M104 T1 L4 Flashcards
How long is the digestive system in life compared to when fully lengthened?
approx 5 - 7m
79m
What three salivary glands are present in the oral cavity?
parotid
sublingual
submandibular
What are the accessory organs of the digestive system present in the thoracic cavity?
liver
gallbladder
pancreas
In which two places are the accessory organs of the digestive system located?
oral cavity
thoracic cavity
What substances does the GI tract extract from ingested products?
chemical energy
vitamins, minerals & water
What are the six processes the GI performs on ingested products?
ingestion secretion motility mechanical digestion chemical digestion absorption elimination of waste
What are the four layers of the GI tract?
the inner mucosa
the sub mucosa
the muscularis externa
the outer serosa
What are the three layers of the mucosa?
inner epithelial layer
lamina propria
muscularis mucosae
What cells does the lamina propria contain in the gut?
lymphatic cells
are associated with lymphoid tissue
What layer is on top of the inner epithelial layer of the mucosa?
the lamina propria layer of connective tissue
What is a benefit of having lymphatic cells in the lamina propria of the gut?
the cells have immune function
act as an additional protective barrier against pathogenic species which may cross from the gut lumen into the mucosal layer
What structures does the sub mucosa layer contain?
blood vessels
lymphatic supply to the gut wall
the sub mucosal nerve plexus
Which muscle types are in the the muscularis externa layer?
inner circular muscle
outer longitudinal muscle
What lies in between the inner circular muscle and the outer longitudinal muscle of the muscularis externa layer?
the myenteric nerve plexus
What is the layer of the GI tract that comes after the muscularis externa layer?
the outer serosa layer
What material is the oesophagus made up of?
flat epithelium
What structures are in the inner surface of the stomach and in the inner SI surface?
stomach - gastric pits
SI - villi and mv
What does the LI contain?
gut microbiota
What is the motility within the GI tract mainly governed by?
the contraction of smooth muscle - involuntary control
Which areas of the GI tract is instead governed by the voluntary contraction of striated skeletal muscle?
the upper oesophagus
the external anal sphincter
What is a single-unit smooth muscle cell innervated by?
an autonomic nerve fiber
How do muscle cells work as a syncytium?
the single-unit smooth muscle cells connected to eachother by gap junctions
this allows for the electrical coupling of the cells
so the contraction can occur in peristaltic waves
the cells contract as a functional syncytium
What is the enteric NS responsible for?
controlling gut motility
controlling secretion
What does the enteric NS give the gut the ability to do?
gives the gut the ability to contract completely independently of external neurostimulation
What does the enteric NS consist of?
two interconnected plexuses in gut wall
What are the two types interconnected plexuses in gut wall?
Myenteric plexus
Submucosal plexus
What type of innervation allows for the external modification of autonomous motility and secretion occur?
extrinsic autonomic sympathetic innvervation
parasympathetic innervation
Which local stimuli might cause the intrinsic enteric NS to undergo reflexive contraction?
stretch
nutrients
irritation
hormones
What is the Myenteric plexus primarily responsible for?
motility
What is the Submucosal plexus primarily responsible for?
secretion
local blood flow
What is the basic activity of the enteric NS controlled centrally by?
the autonomic NS
How does the autonomic NS supply the GI tract?
sympathetic and parasympathetic pathways
What is the effect of parasympathetic innervation on the GI tract?
it is excitatory to motility and secretion
rest and digest - promotes digestion
What part of the GI tract is innervated by the vagus nerve?
spans from the anterior part of the GI tract up until the transverse colon
What part of the GI tract is under sacral parasympathetic innervation?
the parts of the GI tract beyond the transverse colon
What is the effect of sympathetic innervation on the GI tract?
it is inhibitory to motility and secretion
promotes fight or flight portion
represses mechanisms that promote digestion
What two main types of mechanisms are responsible for regulating GI motility?
neural mechanisms
endocrine hormones
Where are endocrine hormones secreted from?
endocrine cells in the epithelial layer of the GI mucosa
What is the pathway of endocrine hormones to access the GI tract?
they leave the endocrine cells in the GI mucosa
they enter the portal blood circulation
they come back round through the vasculature
What is cholecystokinin released by?
