GI Flashcards
What are the main functions of the GIT?
Nutrition
Excretion
Microbiome
Electrolyte balance
Immunity
What is the definition of motility?
Motility describes the contraction of the muscles that mix and propel contents in the gastrointestinal (GI) tract.
What are the two main excretory products?
Carbon dioxide and Urea.
GI motor activity can be divided into two sections. What are the two sections? and explain their individual role.
Functional activity: segmentation, peristalsis and storage
Contractile activity: phasic (alternative contractions – said to be rhythmic) and tonic (sustained)
Why is contractile activity referred as highly coordinate and regulated? / What controls the relaxation and contraction of the GI tract?
Segmentation and peristalsis
What coordinates the movement of food from the stomach to the small intestines?
pyloric sphincter
Outline the differences between peristalsis and segmentation.
Segmentation is another kind of involuntary muscle movement that occurs in your digestive system. But unlike peristalsis, which occurs throughout your GI tract (especially oesophagus), segmentation occurs mainly in your intestines.
What is gastric motility?
Gastrointestinal (GI) motility refers to the movement of food from the mouth through the pharynx (throat), esophagus, stomach, small and large intestines and out of the body
Explain why the stomach withholds a specific amount of gastric content.
To reduce pressure and allow hormones to mix
Describe the motility patterns for gastric emptying and explain how gastric emptying is regulated.
Stomach stage
When food is chewed and swallowed, the mushed-up food travels down the oesophagus and into the stomach, where it sits for a while. The stomach then releases gastric acid and an enzyme called pepsin to start the process of digestion, turning the mush into a semi-digested acidic liquid called chyme.
The stomach has four parts. The upper part is called the fundus (food is stored here temporarily). Next is the body of the stomach. The lower part of the stomach is called the antrum - mixing occurs here and the end of the stomach is called the pylorus (contracts to limit chyme from stomach). The pyloric sphincter sits at the bottom end of the pylorus where it connects to the first part of the small intestine, called the duodenum. This sphincter is like a valve that opens slightly (about 3.75 mm) and periodically squirts small bits of chyme into the duodenum. When chyme goes into the duodenum, the muscle becomes distended, and this triggers the enterogastric reflex. When this reflex happens, the pyloric sphincter takes a temporary pause. No more gastric acid is secreted, no more chyme is released into the duodenum, and gastric motility is halted until the duodenum has digested the chyme and is ready to receive more. A functioning pyloric sphincter is important for proper digestion. If the sphincter is diseased and does not open and close properly, it may lead to problems with digestion and nutrient absorption.
Small intestine
But just how is the chyme digested? The contraction of intestinal circular smooth muscles that mixes chyme is called segmentation. The small intestine is the site where segmentation occurs. Segmentation plays a large part in both digestion and nutrient absorption and begins once chyme is dumped into the duodenum (beginning of the small intestine). However, these muscle contractions do not transport partially digested food through the intestines but rather mechanically mix them in one place.
What is peristalsis?
Peristalsis is a type of involuntary muscle movement that occurs in your digestive system. Peristalsis occurs throughout your GI tract, but especially in your esophagus. When food or fluids enter your GI tract, nerves trigger the muscles to initiate a series of wave-like contractions. These muscle contractions automatically move food and fluids forward until they reach their exit at your anus or urethra.
What are the three main controls of gut motility movement?
Myogenic control: Intrinsic rhythm of GI smooth muscles set by pacemakers cells of ICC. RHYTHM IS USUALLY SLOW WAVES
Hormonal control: Utilizes various hormones including cholecystokinin, gastrin, and secretin, among multiple others for a myriad of functions
Neuronal control: The gastrointestinal (GI) tract is controlled both intrinsically by the enteric nervous system (ENS) – known as the “brain of the gut” is pivotal for normal muscle activity in the gut and is independent of the CNS, and extrinsically by visceral sensory afferent and visceral motor efferent (sympathetic and parasympathetic) fibers.
Where is the ENS located?
Within the GI Tissue inside the:
myenteric plexus (controls motility)
submucosal plexus (controls secretory functions)
Explain the process of how myogenic muscles regulate their movement?
