2 Motility Of The GI Tract Flashcards
Digestive process
GI motility
Ingestion
Propulsion
Mechanical digestion
Chemical digestion
Absorption
Defecation
Lines the lumen of the GI tract
Mucosa
Fx of submucosa
Relays info to and away from the mucosa
Fx of muscularis external
Motility of the GI tract
What do parietal cells secrete?
HCl
Intrinsic factor
Chief cells secrete ______.
Pepsinogen
Gastrin is secreted by ________.
Enteroendocrine cells
Specialized group of cells in the intestinal wall
Involved in transmission of info from enteric neurons to smooth m.
Interstitial cells of Cajal (ICCs)
What are the pacemaker cells in the intestinal wall?
What do they generate?
ICCs
Generate the basic electrical rhythm (slow-wave activity) of GI smooth m.
What changes do the ICC cells undergo?
Why?
Cyclic changes in the membrane potential
Due to unique ion channels that periodically open and produce inward (pacemaker) currents that generate the slow wave activity
Two basic electrical waves in the smooth m of the GI tract
Slow waves
Spike potentials
Slow waves make it possible for contractions to be stimulated more _________ by raising the RMP ________ to threshold and less _________.
Easily
Closer
Negative
Where is the rate of slow waves lowest?
Highest?
Stomach (3/min)
Duodenum (12/min)
T/F: slow waves are true action potentials.
FALSE
Not AP, instead they are slow changes in the RMP
Not sufficient to completely depolarize the membrane and stimulate contractions
Spike waves are true_____.
Action potentials
What stimulates spike waves (depolarization)?
Stretching of the muscle
ACh
Parasympathetics
Several specific GI hormones
When do spike waves occur?
Automatically when the RMP of the GI smooth m is more positive than about -40 millivolts
The spike potentials last ____ to ____ times as long in GI muscle as the AP in large nerve fibers.
10 to 40 times longer
Hyperpolarization is stimulated by _____.
NE or epinephrine on the fiber membrane
Sympathetic nerves that secrete NE at their endings
What is the RMP in the gut?
-56 millivolts
Depolarization in the GI tract is stimulated by _____.
How is this released?
What receptors does it act through?
What does it do?
ACh
Released by postganglionic axons
Acts through muscarinic receptors
Increases the amplitude and duration of the slow waves
T/F: slow waves cause Ca to enter the smooth m fiber.
FALSE
Slow waves cause Na to enter the smooth m
What ion causes the contraction of smooth m in the GI tract?
Calcium
When are spike potentials generated?
Why?
At the peak of slow waves
To allow enough Ca ions to enter the fibers and cause a contraction
Name the two effects of Calcium
The rising phase of an AP
Triggers a Contractile response
What happens at threshold?
Voltage-gated Ca channels are activated
Ca influx into smooth m
What determines the intensity/strength of the contractions?
The number of AP that occur when the slow-wave potential reaches threshold
Describe phasic contractions and their location
Cyclic contractions that permit mixing and propelling
Pylorus, distal 2/3 of corpus, antrum (distal stomach)
Describe tonic contractions and their location
Continuous contractions that relax under neural stimulation
Cardia, fundus, first 1/3 of corpus (proximal stomach) and sphincters that control the flow of GI contents from one region of the GI tract to another
Where and what is the ENS?
Function?
Walls of the intestines
Aggregates of neurons and glia (enteric ganglia) interconnected to form plexuses (myenteric and submucosal)
Controls the activities of the GI tract
What two hormones are produced by gut bacteria?
Dopamine and serotonin
How are the intrinsic nerves of the GI system arranged?
Two main plexuses: myenteric and submucosal
Where is the myenteric plexus and what does it contain?
Between the circular and longitudinal muscle layers of the GI tract
Inhibitory and excitatory nerves that control the function to the muscle layers and controlling movement
Location and containts of the submucosal plexus
Submucosa
Secretomotor neurons that promote vasodilation, regulate the secretion of fluid and electrolytes, and contractions of the muscularis mucosa
Functions and contents of saliva
Hydrolysis of starch
Buffers neutralize acids
Antibacterial agents kill some bacteria ingested with food
Water, electrolytes, mucin, IgA, lysozyme, salivary amylase
Chewing, voluntary and involuntary grinding, ripping, and tearing of food
Mastication
Moving bonus towards the pharynx
Deglutition
Functions of salivary amylase
Starts the breakdown of carbs
Lubricates and cleanses oral cavity
Dissolves chemicals
Suppresses bacterial growth
Muscles of chewing and chewing process are innervated by what nerves?
