Digestive system lefcture 5 Flashcards
What are the electrical characteristics of GI smooth muscle BER?
-What is the mechanism for gastric mixing
-What is gastric emptying for liquids dependent on?
Electrical Characteristics of GI Smooth Muscle BER, “spikes”, contractions
-Mechanism for Gastric Mixing:
The role of antral systole and the very narrow lumen pyloric sphincter
Gastric Emptying for Liquids:
depends on the pressure difference between the proximal stomach and the duodenum
What does gastric emptying for solids depend on?
How do gastric factors contribute to gastric emptying?
What are the Duodenal factors that inhibit gastric emptying?
-depends on the frequency of antral peristalsis and the amplitude of antral perisitalsis
Gastric Factors Contribute to Gastric Emptying :Antral peristalsis - distension, ACh release
Duodenal Factors Inhibit Gastric Emptying : for release of small amounts of chyme: distension, pH, osmotic pressure, Fat>Protein>Carbohydrate
What is the duodenum less protected against?
WHat is the enterogastric reflex via?
What do the para and sympathetic nervous system activate?
-it is less protected than gastric mucosa from acids and takes more time to absorb nutrients
-via enteric nervous systema and ANS
-parasympathetic vagus nerve activates inhibtory ENS neuron
-sympathetic, inhibit excitatory ENS neuron
WHat is rate of gastric emptying due to?
What is vomiting?
What does vominiting result from?
-due to a balance between gastric and duodenal conditions
-Emptying of the contents of the upper GIT
-Results from an increase in intraabdominal pressure due to the action of the diaphragm and abdominal muscles – the GIT is mostly passive
What are the main steps that occur in the process of vomiting?
-Proximal Stomach and above relax
Upper Duodenum and Distal Stomach contract
-Gradient of Pressure due to concerted contraction of abdominal muscles
-Diaphragm Lowers (decreases resistance from LES)
-Abdominal Muscles Contract
-Intraabdominal pressure overcomes LES
What is there an imbalance of in vomiting?
What are the factiors that accompany vominting?
Imbalance between parasympathetic and sympathetic activities
… precede and accompany vomiting are sweating, vasoconstriction, salivation, alternating bradycardia, tachycardia
WHat are the first 3 of the afferent regulation of vomiting?
Pharyngeal Stimulation
-GIT or urogenital distension
-Pain, cardiac ischemia, also childbirth
What are the last 3 afferent regulation of vomiting
Biochemical disequilibrium
- Vestibular Signals
-Psychogenic Factors (certain smell/sight)
-can lead to vomiting center activation
What are some efferent regulation of vomiting?
-widespread autonomic discharge, nausea, retching and emesis
What are 2 ways that emesis can occur?
-relaxation of upper GIT+spasm of pyloric antrum and duodenum (so contents can move in one direction)
-contraction of abdominal muscles and diaphragm
Where can afferent impulses to vominiting center arise from?
What can agents in the bloodstream can act on?
-can arise from many places
-Agents in the bloodstream can act on the Chemoreceptor Trigger Zone within the medulla
What is CTZ distinct from?
Where does CTZ send signals
WHat is necessary for vomiting?
-Distinct from the vomiting center
and outside the blood-brain barrier.
-The CTZ sends signals to the
Vomiting Center.
Vomiting Center is necessary for vomiting.
WHat does the CTZ (chemreceptor trigger zone) allow for?
-allows for circulating emetic (vomit inducing) agents to activate CTZ
What are the 3 steps involved in vomiting?
-Nausea – a psychic experience
Retching – abrupt, uncoordinated respiratory movements with glottis closed
Emesis – actual expulsion of contents of upper GIT
What happens when an individual takes a deep breath for vomiting?
How is emesis completed, what causes the pressure change, and what forces the esophageal components to be expelled from mouth?
-The individual takes a deep breath, glottis closes, abdominal muscles contract, exerting pressure on gastric contents.
– Emesis is completed with the reversal of thoracic pressures from
negative to positive, as the diaphragm is displaced upwards, forcing
esophageal contents to be expelled through the mouth
Where does most digestion and all absorption of nutrients occur?
WHat are the 3 parts of the SI?
What part of the GIT does not absorb nutrients?
-Most digestion and ALL absorption of nutrients occur in the small intestine
-Made up of three different regions:
- Duodenum (main absorption occurs here)
-jejunum
- Ileum
-no nutrient absorption in colon
What are the 3 factors that regulate intestinal contractions
-Frequency – governed by BER (basic electrical rhytm) (ECA)
-ERA (spikes) – phase-locked to BER
– initiated by stretch or ACh
-Amplitude of Contraction – related to number of spikes/burst of ERA (spikes
Where does intestinal frequency of BER vary?
Where does it decline from?
Intrinsic f of BER varies in different cells of SI,
It declines systematically from the proximal to distal intestine (from duodenum to ileum)
What is the function of segmentation?
-mixing and propulsion
What are the contractions like in the proximal vs distal portion of SI?
What type of movement does this lead to?
proximal=more contractions and more vigorous contractions
distal=fewer contractions and less vigorous contractions
-therefore net aboral movement
What is the frequency/activity of peristalsis in the SI?
When would there be peristalsis in SI?
-Infrequent, irregular, Weak, shallow
Travels for short distances only a few centimeters
-for example diarrhea would cause this to empty stomach
What is the colon contractile activity similar to,how does it differ?
Where is digestion and absorption completed, what does the colon absorb?
-similar to si, but slower, more sluggish and irregular
Digestion and Absorption of nutrients is completed in SI
Some H2O and ions are absorbed by colon
What is governed by irregular BER?
-segmentation and peristalsis
how often does large intestine empty its contents?
2-3x a day, corresponding to the intake of a new meal, increased activity in colon and distal SI
What is the gastroileal reflex?
What about ileocolic reflex
gastroileal reflex= when a new meal arrives and stretches stomach it leads to activation of the musculature in the distal ileum and opening of ileocecal spincter
-ileocolic reflex is activity in the iluem and colon
What is the gastrocolic reflex?
-when activity in the stomach increases activity in distal part of colon to move contents forward into rectum
