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 4 functions of upper small intestine?
-1. neutralization
2.osmotic equilibrium
3.digestion
4.absorption
What does neutralization do in the upper SI?
What is well protected from acid and what is not?
WHen is chyme isotonic?
Neutralization – Chyme entering from the stomach is highly acidic and must be rapidly neutralized.
The stomach mucosa is well protected from acid, but Small Intestine mucosa is not
-by the time it leavs the duodenum
What are the motor activities of the SI?
WHat are intestinal contractions governed by?
- Effective Mixing
- Slow Propulsion which takes 2- 6 hours
-electrical chracteristics of SM
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)
How does the proximal part of the SI differ from the distal (what are the 3 reasons)
What is greater in the proximal SI?
- f of BER is greater
- Excitability of smooth muscle is greater
- Thickness of smooth muscle is greater
-both frequency and the amplitude of contractions are greater in the proximal SI
WHat does the BER (ECA) generated bu the muscle fibers in SI show?
Where is the highest and lowest frequency?
shows an aborally declining frequency gradient, with the highest
frequency (12/min) in the duodenum and the lowest (8/min) in the terminal ileum.
What is the gradient of intestinal motility determined by?
What does distribution of BER in time and space along the intestine establish?
-gradient is determined by a series of pacemaker regions along the intestine, each with a slightly lower frequency than the preceding one.
- establishes the distribution of spikes (ERA) and consequent contractions; thus, the proximal portions of the intestine exhibit more activity than the distal ones.