I cells of the SI
What is the effect of cholecystokinin?
it is inhibitory to gastric emptying
allows the deudenum to deal with the contents that are currently present in the lumen
stimulates the digestion of fat and protein
How does cholecystokinin inhibit gastric emptying?
it causes gallbladder contraction
it causes the growth of exocrine pancreas and thereby stimulates the secretion of pancreatic enzymes for digestion
What is motilin released by?
M cells of the duodenum and jejunum
What is the effect of motilin?
it promotes gastric and intestinal motility
What are the two different types of electrical activity in excitable smooth muscle cells?
Slow waves and Spike potentials
When are spike potentials generated?
once the threshold is reached
causes an influx of Ca2+ influx
smooth muscle contracts
What is the function of slow waves?
they provide a basic electrical rhythm via interaction with the Interstitial Cells of Cajal
In waves/min, what is the basic electrical rhythm responsible smooth muscle contraction stimulation?
3 - 12 waves/min
In terms of slow waves and spike potentials, what will and won’t lead to a contraction?
slow - doesn’t in itself lead to contraction
spike - causes contraction by further depolarisation to threshold levels towards a more +ve membrane pt
What happens when successful spike potentials occur?
receptors on the smooth muscle cell are stimulated
What can stimulate smooth muscle cell receptors after a spike potential? (MADD)
endocrine hormones (Motilin) excitatory NTs (Acetylcholine) stretch from GI lumen contents (e.g. Duodenal Distension)
Through which methods can smooth muscle contraction be inhibited?
symp stimulation - norepinephrine
hormones - secretin
inhibitory enteric NS
How is smooth muscle contraction inhibited?
via hyperpolarization - it makes the membrane pt more -ve rather than less -ve
so it’s harder to reach the threshold pt and for an actpt to occur
What are the two main categories of contraction that occur in the GI tract?
segmentation
peristalsis
What happens during segmentation contraction in the GI tract?
there are bursts of circular muscle contraction and relaxation which pushes the contents back and forth over a short short distances in a pendulum movement allows mixing to occur
What is the effect of segmentation contraction in the GI tract?
it allows the mixing the contents of the lumen
What is the effect of peristalsis in the GI tract?
it allows the propulsion of the contents of the lumen
What happens during peristalsis contraction in the GI tract?
local distention triggers contraction behind the bolus within the GI lumen and relaxation of the muscle in front
causes a wave of contraction to ripple along the gut
What regulates peristalsis?
the functional myenteric plexus
What does the law of the intestines state?
that peristalsis can only move food along the GI tract aborally
What is Hirschsprung’s disease caused by?
the myenteric plexus is missing from the distal portion of the colon
What happens in Hirschsprung’s disease?
the pathologic aganglionic section of colon lacks peristalsis
it undergoes continuous spasm
leads to functional obstruction and severe constipation
How is Hirschsprung’s disease treated?
surgery is performedto bypass the part of the colon that’s lacking nerve cells
What are the three stages of deglutition?
Oral
Pharyngeal
Oesophageal
What happens during the oral stage of deglutition?
voluntary initiation of swallowing in the oral cavity
What happens during the pharyngeal stage of deglutition?
involuntary passage of food through pharynx into oesophagus
What happens during the oesophageal stage of deglutition?
involuntary passage of food from pharynx to stomach
What is the oesophagus lined by?
protective, stratified squamous epithelium
What type of muscle is in the muscularis layer of the upper part of the oesophagus?
striated skeletal muscle
What is the oral phase of swallowing regulated by?
voluntary control
How does the oral stage of deglutition occur?
the tongue pushes up and against the hard palate
it contracts to force lubricated bolus into the pharynx
this initiates the pharyngeal stage swallowing through stimulation of sensory receptors
What are the three sections of the pharynx?
oropharynx
nasopharynx
larygopharynx
Which three nerves are involved in the pharyngeal stage of deglutition?
