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99 Cards in this Set

  • Front
  • Back
Incisers are important for:
-How much weight can they bear?
Cutting - 50lbs
Molars important for:
-how much weight can they bear?
Grinding - 200 lbs
Mastication muscle innervation:
What controls chewing?
Brainstem nuclei
What 3 things is chewing vital for?
-Effective breakdown (cellulose)
-Enzymatic activity (surf area)
-Prevents GI tract excoriation
3 Stages of swallowing:
function of voluntary stage:
initiates swallowing
Function of pharyngeal stage:
Involuntary passage of food from the pharynx to esophagus
Function of Esophageal stage:
Involuntary passage of food from esophagus into stomach
What nerves control voluntary swallowing?
5, 9, 10
What nerves control involuntary swallowing?
Brainstem nuclei
What are the 5 steps that occur in the Pharyngeal stage?
1. Soft palate raise/close nares
2. Palatopharyngeal folds pull medially so only food that's chewed enough can pass thru slit
3. Epiglottis covers larynx
4. Larynx mvmt opens esophagus to allow fod entry
5. Pharynx muscle contracts to propel food into esophagus.
What sphincter must relax in order for pharyngeal swallowing to work?
upper esophageal sphincter
What gives the neural control of the pharyngeal stage?
CN's 5 & 9 transmit tactile sensations to STN in medulla
What areas of the brain control the pharyngeal stage of swallowing?
-Reticular substance in medulla and Lower pons - in brain stem
Motor nerves to the pharynx/upper esophagus:
5, 9, 10, 12
What is important during pharyngeal swallowing?
That it remain short in duration - <6 sec, so that it has minimal impact on ventilation.
How is skipping 1 breath per swallow achieved?
The swallowing center inhibits the respiratory center during this stage.
What 2 movements make up the Esophageal stage of swallowing?
1. Primary peristalsis - the wave begun at pharynx moves to stomach in 8-10 sec
2. Secondary peristalsis - moves leftover food in response to distention that activates NES circuits.
What is secondary peristalsis during esophageal swallowing?
The initiation of increase esophageal contraction caused by intrinsic neural circuits from myenteric NS via the Vagus to the Medulla
What nerves carry the impulse for secondary peristalsis to the medulla?
What type of muscle makes up the esophagus?
-Upper 1/3 = striated
-Lower 2/3 = smooth
What happens after food swallowing?
Food ingestion
3 phases of food ingestion:
1. Stomach receptive relaxation
2. Gastroesophageal sphincter relaxation
3. Esophageal valve opening
Receptive Relaxation of the Stomach:
-What is it
-What causes it
-What is its function
-A wave of relaxation preceding the peristaltic wave
-Cause by GIP - myenteric inhibitory neurons
-Prepares somach to recieve esophageal contents
Normal state of the gastroesophageal sphincter:
Constricted - to prevent reflux of somach contents into sensitive esophageal mucosa
What makes the gastroesophageal sphincter relax?
The peristaltic wave coming thru the esophagus
What is the result of failure of the esophageal sphincter to relax?
What is the Esophageal valve?
The portion of it just distal to the diaphragm; its tonic contraction prevents acid reflux.
What is the Cardia?
Opening of the stomach
What is the fundus?
Area above the cardia
What is the Orad?
Storage part of the stomach
What is the antrum?
The part of stomach right before the pylorus
3 motor functions of the stomach:
1. Storage
2. Mixture w/ secretions
3. Slow emptying of chyme at appropriate rate
How does the stomach allow for STORAGE? (neurally)
-Food enters
-Vasovagal reflex from stomach to brainstem and back
-Reduced wall tone
-Stomach Vol incr but Press low
What other structure in the body is the stomach similar to?
Veins - highly distensible; can increase vol a lot without increasing pressure
How does the stomach achieve mixing?
When it contains food its walls have weak mixing waves that start in the MIDDLE and move toward the ANTRUM.
What initiates the slow mixing movements of the stomach?
Slow waves via interstitial pacemaker cells
What is different about slow wave generated oscillations in the stomach?
-Peaks sufficient to cause excitation of SM w/out AP!
-Higher intensity as you go twrd antrum; forms peristaltic AP-driven constrictor rings.
Purpose of peristaltic AP-driven constrictor rings at antrum:
Drives food bolus to grind it at pylorus, then forces small amts through pyloric sphincter.
What happens as pyloric contractions force small amts through the sphincter?
Then the rest of it is forced back into the body of the stomach via RETROPULSION.
What is the result of stomach mixing?
CHYME - mixture of stomach secretions and food that moves down the gut.
What % of the mixing motions of the stomach are the strong peristaltic contrcactions?
ONly 20%
So what do we say promotes stomach emptying?
the Pyloric Pump
How does the Pyloric Sphincter function?
To be selective in what moves past it; fluid moves easily, but food must be reduced to chyme.
