GI physiology Flashcards
besides mechanical ingestion, what systems are necessary to acquire and ingest food?
sensory
- tactile
- visual
- olfactory
- memory
prehension
seizing food and conveying it into the mouth
Mastication
mechanical breakdown of food in the mouth
chewing
deglutition
swallowing
3 stages:
- through the mouth (voluntary)
- through the pharynx (reflex)
- through esophagus (reflex)
segmentation
back and forth mixing due to intermittent contraction of circular smooth muscle
peristalsis
unidirectional (usually aboral) waves of contraction
propulsive motility
moving bolus aborally
retentive motility
material is retained longer
mixing motility
material in lumen is churned
digestive transit time
timing of getting material from one area to another
short in birds (less digestion of high energy berries)
long in ruminants (30+ hours)
digestion vs absorption
digestion is a reduction in size using physical, chemical, and enzymatic breakdown. Aim is to make molecules small enough to be absorbed.
Absorption: transport of nutrient particles into vascular system
mechanical digestion
simple decrease in size
mastication
gastric digestion through contractions, mixing
enzymatic digestion
hydrolysis of chemical bonds via enzymes produced by alimentary tract or bacteria
chemical digestion
hydrolysis of chemical bonds via HCl
mostly in stomach
ruminant saliva
buffered solution required to help support rumen microbes buffer acid produced in fermentation
antifoaming characteristics
flow is continuous but varies with activity
major digestive enzyme in saliva
salivary amylase
maldigestion and malabsorption diseases
share clinical signs but etiologies are different and are treated differently
elimination
Production, temporary storage, expulsion of fecal mass
detoxification
liver is integral
GI bacteria management
all species must:
- prevent bacteria from leaving gut
- maintain correct types of bacteria
- keep colonic bacteria out of small intestine
- provide a good environment for fermentation bacteria
GI intrinsic neuronal control
enteric nervous system
component of ANS
controls majority of GI functions independent of CNS
intrinsic GI hormones
regulate secretions, not released into lumen
made by alimentary tract
have local and systemic functions (secreted into circulation)
extrinsic neuronal control of GI system
parasympathetic: vagus, pelvic n
sympathetic: splanchnic, and hypogastric nerves
only extrinsic gut hormone is aldosterone (water absorption)
aldosterone
extrinsic GI hormone that regulates water absorption
immune function of the GI system
pathogens can enter GI since its exposed to environment
peyer’s patches
immune surveillance of intestinal lumen
facilitate immune response in gut
especially in ileum
paneth cells
secrete antimicrobial peptides and proteins in gut
luminal phase of digestion
within the lumen of the GI tract
varies in region of GI tract (chemical, physical, and chemical)
mouth through at least small intestine
enzymes produced by the organ itself, accessory organs, and/or hosted microbes
luminal digestion produces:
short chain polymers that are still to big to be absorbed
in ruminant and equine symbiotic bacteria can produce some absorbable products
mucosal phase of digestion
only in small intestine
enteric enzymes further digest end products of luminal digestion
absorbable products
intracellular phase of digestion
only in small intestine
important only for protein
short GI reflexes
from gut directly back to gut
named from origin to destination (ex gastrocolic)
usually affect motility or secretion
long GI reflexes
from gut to spinal cord or brainstem the back to gut
ex: defecation, vomiting
starch
repeting units of glucose
highly digestible
cellulose
repeating units of glucose
not digestible without microbial flora
hindgut fermenters
horse
large intestine is modified to host microbes and support fermentation
microbial mass passed out in feces
foregut fermenters
ruminants
stomach modified to host fermentative microbes