CN V - trigeminal
CN IX - glossopharyngeal
CN X - vagal
What happens to the soft palette during the pharyngeal stage of deglutition?
it is elevated over the posterior nares to close nasal pharynx
How is the bolus moved from the orpharynx into the oesophagus in the pharyngeal stage of deglutition?
the presence of the bolus in the oropharynx signals the swallowing centre in the brain
motor efferents in three nerves (CN V, IX & X) cause a series of muscle contractions, moving the bolus through the oropharynx into laryngopharynx and into oesophagus
What happens to the epiglottis during the pharyngeal stage of deglutition?
is shuts to close the larynx
What happens to the upper oeophageal sphincter during the pharyngeal stage of deglutition?
it relaxes
What happens to respiration during the pharyngeal stage of deglutition?
it is inhibited
What happens during the oesophageal phase of deglutition?
ther is a slower primary peristaltic wave that moves the bolus downwards towards the stomach
What muscle types are involved in the oesophageal phase of deglutition and how?
circular muscle contraction behind the bolus
longitudinal muscle contracts in front to shorten the fibres and to push the wall outwards
What substance is secreted in the lower oesophageal area during the oesophageal phase of deglutition?
mucus IOT lubricate and reduce friction
What structures relax during the oesophageal phase of deglutition and why?
the lower oesophagus and the lower oesophageal sphincter
IOT allow the bolus to move into the stomach
What will happen if the 1o peristaltic wave isn’t successful in moving the bolus into the stomach?
a 2o peristaltic wave will be stimulated by stretch within the oesophagus
What innervation is responsible for the co-ordination behind swallowing?
intrinsic - myenteric innervation
extrinsic - vagal innervation
What happens during achalasia?
the lower esophagus sphincter muscle fails to relax causing food to remain in the oesophagus
What are the harmful effects of achalasia? (DUI.i - driving under influence idiot)
distention
ulceration
inflammation
infection
Which two conditions are caused by a problem with oesophageal motility?
gastro-oesophageal reflux
achalasia
How does gastro-oesophageal reflux occur?
the lower oesophageal sphincter loses its tone
AAR the acidic gastric contents flow into the oesophagus
What might gastro-oesophageal reflux be linked to?
hiatus hernia
What are the harmful effects of gastro-oesophageal reflux?
inflammation
ulceration
What anatomical defects could cause achalasia?
anatomical defects of the vagal or myenteric nerves
What can hiatus hernia cause?
gastric reflux
What happens during a hiatus hernia?
a portion of the stomach protrudes through diaphragm into thorax
What are the five regions of the stomach?
cardia fundus main body antrum pylorus
How is the stomach adapted to motility?
a third inner oblique muscle layer
rugal folds
When do rugal folds appear and disappear?
appear - when the stomach is empty / contracted
disappear - when stomach is full
What is the role of rugal folds?
they allow the stomach to stretch out
What are the three primary functions of the stomach?
to act as a reservoir for boluses
mixing process
emptying process
How is the stomach allowed to store boluses?
via the vagovagal reflex
What is the function of the vagovagal reflex?
it allows the reservoir function in the stomach so that it can store boluses
it mediates receptive relaxation in which the muscle tone in the stomach relaxes
What happens during the process of mixing in the stomach?
slow peristaltic waves
leads to the fragmentation of food
which is mixed with secreted gastric juice for digestion
What happens during the process of emptying in the stomach?
slow release of contents into the duodenum at a controlled rate
What is the primary function of the fundus?
as a reservoir
it stretches out IOT accommodate the contents from the oesophagus
How does food get ready to leave the stomach?
grinding - mixing of contents in the body of the stomach
propulsion - stomach contents are propelled towards the pyloric antrum and towards the pyloric sphincter
retropulsion - it is then forced back for further mixing and digestion
repeats - this process continues over time
chyme - until chyme is produced, ready for expulsion from the stomach
What is gastric emptying regulated by?
hormonal
neuronal (enteric NS & parasymp ANS)
How does gastric emptying occur?
peristaltic contractions increase in strength to force contents through the pyloric sphincter and out into the jejunum
the jejunum starts to secrete regulatory hormones as a way of providing regulatory feedback
initiates segmental mixing
What is the effect of hormones such as motilin on gastric emptying?
cause further excitation and gastric emptying
What can inhibitatory gastric emptying be stimulated by?
