Structure of GI tract & Motility Flashcards
What are the important structures of the alimentary canal?
(6)
- Mouth + oropharynx
- Oesophagus
- Stomach
- Small intestine
- Large intestine
- Rectum & Anus
What are the accessory structures of the alimentary canal? (3)
- Salivary glands
- Pancreas
- Liver & Gall bladder
What are the layers (inwards going out) of the digestive tract wall? (4)
- Mucosa
- Submucosa
- Muscularis externa
- Serosa
Main cells type found in mucosa?
Epithelial cells
Lamina propria
Main cells type found in Sub-mucosa?
Connective Tissue
Main cells type found in Muscularis externa?
Connective tissue. Consists of circular and longitudinal muscle layer.
Main cells type found in Serosa?
Connective tissue
What are the main smooth muscle layers involved in GI motility?
Circular muscle layer
Longitudinal muscle layer
muscularis Mucosa
What are the effects of Circular muscle contraction on Lumen?
Narrower & Longer
What are the effects of Longitudinal muscle contraction on Lumen?
Fatter & Shorter
What is the role of muscularis Mucosa?
change in secretory/ absorptive Area of Mucosa (folding).
What is the function of gap junctions in smooth muscle cells?
Allows electrical conduction between adjacent cells.
Smooth muscle- contracts as a unit
Are the waves of depolarisation in the stomach, small & large intestine Fast or Slow?
Slow.
Which cells are these slow electrical impulses driven by?
Interstitial cells of Cajal. Pacemaker cells of the GI tract.
Where are the interstitial cells of Cajal found?
Between circular and longitudinal muscle layer.
And in Submucosa
Why don’t all slow waves lead to smooth muscle contraction?
Not all of them reach the threshold for the AP.
What factors affect the slow wave impulse?
- Hormonal stimuli
- Neuronal stimuli
- Mechanical stimuli
What is the significance of the duodenum having a faster slow wave impulse than the terminal lieum?
Drives luminal contents in Aboral direction
What is the significance of the slow rate of the proximal colon being half of the distal colon?
Favours retention of luminal contents
Where are the neurones of the enteric nervous system located?
Ganglia of-
- Myenteric Plexus
- Sub-mucous plexus
Function of myenteric plexus?
Maintains motility and sphincter.
Function of sub mucous plexus?
Modulates epithelia and blood vessels
Is the Enteric nervous system an intrinsic or extrinsic stimulation?
Intrinsic. Found in GI tract.
How does the ENS coordinate muscular, secretive & absorptive activities?
- Sensory neurones
- Inter- neurones (Main ones. Coordinates reflexes & motor programme)
- Effector neurones
Where does parasympathetic innervation of the GI tract synapse?
Preganglionic fibres synapse with ganglionic cells at the ENS.
What are the excitatory effects of parasympathetic stimulation?
- Increased gastric, pancreatic
- ” small intestinal secretion
- ” SM contraction and blood flow
What are the inhibitory effects of parasympathetic stimulation?
Relaxation of
- Stomach
- Sphincter.
Where does sympathetic innervation synapse?
Preganglionic synapse at pre-vertebral ganglia
Post-ganglionic– synapse neurones in ENS
What is the excitatory effect of sympathetic stimulation
Increased sphincter tone
What is the inhibitory effect of sympathetic stimulation
Reduced motility, secretion and blood flow
Example of local Reflex in GI tract?
Peristalsis
Example of short reflex?
Intestino-intestinal inhibitory reflex
Example of long reflex?
Gastro-ileal reflex
What is peristalsis?
Wave of relaxation followed by contraction which travels in aboral direction.
What factor triggers peristalsis?
Distension of gut wall
How does distension cause peristalsis?
- Distension
- Sensory neurones activated
- Altered activity of motoneurons and interneurones.
- Either causes contraction or relaxation via circular or longitudinal SM.
What is segmentation?
Rhythmic contractions of Circular muscle layer that mixes and churns luminal contents.
What is colonic mass movement?
Sweeping contraction forces faeces into rectum
What is the migrating motor complex (MMC)
Powerful contraction stretching from stomach to terminal ileum
Where are tonic (sustained) contractions low and high pressure?
Low- organs w major storage functions
High- Sphincter
What are the major 6 Sphincters of the body?
- Upper Oesophageal
- Lower “
- Pyloric
- Ileocaecal valve
- Internal Anal
- External Anal
The above sphincters are generally composed of smooth muscle except?
Upper oesophageal sphincter. Composed of skeletal muscle.
What are the important structures of the mouth?(5)
- Lips
- Teeth
- Pallate
- Tongue
- Pharynx
What are the 3 phases of swallowing?
- Oral/ Voluntary
- Pharyngeal
- Oesophageal
What happens in oral phase?
Tongue pushes food upwards & Backwards into the pharynx.
- Mechanoreceptors stimulated
- Afferent nerve impulses via CN IX, X sent to pons & medulla.
- Efferent nerve impulses via CN VIII, IX, X, XI to laryngeal pharyngeal skeletal muscle.
What happens in the pharyngeal phase? (4)
Involuntary phase
- Epiglottis closes over larynx/trachea. Breathing is stopped
- Vocal folds closed.
- Soft palate flicks up to block access to nasopharynx..
- Tongue blocks off food from going back into oral cavity
What happens in the oesophageal phase?
Closure of the upper oesophageal Sphincter.
Primary peristalsis triggered
What happens if food remains in the oesophagus after this?
Second wave of contraction pushes them down.
Which nerves stimulate the process of swallowing? (3)
- Trigeminal
- Glossopharyngeal
- Vagus
