Chapter 63 - Guyton Flashcards
Two reasons why mastication is essential to digestion.
exposes more food particles to digestive enzymes and eases the work of the GI tract by breaking food down into smaller portions
Three stages of swallowing.
1) voluntary stage that initiates swallowing; 2) pharyngeal stage - involuntary and food passes from pharynx to esophagus; 3) esophageal stage - involuntary and food passes from pharynx to stomach
What is the chewing reflex?
bolus of food in the mouth initiates reflex inhibition of the muscles of mastication–>jaw drops–>stretch reflex of the jaw muscles that leads
to rebound contraction–>compresses the bolus again against the linings of the mouth–>inhibition again and repeat process
Pharyngeal stage of swallowing.
1) tactile stimulation by food in pharynx
2) soft palate pulled upward
3) palatopharyngeal folds pulled together
4) trachea is closed (respiration inhibited) - vocal cords approximated and larynx raises, epiglottis covers larynx
5) relaxation of upper esophageal sphincter
6) peristaltic contraction of pharynx
Nervous initiation of the pharyngeal stage of swallowing.
sensory input from pharynx and esophagus (CN V and IX); motor impulses from the swallowing center to the pharynx and upper esophagus that cause swallowing are transmitted by the 5th, 9th, 10th,
and 12th cranial nerves and even a few of the superior cervical nerves; pharyngeal stage of swallowing is principally a reflex act (swallowing center in the medulla)
How does the pharyngeal stage of swallowing affect breathing?
swallowing center specifically inhibits the respiratory center of the medulla
Primary peristalsis
continuation of pharyngeal peristalsis, coordinated by swallowing center, cannot occur after vagotomy (striated muscle)
Secondary peristalsis
results from distention of the esophagus, initiated
partly by intrinsic neural circuits in the myenteric nervous system and partly by reflexes that begin in the pharynx (CN X), can occur after vagotomy (smooth muscle)
What is the difference in musculature between the upper and lower esophagus?
upper 1/3 is striated muscle (controlled by CN IX and X) and lower 2/3 is smooth muscle (CN X but strongly by myenteric plexus)
What is receptive relaxation of the stomach?
ahead of the peristaltic wave, the stomach and even the duodenum will relax to accommodate food, vagal inhibitory effect through vasoactive intestinal peptide (VIP) neurotransmitter
What is the primary reasoning for the tonic contraction of the lower esophageal (gastroesophageal) sphincter?
prevent significant reflux of stomach acid into the esophagus
Why are the resting pressures high at the upper and lower esophageal sphincters?
UES - prevent air from entering esophagus; LES - prevent stomach contents from entering esophagus
Why are individuals particularly susceptible to aspiration following a CVA or cranial nerve damage?
UES and pharyngeal contractions are not coordinated (secondary peristalsis is still functional)
Achalasia
LES does not receptively relax to allow food to enter stomach, organized peristaltic contractions are absent, megaesophagus can develop, esophageal ulcers, rupture, and death can occur, can result from neurological problem with ENS - myenteric plexus
Orad portion of the stomach.
first 2/3 of the body
Caudad portion of the stomach.
last 1/3 of the body and the antrum
The mixture of food that passes into the gut is known as?
chyme
Explain gastric motility in different regions of the stomach.
orad area - receptive relaxation to accommodate food (vagovagal reflex - VIP is neurotransmitter)
caudad area - retropulsion to mix food with gastric juices, antral pump propels chyme into duodenum
Signals from where primarily dictate the rate of stomach emptying?
duodenum
Gastrin _________ stomach emptying.
increases
Stretching of the stomach wall does elicit local myenteric reflexes in the wall that greatly accentuate activity of the pyloric pump and at the same time _______ the pylorus.
inhibit
Factors that initiate enterogastric inhibitory reflexes:
- The degree of distention of the duodenum
- The presence of any degree of irritation of the
duodenal mucosa - The degree of acidity of the duodenal chyme
- The degree of osmolality of the chyme
- The presence of certain breakdown products in
the chyme, especially breakdown products of
proteins and fats
CCK ________ stomach emptying.
decreases
Gastroenteric reflex
stretching of the stomach walls increases peristaltic activity of the small intestine (myenteric plexus)
Gastroileal reflex
stretching of the stomach walls intensifies peristalsis in the ileum, and emptying of ileal contents into the cecum
Longitudinal muscle of the colon.
teniae coli
Appearance of mass movements after meals is facilitated by __________ and ____________ reflexes. These reflexes result from distention of
the stomach and duodenum. (autonomic nervous system)
gastrocolic; duodenocolic
The external anal sphincter is controlled by nerve fibers in the _________ nerve, which is part of the somatic nervous system and therefore is under voluntary control.
pudendal
Defecation reflexes.
intrinsic reflex mediated by myenteric plexus causes movements and relaxes internal anal sphincter (weak), parasympathetic defecation reflex that involves sacral segments of the spinal cord (stronger), conscious efforts to take a deep breath and contract abdominals (relax external anal sphincter)
Enterogastric reflex ________ motility.
decreases
The peritoneointestinal reflex (peritoneum), renointestinal reflex (kidney), and vesicointestinal reflex (bladder) ________ intestinal activity as a result of an irritation.
inhibit
