GIT - Lecture 5 Flashcards
What is vomiting?
the emptying of the contents of the upper GIT
What does vomiting result from?
an increase in intraabdominal pressure
What increases intraabdominal pressure during vomiting?
the action of the diaphragm and the abdominal muscles
Is the GIT passive or active during vomiting?
passive
What happens to the proximal stomach and above before vomiting?
they relax
What happens to the upper duodenum and distal stomach before vomiting?
they contract
What happens to the diaphragm and the abdominal muscles during vomiting?
diaphragm: lowers
abdominal muscles: contract
During vomiting, the intraabdominal pressure overcomes ___.
LES
What is the vomiting centre near?
fourth ventricle
What activates the vomiting centre?
afferents
What can send afferents to the vomiting centre? (6)
Pharyngeal Stimulation
GIT or urogenital distension
Pain, cardiac ischemia
Biochemical disequilibrium
Vestibular Signals
Psychogenic Factors
What does the vomiting centre activate once it has activated?
efferents
What are the 4 efferent outputs of the vomiting centre?
- widespread autonomic discharge
- nausea
- retching
- emesis
Why do you feel cold/sweaty when you want to vomit?
because the efferents are involved in both the sympathetic and the parasympathetic system which are imbalanced
What do the efferents lead to in the parasympathetic and the sympathetic activities?
an imbalance
What actions precede and accompany vomiting?
sweating, vasoconstriction, salivation, alternating bradycardia, tachycardia
What does emesis do to the upper GI tract + pyloric antrum and duodenum?
upper GI tract: relaxation
pyloric antrum and duodenum: spasm
What does emesis do to the abdominal muscles and diaphragm?
contraction
What is the second region in the brain that can lead to vomiting?
chemoreceptor trigger zone
Is the chemoreceptor trigger zone inside or outside the blood-brain barrier?
outside
What can act on the chemoreceptor trigger zone within the medulla?
circulating emetic agents
Where does the CTZ send signals to?
the vomiting centre
Why is it important that the CTZ is outside the blood-brain barrier?
so that it can be activated by the circulating emetic agents
What are the 3 stages of vomiting?
- nausea
- retching
- emesis
What is nausea?
a psychic experience
What is retching?
abrupt, uncoordinated respiratory movements with glottis closed
What is emesis?
actual expulsion of contents of upper GIT
What is the process of vomiting?
the individual takes a deep breath, glottis closes, abdominal
muscles contract, exerting pressure on gastric contents
What happens to the thoracic pressure and diaphragm once emesis is completed?
thoracic pressures: negative -> positive
diaphragm: displaced upwards
Where does most digestion and all absorption of nutrients occur?
the small intestine
What are the 3 regions of the small intestine?
- duodenum
- jejunum
- ileum
What are the 4 functions of the upper small intestine (mostly duodenum)?
- neutralization
- osmotic equilibration
- digestion
- absorption
Why does chyme entering the stomach need to be rapidly neutralized?
because it is highly acidic
Which mucosa is well protected from acid? Which one isn’t?
stomach mucosa is, small intestine isn’t
When will chyme be isotonic?
by the time it leaves the duodenum
What are the 2 motor activities of the small intestine?
- effective mixing
- slow propulsion
How long can an eaten meal be in the small intestine for?
2-6 hours
What are the intestinal contractions governed by?
electrical characteristics of smooth muscle
What is frequency of the small intestine governed by?
BER (ECA)
What are the spikes of the small intestine initiated by?
stretch or ACh
What is the amplitude of contraction of the small intestine related to?
the number of spikes/burst of ERA
What does intrinsic frequency of BER vary in the small intestine?
different cells of the small intestine
What happens to the frequency of BER from proximal to distal intestine?
it declines
What is present along the entire length of the SI?
pacemaker cells
What is the frequency of BER in the duodenum compared to the ileum?
duodenum: 12 cycles/min
ileum: 8 cycles/min
What do the contractions of the small intestine contribute to?
the foreward movement of contents
Both the frequency and the amplitude of muscle contractions are ___ in the proximal small intestine.
greater
Does the maximal contractile activity in the small intestine exceed the BER frequency of that gut segment?
no, it cannot
What is the most common type of contractile activity in the SI after a meal?
segmentation
What initiates segmentation in the SI?
myogenic response to distention
What coordinates and organizes contraction over a length of small intestine in the GI?
ENS
What can modulate what happens at the musculature of the SI?
ANS and hormones
What happens to parasympathetic and sympathetic in the SI after a meal?
parasympathetic: increases
sympathetic: decreases
What is the function of segmentation?
mixing and slow propulsion
How does mixing cause slow propulsion?
since there are more contractions and stronger contractions
proximally, there will be a slow, net aboral propulsion of contents
Proximal:
___ contractions
more + stronger
Distal:
___ contractions
fewer + weaker
How is peristalsis in the small intestine characterized?
- infrequent, irregular
- weak, shallow
- travels for short distances
What is intestinal peristalsis mediated by?
a series of local reflexes
Intestinal peristalsis involves interactions of which 2 muscles?
longitudinal and circular
Maximum frequency ___ exceed frequency of BER.
cannot
What is intestinal peristalsis modulated by (2)?
ANS and hormones
What is the pathway of the “Law of the Intestine”?
radial stretch -> receptors -> neurally mediated
When does contraction of longitudinal muscle and relaxation of circular muscle occur?
ahead of the bolus
What is found between the ileum and the colon?
ileocecal sphincter
What is the first portion of the colon called?
cecum
Is the ileocecal sphincter open or closed normally?
closed
What is the colon contractile activity similar to?
SI but slower and more sluggish/irregular
What does the colon absorb?
water and some ions
How much water enters the ileocecal sphincter per day?
1500 mL
How much water is expelled from the colon each day?
200 mL
What are the functions of the colon?
- mixing
- propulsion
- storage
What is the rate of colon propulsion?
slow
How long does the colon take to convert chyme to feces?
50-60 hours
What is governed by irregular BER in the colon?
segmentation and peristalsis
How and when does the large intestine empty its contents?
2-3x a day, corresponding to the intake of a new meal
Why does the large intestine empty its contents?
because there is increased activity in the colon and distal SI
What are the 3 reflexes produces after the intake of a meal?
- gastroileal reflex
- gastrocolic reflex
- ileocolic reflex
