Parasympathetic and Sympathetic can raise or lower baseline to increase or decrease. ACH spikes, noreph lowers
3 parts Fundus, Body, Antrum
functions of 3 parts of simple stomach in gastric motility
Fundus: receives and stores by adapting volume
Body: mixing vat for saliva, food and gastric secretions
Antrum: pump, regulates the propulsion of food past pyloric sphincter into duodenum
relaxation of the walls of proximal simple stomach in response to injestion of a large amount of food at one time
Distal stomach gastric motility
peristalsis is weak in fundus and body, strong in antrum, grow as preceed (distally) towards pylorus
Functions of gastric peristalsis
Fragment food into smaller particles
empty gastric contents into duodenum at a controlled rate (pyloric sphincter constricts as peristalsis approaches, allowing only very small molecules (chyme) through. large are retropulsed or sent back.
vigorous backward motion of gastric contents from pylorus to antrum, to mix and grind the contents further (for larger molecules)
Control of gastric motility
Neuro control of gastric motility
Neuro: fibers from vagus to gastric myenteric plexus. High degree of control over motility.
Proximal: vagus suppresses contractions (adaptive relaxation, fundus relaxes for more food in)
Distal: vagus stimulates lots of peristaltic activity.
distal simple stomach gastric motility
Max # of contraction controlled by slow waves(undulating baseline resting potential)--not all result in contraction (spikes on top)
Ach of Vagus can bring membrane potential closer to threshold (stimulated by CNS, stomach and intestine. Thought of food or stomach distension)
Hormonal control of gastric motility
Gastrin: secreted by cells in gastric antrum, ENHANCES gastric motility
Cholecystokinin (CCK) and Gastric inhibitory peptide: SUPPRESS gastric motility (dog)
Regulation of rate of gastric emptying
Enterogastric reflex: sensory receptors in duodenal wall slow gastric emptying
Prevent too much water to leave the body if chyme is hypertonic, and allows proper reabsorption etc to occur
Sensory receptors in duodenal wall slow rate of gastric emptying by slowing and decreasing force of gastric contractions, increase contraction of pyloric sphincter
Stimulated by too much chyme, low chyme pH, high amino acids or fatty acids in chyme, hyper or hypotonic chyme.
Hormonal reflex, use of CCK
cholecystokinin secreted when chyme has too much amino acid or fatty acids, or low pH.
Secreted by duodenal mucosa into blood stream.
slows gastric emptying by further constriction of pyloric sphincter (slows chyme for normal digestion)
Hormonal reflex, use of GIP
Gastric inhibitory polypeptide
secreted by jejunal mucosa in response to presence of lipids and carbohydrates
delays gastric emptying.
expulsion of contents of stomach and proximal duodenum through mouth.
Controlled by emetic center in brain (brainstem--medulla?)
Series of reflexes initiates and closes glottis and nose.
Easy for pigs, d/c. Ruminant vomits abomasal into forestomach.
Horses can't/shouldn't. Terminal. Stomach rupture
Motility in ruminant stomach
2-3 per minute. 2 parts
Primary is mixing and separating large and small molecules
Secondary is eructations, contractions moving liquid down so gasses can go up.
Process of bringing food material back from the ruminant stomach to the mouth for further mastication.
Allows for rapid food intake during grazing, chew later. Spread out evenly throughout day. Different hours with diet (8 for hay)
4 phases include regurgitation, remastication, reinsalivation, reswallowing (redeglutition).
step one in rumination.
Reticulum contracts, bringing material from dorsal to cardia. Cardiac sphincter relaxes, animal takes breath against closed glottis, negative pressure in thorax, dilates esophagus and cardia, rumen contracts, pressure in rumen rises, bolus goes to esophagus for lower pressure, reverse peristalsis, bolus in mouth.
Remastication and Resalivation
steps 2-3 in rumination. Occur together
Immediatly after bolus in mouth, liquid squeezed out and swallowed.
Thorough and deliberate remastication, # based on diet, roughage chewed more than 100 times.
100-200 L (25-50 gallons) saliva in 24 hours.
last step in rumination. Reswallowing of bolus.
Occurs when food is ready. Next cycle begins in 5 seconds.
Process by which gas from forestomach is removed by esophagus and pharynx
Gasses produced during fermentation are mainly CO2 and methane.
CO2 from fermentation of carbs and deamination of amino acids (60-70%)
Methane is reduced from CO2 by bacteria (30-40%)
Process of Eructation
Gas bubble moves cranially and ventrally towards cardia with contractions/relaxation, making sure there is no injesta. (like belch but no sound)
Nasopharyngeal sphincter contracts, directing part of gas into trachea, where it is moved into lungs on inspiration.
types of movement in small intestine (2)
Segmentation in small intestine
Stretching of intestinal wall trigters ring of circular muscles to contract. As one area relaxes, another contracts.
Mix digesta with enzymes/juices and increase contact with membrane for absorption.
Large intestine functions
absorption of water and electrolytes
storage of feces
in non-ruminant herbivores, fermentative digestion and absorption of nutrients
Large intestine motility patterns
segmentation - like small intestine, localized circular contractions to make sacs
antiperistalsis - to mix and bring near membrane
mass movement - moves entire contents nearer rectum.
modified form of segmentation in which intense local contractions of circular muscle cause large intestine to appear to bulge into sacs.
Consequences of LI activity
Activity of colon is for delay of transit and filling of parts (reservoir)
Increased activity = constipation
decreased activity = diarrhea
Mass movement (LI)
Period of intense propulsive activity that moves entire contents of colon distally towards rectum.
Colon, sometimes equine cecum.
Complex reflex act in which feces are evacuated from terminal colon and rectum.
Frequency depends on species/animal (5-10/day horses; 10-20 cows; 2-3 carnivores)
Intestinal transit time
Amount of time it takes for material to travel from one part of the gut (or whole gut) to another. (fast = decreased intestinal transit time)
Varies with species (Pig 48h, horse 24-48h, cattle see in 12-24, 80% in 3-4d, all in 7-10d).