Motor branch of the 5th CN
Chewing process regulated by brain stem nuclei
Three functions of chewing
Reduces size of ingested particles to help swallowing
Mixes food with saliva and exposes it to enzymes and lubrication
Increases the surface area of ingested material therefore increases digestion rate
Three phases of swallowing
Voluntary oral phase
Involuntary pharyngeal phase
Esophageal phase
Sensory signals use what nerves during swallowing?
Glossopharyngeal
Vagal
Trigeminal
Motor impulses pass through _____ to control a _____ process that directs food into the ______ and away from the airway.
CN
Involuntary
Esophagus
Describe the oral phase of swallowing
Voluntary
Chewing completed
Swallowing begins by the tongue moving up and back against the palate
Tongue pushes the bolts to the back of the oral cavity into the oropharynx
When does swallowing change from voluntary to involuntary?
After the oral phase
Beginning of the pharyngeal phase
Describe the pharyngeal phase of swallowing
Involuntary
Soft palate pulled up and pharyngeal folds move inward to make a passage for food
Larynx moves forward and up against epiglottis to block trachea and open UES
UES relaxes to receive bonus
Constrictor muscles of pharynx contract to force bonus through UES
The pharyngeal phase of swallowing stimulates ______ receptors in the pharynx
Touch
What forces the bolus through the UES?
Middle pharyngeal constrictor m.
Inferior pharyngeal constrictor m.
What action prevents the bolus from entering the trachea during swallowing?
Larynx moves forward and upward against the epiglottis
When does the esophageal phase of swallowing begin?
When the bolus passes through the UES
The bolus passing through the UES initiates ________.
Peristaltic wave along the esophagus (primary peristalsis)
Primary peristalsis reaches the LES, it relaxes and allows the bolus into the stomach. Distention of the stomach my the bolus initiates _______.
A second wave of contraction (secondary peristalsis)
T/F: if the vagus N was cut (vagotomy), secondary peristaltic waves would still exist
TRUE
Primary peristaltic waves would be affected
What is primary peristalsis and when does it occur?
How long does it last?
Continuation of the peristaltic wave that begins in the pharynx and spreads to the esophagus
Pharyngeal phase
8-10 seconds
Primary peristalsis is regulated by______.
Medulla
When and why does the secondary peristaltic wave occur?
When the food crosses the LES and until all the food is emptied into the stomach
If the primary peristaltic wave doesn’t move all the food into the stomach
Regulation of the secondary peristaltic wave
Medulla and myenteric NS
Resting pressures are ______ at the UES and LES.
Why?
High
Because both sphincters have continuous resting smooth m tone
Receptive relaxation is a ______ reflex that causes what?
Vagovagal reflex
Causes the muscles of the proximal stomach to relax
Opens the LES allowing the bolus to enter the stomach
Allows the stomach to expand without increasing intragastric pressure
Esophageal pressure drops to match the low pressure in the proximal stomach during ______.
Receptive relaxation
What mediates the vagovagal reflex?
Mediated by myenteric neurons releasing vasoactive intestinal peptide and nitric oxide
Components of the UES
Instinct striated circular muscle
Components of the LES
Smooth muscle
UES and LES are _______ between swallows.
Why?
Closed
Prevents air and gastric acid back flowing into the esophagus
LES controls and prevents what?
Controls the passage of bolus into the stomach
Prevents the reflux of gastric contents into the esophagus so can’t damage mucosa
What controls the contraction of the LES between swallows?
Vagal cholinergic mechanisms
What allows the LES to relax during swallowing?
Vagal inhibitory fibers
What neurotransmitters cause the Vagal inhibitory fibers to allow the LES to relax?