ANS - sympathetic
duodenal enterogastric reflexes
jejunal hormones
What is the process by which enterogastric reflexes occur?
parasympathetic impulses are sent to the stomach
they inhibit peristaltic waves
inhibits the gastric emptying function
What are enterogastric reflexes triggered by?
duodenal distension
What are examples of hormones from the jujenum that inhibit gastric emptying?
CCK
secretin
What type of cells produce endocrine hormones that slow gastric emptying?
S cells - secretin
K cells - GIP & CCK
I cells - CCK
What factors makes duodenal receptors aware that gastric chyme has entered?
increased acidity
increased levels of fat digestion products
changes in the osmotic potential of the duodenum
What happens to the rate of gastric emptying when physiological changes are detected in the duodenum?
triggers receptors within the duodenal wall
activates short reflexes by the enteric NS
decreases the rate of gastric emptying
What receptors are present in the duodenal wall? (MOC)
mechanoreceptors
osmorereceptors
chemoreceptors
What are two examples of gastric motility dysfunctions?
dumping syndrome
gastroparesis
What might dumping syndrome be caused by physiologically?
hypertonic duodenal contents causing rapid entrance of fluid into the duodenal lumen
What might dumping syndrome be associated with?
the ingestion of a large meal for patients who’ve had a gastrectomy
What symptoms are associated with dumping syndrome?
nausea, cramps
pallor, sweating
vertigo, fainting
When does gastroparesis occur?
when the stomach fails to empty properly
prevents proper digestion
What symptoms are associated with gastroparesis?
bloating and nausea
What conditions might cause gastroparesis?
gastric cancer
peptic ulcers
When might gastroparesis be observed in severely diabetic patients?
impaired vagal stimulation to the stomach, will develop autonomic neuropathy
Where does the majority of digestion and absorption of nutrients occur and for how long?
in the SI over a period of 3 - 5 hrs
What structures give the SI a large SA?
plicae circulares
villi
‘brush border’ microvilli
What are the two types of motility that occur in the SI?
mixing & circulation
propulsive peristalsis
What does mixing & circulation motility allow for?
the maximum exposure and circulation of digesting products for absorption via epithelial cells
What is motility in the SI controlled by?
intrinsic motor patterns modified by hormonal and ANS neural stimuli
How does mixing occur in the SI?
chyme leaves the stomach enters the SI stretch receptors respond to its presence triggers myenteric innervation causes muscle contraction - segmentation
What is the effect of segmentation in the SI?
mixing and churning of chyme
it doesn’t cause peristaltic movement
What does GoldSIMCard stand for?
Serotonin, Insulin, Motilin
CCK, Gastrin
What do the substances listed in GoldSIMCard have in common?
they’re all propulsive peristalsis causing hormones (excitative, SI)
What are examples of inhibitory hormones from the SI that reduce propulsive peristalsis?
secretin and glucagon
What are the three propulsive peristaltic reflexes?
Gastroenteric reflex
Gastroileal reflex
Migrating motor complex
When do migrating motor complexes occur?
in between meals
How often do migrating motor complexes occur?
every 90 mins - sweeps SI contents into the LI
What are gastroenteric and gastroileal reflexes triggered by?
gastric distention of the gastric wall
What is the effect of gastric distention in a gastroenteric reflex?
the myenteric plexus is activated to promote SI peristalsis
What is the effect of gastric distention in a gastroileal reflex?
distension promotes peristalsis in the ileum to force chyme through ileocecal valve into caecum
What are migrating motor complexes regulated by?
