GI physiology Flashcards
prehension
the act of moving food into the mouth
what directly controls prehension
CNS- facial nerve, glossopharyngeal and the motor branch of the trigeminal nerve
mastication
the first act of digestion (in the mouth eg- chewing)
what is the purpose of mastication
break down food particles to increase surface area for digestion, it moistens and lubricates food
3 main salivary glands in all animals
-parotid
-mandibular
-sublingual
salivary gland unique to dogs
zygomatic
what type of saliva comes from the zygomatic and sublingual glands
mucous
mucous saliva properties
thicker, important for binding food into a bolus
what type of saliva comes from the parotid gland
serous
properties of serous saliva
watery, contains amylase
what controls the salivary glands
parasympathetic nervous system
where do nerve fibres end in the salivary gland
the acini
mucins (glycoproteins) role in saliva
lubrication, mix with water to form mucous
HCO3- role in saliva
pH regulation, neutralisation
lysosomes and antibodies role in saliva
antibacterial, keep the amount of bacteria in check
how is starch digested
amylase
how is fat digested in young cows
lingual lipase
how does thermoregulation occur in canines and rodents
panting, spreading saliva (evaporative cooling)
how does urea get to the saliva
diffuses from the blood
why is ruminant saliva alkaline
necessary for neutralisation of fermentation products
deglutition
action/ process of swallowing
2 phases of deglutition
voluntary and involuntary
voluntary
chewed food is moulded into a bolus and moved to the pharynx
involuntary phase of deglutition
1) breathing stops momentarily
2) soft palate is elevated
3) tongue is pressed against the hard pallet
4) glottis is pulled under the epiglottis
5) when all openings into the pharynx are closed a wave of muscular contraction passes over the walls of the pharynx
6) the upper oesophageal sphincter relaxes
what controls the involuntary phase of deglutition
motor neurons- efferent nerve fibres travel in the facial, vagus, hypoglossal and glossopharyngeal nerves
3 layers within the tunica mucosa
epithelium, lamina propria, muscularis mucosae
what type of muscle is found in dog, cow and sheep oesophagus
striated
what type of muscle is found in horse, primates and cats oesophagus
smooth muscle
what nerve innovates striated muscles
vagus nerve
what innovates smooth muscle
ENS
oesophagus during deglutination
oesophagus is relaxed but upper and lower sphincters are tightly constricted
where does peristalsis occur
at all levels of the gut
what is peristalsis
moving ring of constriction
what are the three main tasks of the stomach
- temporary food store
-some degradation of protein and starch
-hydrochloric acid kills bacteria in food
what part of the stomach is the proximal stomach referring to
cardia and funds
is contraction maintained when stomach is emptying
yes
when do promiml stomach muscles relax
when animal eats regulated via vagus nerve
what is the distal stomach relating to
pyloric region
why does more active digestion occur in the distal stomach
stronger peristaltic contractions
4 types of cells in pits in the stomach wall
1) mucin producing
2) parietal
3) chief
4) endocrine
what type of epithelium lines the lumen of the stomach
simple columnar
in which parts of the stomach are most of the gastrin juices produced
fundus and corpus (body of the stomach)
what do glands in the cardia region of the stomach produce
mucus
what do gastric juices mainly consist of
HCl and pepsinogen
which gland secretes HCl
parietal
what does HCl do to pepsinogen
transforms it to pepsin
why does pepsinogen. only turn to pepsin with stomach HCl
pepsinogen is inactive, pepsin would degrade connective tissue and muscle
how is HCl produced
H/K ATP-ase pump (provides H+)
HCO3-/Cl- pump (provides Cl-)
what cells synthesise and store pepsinogen
chief cells
what is the role of pepsin
degrades proteins to peptides
what 3 substances exert stimulatory effects on regulating gastric secretions
ACH, Gastrin, Histamine
what happens when gastrin is released into the blood
stimulates the secretion of HCl, pepsinogen and promotes gastrin motility
what is the role of histamine
acts as a pancreatic hormone, stimulating HCl secretions
what reflexes are stimulated by stomach expansion
vagal
what organ inhibits secretion
signals from the duodenum
what causes secretion to be inhibited
if pH falls too low
At the start of eating a meal HCl secretion is high but then the stomach is supplied with a buffer which decreases gastrin release
why does food layer in the order we eat it in the order it was eaten in the proximal stomach
contractions here are weak
factors affecting rate of stomach emptying
expansion of the stomach wall and gastrin
what is optimal digesting
when the rate of the stomach emptying equals the capacity of intestines to digest food
distension of the duodenum in affecting rate of stomach emptying
as duodenum fills the pyloric sphincter will close, slowing and eventually
stopping the transfer of chyme from the stomach to the intestine
reduced pH in affecting rate of stomach emptying
If more acid is transferred to the duodenum than can be neutralised then intestinal enzymes cannot function
what mediates the rate of stomach emptying
secreting, CCK and GIP
what do young ruminate produce in the abomasum to aid milk digestion
rennin
