Motility of the GI tract Flashcards
What are the 4 physiological processes the GI tract is involved in?
Motility
Secretion
Digestion
Absorption
Name some accessory glands in the GI tract
Salivary
Gall bladder
Pancreas
Liver
What are sphincters?
Made of smooth muscle
Separate parts of the GI tract from one another
Act as a valve of a reservoir
What is the common cause of most GI motility disorders?
Dysfunction of sphincters
Why is movement controlled along the gut?
Gut is an integrated system of different compartments
Food must be delivered at the appropriate time
Food must be delivered in the appropriate composition
Food must stay in the different compartments for the appropriate duration
Time and digestion are key components of this
What are the layers of the gut wall?
Mucosa
Submucosa
Muscularis externa
Serosa
Describe the structure of the mucosa
Epithelial layer
Lamina propria
Muscularis mucosa
Describe the structure of the submucosa
loose CT, large BVs, lymphatic vessels
Glands in some GI regions
Submucosal nerve plexus - Meissners plexus - regulates blood flow and secretion
Describe the structure of the muscularis externa
Thick muscle whose contraction contributes to major gut motility (segmentation and peristalsis)
Two substantial layers of smooth muscle cells: Inner Circular and outer longitudinal layer.
Myenteric nerve plexus
Describe the structure of the serosa
Connective tissue and connects to the abdominal wall, supporting Gi tract in the abdominal cavity. Several major structures enter through the serosa, including blood vessels, extrinsic nerves, and the ducts of the large accessory exocrine glands.
What is the intrinsic pathway of GI innervation?
The enteric nervous system
What is the extrinsic pathway of GI innervation?
The gut brain axis
What effect does parasympathetic control have on the GI tract?
Increases
What effect does sympathetic control have on the GI tract?
Decreases
When are spike potentials stimulated?
When slow waves reach a threshold
When are spike potentials stimulated?
When slow waves reach a threshold
Ca2+ channels open and allow entry into the smooth muscle cell. This triggers muscle contraction
What is the major function of the basic electrical rhythm?
Determine whether contraction can occur
The strength of contraction depends on…
The number of spikes
What does epinephrine do?
Inhibits muscle contraction
What neurotransmitter stimulates muscle contraction of the gut?
Acetylcholine
List the 3 types of gut motility
Segmentation
Tonic contraction
Peristalsis
What is migrating motor complex?
Pattern of motility that occurs about every 90 minutes between meals
Sweeps the stomach and small intestine of indigestible materials
Prevents bacterial overgrowth of the upper intestine
Migrating motor complexes may decrease when? What may this cause?
In radiotherapy patients
Bacterial overgrowth
What is paralytic ileus?
Temporary cessation of gut motility that is most commonly caused by surgery
What is vomiting in terms of swallowing?
The reversal of the process
Name the 3 types of movement of the stomach
Receptive relaxation
Mixing
Emptying
Where are the pacemaker cells in the stomach located?
Longitudinal layer of the greater curvature
What is gastrin?
Hormone released in response to food in the stomach
What is the enteric nervous system?
Controls the elaborate processes of the GI tract to ensure overall function is met.
Involves many neurons in the GI tract walls and several hormones
Dysfunction is sphincters can lead to…
Many types of GI motility disorders including GERD, peptic ulcer disease and diarrhoea
Describe the epithelial layer of the mucosa
Exocrine (secrete mucus and digestive enzymes) and endocrine (secrete hormones) gland cells
Describe the lamina propria layer of the mucosa
small blood vessels(BVs), nerve fibers, lymphatic cells/tissue (GALT-gut associated lymphatic tissue) loose connective tissue(CT)
Give the two main functions of the gut associated lymphatic tissue
Secretes antibodies to specific food or bacterial antigens
Triggers immunological reactions against them leading to mucosal inflammation and damage
Activation in the GI immune system is involved in which diseases?
Inflammatory bowel diseases and coeliac disease
Describe the muscularis mucosa layer of the mucosa
thin layers smooth muscle
responsible for controlling mucosal blood flow and GI secretion
Give the effect of the intrinsic pathway
Increases gut motility
Secretion of digestive enzymes for absorption and digestion
Describe the gut brain axis
The link between the sensory and motor neurons of parasympathetic and sympathetic supply
Where are the intrinsic enteric neurons found?
In gut plexuses such as the submucosal (or Meissner’s plexus) and the myenteric (or Auerbach’s plexus)
What is the basic electrical rhythm?
Smooth muscle cells display pacemaker activity – resting membrane potentials close to threshold - slow spontaneous depolarisation initiates contraction.
