- Effect = Stimulates pancreatic bicarbonate (HCO3-)
- -> to neutralise acidity of food from stomach so enzymes in SI can work
What role does Cholecystokinin (CCK) have on GI
- Produces
- Stimulation
- Effect
- P = Mainly Duodenum
- Stimulation = Fatty Acids, monoglycerides, AA, peptides
- Effect = stimulates pancreatic enzymes, contracts gall bladder
What role does Gastric Inhibitory Peptide (GIP) have on GI
- Produces
- Stimulation
- Effect
- P = Cranial Small Intestine
- Stimulation: Fat, Glucose, amino acids
- Effect: Inhibits HCL, stimulates insulin production
Phases of regulation
- relate to the site of the stimulus
- cephalic phase - head - anticipation of food and emotion
- Gastric phase - stomach, coordinated by ANS, ENS, hormones (mainly gastrin)
- Intestinal phase - intestines - coordinated by ANS, ENS hormones (mainly CCK and GIP)
Where is regulation of appetite controlled
- hypothalamus
- within H = appetite centre = stimulates to want to eat
- Satiety centre = inhibits appetite centre
What is motility
- coordianted contraction of smooth muscle in GI tract
What are the 4 types of motility
- Segmental: contractions occurring in segments of the gut
Mixes lumen contents
Mechanical breakdown - Peristalsis (main, occurs all time)
Move intestinal contents in GRADUAL aboral direction - enable all nutrients absorbed
Main type of movement - Anti peristalsis
Moves intestinal contents in oral direction - Mass Movement
Empties entire section GI tract
Why is segmental contraction important for digestion
- Food in between contractions doesn’t go anywhere
2. Enzymes secreted at edges and needs to reach food in middle for efficient digestion
Where does the 4 types of motility occur in GI
ALL OCCUR EVERYWHERE!
stomach, SI, LI
but some occurs more than another in diff areas
What is the aim of pacemaker cells and where are tehy located?
- To set the rate at which contractions occur to get things to move down the GI
- Located = Between circular and longitudinal smooth muscle of GI tract