Nitric oxide and vasoactive intestinal peptide (VIP)
Factors that increase LES tone (5)
ACh
Increase intraabdominal and intragastric pressure
Gastrin
Motilin
Protein-rich food
Factors that decrease LES tone (9)
Nitric oxide VIP CCK GIP Beta adrenergic receptor agonists Secretin Progesterone Prostaglandin E Fat-rich food
Inappropriate relaxation of the LES
GERD
GERD can be caused by_______. (5)
Loss of LES tone
Increased frequency of transient relaxations
Loss of secondary peristalsis after transient relaxation
Increased stomach volume or pressure
Increased production of acid
LES does not open fully with the peristaltic wave, food becomes retained at the level of the LES
Achalasia
Achalasia is caused from a degeneration of ________.
Neurons in the myenteric plexuses
Specifically a loss of inhibitory neurons in the wall of the esophagus
Symptoms and treatment of achalasia
Regurgitation of food, CP, difficulty swallowing, cough, weight loss
Drugs to reduce the tone of the LES
Pts with achalasia lack what enzyme and neurotransmitters?
Nitric oxide synthase
Other inhibitory neurotransmitters VIP and nitric oxide
Loss of inhibitory neurons in achalasia prevents _______.
Relaxation of the LES after swallowing
propagation of the esophageal peristaltic wave
Two sphincters of the stomach
LES and pyloric sphincter
Function of orad region of stomach
Reservoir and move gastric contents to the distal stomach
Little mixing of ingested contents
Function of caudad region of stomach
Grind, mix, and propel gastric contents
The musculature of the orad stomach is ______ and contractions are ________.
Include what type of contractions?
Think
Weak
Tonic contractions
Hormone that decrease contractions and increases gastric distensibility in the orad stomach
CCK
Peristaltic waves ______ in velocity as they approach the gastroduodenal junction.
What does this cause?
Increase
Retropulsion
What is retropulsion of the stomach?
What does it cause?
The gastric contents are propelled back into the body of the stomach and remain until the next contraction
Causes a thorough mixing of gastric contents and mechanically reduces the size of solid particles
Stomach contractions go from _______region to ________region and ________ in force and velocity.
Orad
Caudad
Increase
How long do stomach contractions last?
2-20 seconds
3 contractions per minute
What happens when the chyme that was being propelled forward hits the closed pyloric sphincter?
What is this process called?
When does it happen?
The chyme is tossed back into the antrum for more mixing
Retropulsion
During each peristaltic contraction
What three things INCREASE the number and force of contractions?
Vagal N, gastrin, motilin
What three things depress/inhibit contractions?
Sympathetic N, secretin, gastrin inhibitory peptide (GIP)
What causes changes in gastric emptying? (3)
Alterations in motility of the stomach, gastroduodenal junction, and duodenum
Three factors that increase gastric emptying?
Decrease in distention of orad stomach
Increase in force of peristaltic contractions of caudad stomach
Increase diameter and inhibit segmenting contractions of proximal duodenum
Four factors that inhibit gastric emptying
Relaxation of orad stomach
Decrease number and force of contractions of caudad stomach
Contractions of pylorus
Increase segmenting contractions of duodenum
Acidic chyme in the duodenum stimulates the release of _______ which ______.
Secretin
Reduces gastric motility and increases tone of pyloric sphincter
Products of lipid digestion stimulate the release of what hormones?
CCK, GIP
Also reduce gastric motility
Protein digestion stimulates the release of what hormones?
Gastrin, CCK, GIP
Slow gastric emptying
Factors in duodenum that inhibit further emptying are part of _______ reflex.
Entero-gastric reflex
Housekeeper of the stomach
Migrating motor complex (MMC)
During fasting state, stomach had regular contractions every ______ minutes called _______.
90-120 minutes
Migration motor complex (MMC)
MMC increases from _______ region of stomach to _______.
Function?
Proximal stomach to antrum and duodenum
Removes large non digestible solids left behind in stomach and SI
Removes mucus, sloughed cells, bacteria from SI
Collection of disorders that delay gastric emptying (no evidence of obstruction)
Gastroparesis
Causes of gastroparesis
Idiopathic
Systemic disease with abnormalities of neuromuscular fx like diabetes or scleroderma
Injury of vagus N (extrinsic input to stomach) impairs gastric emptying
Part of the digestive tract that does most of the chemical and mechanical digestion
small intestine
_______ is stored then released slowly in a controlled fashion in the ______ part of the SI.
Chyme
Duodenum
This is in the lining of the SI and absorbs digested food into capillaries
Villi
Most food absorption occurs where in the SI?
Jejunum and ileum
Fx of the small intestine
What does it degrade?
