GI Tract: Motility Flashcards
What are the four layers of the GI tract from inside of the lumen to outside (serosa)?
Mucosa
Submucosa
Muscularis Externa
Serosa
What layer of the mucosa is a thin layer of smooth muscle and throws the mucosa into folds and helps mix luminal contents?
Muscularis mucosae
What layer of the mucosa is loose connective tissue which attaches to epithelia and contains blood vessels, lymph nodes and some glands?
Lamina propria
What layer of the GI tract is composed of loose connective tissue, blood and lymphatic vessels, major nerve tracts and some glands?
Submucosa
What layer of the GI tract is made up of INNER circular layer and OUTER longitudinal layer of muscle?
Muscularis externa
What is the outer most layer of the GI tract that is made of connective tissue?
Serosa
What is another name for myenteric plexus?
Auerbach’s plexus
What is another name for submucosal plexus?
Meissner’s Plexu
What is the larger of the two plexuses?
Myenteric plexus or Auerbach’s plexus
What plexus is located between the circular and longitudinal muscle layers (muscularis externa)?
Myenteric plexus or Auerbach’s plexus
What plexus lies in the submucosa of the small and large intestine?
Submucosal plexus or Meissner’s plexus
What plexus is concerned primarily with the control of motility?
Myenteric plexus or Auerbach’s plexus
What plexus is concerned primarily with control of secretion from glands of GI tract?
Submucosal plexus or Meissner’s plexus
Sympathetic innervation is supplied by postganglionics from cells in the ___________ and ___________________ ganglia.
Paravertebral and Prevertebral
What does the sympathetic innervation do to the GI tract?
Inhibits contraction of the muscularis externa &
Stimulates contraction in certain sphincters
The parasympathetic innervation is supplied by _____________ (cholinergic) fibers from the vagus and pelvic nerves.
Preganglionic
How are smooth muscles and glands of the GI tract innervated by parasympathetic innervation?
Preganglionic fibers terminate on ganglion cells in the myenteric and submucosal plexuses, and the axons of the ganglion cells innervate the GI tract.
How does the parasympathetic system act on the GI tract?
Activation increases contraction and secretion
About _____% of vagal fibers and 50% of gut sympathetics are afferent fibers.
75%
Where do the cell bodies of sensory neurons lie?
In the submucosal and myenteric plexuses. The cell bodies of other sensory neurons are located in the DRG and cranial ganglia.
Where do the cell bodies of sensory neurons lie?
In the submucosal and myenteric plexuses. The cell bodies of other sensory neurons are located in the DRG and cranial ganglia.
The cell bodies of the sensory neurons that lie in the submucosal and myenteric plexuses are located in what type of reflex arcs?
Local reflex arcs
The cell bodies of the sensory neurons that lie in the submucosal and myenteric plexuses are located in what type of reflex arcs?
Local reflex arcs
The cell bodies of other sensory neurons are loc
d
The cell bodies of other sensory neurons are located in the DRG and cranial ganglia and these participate in what reflex arc?
Central reflex arcs
What is the membrane potential of GI smooth muscle?
-140 to -80 mV
T/F - Different regions of GI tract have different frequencies.
True
What is the purpose of saliva?
Lubricates food and contains alpha-amylase which begins digestion of starches
Sympathetic activity ________ amplitude of slow waves, where as parasympathetic activity _________ amplitude of slow waves.
Sympathetic activity DECREASES amplitude of slow waves, where as parasympathetic activity INCREASES amplitude of slow waves.
What is mastication?
Chewing
What is the purpose of saliva?
Lubricates food and contains alpha-amylase which begins digestion of starches
What type of input by the brain stim functions to initiate and modify masticatory movements?
Cortical input
What input from the oral cavity terminates primarily in the trigeminal and mesencephalic nuclei and acts to modify chewing movements?
Sensory input
What is deglutition?
Swallowing
The swallowing reflex is modulated by the swallowing center located where?
Medulla and pons
What is the voluntary phase of deglutition also known as?
Oral phase
What is the involuntary phase of deglutition also known as?
Reflex phase or pharyngeal phase
What does the upper esophageal sphincter do?
Keeps air out of GI tract
What does the lower esophageal sphincter do?
Prevents reflux of acid and gastric contents
What is the upper sphincter and upper 1/3 of esophagus composed of?
