GI physiology 1 and 2 Flashcards
Prehension
The act of moving food into your mouth
What controls the Prehension process?
The CNS
What primary nerves are involved in prehension
facial nerve, glossopharyngeal nerve and the motor branch of the trigeminal nerve
Mastication
chewing: breaking down food into smaller particles, also moisturises dry food
What type of cells are found within the mouth
stratified squamous epithelium, hardy against digestive jices
What sensory neurons are found within the mouth?
terminal branch of the sensory neurons
What are the two types of saliva?
Mucous (from zygomatic and sublingual) and Serous saliva (from the parotid)
What is mucous saliva?
Thicker, helps form a bolus/ ball to move through the GI Tract
What is Serous saliva?
more watery, contains amylase
What are our salivary glands mainly controlled by?
The parasympathetic nervous system
What receptors do salivary secretory cells contain?
Beta adrenergic receptors which can be activated by sympathetic nerve stimulation (e.g dog drooling when it smells food)
What are the 3 main functions of saliva?
Lubrication, pH regulation and antibacterial
Mucins (glycoproteins)
Mix with water to form mucous in the oesophagus
What do binding proteins in the saliva do?
Bind to tannins, makes them less bitter and easier to consume
Deglutition
The process of swallowing
What happens when an animal swallows
Soft palate is raised, epiglottis springs back to close the trachea and protects the food from entering
Voluntary phase
first phase, producing a bolus and moving it to the back of the mouth for swallowing
Involuntary
Involuntary swallowing of the food, breathing stops, soft palate is elevated, glottis is pulled under the epiglotis
What controls deglutition?
controlled by motor neurons in various centres of the brainstem (involuntary)
The Serosa
outside of the muscularis, a serous membrane
What is the function of the mucousal layer?
To secrete mucus
Oesophagus in dogs, cattle and sheep
entire length is striated
Oesophagus in horses primates and cats
partially smooth, partially striated (smooth muscle is under the control of the enteric nervous system)
What happens in the oesophagus when deglutition is not taking place
Oesophagus is relaxed but both sphincters are tightly constricted
What happens in the oesophagus when deglutition is not taking place
Oesophagus is relaxed but both sphincters are tightly constricted
What are the three main tasks of the stomach?
Acts as a temporary food store for kine (food mixed with gastric juices), degredation of protein and starch and production of HCL to kill off bacteria
Oesophageal sphincter
At the top of the stomach (fundus), lined with stratified squamous epithelium to resist the effect of acid erosion (could cause ulcers)
What animal has a large cardia?
Pigs, because they need a place to store food for long periods of time
Where do most of the gastric secretions occur?
In the corpus
Proximal stomach
parts of the stomach that are closer to the mouth, fundus and cardia region
Distal stomach
parts of the stomach that are closer to the small intestine, pylorus
tonic contraction
when the stomach is empty muscle contraction is maintained (otherwise it would just collapse in on itself)
receptive relaxation
when an animal eats, the muscles relax, under control of vagal nerve fibres- tells the CNS that the stomach is receiving food and to prepare for digestion
Which part of the stomach has stronger waves of peristalsis?
The distal part (pylorus) as this is the “cement mixer part” that churns up your food
How does chyme get pushed out the stomach?
pylorus wall contracts simultaneously, pushing it through the partially open sphincter
What cells line the lumen?
simple columnar epithelium, these secrete a bicarbonate
Mucin producing cells
found in pits in the stomach wall, produce a mucus
Parietal cells
located further down in the pits/crypts, secrete HCL and an intrinsic factor that is required for the absorption of vitamin B12 in the small intestine
Chief cells
found further down in the pits, produce a precurser enzyme, pepsinogen,
Endocrine cells in the pyloric region
G cells that produce gastrin, this is secreted into the blood and regulates the secretion of of HCL from parietal cells
ECL cells
found in the fundus and corpus, produce histamine
What produces HCL?
hydrogen/potassium ATPase pump in the wall of the parietal cell
Auto catalysis
Pepsin degrades other pepsin molecules to make them active/ an example of positive feedback
What are three substances that regulate gastric secretion?
acetylcholine, Gastrin and histamine
What inhibits gastric secretion in the stomach?
signals from the duodenum or if the pH becomes too low, therefore less HCL is released
What are two ways of increasing the rate of stomach emptying?
Expansion of the stomach wall ( controlled by acetylcholine) and secretion of gastrin
What happens when you have a high fat/ protein meal?
(makes you feel more full) CCK stimulates the release on pancreatic enzymes and acts as a hunger suppressant
Which animal produces rennin in the abomasum
young ruminants
Stimulation of salivary glands by B adrenergic receptors
Not digestive activity, occurs in carnivores about to attack
What is the function of lysozymes in saliva
To keep the amount of bacteria ‘in check’
How much saliva does an adult cow excrete every day?
100-200 Litres