How do excitatory transmitters work?
Excitatory transmitters often cause nonselective cation channels in the smooth muscle cells to open; the resting membrane potential is depolarized and more slow waves cross the threshold for the generation of a spike potential.
How do inhibitory transmitters work?
Inhibitory transmitters often act by opening the K+ channels in smooth muscle cells, hyperpolarizing the membrane potential and preventing the slow waves from reaching threshold.
Describe segmentation
Mainly small intestine, for mixing food with enzymes.
Closely spaced contractions of circular smooth followed by relaxation.
No net forward movement.
Describe peristalsis
Longitudinal smooth muscle contracts first, followed half way through its contraction by the circular muscle. Longitudinal relaxes during latter half of circular contraction …leads to a progressive wave. Distension of gut by food is trigger for peristalsis. Net effect – propel food along GI tract
What is paralytic ileus? State the signs and symptoms
Temporary cessation of gut motility caused by abdominal surgery or infection, inflammation, drugs and electrolyte abnormality. Signs and symptoms include nausea, abdominal distention, absent bowel sounds and vomiting.
Upon swallowing what occurs in the oesophagus?
The upper oesophageal sphincter briefly relaxes, allowing the food bolus to pass into the esophagus. A contractile (peristaltic) wave sweeps down the oesophagus. The lower oesophageal sphincter and the proximal stomach relax to allow the bolus to enter the stomach
Does oesophageal muscle have pacemakers?
No- spontaneous contraction
What are the 3 functions of the stomach which define the motility of the stomach?
- Storage. Ingest food faster than can be digested, aided by receptive relaxation.
- Physical and chemical disruption - mixing.
- Deliver resultant chyme to intestine at optimal rate – gastric emptying
What regulates the mixing of the stomach?
Distension of stomach activates mechanoreceptors, ENS/extrinsic
Gastrin release in response to food in stomach also stimulates stomach motility
An increase in … causes antral contractions and opening of the sphincter as peristaltic waves approach
Chyme
Why is emptying of the stomach regulated?
To ensure optimal intestinal digestion
Describe the enterogastric reflex and its function
Inhibits emptying and consists of complex hormonal and neural signals. It stimulates pyloric contractions and also increases tone of pyloric sphincter to prevent emptying, thereby preventing the upper small intestine from being overwhelmed by material from the stomach.
Describe the hormonal pathway for gastric emptying
presence of fatty acids/monoglycerides in duodenum (not emulsified), Low pH –
stimulates release of hormones (e.g. Secretin, GIP (Gastric inhibitory Peptide), CCK Cholecystokinin
Describe the neural pathway for gastric emptying
Via ENS and/or extrinsic nerves from duodenum to stomach wall
What is dumping syndrome?
Rapid emptying of the stomach
Characterised by nausea, pallor, sweating, vertigo and syncope after eating
What is gastroparesis?
Impaired/absent ability of the stomach to empty
Prevents proper digestion
Patients complain of early satiety (feeling of being full), abnormal bloating, and nausea.
Present in severely diabetic patients who develop autonomic neuropathy
Describe the motility of the small intestine
Segmentation- multiple short contractions, frequency varies along a proximal to distal gradient. The decreasing gradient of BER frequency promotes the distal movement of intestinal chimes
Peristalsis- short contractions stimulated by both extrinsic and intrinsic factors
Villus movement- swaying and piston-like movements - to mix and to drain lymphatics of fat absorption
Describe intestinal blind loop syndrome
Impaired peristalsis in the small intestine leading to abnormally high levels of bacteria causing diarrhoea and streahorreoa
Describe the motility of the large intestine
Movements are slow and irregular
Mixing movements by segmentation or haustral shuffling
What is the main role of the motility of the large intestine?
squeeze and roll to expose fecal material for reabsorption of water and electrolytes, and secretion of mucus to lubricate for expulsion
Describe mass movement and gastric colic reflex of the large intestine
Mass movement occurs when segmental contraction of the left colon disappears and a simultaneous contraction of the right colon propels its content distally. Occurs several times a day but especially after meal – referred to Gastric colic reflex
How is mass movement linked to defecation?
Propels faeces into rectum and distends stretch receptors to provoke defecation reflex
Name the 2 sphincters which are normally contracted stating what type of control the body has on them
Internal anal sphincter - involuntary control
External anal sphincter - voluntary control – skeletal muscle
What does afferent stimulation do to the internal sphincter?
Leads to parasympathetic signal to relax internal sphincter
If voluntary relaxation of external sphincter does not occur via pudendal nerve…
Reverse peristalsis returns to colon