5- Motility of GI System Flashcards
________ involves the contraction and relaxation of the walls and sphincters of the GI tract.
Motility
Motility _______ is regulated along the GI tract.
Rate
Contractions of the ________ ________ mix and circulate the content of the lumen and propel through the GI tract.
Muscularis Propria
What are the functional layers of the GI tract?
Mucosal Layer
Submucosa
Muscle Layers (Muscularis Propria)
Serosa
The mucosal layer of the GI tract consists of the ________ ________, which is composed of smooth muscle and its contractions change the shape and surface area of the epithelium.
Muscularis Mucosae
The muscle layers (Muscularis Propria) of the GI tract are made of smooth muscle layers and provide motility to the GI tract. What muscles are contained in this layer?
Circular Muscle
Longitudinal Muscle
The contraction of this GI tract muscle decreases the diameter of the segment.
Circular Muscle
The contraction of this GI tract muscle decreases the length of the segment.
Longitudinal Muscle
These are the depolarization and depolarization of the membrane potential in the GI smooth muscle. They are NOT action potentials.
Slow Waves
For slow waves, the ________ response follows the electrical response.
Mechanical
T/F. Slow waves can sometimes create enough depolarization to reach threshold and create action potentials.
True
These type of contractions are periodic, followed by relaxation. It occurs in the esophagus, stomach (antrum), small intestine, and all tissues involved in mixing and propulsion.
Phasic Contractions
These type of contractions maintain a constant level of contraction without regular periods of relaxation. It occurs in the stomach (orad), lower esophageal, ileocecal, and internal anal sphincters.
Tonic Contractions
***This is important because it maintains a contraction to close off certain parts of the GI tract. It relaxes when things need to pass through!
The greater the number of action potentials on top of the slow wave, the (SMALLER/LARGER) the contraction.
Larger
Explain the difference between the stomach and the intestines regarding the slow wave that does NOT reach threshold to create action potentials.
In the stomach, a slow wave that does not reach threshold can still create a small contraction. In the intestines, a slow wave that does not reach threshold can NOT create any contraction.
_________ increases the amplitude of slow waves and the number of action potentials, while _________ decreases the amplitude of slow waves.
ACh
NE
***Think parasympathetics and sympathetics!
What are the 3 main things that can stimulate slow waves and help to reach threshold and create action potentials?
- Stretch
- ACh
- Parasympathetics
What are the 2 main things that will decrease slow waves and cause hyperpolarization?
- NE
2. Sympathetics
What makes up the Enteric Nervous System (ENS)?
Submucosal Plexus
Myenteric (Auerbach’s) Plexus
This portion of the ENS mainly controls GI secretions and local blood flow.
Submucosal Plexus
This portion of the ENS is between the longitudinal and circular layers, and mainly controls GI movements.
Myenteric (Auerbach’s) Plexus
_________ regions in the Myenteric and Submucosal Plexuses generate spontaneous slow wave activity.
Pacemaker
These cells are the pacemaker for GI smooth muscle. They generate and propagate slow waves.
Interstitial cells of Cajal (ICC)
Slow waves occur spontaneously in the ICC and spread rapidly to smooth muscle via…
Gap Junctions
_________ activity in the ICC drives the frequency of contractions.
Electrical
ICC generate and propagate slow waves. Electrotonic conduction of slow waves cause smooth muscle cells to respond to the slow depolarizations with increased ________ channel open probability. This results in action potentials and contraction.
Calcium
Most of the muscles of mastication are innervated by the motor branch of what nerve?
CN V (Trigeminal)
The act of ________ is both voluntary and involuntary. It is controlled by nuclei in the brain stem and caused by a chewing reflex.
Mastication
What are the phases of swallowing, both voluntary and involuntary?
Oral Phase (Voluntary) Pharyngeal Phase (Involuntary) Esophageal Phase (Involuntary)
This phase is voluntary and initiates the swallowing process.
Oral Phase
This phase consists of striated muscle and lasts 1-2 seconds. Food bolus is propelled through the upper esophageal sphincter (UES).
Pharyngeal Phase (Involuntary)
Describe what happens in the Pharyngeal Phase of swallowing.
Soft Palate is pulled upward —
Epiglottis moves —
UES relaxes —
Peristaltic wave of contractions initiated in pharynx —
Food propelled through open UES
This phase consists of smooth muscle and lasts 8-10 seconds. It is controlled by the swallowing reflex and ENS. It has a primary and secondary peristaltic wave.
Esophageal Phase (Involuntary)
What is the difference between the primary and secondary peristaltic waves in the Esophageal Phase?
Primary Peristaltic Wave – transfers food bolus
Secondary Peristaltic Wave – backup plan for any remnants of bolus left behind
The involuntary swallowing reflex is controlled by the…
Medulla
Describe the neurological steps involved the Pharyngeal Phase of swallowing.
