Intestine and colon motility Flashcards
What species cannot vomit?
horses, rats, and rabbits
What are the two vomiting centers?
vomiting center in the reticular formation of the medulla and the chemoreceptor trigger zone
What does the vomiting center in the reticular formation receive information from?
directly from anywhere in the GI tract via vagal and sympathetic afferent fibers
What does the vomiting center in the reticular formation receive information do?
it initiates widespread autonomic discharge to the salivary glands, esophagus, stomach, heart and upper duodenum, activates cranial nerve motor fibers to the pharynx and esophagus, and activates spinal nerve motor fibers to the diaphragm and adominal muscles
What does the chemoreceptor trigger zone recognize?
blood borne chemicals reaching the chemoreceptors in the fourth ventricle; smells, apomorphine, ipecac, and certain tastes
What does the chemoreceptor trigger zone send signals to?
the vomiting center in the reticular formation
What are some immediate physiological changes that occurs before vomiting happens?
salivating, sweating, pallor, and tachycardia
What occurs during vomiting?
pyloric end of the stomach and duodenum contracts, the rest of the stomach and lower esophageal sphincters relax pushing it up to the upper esophageal sphincter until it releaxes and lets it come out; abdominal muscles and diaphragm also contract to raise pressure and push contents into mouth
What can continuous vomiting do to the body?
depletion of the bodies chloride, dehydration, and lack of nutrition
Why can’t rats vomit?
they do not have a vomiting center in the medulla so they can’t coordinate diaphragm muscles and the contraction of the stomach to overcome the lower esophageal sphincter
Why can’t rabbits vomit?
their lower esophageal sphincter muscle does its job too well
Why can’t horses vomit?
their lower esophageal sphincter muscle does its job too well and the angle of the connection between the esophagous and the stomach does not allow for it
What dogs does gastric dilation volvulus usually occur in?
narrowly chested dogs
What happens in gastric dilation volvulus?
the stomach esentially rotates 270 degrees to the right blocking off the esophagus from the stomach; the spleen twists too
How does gastric dilation volvulus lead to necrosis?
the rotation leads to constriction of the splenic and gastric arteries and veins leading to congestion
What seems to be the cause of gastric dilation volvulus?
aerophagia, quick eating, or infrequent meals and boisterous excercise
What is aerophagia?
gulping and swallowing of air
How can quick eating or infrequent meals and boisterous exercise lead to gastric dilation volvulus?
the gastrohepatic ligament stretches as a result alowing the stomach to flip
How can a displaced abomasum occur?
the free space after calving can cause it to move or the abomasal anatomy prevents it from removing gasses so if gasses accumulate it can cause it
What can lead to gas build up in the abomasum?
hypocalcemia, high grain feeding around calving, loss of rumen raft
What are the three types of contractions of the small intestine?
tone, segmental or mixing, and peristaltic waves
What is the purpose of tone contractions?
they prevent the total distention of the gut
What are tone contractions dependent on?
parasympathetics
What are segmental or mixing contractions initiated by?
ingesta in the lumen
What muscles are involved in segmental or mixing contractions?
the circular muscle layer more than longitudinal
What type of reflex are the segmental or mixing contractions?
intrinsic
What is the function of peristaltic waves?
to propel ingesta down the digestive tract
What muscles are involved in peristaltic wave contractions?
coordinated contraction of circular and longitudinal muscle layers
After a small meal in carnivores and omnivores what contractions usually occur in the small intestine and how far do they usually push the ingesta?
segmental contractions and peristaltic contractions which only go about 6-12 inches at a time
Normally, why does the ingesta move so slowly through the small intestine?
it ensures chyme has good contact with enzymes and absorptive surfaces
During the fasting phase how far can peristaltic waves push ingesta?
it can go the length of the entire small intestine
During fasting, why does the ingesta move so fast through the small intestine?
to protect against stagnation and bacterial growth and toxins
What is the primary stimulus for contractions in the small intestine and what does it activate?
distension which activates stretch receptors
What do peristaltic contraction require in order to function?
vagal coordination
What hormones stimulate intestinal motility?
gastrin and CCK
What hormones inhibit intestinal motility?
glucagon, secretin, and epinephrine
What does severe distension of the small intestine lead to?
pain which leads to ileus and sweating
What relaxes the ileocecal sphincter?
distension in the ileum and gastrin
What increases contraction of the ileocecal sphincter?
distension pressure in the cecum or colon
What is the job of the colon and cecum in simple stomached individuals?
absorb remaining water, sodium, other minerals, and volatile fatty acids
What are the fibers of longitudinal muscle layers collected into
bands called teniae coli
True or false: The mucosa of the cecum and colon only have crypts
TRUE
What do colinic glands secrete?
mucus only
What type of contractions occur in the ascending colon?
peristaltic and segmental
What do peristaltic contractions in the ascending colon do?
push towards the ileum to fill the cecum in some species
What do segmental contractions in the ascending colon do?
expose ingesta to the surface area for water and electrolyte absorption
What type of contractions occur in the transverse colon?
segmental contractions
What type of contractions occur in the descending colon?
peristaltic contractions and in some species segmental contractions
In the species that utilize segmental contractions in the descending colon, what is the purpose of them?
they give time to remove even more water leading to pelleted feces
What part of the colon does the vagus nerve send parasympathetic fibers to?
the ascending colon and part of the transverse colon
What part of the colon do the sacral spinal nerves send parasympathetic fibers to?
the remainder of the transverse colon and the descending colon
In the sheep, cow, and dog, how do they get proximal colon material to the cecum?
retrograde peristalsis
What are the three physiologically separate mixing entities of the horse cecum and colon?
the cecum, ventral colon, and dorsal colon
What type of contractions occur within the ventral colon?
segmental and peristaltic contractions
What type of contractions occur within the dorsal colon?
segmental and peristaltic contractions
Material in the dorsal colon can be sent where?
all the way back the entire length of the ventral colon
What does each mixing segment (cecum, ventral colon, dorsal colon) act as?
an independent fermentation vat
What are common areas of constriction in the horses colon?
cecocolic orifice, pelvic flexure, and transverse colon
What does the appendix do?
unknown but contains a lot of lymphoid tissue and serves as a reservoir for commensal bacteria
What occurs in the sprial colon of the pig?
some fermentation
What type of contractions can occur in the spiral colon?
retrograde peristalsis
What is defecation?
a temporary reflex interrupting anal continence by the anal sphincter
How does the defecation reflex occur?
material in the rectum tell the brain via afferents from the sacral nerves that defecation needs to happen, efferents then cause the internal anal sphincter muscle to relax, the external anal sphincter then can be relaxed by the sacral nerve motor neurons
What is the gastrocolic reflex?
distension of stomach can initiate contraction of the rectum and frequently a desire to defecate
What is the gastrocolic reflex mediated by?
gastrin
What is megacolon?
there are no myenteric or submucosal ganglia in a segment of the colon leading to no contractions
What is ileus?
lack of motility in any portion of the gut
What is ileus secondary to?
vagal disruption, opiates, and surgery of the gut
What is borborygmi?
rumbling sound made by gas passing through the small intesine or colon
