p.7
Functional Types of Movements in the Gastrointestinal Tract
What are the two types of movements in the gastrointestinal tract?
Propulsive movements and mixing movements.
p.5
Gastrointestinal Reflexes
What is the gastrocolic reflex?
A reflex that transmits signals from the stomach to cause evacuation of the colon.
p.6
Hormonal Control of Gastrointestinal Motility
What is the function of Glucose-dependent insulinotropic peptide (GIP)?
It decreases motor activity of the stomach and slows gastric emptying.
p.1
Physiological Anatomy of the Gastrointestinal Wall
What are the layers of the gastrointestinal wall from outer to inner?
Serosa, longitudinal smooth muscle layer, circular smooth muscle layer, submucosa, and mucosa.
p.9
Gastrointestinal Blood Flow and Splanchnic Circulation
How much can intestinal blood flow increase due to decreased oxygen concentration in the gut wall?
At least 50 to 100 percent.
p.9
Gastrointestinal Blood Flow and Splanchnic Circulation
What is the significance of the countercurrent blood flow in the villi?
It allows blood oxygen to diffuse from arterioles directly into adjacent venules.
p.6
Hormonal Control of Gastrointestinal Motility
What is the primary action of secretin?
To promote pancreatic secretion of bicarbonate to neutralize acid in the small intestine.
p.7
Hormonal Control of Gastrointestinal Motility
What is the effect of glucose-dependent insulinotropic peptide on insulin secretion?
It stimulates insulin secretion even at low blood levels.
p.8
Gastrointestinal Blood Flow and Splanchnic Circulation
What role do liver sinusoids play in blood flow?
They allow reticulo-endothelial cells to remove bacteria and particulate matter from the blood.
p.8
Gastrointestinal Blood Flow and Splanchnic Circulation
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.
p.3
Electrical Activity of Gastrointestinal Smooth Muscle
What is the resting membrane potential of gastrointestinal smooth muscle?
The resting membrane potential averages about -56 millivolts.
p.6
Hormonal Control of Gastrointestinal Motility
What role does bile play in the small intestine?
It emulsifies fatty substances, allowing them to be digested and absorbed.
p.7
Gastrointestinal Reflexes
What initiates peristalsis in the gastrointestinal tract?
Peristalsis is primarily initiated by the distention of the gut.
p.9
Types of Neurotransmitters in the Enteric Nervous System
What role does adenosine play in gastrointestinal blood flow?
It is a vasodilator that can increase blood flow by as much as fourfold.
p.2
Electrical Activity of Gastrointestinal Smooth Muscle
What causes the action potentials in nerve fibers?
Rapid entry of sodium ions.
p.7
Hormonal Control of Gastrointestinal Motility
What happens to motilin secretion after food ingestion?
Motilin secretion is inhibited by mechanisms that are not fully understood.
p.4
Types of Neurotransmitters in the Enteric Nervous System
Which neurotransmitter is possibly secreted by inhibitory neurons in the myenteric plexus?
Vasoactive intestinal polypeptide.
p.3
Electrical Activity of Gastrointestinal Smooth Muscle
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.
p.2
Electrical Activity of Gastrointestinal Smooth Muscle
What are the interstitial cells of Cajal believed to act as?
Electrical pacemakers for smooth muscle cells.
p.9
Neural Control of Gastrointestinal Function
What effect does stimulation of parasympathetic nerves have on gastrointestinal blood flow?
It increases local blood flow, leading to mucosal vasodilation.
p.6
Hormonal Control of Gastrointestinal Motility
What is the effect of CCK on appetite?
It inhibits appetite to prevent overeating during meals.
p.7
Functional Types of Movements in the Gastrointestinal Tract
How does peristalsis function?
A contractile ring forms around the gut and moves forward, pushing material ahead.
p.3
Gastrointestinal Smooth Muscle Functions
What factors can cause tonic contraction?