Hormonal and neuronal activity determines whether slow waves reach their threshold and cause an action potential. These action potential leads to smooth muscle contraction.
What are the pacemakers of the gut called?
Interstitial Cells of Cajal (ICC) generates slow waves that may lead to contraction.
What are the pacemakers affected by?
ENS
How does the ANS regulate GI function?
Autonomic NS
Parasympathetic NS
- post ganglionic cells reside in smooth muscles and secretory cells
- acetylcholine is the main neurotransmitter
- excitatory upon gut function
Sympathetic NS
- inhibits GI function
- stimulates sphincter and blood vessel contraction (butterflies in stomach when nervous)
What activates motility patterns
reflexes:
- Peristalsis
- Enterogastric reflex
mood
contents of lumen
Describe the main difference between motility disorders and functional disorders.
Motility disorders there is a definite cause and Functional disorders there is no cause.
Examples of motility disorders.
Megacolon
Hirschprung’s disease
Acute/Chronic Intestinal Pseudo-obstruction
Gastroparesis
List a few examples of functional disorders.
IBS
Functional constipation
Functional diarrohea
What is Hirschsprung’s disease?
Hirschsprung’s disease is a rare condition that causes poo to become stuck in the bowels.
What is IBS and what are the causes?
Umbrella term for functional bowel disorders
Chronic abdominal complaint with no obvious physiological abnormalities
stress and gastroenteritis are triggers
affects females more than men
How can we diagnose IBS?
abdominal pain once a week and at least one of the following:
- pain with defecation
change in frequency of stools
change in appearance of stools
What are symptoms of IBS?
abdominal pain, diarrhoea, constipation, mucous in stools, bloating, alternating diarrhoea and constipation
depression, anxiety, and stress
IBS-C
IBS-D
IBS-M
IBS-U
What evidence is there to support altered motility in IBS?
Delayed transit in constipation
accelerated transit in diarrhoea
migrating in motor complex
impaired transit in gas
exaggerated gut responses to stimuli: food, bile acids, distensions, stress, CRH (Corticotrophin-releasing hormone)
What is functional constipation?
Also known as chronic idiopathic constipation (CIC)
infrequent bowel movements
feeling of incomplete evacuation
needing fingers to get stools out
feeling that something is blocking the stools from coming out
What is functional diarrhoea?
diarrhoea that occurs without abdominal pain or discomfort with no known cause
loose stools in at least 75% of bowel movements
present for at least 3 months
no red flags
Explain what serotonin is and the role of serotonin in GI function?
- Serotonin (5-HT) is a major neurotransmitter and paracrine signalling molecule in the GI tract
- Synthesised from the essential amino acid L-tryptophan.
- Gut serotonin (5-HT) controls:
Emetogenic reflexes
Intestinal motility and secretion
Pain.
Where is gut serotonin contained?
EC cells
Some in neurons
Name the serotonin receptors in the gut and explain what effect they produce when they bind to serotonin.
5-HT3 and 5-HT4
Serotonin has excitatory effects on the gut including gastric accommodation, transit, tone, sensation and secretion
Explain the action that drugs have on 5-HT4 receptors.
They have an agonist effect on the receptors which causes the stimulation of peristalsis
The drugs bind to the 5-HT4 receptor to stimulate the release of acetylcholine from excitatory neurones
They also cause the release of inhibitory neurones
Overall effect is to boost neurotransmission in ENS and to enhance motility
Doesn’t directly stimulate peristalsis, but amplifies whatever signals are present.
What is the drug treatment for functional constipation/CIC
Prucalopride -5-HT4 agonist
Increases intestinal motility and transit
When can Prucalopride be used and what are the side effects?
Used in treatment of chronic constipation in adults.
Side effects: headache, nausea and diarrhoea
What is a drug treatment for IBS-C and what properties gives it this trait?
GC-C agonists to activate guanylate cyclase C
e.g. Linaclotide - increases transit through lumen aka laxative effect
- also reduces pain through GC-C
What receptor does Linaclotide bind to and what is the benefit of the binding?
Linaclotide binding with GC-C receptor causes pain relief
What is a drug treatment for IBS-D and what properties gives it this trait?
Loperamide
Eluxadoline - not used in UK, mixed opioid