Skeletal muscle
What is the lower sphincter and distal 1/3 of esophagus composed of?
Smooth muscle
What is the intermediate section of the esophagus composed of?
Mixed smooth and skeletal muscle
What are the two types of esophageal peristalsis?
Primary and secondary peristalsis
Describe primary esophageal peristalsis.
The peristaltic wave that began in pharynx during swallowing continues through esophagus taking about 10s to go from upper esophagus to stomach and is controlled by the swallowing center.
T/F - Esophageal peristalsis is not influenced by the rate of swallowing.
False - it is influenced by the rate of swallowing
What does the intensity of peristalsis depend on?
Size and viscosity of the bolus
Is peristalsis required for liquid bolus in an upright position?
NO
T/F - Esophageal peristalsis is not influenced by the rate of swallowing.
False - it is influenced by the rate of swallowing
Fragments > _____mm do not leave the stomach.
2 mm
What is the extrinsic motor innervation for the stomach?
Vagus and celiac plexus
What is the intrinsic motor innervation for the stomach?
Myenteric plexus
T/F - Little mixing of chyme in stomach occurs in fundus and body.
TRUE
How are contents of the stomach emptied?
They are emptied based on layers made due to their densities. For example, fats form an uper oily layer and are thus emptied last
T/F - Liquids leave the stomach last.
False, liquids leave the stomach more quickly than solids
What is the site where most mixing occurs in the stomach?
Antrum
It produces vigorous contractions and food is broken down and mixed with gastric juice. Only a small fraction of chyme is emptied into duodenum
What are some factors that slow emptying?
1) Acid in duodenum (ph<3.5)
2) Fatty acids, mono- or diglycerides in duodenum
3) Hypertonicity in duodenum
4) Peptides and amino acids in duodenum
Vomiting causes ejection of gastric (and sometimes duodenal) contents through the esophagus and mouth, usually preceded by ________, in which some of the stomach content is forced into the esophagus but does not reach pharynx.
Retching
Where is the chemoreceptor trigger zone?
Rostral medulla
What are the different stimuli for vomiting?
1) Distention of the stomach and duodenum
2) Tickling of the back of the throat
3) Noxious stimuli to the genitourinary system
4) Certain smells and sights
5) Semicircular canal stimulation (motion sickness)
6) Emetic agents (ex: ipecac)
What are the consequences of vomiting?
1) Metabolic alkalosis
2) Hypokalemia
3) Dehydration
What movement of the small intestine produces small net movement of chyme?
Peristalsis
Where does the majority of digestion and absorption occur?
Small intestine
What is the most common type of movement of the small intestine?
Segmentation
Contractions of circular muscle layer dividing the small intestine into small segments. It propels chyme in an aboral direction.
What movement of the small intestine produces small net movement of chyme?
Peristalsis
T/F - The MMC that can begin in the stomach and continues in the small intestine can also arise anew anywhere in the small intestine.
True
Most salts and water that enter the colon are absorbed so feces contain only about ____ to _______ ml of water.
50 to 100 ml of water
Where is the majority of transit time of feces?
Colon.
How long does it take after entering the colon for the feces to be evacuated?
1-3 days
What is the parasympathetic innervation that increases motility in the proximal colon (cecum through transverse colon)?
Vagus innervation
What is the parasympathetic innervation that increases motility and innervates the descending colon through the anal canal?
Pelvic nerves (from sacral spinal cord)
How does the sympathetic innervation affect the colons motility?
Inhibits motility
In what disease is there an absence of intramural plexuses and causes the colon to remain constricted?
Hirschsprung’s disease
Is there MMC in the colon?
NO
What are the contractions in the colon?
Haustral contractions and mass movements
What type of contractions in the colon increases mixing and exposure of chyme to gut epithelium?
Haustral contractions
What type of colon contractions pushes the contents over long lengths of colon towards the anus (occurs 1-3 times per day)?
Mass movements
What are the types of reflexes of the colon?
Colonocolonic and Gastrocolic
Which of the two types of reflexes is mediated by the sympathetic innervation and causes distention of one part of colon and relaxes the rest?
Colonocolonic
Which of the two types of colonic reflexes is mediated in part by the nervous system and CCK/Gastrin and causes increase in frequency of mass movements and motility of proximal and distal colon after ingestion of a meal?
Gastrocolic