Tonic contraction can be caused by continuous repetitive spike potentials, hormones, or continuous entry of calcium ions.
p.5
Autonomic Control of the Gastrointestinal Tract
What can strong stimulation of the sympathetic system cause in the gut?
It can inhibit motor movements of the gut significantly.
p.3
Neural Control of Gastrointestinal Function
What role does the submucosal plexus play?
The submucosal plexus mainly controls gastrointestinal secretion and local blood flow.
p.1
Electrical Activity of Gastrointestinal Smooth Muscle
What allows electrical signals to travel between smooth muscle fibers?
Gap junctions that permit low-resistance movement of ions.
p.10
Gastrointestinal Blood Flow and Splanchnic Circulation
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.
p.5
Neural Control of Gastrointestinal Function
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.
p.2
Electrical Activity of Gastrointestinal Smooth Muscle
What is the frequency range of spike potentials in the gastrointestinal tract?
Usually between 1 and 10 spikes per second.
p.5
Autonomic Control of the Gastrointestinal Tract
How does parasympathetic stimulation affect the enteric nervous system?
It increases activity of the enteric nervous system, enhancing most gastrointestinal functions.
p.4
Neural Control of Gastrointestinal Function
What is the effect of stimulation of the myenteric plexus?
Increased tonic contraction, intensity of contractions, rate of rhythm, and velocity of excitatory waves.
p.8
Gastrointestinal Blood Flow and Splanchnic Circulation
How does blood flow change during gastrointestinal activity?
Blood flow can increase as much as eightfold during active absorption of nutrients.
p.9
Gastrointestinal Blood Flow and Splanchnic Circulation
What can happen to the villi during circulatory shock?
The villus tip or the whole villus can undergo ischemic death and disintegrate.
p.1
Electrical Activity of Gastrointestinal Smooth Muscle
What determines the rhythm of gastrointestinal contractions?
The frequency of slow waves of smooth muscle membrane potential.
p.1
Electrical Activity of Gastrointestinal Smooth Muscle
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.
p.2
Electrical Activity of Gastrointestinal Smooth Muscle
What is the resting membrane potential threshold for spike potentials to occur?
More positive than about -40 millivolts.
p.2
Electrical Activity of Gastrointestinal Smooth Muscle
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.
p.4
Neural Control of Gastrointestinal Function
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.
p.6
Hormonal Control of Gastrointestinal Motility
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.
p.1
Gastrointestinal Smooth Muscle Functions
What is the role of smooth muscle in the gastrointestinal tract?
It performs the motor functions of the gut.
p.7
Neural Control of Gastrointestinal Function
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.
p.4
Neural Control of Gastrointestinal Function
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.
p.10
Gastrointestinal Blood Flow and Splanchnic Circulation
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.
p.8
Gastrointestinal Blood Flow and Splanchnic Circulation
What is the splanchnic circulation?
The blood vessels of the gastrointestinal system that include blood flow through the gut, spleen, pancreas, and liver.
p.3
Neural Control of Gastrointestinal Function
What are the two main plexuses of the enteric nervous system?
The myenteric plexus (Auerbach’s plexus) and the submucosal plexus (Meissner’s plexus).
p.3
Neural Control of Gastrointestinal Function
What does the myenteric plexus primarily control?
The myenteric plexus primarily controls gastrointestinal movements.
p.3
Gastrointestinal Reflexes
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.
p.8
Gastrointestinal Blood Flow and Splanchnic Circulation
What kinins are released by gastrointestinal glands?
Kallidin and bradykinin, which are powerful vasodilators.
p.1
Functions of the Alimentary Tract
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.
p.5
Neural Control of Gastrointestinal Function
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.
p.10
Gastrointestinal Blood Flow and Splanchnic Circulation
What is the primary effect of sympathetic stimulation on the gastrointestinal tract?
It causes intense vasoconstriction of the arterioles, greatly decreasing blood flow.
p.9
Gastrointestinal Reflexes
What happens to the intestinal absorptive capacity in many gastrointestinal diseases?
