What are the main functions of the alimentary tract?
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Movement of food, secretion of digestive juices, absorption of nutrients, circulation of blood, and control by nervous and hormonal systems.
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What are the main functions of the alimentary tract?
Movement of food, secretion of digestive juices, absorption of nutrients, circulation of blood, and control by nervous and hormonal systems.
What are the layers of the gastrointestinal wall from outer to inner?
Serosa, longitudinal smooth muscle layer, circular smooth muscle layer, submucosa, and mucosa.
What is the role of smooth muscle in the gastrointestinal tract?
It performs the motor functions of the gut.
How are smooth muscle fibers in the gastrointestinal tract arranged?
In bundles of 200 to 1000 parallel fibers.
What happens to splanchnic blood flow during heavy exercise?
Sympathetic stimulation can decrease splanchnic blood flow significantly.
What allows electrical signals to travel between smooth muscle fibers?
Gap junctions that permit low-resistance movement of ions.
What percentage of oxygen may take a short-circuit route to the tips of the villi?
As much as 80 percent.
What is the effect of sympathetic stimulation on large-volume intestinal and mesenteric veins?
It causes strong vasoconstriction, decreasing their volume and displacing blood into other parts of circulation.
What are the two basic types of electrical waves in gastrointestinal smooth muscle?
Slow waves and spikes.
What can happen to the villi during circulatory shock?
The villus tip or the whole villus can undergo ischemic death and disintegrate.
What are the interstitial cells of Cajal believed to act as?
Electrical pacemakers for smooth muscle cells.
What is the role of the myenteric plexus in peristalsis?
An active myenteric plexus is required for effective peristalsis; its absence leads to weak or absent peristaltic movements.
How much extra blood can sympathetic stimulation provide during hemorrhagic shock?
It can provide 200 to 400 milliliters of extra blood.
What hormone strongly contracts the gallbladder and expels bile into the small intestine?
Cholecystokinin (CCK).
What determines the rhythm of gastrointestinal contractions?
The frequency of slow waves of smooth muscle membrane potential.
What effect does stimulation of parasympathetic nerves have on gastrointestinal blood flow?
It increases local blood flow, leading to mucosal vasodilation.
What is the 'law of the gut'?
It describes how peristaltic waves normally move toward the anus with downstream receptive relaxation.
What do slow waves in gastrointestinal smooth muscle primarily excite?
The appearance of intermittent spike potentials.
What is autoregulatory escape in the context of gastrointestinal blood flow?
It is a mechanism where local metabolic vasodilators override sympathetic vasoconstriction, restoring blood flow.
What role does bile play in the small intestine?
It emulsifies fatty substances, allowing them to be digested and absorbed.
What is the significance of the resting membrane potential in gastrointestinal smooth muscle?
Changes in voltage can affect the motor activity of the gastrointestinal tract.
What types of stimuli can activate afferent sensory nerve fibers in the gut?
Irritation of the gut mucosa, excessive distention of the gut, or the presence of specific chemical substances.
How much can intestinal blood flow increase due to decreased oxygen concentration in the gut wall?
At least 50 to 100 percent.
What initiates peristalsis in the gastrointestinal tract?
Peristalsis is primarily initiated by the distention of the gut.
What is the resting membrane potential threshold for spike potentials to occur?
More positive than about -40 millivolts.
What is the primary effect of sympathetic stimulation on the gastrointestinal tract?
It causes intense vasoconstriction of the arterioles, greatly decreasing blood flow.
What is the role of the submucosal plexus in the gastrointestinal tract?
It helps control local intestinal secretion, absorption, and contraction of the submucosal muscle.
How does CCK affect stomach contraction?
It inhibits stomach contraction moderately.
What is the role of afferent fibers in the vagus nerves?
They transmit sensory signals from the gastrointestinal tract to the brain medulla, initiating vagal reflex signals that control gastrointestinal functions.
What role does adenosine play in gastrointestinal blood flow?
It is a vasodilator that can increase blood flow by as much as fourfold.
How long do spike potentials last in gastrointestinal muscle compared to action potentials in large nerve fibers?
10 to 40 times as long, lasting 10 to 20 milliseconds.
What are the two types of movements in the gastrointestinal tract?
Propulsive movements and mixing movements.
What neurotransmitter is most often associated with exciting gastrointestinal activity?
Acetylcholine.
Why is the nervous depression of gastrointestinal blood flow important?
It allows for the shunting off of blood flow to prioritize other vital organs during times of need.
What is the effect of CCK on appetite?
It inhibits appetite to prevent overeating during meals.
What are the three types of gastrointestinal reflexes?
What is the significance of the countercurrent blood flow in the villi?
It allows blood oxygen to diffuse from arterioles directly into adjacent venules.
What is the frequency range of spike potentials in the gastrointestinal tract?
Usually between 1 and 10 spikes per second.
What is the basic propulsive movement of the gastrointestinal tract?
Peristalsis.
Which neurotransmitter is known to inhibit gastrointestinal activity?
Norepinephrine.
What hormone is secreted by 'S' cells in the duodenum in response to acidic gastric juice?
Secretin.
What is the gastrocolic reflex?
A reflex that transmits signals from the stomach to cause evacuation of the colon.
What happens to the intestinal absorptive capacity in many gastrointestinal diseases?
The villi become seriously blunted, leading to diminished absorptive capacity.
What is the typical frequency of contractions in the body of the stomach?
About 3 per minute.
How does peristalsis function?