Intrinsic enteric control
motilin hormone
What can happen if migrating motor complexes don’t occur?
bacterial overgrowth in the SI
What is the role of the iIleocecal valve?
prevents backflow contents from the colon back into the SI
responds to pressure to relax the sphincter
promotes peristalsis through the SI into the LI
What causes a peristaltic rush?
mucosal irritation
it stimulates the ENS and ANS neural reflexes
they rapidly sweep contents of SI into colon
What causes paralytic ileus?
a loss of peristalsis following mechanical trauma
When might paralytic ileus occur?
after surgery
What structures cause vomiting?
SI receptors
two brain centres (VC, CTZ)
What type of receptors in the distal SI are triggered that then cause vomiting ?
chemical sensory receptors
How can the brain cause vomiting?
the vomiting centre in the brain causes reverse peristalsis to expel intestinal and gastric contents
Why is motility in the LI more sluggish?
allows for sufficient water and electrolyte absorption
allows for the formation and storage of faeces
Where does water and electrolyte absorption occur?
the proximal portion of the LI
Where does the formation and storage of faeces occur?
the distal portion of the LI
What type of bacteria does the LI contain?
commensal microbiota
Why are the commensal microbiota in the LI beneficial?
they aid digestion
they synthesise vitamins B and K
What are the structural adapatations of the LI?
the formation of the muscularis into the taenia coli
What does the taniae coli do?
it tonically contracts to form haustral bulges
How often do mass movements of peristalsis occur?
2-3x per day
What is the effect of forceful peristaltic contractions?
they force LI contents into sigmoid colon and rectum
What are the two types of reflexes in the LI responsible for mass movements of peristalsis?
the gastro-colic reflex
the duodeno-colic reflex
What are the two types of peristalsis that occur in the LI?
slow waves of peristalsis
mass movements of peristalsis
What are the reflexes responsible for mass movements of peristalsis triggered by?
stretch in the stomach and duodenal walls via the ANS
What substances does faeces contain the residues of?
digestion
bacteria
bile pigment
mucosal debris
What is the defaecation reflex initiated by?
when mass movements push faecal matter into the normally empty rectum
What happens once faecal matter enters the rectum?
the afferent nerve fibres are stimulated by stretch receptors
they activate the enteric NS and parasympathetic ANS
What happens once the defaecation reflex is triggered?
the longitudinal muscle in the rectum involuntary contracts
opening the internal anal sphincter
the constricted external anal sphincter is voluntarily relaxed to allow defecation
How does the constricted external anal sphincter voluntarily relax?
via the skeletal motor neuron innervation
What are the nerves of the submucosal plexus derived from?
the myenteric plexus
What are the nerves of the myenteric plexus derived from?
the plexuses of parasymp nerves around the superior mesenteric artery
What do slow waves involve?
cyclical oscillations of membrane pt
What are the two 1o lymphoid tissues?
bone marrow and thymus
What are the three examples of 2o lymphoid tissues?
lymph nodes, spleen, tonsils
Why are they called inclusion cells?
bc they are abnormal fibroblasts with lots of dark inclusions in the central area of the cytoplasm
What is the role M cells have in immunity?
they transport antigens from the GI lumen to immune cells, thereby initiating an immune response or tolerance.
Where are M cells located?
lymphoid tissues in the mucosa
What are the three extrinsic reflexes that can occur in the GI tract? (ICE)
gastroileal, gastroColic and Enterogastric
What are two pancreatic proteases?
trypsin and chymotrypsin
What four digestive enzymes are produced by the exocrine pancreas?
lipase, amylase, chymotrypsin, trypsin
What is the pH of chyme in the duodenum (emerging from the stomach)?
~pH2
What does the duodenum do in response to acidic chyme entering from the stomach?
secretes CCK < gallbladder contraction < alkaline bile released into the duodenum
What is the difference between the basolateral and apical membranes?
baso - the membrane away from the lumen and close to the serosa (external tubing)
apical - the membrane lining the lumen and away from the serosa
What is the difference between trypsin and chymotrypsin?
they hydrolyse bonds on different parts of the proteins they’re lysing
What cells release gastrin and where?
G cells in the pyloric antrum of the stomach, duodenum, and the pancreas
