Motility of GI tract Flashcards
what are sphincters?
Smooth muscle, that hold luminal content adequately before emptying into next segment
What are the 4 layers of the gut wall
Mucosa
submucosa
Muscularis externa
Serosa
Describe the mucosa layers
Epithelial layer-endocrine-mucus
Lamina propria-VAN
GALT-Gut associated lymphoid tissue-
1-secretes antibiotics
2-Mucosa inflamm and damage
3-Provides permission of immunological tolerance
Muscularis mucosa- thin muscle that controls blood flow and GI secretion
Describe the submucosa
Large Blood vessels and lymphatics
Submucosal nerve plexus-regulates blood flow and secretion
describe the muscularis externa
Thick muscle-whose contractions contribute to major gut motility
2 substantial layers of smooth muscle cells
Serosa
Connective tissue & connects to abdominal wall supporting GI tract
GI innervation: what does the ENS do
Controls gut motility
innervates longitudinal and circular muscle
describe extrinsic pathway
t8-l2
preganglionic fibres
sympathetic activity inhibits gut motility and secretion and constics sphincters
Describe the intrinsic pathway
The Myenteric plexus-between circular and longitudinal muscle layers
What does the myenteric plexus innervate
Longitudinal muscles and outer lamella of circular muscles
What’s Hirschsprungs disease
Congenital absence of myeteric plexus-mainly in distal colon.
Resulting in spasms of large bowel-severe constipation
What is the BER-basic electrical rhythm/slow wave rhythm and where
Small intestine and distal stomach
Consists of spike potentials: Triggered if peak of slow wave depolarises membrane to threshold potential- opening of Ca2+ channels
it determines when contractions can occur
Force of contraction in sync with
Number of spikes within each wave = neural & hormonal input = 2 major types contractile responses : 1-segmentation and peristalsis
What are the 3 types of gut motility patterns
Segmentation
Tonic contraction
Peristalsis
What does segmentation do
Small intestine-mix chyme with enzymes and fragment bolus
No net forward movement
What does intestinal peristalsis do
Contraction of circular muscles behind bolus,
then contraction of longitudinal muscles in the middle of circular musces, ahead of bolus. Then contraction of circular muscles again hafway through when longitudinal muscles where contracting to force bolus forwards.
What triggers peristalsis
Distention of gut
what is MMC
Migrating motor complex
WHat rlly is mmc
Intervals of strong propulsive contractions, which pass down distal stomach & small intestine of indigestible materials.
What is the purpose of MMC
Prevents colonisation of upper intestine
Does MMC require External innervation
No its an intrinsic property
What is paralytic ileus ?
Temporary cessation of gut motility- caused by-abdominal surgery infection drugs Signs and symp include: Nausea, vomiting and absent bowel sounds
Movement along GI- what is another word for swallowing
Deglutition
Describe the process of swallowing
Bolus formed via mastication
propelled to pharynx as tongue moves up & down, against hard palate
Only the above is voluntary rest is autonomic
Bolus stimulates mechanoreceptors in pharynx
Efferent impulses from vagus -pharynx
Soft palate ecevates and sup constrictor of pharynx contracts to close off nasopharynx
Resp inhibited
Larynx rises so epiglottis covers trachea
Upper Esophagal sphincter relaxes and bolus enters
Peristalic wave initiated in pharynx
If insufficient, vago-vagal reflex triggers 2nd
OesophagL MOTILITY: WHAT 3 STEPS OCCUR
Upper oesophageal sphincter briefly relaxes allowing food bolus to pass into oesophagus
Contractile wave sweeps down
Lower esophageal sphincter & proximal stomach relax to allow bolus to enter stomach
What occurs in Gastro-Esophageal reflux disease
Heart burn
When Lower esophageal sphincter-LES is incompetent, allowing flow of corrosive gastric juices into oesophagus
What occurs when theres dysfunction in esophageal motiity
Achalasia- dysphagia, from failure of LES to relax: obstruction and Loss of peristalsis
what are the 3 functions and motility of stomach
Storage - Ingest food faster than can be digestsed aided by receptive relaxation
Physical and chemical disruption-mixing
Deliver resultant chyme to intestine @ optimal rate- gastric emptying
What regulates gastric peristalsis
Pace maker cells
in mid portion of greater curvature
Describe receptive relaxation:
increase in stomach pressure triggering dumping & reflux
1st is relaxation-increase in fibre length ;muscle tone same, therefore increase in size and without increase in intragastric pressure,
What is receptive relaxation mediated by
Vagus nerve
Describe Mixing
Peristalsis via strong coord control of 3 muscle layers
As spread distally, force and speed increase
therefore little chyme goes into the duodenum but sphincter only transiently open, so back pressure in distal region- retropulsion
How is the stomach motility regulated
1) distention- activates mechanoreceptors -extrinsic
2) gastrin release in response to food in stomach and therefore motility
Describe stomach emptying
Terminal part- Pyloric ontrum has thickened muscle layers
Pyloric sphincter controls exit
Increase in chyme: antral contractions & opening of sphincters
Liquid then solid, each time small amounts into duedenum
How do we control the emptying
1)small intestine has limited capacity- & only allows small amounts
2-via diff hormones to inhibit gastric emptying
3- Enterogastric reflex inhibits emptying & consists of complex hormonal and neuronal signals-stimulates pyloric contractions & increases tone of pyloric sphincter to prevent emptying
Control of stomach emptying -whats the hormonal pathway
Presence of fatty acids/ monoglycerides, in duodenum & low PH stimulates release of hormones:
1) secretin - cause pancreas to secrete bicarb- decrease acid
2) GTP CCK-increase satiety by releasing bile, inhibiting gastric emptying
3) Enterogastrone-stop production of gastrin and acid produced
What is the neural pathway of emptying
Via ENS- presence of acid /fat, digestion products and hypertonic solutions are detected by: Duodenal Mechano Chemo & osmo receptors This deceases sympathetic activity Increasing sympathetic activity or via ENS short reflex & fear anger depression...leads to change in gastric motor activity
What is dumping syndrome
a gastric motility dysfunction-rapid emptying of gastric contents into small intestine causing nausea Pallor
Fainting after meal of hypotonic solution
What is Gastroparesis
Impaired function of stomach to empty,
loss of vagal stimulation to stomach
abnormal bloating and nausea
In diabetics who develop neuropathy
Motility in small intestine: what are the 2 major functions
Segmentation: Mixing- Mutiple shrt contractions from proximal to distal ileum. Decreases BER frequency to promote distal movement
Peristalsis-propulsion -short range contractions
Small intestine Motility dysfunction describe 1
Intestinal blind loop syndrome:impaired small intestine peristalsis can lead to abnormally high levels of bacteria-diarrhoea
Motility in large intestine: describe
Slow and regular to increase contact with absorbing surface
What are the thick bands in large intestine muscles called
(3-muscles)- Taeha coli
What are haustrations
Segmental contractions of circular muscles that divide colon into segments
What occurs in the descending colon
Propulsive movement via peristalsis
What is mass movement
Segmental contraction of right colon disappears & a simultaneous contraction of whole right colon propels food forward -occurs after a meal & is gastric colic reflex
Rectum and defecation: what is main process
Mass movement
When the stretch receptors of the rectum are distended what 2 things occur
1-internal and external anal sphincter contract
internal involuntary but external voluntary
Is rectum controlled by afferent stim
Yes- via parasympathetic signal to relax sphincter
What happens if voluntary relaxation of external sphincter doesn’t occur via pudendal nerve
Reverse peristalsis occurs, driving faces back into colon