Food in Pharynx —
Afferent sensory input via Vagus/Glossopharyngeal N. —
Swallowing Center (Medulla) —
Brainstem Nuclei —
Efferent input to Pharynx
This type of peristaltic wave is a continuation of the pharyngeal peristalsis. It is controlled by the medulla.
Primary Peristaltic Wave
Primary Peristaltic Waves (CAN/CANNOT) occur after vagotomy.
Cannot
This type of peristaltic wave occurs if the primary wave fails to empty the esophagus or if gastric contents reflux into the esophagus. Medulla and ENS are involved.
Secondary Peristaltic Wave
Secondary Peristaltic Wave (CAN/CANNOT) occur in the absence of oral and pharyngeal phases, and (CAN/CANNOT) occur after vagotomy.
Can
Can
During swallowing there are changes in ________ along the esophagus as food bolus passes through it.
Pressure
***High pressures can mean tonic contraction, like at UES and LES!
Explain the challenges with the intrathoracic location of the esophagus, and how these challenges are overcome.
Problems = Keeping air out of esophagus at the upper end and acidic gastric contents out of the lower end.
Solutions = UES and LES are closed, except when food bolus is passing from pharynx to esophagus or from esophagus to stomach.
This is a motility disorder that occurs from impaired peristalsis. There is incomplete LES relaxation during swallowing, causing elevation of LES resting pressure. LES stays closed during swallowing, resulting in the back up of food.
Achalasia
Why does achalasia happen?
– Decreased number of ganglion cells in Myenteric Plexus
– Degeneration preferentially involves inhibitory neurons producing NO/VIP (these relax the LES)
– Damage to nerves in the esophagus, preventing it from squeezing food into the stomach
What can achalasia result in?
– Backflow of food in the throat (regurgitation)
– Difficulty swallowing liquids and solids (dysphagia)
– Heartburn
– Chest Pain
How can we test for achalasia?
- Barium swallow test
- - Esophageal motility studies
In this disorder, there are changes in the barrier between the esophagus and stomach (i.e., the LES relaxes abnormally or weakens).
GERD (Gastroesophageal Reflux Disease)
Why does GERD occur?
Motor abnormalities that result in abnormally low pressures in the LES.
– If intragastric pressure increases, such as after a large meal, during heavy lifting, or during pregnancy.
– Persistent reflux and resulting inflammation lead to GERD.
Results of GERD include backwash of ______, ______, and ______ into the esophagus. This leads to heartburn and acid regurgitation.
Acid
Pepsin
Bile
Some complications of GERD include GI bleeds, esophagitis, scar tissue in the esophagus (Stricture of esophagus), and _________ esophagus. This is when cells transform into cells resembling intestine, which are more resistant to acid (columnar epithelium).
Barrett’s
What are the anatomical regions of the stomach and the regions based on motility?
Anatomical = Fundus, Body, Antrum
Motility = Orad, Caudad
What are the 3 layers of muscle in the stomach?
Circular
Longitudinal
Oblique
What are the extrinsic and intrinsic innervations of the stomach?
Extrinsic = Parasympathetic and Sympathetic
Intrinsic = Myenteric and Submucosal Plexuses (ENS)
Receptive relaxation occurs in the Orad region of the stomach. There is (INCREASED/DECREASED) pressure and (INCREASED/DECREASED) volume in the Orad region, this is called the Vagovagal reflex to receive the food bolus.
Decreased
Increased
Orad region exhibits minimal contractile activity. There is little mixing of ingested food that occurs here. _______ decreases contractions and there is increased gastric ________.
CCK
Distensibility
***CCK is a hormone released from small intestine!
Mix and digestion occur in the _______ region of the stomach.
Caudad
In the Caudad region, the primary contractile event is peristaltic contraction (mid stomach to pylorus). Contractions (INCREASE/DECREASE) in force and velocity as they approach the pylorus. Max frequency is about 3-5 waves per minute.
Increase
In the _______ region, most of the gastric contents are propelled back into the stomach for further mixing and further reduction of particle size. Called Retropulsion.
Caudad
What increases the gastric action potentials and force of contractions?
Parasympathetic stimulation
Gastrin
Motilin
What decreases the gastric action potentials and force of contractions?
Sympathetic stimulation
Secretin
GIP
Gastric emptying (takes about 3 hrs) is accomplished by coordinated activity of what things?
Stomach
Pylorus
Proximal Small Intestine (Duodenum)
What increases the rate of gastric emptying?
– Decreased distensibility of the Orad stomach (also means increased tone)
– Increased force of peristaltic contractions of the Caudad stomach
– Decreased tone of the pylorus (relaxation)
– Increased diameter and inhibition of segmenting contractions of the proximal duodenum
Gastric emptying is closely regulated to provide adequate time for neutralization of gastric ______ in the duodenum and sufficient time for digestion and absorption.
