27 Propulsion and Mixing of Food Flashcards
What are the two muscular layers in the for every organ of the GI tract, and what do they do? What is the exception to this?
Inner circular – Contracts to decrease diameter
Outer longitudinal – Contracts to shorten segment
Exception: stomach
What are the two types of contractions and where might they occur?
phasic and tonic
what is the phasic contraction and where does it occur?
occur in the esophagus, gastric antrum and small intestine that contract and relax periodically
what is the tonic contraction and where does it occur?
occur in the lower esophageal sphincter, orad stomach, and ileocecal and internal anal sphincters
What is the first phase of consumption/digestion and what happens during it? Know that there are two halves, describe the first half of the first phase
First half of first phase is chewing
-Forms bolus
-Mixes food with saliva to lubricate and begin digestive process
▪ Saliva is hypotonic and alkalinic
-Chewing helps to break down large portions of food for swallowing and breaks open indigestible cellulose to obtain nutrients
-After saliva is mixed, it exposes food to the taste buds
what is the second half of the first phase?
swallowing
Transports food into the esophagus while protecting the airway and so this is Initiated voluntarily, but then relies on involuntary brainstem reflexes
what are the three phases in the second half of the first phase?
oral (voluntary)
pharyngeal (involuntary)
esophageal (involuntary)
describe the oral phase? what phase is this in?
Oral phase (voluntary) of the second half of the first phase
Food is propelled to pharynx
Swallowing reflex is initiated by sensors in pharynx
describe the pharyngeal phase? what phase is this in?
Pharyngeal phase (involuntary) of the second half of the first phase
Soft palate moves upward to protect nasal cavity
Epiglottis closes anterior to posterior to protect airway
Upper esophageal sphincter relaxes
Bolus travels into esophagus
Note: During this phase, respiration is inhibited
describe the esophageal phase? what phase is this in?
Esophageal phase (involuntary) of the second half of the first phase
Upper esophageal sphincter constricts
Swallowing initiates primary peristaltic wave
what is unique about the first of consumption/digestion?
This is the only phase in which the parasympathetic and sympathetic system work together, for the rest of digestion, parasympathetic has primary control. If there is sympathetic activity, it’ll mostly try to slow GI down.
What is the second phase of consumption/digestion and what happens during it?
The second phase involves the movement of food down the esophagus
T/F, The esophagus has both skeletal/striated muscle (upper 1/3) and smooth muscle (lower 2/3)
T
how much of the esophagus is skeletal/striated muscle and smooth muscle?
skeletal/striated muscle (upper 1/3) and smooth muscle (lower 2/3)
how many sphincters does the esophagus have?
two, upper and lower sphincter
what happens to the esophagus during swallowing?
Pharynx constricts
UES opens allowing for bolus to pass
LES and proximal stomach relax
what is the sequence of esophageal motility?
- Pharynx constricts
- UES opens allowing for bolus to pass
- LES and proximal stomach relax
- UES constricts
- Primary peristalsis: a progressive wave of distension and contraction passes through the esophageal body
- LES closes after bolus passes to proximal stomach
what is the transit time through the second phase of digestion and consumption?
~10 sec
Describe primary peristalsis? When does secondary peristalsis occur?
triggered when mechanoreceptors sense distension made by the bolus and so:
Signal travels in afferent fibers to the swallowing center (in the medulla)
Proximal to the bolus – Excitatory efferents cause contraction via acetylcholine (ACh)
Distal to bolus – Inhibitory efferents cause relaxation via nitric oxide
Result – Bolus travels forward
*If all food does not clear in primary peristalsis, secondary peristalsis occurs
T/F, peristalsis occurs the entire length of the esophagus and involves the vagus nerve and enteric nervous system?
T
what NT relaxes the LES?
VIP
What happens in Achalasia?
There is a loss of inhibitory neurons in the LES
-Results in LES being unable to open
Leads to build up of boli in esophagus
where does the third phase of digestion/consumption occur?
occurs in the stomach
what does the stomach consist of?
Stomach consists of four sections: fundus (very top), body (majority of the stomach), antrum (lower portion of the stomach right before pyloric valve), and pylorus
what is the main function of gastric motility?
The main function of gastric motility is to mix bolus with digestive juices, grind to smaller pieces (until chyme is created), and pass the chyme through the pyloric sphincter into the duodenum
how is gastric motility accomplished?
This is accomplished through tonic contraction in the proximal stomach (which is mediated by the vagus nerve/ACh)
▪ Relaxation (through vasovagal reflex) occurs in response to swallowing and distension of the proximal stomach
▪ Vasoactive intestinal peptide (VIP) is mediator for gastric relaxation
▪ Proximal portion of stomach is mostly used for storage
what is the distal stomach responsible for?
propulsion and retropulsion and so Chyme particles must be <2 mm in order to enter duodenum
which parts of the stomach are involved in gastric emptying?
All parts of the stomach are involved in gastric emptying
how does gastric emptying occur?
- Proximal tone increases (ACh), chyme moves distally
- Antral contractions become more forceful (ACh, gastrin) and open pylorus
- Several mL of chyme are propelled per contraction
- Residual food is emptied in the interdigestive period by the migrating motor complex
where does the fourth phase of consumption/digeston occur?
occurs in the small intestine
what are the three parts of the small intestine?
Duodenum, jejunum, and ileum with highest frequency slow waves in the duodenum
what are the three type of motility?
Segmentation contraction
Peristaltic contraction
Migrating motor complex