A contractile ring forms around the gut and moves forward, pushing material ahead.
What are the main functions of the myenteric plexus?
It controls muscle activity along the length of the gut, increasing tonic contraction, intensity of contractions, rate of rhythm, and velocity of excitatory waves.
What is the primary action of secretin?
To promote pancreatic secretion of bicarbonate to neutralize acid in the small intestine.
How does parasympathetic stimulation affect the enteric nervous system?
It increases activity of the enteric nervous system, enhancing most gastrointestinal functions.
What is tonic contraction in gastrointestinal smooth muscle?
Tonic contraction is a continuous contraction that can last several minutes or hours, not associated with the basic electrical rhythm of slow waves.
What causes the action potentials in nerve fibers?
Rapid entry of sodium ions.
What hormone stimulates gastrointestinal motility during fasting?
Motilin.
What is the primary difference between the myenteric and submucosal plexuses?
The myenteric plexus controls muscle activity along the gut, while the submucosal plexus mainly regulates local secretion and absorption.
What is the function of Glucose-dependent insulinotropic peptide (GIP)?
It decreases motor activity of the stomach and slows gastric emptying.
Where do sympathetic fibers to the gastrointestinal tract originate?
In the spinal cord between segments T5 and L2.
What is the splanchnic circulation?
The blood vessels of the gastrointestinal system that include blood flow through the gut, spleen, pancreas, and liver.
What factors can cause tonic contraction?
Tonic contraction can be caused by continuous repetitive spike potentials, hormones, or continuous entry of calcium ions.
What is the typical range of slow wave intensity in gastrointestinal smooth muscle?
Between 5 and 15 millivolts.
What is the effect of glucose-dependent insulinotropic peptide on insulin secretion?
It stimulates insulin secretion even at low blood levels.
What is the effect of stimulation of the myenteric plexus?
Increased tonic contraction, intensity of contractions, rate of rhythm, and velocity of excitatory waves.
What stimulates the secretion of gastrin?
Ingestion of a meal, such as stomach distention and protein products.
What is the general effect of sympathetic stimulation on gastrointestinal activity?
It usually inhibits gastrointestinal tract activity.
How does blood flow from the gastrointestinal tract to the liver?
All blood from the gut, spleen, and pancreas flows into the liver via the portal vein.
What is the enteric nervous system?
The enteric nervous system is a complex network of about 100 million neurons located in the wall of the gastrointestinal tract, controlling movements and secretion.
What physiological conditions can affect membrane potentials in intestinal smooth muscle?
Stimulation by norepinephrine, stretch, acetylcholine, and parasympathetics.
What happens to motilin secretion after food ingestion?
Motilin secretion is inhibited by mechanisms that are not fully understood.
What type of neurons are found in the myenteric plexus?
A mixture of excitatory and inhibitory neurons.
What are the primary actions of gastrin?
Stimulation of gastric acid secretion and growth of the gastric mucosa.
What neurotransmitter is primarily secreted by sympathetic nerve endings in the gastrointestinal tract?
Norepinephrine.
What are the two main plexuses of the enteric nervous system?
The myenteric plexus (Auerbach’s plexus) and the submucosal plexus (Meissner’s plexus).
What role do liver sinusoids play in blood flow?
They allow reticulo-endothelial cells to remove bacteria and particulate matter from the blood.
Which neurotransmitter is possibly secreted by inhibitory neurons in the myenteric plexus?
Vasoactive intestinal polypeptide.
What are the effects of gastrointestinal hormones on motility?
They exert physiological actions on target cells and can persist even after nervous connections are severed.
What can strong stimulation of the sympathetic system cause in the gut?
It can inhibit motor movements of the gut significantly.
What does the myenteric plexus primarily control?
The myenteric plexus primarily controls gastrointestinal movements.
What happens to nonfat, water-soluble nutrients absorbed from the gut?
They are transported in portal venous blood to the liver sinusoids for absorption and temporary storage.
What is the function of the pyloric sphincter?
It controls the emptying of the stomach into the duodenum.
How are fats absorbed from the intestinal tract?
Fats are absorbed into intestinal lymphatics and conducted to systemic circulation via the thoracic duct, bypassing the liver.
What role does the submucosal plexus play?
The submucosal plexus mainly controls gastrointestinal secretion and local blood flow.
What is the role of sensory signals originating from the gastrointestinal epithelium?
They are integrated in the submucosal plexus to help control local functions.
What arteries supply blood to the gut?
The superior mesenteric and inferior mesenteric arteries supply the small and large intestines.
How do sensory nerve endings contribute to gastrointestinal function?
Sensory nerve endings send afferent fibers to the enteric plexuses and can elicit local reflexes within the gut wall.
How does blood flow change during gastrointestinal activity?
Blood flow can increase as much as eightfold during active absorption of nutrients.
What is the resting membrane potential of gastrointestinal smooth muscle?
The resting membrane potential averages about -56 millivolts.
What are some vasodilator substances released during digestion?
Peptide hormones such as cholecystokinin, vasoactive intestinal peptide, gastrin, and secretin.
What causes depolarization of the smooth muscle membrane?
Factors such as stretching of the muscle, stimulation by acetylcholine, and specific gastrointestinal hormones can cause depolarization.
What kinins are released by gastrointestinal glands?
Kallidin and bradykinin, which are powerful vasodilators.
How does calcium ion entry affect smooth muscle contraction?
Calcium ions enter the muscle fiber and activate myosin filaments, causing contraction through a calmodulin control mechanism.