H+
What decreases the rate of gastric emptying?
– Increased distensibility of Orad stomach (decreased tone)
– Decreased force of peristaltic contractions of Caudad stomach
– Increased tone of pyloric sphincter
– Segmentation contractions in intestine
This reflex is a result of negative feedback from the duodenum that will slow down the rate of gastric emptying.
Entero-Gastric Reflex
Describe the Entero-gastric reflex when there is acid in the duodenum.
Acid in duodenum stimulates Secretin release —
Secretin inhibits stomach motility via Gastrin inhibition
Describe the Entero-gastric reflex when there are fats in the duodenum.
Fats in duodenum stimulates CCK and GIP —
Inhibit stomach motility
This is the most common problem associated with disorders of gastric motility. Symptoms include fullness, loss of appetite, nausea, and sometimes vomiting.
Slow gastric emptying
Slow gastric emptying can be caused by gastric ulcers (scar tissue), cancer (physical obstruction), eating disorders (anorexia nervosa, bulimia nervosa, obesity), vagotomy (once used to reduce acid secretion). What are treatments for slow gastric emptying?
Pyloroplasty
Balloon Dilation
This is a disorder due to the slow emptying of the stomach or paralysis of the stomach in the absence of mechanical obstruction. Diabetes Mellitus is a common cause of this due to the neuropathy to the Vagus N.
Gastroparesis
Symptoms of Gastroparesis include nausea, vomiting, an early feeling of fullness when eating, weight loss, abdominal bloating, and abdominal discomfort. Gastroparesis can be caused by injury to what nerve?
Vagus N.
This is a complex that empties large particles of undigested residue remaining in the stomach. It consists of periodic, bursting peristaltic contractions at 90 minute intervals during fasting ONLY. Inhibited during feeding.
Migrating Myoelectric Complex/Migrating Motor Complex (MMC)
_______ plays a significant role in mediating the MMC.
Motilin
_______ is a condition of colonic bacteria overabundance in the small intestine. MMC is important for cleansing mechanisms in the small intestine of debris and prevention of this. Can cause small bowel motility disruption resulting in nausea, anorexia, and bloating.
SIBO (Small Intestinal Bacterial Overgrowth)
Motility in the small intestine is key for its digestive and absorptive functions. What are these functions?
– Mix chyme with digestive enzyme and pancreatic secretions.
– Expose nutrients to intestinal mucosa for absorption.
– Propel unabsorbed chyme along small intestine to large intestine.
(PERISTALTIC/SEGMENTATION) contractions generate back-and-forth movements. This produces no forward or propulsive movements along the small intestine. Only used for mixing!
Segmentation
(PERISTALTIC/SEGMENTATION) contractions utilize the circular and longitudinal muscles working in opposition to complement each other’s actions. They are reciprocally innervated. This propels food.
Peristaltic
Slow wave activity is always present whether contractions are occurring or not. Unlike in the stomach, slow waves themselves (DO/DO NOT) initiate contractions in the small intestine. Action potentials are necessary for contraction to occur. Slow wave frequency sets the maximum frequency of contractions.
Do Not
What is the slow wave frequency gradient across the small intestines?
Duodenum = 12 cycles/min Jejunum = 10 cycles/min Ileum = 8 cycles/min
__________ is released by enterochromaffin cells and binds to receptors in IPANs (Intrinsic Primary Afferent Neurons), initiating the peristaltic reflex.
Serotonin (5-HT)
IPANs will lead to interneurons, which then go on to either Excitatory Motor Neurons (contraction) or Inhibitory Motor Neurons (relaxation). What NTs lead to each of these?
Excitatory Motor Neurons = ACh or Substance P
Inhibitory Motor Neurons = VIP or NO
The ________ Plexus mainly regulates the relaxation and contraction of the intestinal wall. The ________ Plexus senses the lumen environment.
Myenteric (Auerbach’s)
Submucosal (Meissner)
Contractions of the intestine are controlled by activities of the ICCs and smooth muscle cells, as well as neural and hormonal responses. What is the neural input?
– Peristaltic reflex mediated by ENS
– Parasympathetics stimulate and sympathetics inhibit contractions
Contractions of the intestine are controlled by activates of the ICCs and smooth muscle cells, as well as neural and hormonal responses. What is the hormonal input?
Stimulate Contractions =
- Serotonin
- Prostaglandins
- Gastrin
- CCK
- Motilin
- Insulin
Inhibit Contractions =
- Epinephrine
- Secretin
- Glucagon
The vomiting reflex is coordinated by the ________. Nerve impulses are transmitted by Vagus and Sympathetic afferents to multiple brain stem nuclei.
Medulla
What are the events of the vomiting reflex?
