6. Motility In The GI Tract Flashcards
How many phases are there in swallowing?
3
Is the oral phase of swallowing voluntary or involuntary?
Voluntary
What cranial nerve is most important in the oral phase of swallowing?
Hypoglossal (12th cranial nerve)
What is the function of the hypoglossal nerve in swallowing?
Oral phase
Provides key motor innervation to the tongue and many of the suprahyoid muscles that stabilise lower jaw
Supports preparation, formation, positioning and transport for the food bolts ready to swallow
What receptors lead to the swallowing reflex when activated?
Tactile receptors
Where are the tactile receptors located?
Pharynx
What is the function of tactile receptors?
Activate afferent nerves which signal to the brainstem
What are the key nerves involved in the pharyngeal phase of swallowing?
Glossopharyngeal nerve (9th)
Pharyngeal branches of the vagus (10th)
What happens to the soft palate, the epiglottis, the pharynx, and the upper oesophageal sphincter during the pharyngeal phase?
Soft palate rises
Epiglottis closes
Pharynx contracts
Upper oesophageal sphincter relaxes
What happens to the upper oesophageal sphincter, the bolus, and the lower oesophageal sphincter during the oesophageal phase?
Upper oesophageal sphincter contracts
Bolus is moved
Lower oesophageal sphincter relaxes
What nerves are involved in the oesophageal phase of swallowing?
Glossopharyngeal (9th)
Vagus (10th)
What is primary peristalsis?
Upper oesophageal sphincter to lower oesophageal sphincter wave of contraction
Gradient of striated to smooth muscle
When does secondary peristalsis occur?
When there is a blockage
What is the function of reflex opening and closing of lower oesophageal sphincter and the crural diaphragm?
Reflex opening - food to enter stomach
Reflex closing - prevents gastric content refluxing
How does food enter the stomach?
Bolus creates pressure and distension of muscle at bottom of Oesophagus
Stimulates vagal afferent fibres that send signals to the brain stem
Relays signals back to the lower oesophageal sphincter via vagal efferent nerves and to the diaphragm by acetylcholine in efferent phrenic nerves
What happens in the corpus region of the stomach when food first arrives?
Relaxes to accommodate the meal
What is the second response of the stomach when food arrives?
Fundus - pacemaker zone
Initiates peristaltic contractions that moves down the body of the stomach increasing in frequency and amplitude towards the antrum
Retropulsion occurs
What is the name of the process where grinded food is sent back up into the main body of the stomach by the antrum?
Retropulsion
What part of the stomach that controls entry from stomach to the small intestine?
Pyloric sphincter
Define gastric emptying
Process by which the contents of the stomach (chyme) are moved into the duodenum
What are the 4 mechanisms that help accomplish gastric emptying?
Peristaltic waves
Systolic contractions of the antrum
Reduction in size of the stomach
Reflex relaxation of the pyloric sphincter
What types of meals delay gastric emptying?
Fat rich
Carb rich
Hypertonic
Acidic
High viscosity
Indigestible
What structure is the rate of emptying controlled by?
Duodenum
What hormones are released in response to the duodenum receiving food that feedback to gastric emptying?
Cholecystikinin CCK - duodenum
GLP1 - ileum
Peptide YY - ileum
What are the pacemakers of the gut?
Interstitial cells of cajal
What is the migrating myoelectric complex MMC?
Pattern of electrical activity in the GI tract during fasting - stops when a new meal is eaten
What cells secrete HCl?
Parietal cells
What cells secrete pepsinogen?
Chief cells
What do G cells secrete?
Gastrin
What does submucosal plexus do in the stomach?
Regulates gastric secretions and controls blood flow to stomach
How does distention by a bolus cause intestinal movement - peristaltic movement?
Distention reflex activates neurones in gut wall that release serotonin (5-HT)
Connects to neurones both behind and infront of the bolus
Behind - ascending contraction orad [towards the mouth]
In front - descending relaxation caudal [towards the tail]
What is the name of the process of alternate contraction and relaxation of adjacent segments that causes thorough mixing of food contents in the intestines?
Segmentation
Which has stronger peristaltic waves?
The small or large intestine
Large
What is the function of segmentation in the large intestine?
Mixes indigestible matter
Helps microbial fermentation of dietary fibre
Facilitates fat and water absorption
Formation of stools
What is the defaecation reflex triggered by?
Distention of rectum by faeces or gas
What happens to rectum, internal anal spincter, pelvic floor muscles and external anal spincter during defaecation reflex?
Rectum contracts
IAS relaxes
Pelvic floor relaxes
EAS remains contracted
What nerve controls defaecation?
Pudenal nerve