Digestion of proteins into peptides and AA (mostly in stomach but some in SI)
Peptides degraded into AA
Lipids degraded into fatty acids and glycerol
Carbs degraded into simple sugars
Chyme is propelled through the SI by ______.
How long does it take chyme to pass from the pylorus to ileocecal valve?
Peristaltic waves
3-5 hours
Peristalsis is faster in the _______ SI than black SI
Proximal
Terminal
Two types of movement in the small intestine
Peristaltic waves
Segmentation contractions
______ contraction in the SI occurs at regularly spaced intervals along the SI
Alternate segments of contraction and relaxation give the appearance of _______.
They chop the chyme many times.
Segmentation
Rings
Stretch or distention of the SI releases _______ which activates IPANS and then stimulates the _______causing peristalsis.
Serotonin
Myenteric reflex
Intestinal motility is enhanced by what hormonal control?
Gastric, CCK, 5-HT, thyroxine, insulin
Intestinal motility is decreased by what hormonal control?
Secretin and glucagon
What neural control increases intestinal motility and through what nerve?
Parasympathetic
Vagus N
What neural control decreases intestinal movements?
Sympathetic
What is the vomiting reflex?
Thoracic, diaphragmatic, and abdominal muscles contract
LES and diaphragm relaxes
High intraabdominal pressure forces the gastric contents into the esophagus
What coordinates the synchronous contraction of inspiratory and expiratory muscles during the vomiting reflex?
What does this do to the thoracic pressure?
What happens to respiration?
Brain
The reversal of the thoracic pressure gradient
High positive thoracic pressure drives the expulsion of the vomit
Respiration is suppressed
Two factors allowing the ileocecal junction to be a barrier between SI and LI
Valve like folds protruding from the ileum to the cecum
Smooth m at the end of the ideal wall is thickened, making a sphincter
Muscle of the internal anal sphincter?
Muscle of the external anal sphincter?
Circular layer of muscle
Striated muscle
Where are the cell bodies of the intrinsic nervous system in the colon?
Submucosal ganglia (Meissner’s plexus)
Myenteric ganglia (Auerbach’s plexus)
Foregut and midgut innervated by______.
Hindgut innervated by_____.
Both are _______ innervation.
Vagus N (ends at splenic flexure)
Pelvic N (descending and sigmoid colon and anorectum)
Parasympathetic
How does the fecal matter get though the LI and into the rectum?
When?
What controls it?
Mass movements (special type of peristaltic contractions)
3-4 times per day, after meals, contraction for 3 minutes
Parasympathetic innervation
Mass movement is initiated by_____.
Gastronomic or duodenal reflexes
Intense stimulation of parasympathetic nerves
Overdistension of a segment of the colon
What initiates the defecation reflex?
Rectal distension
Contains water, inorganic salts, sloughed-off cells from the mucosa, bacteria, unabsorbed digested materials, indigestible parts of food
90% of water absorption is here
Feces
Large intestine
Smooth m of the rectum and anal canal are controlled by parasympathetic nerves (S2-S4) especially the _______.
Stimulates your rectum and anal canal to _______ assisting in defecation.
Pelvic splanchnic N
Contract
Smooth m of the rectum and anal canal is controlled by the _______ sympathetic nerve (T11-L2).
Stimulate rectum and anal canal to _______.
Hypogastic N
Relax
Internal anal sphincter is controlled by the parasympathetic nerves (S2-S4).
Causes internal anal sphincter to _______ when the rectum and anal canal _______.
Relax
Contract
Internal anal sphincter is controlled by sympathetic nerves (T11-L2).
Cause the internal anal sphincter to ______.
Contract
External anal spinster is controlled by _______ spinal nerves.
S2-S4
Short GI reflexes
Ileogastric reflex
Enterogastric reflex
Gastrocolic reflex
Colonoileal reflex
Long GI reflexes
Vomiting reflex
Pain reflex
Vagovagal reflex
Defecation reflex
Defecation reflex
Internal anal sphincter is _____.
External anal sphincter is ______.
When feces enters rectum, spinal cord reflex is triggered
Involuntary
Voluntary
Urge to defecate occurs when renal pressure is _____.
Internal and external anal sphincters relax and there is reflex expulsion of the rectum contents when renal pressure is _____.
18 mmhg
55 mmhg