– Reverse peristalsis in small intestine
– Stomach and pylorus relaxation
– Forced inspiration to increase abdominal pressure
– Movement of larynx
– LES relaxation
– Glottis closes
– Forceful expulsion of gastric contents
Flow of contents from the small intestine into the large intestine is partly regulated at the ________ _______.
Ileocecal Junction
Distention of the Ileum causes (CONTRACTION/RELAXATION) of the sphincter, and allows flow of contents from the Ileum into the Colon.
Relaxation
Distention of the Colon causes (CONTRACTION/RELAXATION) of the sphincter, prevents passage of contents from the Colon to the Ileum.
Contraction
The longitudinal muscle layer of the large intestine consists of ________ _________, which are 3 flat bands of longitudinal fibers that run from the cecum to the rectum. The _________ muscle layer is continuous from the cecum to the anal canal.
Taeniae Coli
Circular
What are the anal sphincters, and what type of muscle are they composed of?
Internal Anal Sphincter – Smooth Muscle
External Anal Sphincter – Skeletal (Striated) Muscle
These are small pouches that give the large intestine its segmented appearance. They are not fixed, they appear and disappear.
Haustras
What innervates the Internal Anal Sphincter?
Pelvic Splanchnic Nerves (Parasympathetic)
What innervates the External Anal Sphincter?
Pudendal N.
This is what innervates the muscle layers of the large intestine. Concentrated beneath teneae.
ENS (Myenteric Plexus)
What parts of the large intestine does the Vagus N. (Parasympathetic) innervate?
Cecum
Ascending Colon
Transverse Colon
What parts of the large intestine do Pelvic Ns. (Parasympathetic) innervate?
Sacral portion of SC (S2-S4)
Descending Colon
Sigmoid Colon
Rectum
What are the Sympathetic innervations (T10-L2) of the large intestine?
– Superior Mesenteric Ganglion = Proximal regions
– Inferior Mesenteric Ganglion = Distal regions
– Hypogastric Plexus = Distal rectum and anal canal
Motility in the large intestine occurs in mass movements over large distances. Happens 1-3 times per day and stimulates _________ reflex. A final mass movement propels the fecal content into the rectum.
Defecation
Motility in the large intestine is key for what?
– Absorption of water and vitamins
– Conversion of digested food into feces
(POOR/EXCESS) motility in the large intestine causes greater absorption, and hard feces in the transverse colon causing constipation.
Poor
(POOR/EXCESS) motility in the large intestine causes less absorption and diarrhea or loose feces.
Excess
The rectum fills intermittently via mass movements and segmentation contractions. As it fills with feces, the smooth muscle wall of the rectum contracts and the internal anal sphincter relaxes. This is called the…
Rectosphincteric Reflex
The external anal sphincter is tonically closed because it is under ________ control.
Voluntary
The Rectosphincteric Reflex is under neural control partially by the ________ and reinforced by activity of neurons within the ________ ________.
ENS
Spinal Cord
Sensation of rectal distention and voluntary control of the external anal sphincter are mediated by pathways within the _______ _______ that lead to the cerebral cortex.
Spinal Cord
***If these pathways are destroyed you will SHIT YOURSELF. PVS NOT GOOD.
This disease is caused by the absence of ganglion cells from a segment of the colon. It’s due to the abnormal migration of NCCs.
Hirschsprung’s Disease
Hirschsprung’s Disease results in low ______ levels, which causes smooth muscle constriction and loss of coordinated movement. The colon contents then accumulate (colon equivalent of achalasia). When present at birth, it causes difficulty in passing stool (congenital megacolon).
VIP
For Hirschsprung’s Disease, in an affected newborn it is characterized by failure to pass _________. Other symptoms in newborn/infants include poor feeding, jaundice, and vomiting. In older children symptoms include constipation, swollen belly, and malnutrition.
Meconium
How can we treat Hirschsprung’s Disease?
Surgical resection of colon segment lacking ganglia
This is a long reflex that is generally stimulatory and increases motility, secretomotor, and vasodilatory activities. Vagus carries both afferents and efferents.
Vago-vagal Reflex
This reflex depends on extrinsic neural connections and is inhibitory. If an area of the bowel is grossly distanced, contractile activity in the rest of the bowel is inhibited.
Intestino-intestinal Reflex
This reflex is negative feedback from the duodenum that slows down the rate of gastric emptying.
Enterogastric Reflex
This reflex is the gastric distention that relaxes the ileocecal sphincter.
Gastroileal (Gastroenteric) Reflex
This reflex is the distention of the stomach/duodenum that initiates mass movements. Transmitted by way of the ANS.
Gastro- and Duodeno-Colic Reflexes
This reflex is when the rectal distention initiates defecation. When the rectum is distended by feces, the internal anal sphincter relaxes.
Defecation (Rectosphincteric) Reflex