The villi become seriously blunted, leading to diminished absorptive capacity.
p.5
Autonomic Control of the Gastrointestinal Tract
Where do sympathetic fibers to the gastrointestinal tract originate?
In the spinal cord between segments T5 and L2.
p.3
Neural Control of Gastrointestinal Function
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.
p.4
Neural Control of Gastrointestinal Function
What is the role of sensory signals originating from the gastrointestinal epithelium?
They are integrated in the submucosal plexus to help control local functions.
p.1
Gastrointestinal Smooth Muscle Functions
How are smooth muscle fibers in the gastrointestinal tract arranged?
In bundles of 200 to 1000 parallel fibers.
p.6
Hormonal Control of Gastrointestinal Motility
How does CCK affect stomach contraction?
It inhibits stomach contraction moderately.
p.5
Gastrointestinal Reflexes
What are the three types of gastrointestinal reflexes?
1. Reflexes integrated within the gut wall enteric nervous system. 2. Reflexes from the gut to prevertebral sympathetic ganglia and back. 3. Reflexes from the gut to the spinal cord or brain stem and back.
p.4
Neural Control of Gastrointestinal Function
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.
p.2
Electrical Activity of Gastrointestinal Smooth Muscle
What is the typical range of slow wave intensity in gastrointestinal smooth muscle?
Between 5 and 15 millivolts.
p.8
Gastrointestinal Blood Flow and Splanchnic Circulation
What arteries supply blood to the gut?
The superior mesenteric and inferior mesenteric arteries supply the small and large intestines.
p.10
Gastrointestinal Blood Flow and Splanchnic Circulation
What happens to splanchnic blood flow during heavy exercise?
Sympathetic stimulation can decrease splanchnic blood flow significantly.
p.7
Gastrointestinal Reflexes
What is the 'law of the gut'?
It describes how peristaltic waves normally move toward the anus with downstream receptive relaxation.
p.5
Autonomic Control of the Gastrointestinal Tract
What is the general effect of sympathetic stimulation on gastrointestinal activity?
It usually inhibits gastrointestinal tract activity.
p.4
Neural Control of Gastrointestinal Function
What type of neurons are found in the myenteric plexus?
A mixture of excitatory and inhibitory neurons.
p.4
Gastrointestinal Reflexes
What is the function of the pyloric sphincter?
It controls the emptying of the stomach into the duodenum.
p.10
Gastrointestinal Blood Flow and Splanchnic Circulation
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.
p.10
Gastrointestinal Blood Flow and Splanchnic Circulation
How much extra blood can sympathetic stimulation provide during hemorrhagic shock?
It can provide 200 to 400 milliliters of extra blood.
p.2
Electrical Activity of Gastrointestinal Smooth Muscle
What do slow waves in gastrointestinal smooth muscle primarily excite?
The appearance of intermittent spike potentials.
p.3
Gastrointestinal Smooth Muscle 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.
p.6
Hormonal Control of Gastrointestinal Motility
What stimulates the secretion of gastrin?
Ingestion of a meal, such as stomach distention and protein products.
p.2
Neural Control of Gastrointestinal Function
What physiological conditions can affect membrane potentials in intestinal smooth muscle?
Stimulation by norepinephrine, stretch, acetylcholine, and parasympathetics.
p.8
Gastrointestinal Blood Flow and Splanchnic Circulation
What are some vasodilator substances released during digestion?
Peptide hormones such as cholecystokinin, vasoactive intestinal peptide, gastrin, and secretin.
p.8
Gastrointestinal Blood Flow and Splanchnic Circulation
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.
p.6
Hormonal Control of Gastrointestinal Motility
What are the primary actions of gastrin?
Stimulation of gastric acid secretion and growth of the gastric mucosa.
p.8
Gastrointestinal Blood Flow and Splanchnic Circulation
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.
p.3
Gastrointestinal Smooth Muscle Functions
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.