How is the rate of food passing from the stomach to duodenum controlled?
By controlling the degree of constriction of the pyloric sphincter - via nerves/hormones from both stomach and duodenum.
Which signals are more important in regulating stomach emptying?
Those from the duodenum
3 Factors that promote stomach emptying:
-Food volume
-Myenteric reflex - stim pyloric pump, inhibit pyloric sphincter
What activates the myenteric reflex to stim Pyloric Pumping?
Stretch of the stomach wall
What else does stomach stretch stimulate?
Release of Gastrin (also stimulated by contents of stomach)
Effects of Gastrin (2)
1. Mildly increased stomach motility
2. Enhanced pyloric pump
What are the simultaneous effects on the pyloric pump and sphincter when stomach emptying is stimulated?
-Pyloric pump enhances

-Pyloric sphincter inhibited (to relax)
What mainly inhibits gastric emptying?
DENR - Duodenal enterogastric nervous reflex
What does the enterogastric reflex say?
-I'm full mr. stomach
-Please don't empty, I can't take anymore!
Function of the DENR:
to prevent overfilling of the duodenum
What 3 types of nerves transmit the DENR reflex?
-Reflexes entirely within the ENS
-Extrinsic nerves to prevertebral ganglia
-Vagal visceral afferent
What are the effects of DENR?
-Inhibited Pyloric pump
-Stimulated pyloric sphincter
5 factors that activate DENR:
-Duodenal distention
-Duodenal mucosal irritation
-Duodenal chyme acidity
-Duodenal chyme osmolarity
-Presence of protein/fat brkdwn products
What pH in the duodenum will activate the DENR?
3 hormones that inhibit stomach emptying:
Stimulus for CCK
Stimulus for Secretin:
CCK stim is fat
Secretin stim is acid
Effect of CCK to inhibit stomach emptying:
Effect of Secretin to inhibit stomach emptying:
Increases acid in duodenum which is an overall inhibitor of GI motility
What is GIP's effect on gastric emptying?
A mild inhibitor.
Types of motor movements in the small intestine:
What do the mixing contractions look like?
A chain of sausages
Frequency of mixing contractions at terminal ileum:
Duodenum = 12/min
Ileum = 9/min
What blocks the mixing contractions in the small intestine?
Function of atropine:
Muscarinic receptor antagonist
How fast are the propulsive contractions in the small intestine? why?
VERY SLOW - to allow for absorption of nutrients in the small intestine.
How long does it take chyme to move from the pylorus to ileocecal valve?
~4 hrs
What happens to small intestine peristalsis when you eat? How?
It increases - via the stretch and gastroenteric reflexes.
What hormones increase intestinal motility? (4)
What 2 hormones inhibit intestinal motility?
What are the 2 functions of peristaltic waves in sm intestine?
1. Progression of contents
2. Spread chyme out to cover mucosa
What can cause peristaltic rush in the intestine?
Irritation and excess distention
What normally happens to chyme movement when it gets to the tonically closed ileocecal valve?
It stops until the next meal elicits gastroileal reflex to force chyme into cecum.
Function of gastroileal reflex:
forces chyme into cecum
Function of the ileocecal valve:
Prevents backflow of fecal contents into the small intestine
4 things that control the ileocecal sphincter:
1. Cecum distention
2. Cecum irritation
3. ANS
4. Eating
Effect of cecum distention on the ileocecal sphincter:
Increases tone
INhibits ileal peristalsis
What can cause Ilial paralysis and ileocecal sphincter spasms?
Excessive irritation of the cecum - appendicitis
What causes ileocecal sphincter opening after a meal?
The gastroileal reflex!!!
What happens to chyme in the 1st 1/2 of the colon?
-Absorption of H2O/electrolytes to form solid feces
What happens to feces in the distal 1/2?
Storage of fecal matter until defecation
How do colon movements compare to small intestine movements?
Slow and sluggish, but qualitatively similar.
2 types of movements in the colon:
-Haustrations (mixing)
-Propulsive Mass movements
What are haustrations?
Bulging of unstimulated regions that can remain for ~60s
Function of haustrations:
To move junk forward SLOWly - esp in cecum and ascnding colon.
Where do propulsive mass movements mainly occur?
From transverse to sigmoid colon
how many times per day do propulsive mass movements occur; how long do they last?
1-3; last 10-30 minutes
What reflexes facilitate propulsive mass movements?
(after a meal, caused by stomach and duodenal distention)
How is the rectum normally?
What fills the rectum?
Mass movements
What happens when the rectum is filled?
Initiation of defecation reflexes
What reflexes occur to allow defecation?
-Reflex contraction of rectum
-Reflex relaxation of sphincters
What type of control governs the internal sphincter? what type of muscle is it?
Autonomic - smooth muscle
What type of control governs the external sphincter? what type of muscle is it?
Voluntary - striated muscle
What nerve innervates the external sphincter?