7. GIT - physiology 1 Flashcards
What is prehension?
the act of moving food into the mouth, directly controlled by the CNS
what nerves are involved in prehension?
- facial nerve
- glossopharyngeal nerve
- the motor branch of the trigeminal nerve
what is mastication?
the first act of digestion
what does mastication allow?
- breakdown of food particles to increase surface area for digestion
- Moisten and lubricate food to prevent it from getting stuck in the oesophagus
what structures are involved in mastication?
- Stratified squamous epithelium
- Terminal branches of sensory neurons
what are the 2 types of saliva?
- mucous
- serous
what salivary glands produces mucous saliva?
- sublingual
- zygomatic
what salivary gland produces serous saliva?
parotid
describe mucous saliva compared to serous
- mucous is thicker/more viscous
- serous is watery and contains amylase
describe mucous saliva compared to serous
- mucous is thicker/more viscous
- serous is watery and contains amylase
what is mucous saliva important for?
binding food into a bolus
what are salivary gland mainly regulated by?
parasympathetic nervous system
describe the salivary gland structure?
- Striated duct (in and out)
- Intercalated ducts (bunches of grapes)
- Acini (secrete saliva)
- Nerve fibres on the outside of the gland - only controlled by neurons
how are salivary glands controlled?
- regulated mainly by the parasympathetic nervous system
- the stimulation of nerve fibres on the end of the acini results in saliva production
- the sympathetic nervous system activates b-adrenergic receptors in salivary secretory cells: occurs in fight or flight and produces a smaller quantity of vicious saliva. stimulation could be carnivores about to attack.
list the constituents of saliva including
- function
- component
- how it works
Function: lubrication
Component: Mucins (glycoproteins)
How: mix with water to form mucous
Function: pH regulation
component: HCO3-
How: neutralisation
Function: antibacterial
Component: Lysozyme antibodies
how: keep the amount of bacteria in check 21
how are Omnivores, Single-stomached herbivores, and some avians saliva specialised
Starch digestion - amylase in saliva - mixed with food before stomach. Acts in stomach
how are young calves saliva specilised
Fat digestion - using lingual lipase to help digest milk
how are canines and rodents saliva specialised
thermoregulation:
- Panting in canines
- Rodents lick fur to help with evaporation from the skin
how are leaf-eaters saliva specilised
binding of tannins
Tannins bitter and sometimes unpalatable - uses Binding proteins
how are animals with forestomachs saliva specilised
Providing urea; Urea diffuses from the blood into saliva
how are ruminants saliva specilised
saliva is alkaline, this is necessary for the neutralisation of fermentation products
what is the problem with ruminant saliva specialisation
H20 and electrolytes secreted in saliva must be reabsorbed rapidly or else the cow can become dehydrated and become acidotic
what is deglutition?
process of swallowing
what are the 2 phases of deglutition
- voluntary
- involuntary
what happens in the voluntary phase of deglutition?
chewed food is moulded into a bolus and moved to the pharynx (swallowed)
what happens in the involuntary phase of deglutition?
1) Breathing stops momentarily
2) Soft palate is elevated
3) The tongue is pressed against the hard palate
4) The 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
how is deglutition controlled?
Involuntary - controlled by motor neurons in various centres of the brainstem
- Efferent nerve fibres travel in the facial, vagus, hypoglossal and glossopharyngeal nerves
list the layers of the oesophagus
Serosa
Muscularis layer (longitudinal and circular muscle )
Submucosa layer
Mucosa layer (Muscularis mucosae, lamina propria, epithelium)
describe the serosa layer of the oesophagus
connective tissue that covers the longitudinal muscle, which is the base layer of the muscularis
describe the muscularis layer of the oesophagus
has 2 sublayers: longitudinal and circular muscle.
- Longitudinal - runs down the oesophagus from mouth to stomach
- Circular muscle - runs around the oesophagus in rings
describe the submucosa layer of the oesophagus
all the blood vessels and nerves that supply and stimulate the muscle layers
what is the mucosa layer of the oesophagus made up of
Muscularis mucosae
Lamina propria
Epithelium
what is the function of the mucosa layer of the oesophagus
secrete mucus
what are the muscle types in the oesophagus
Striated muscle
Smooth muscle
what is the structure of stratified muscle?
multinucleated layer, made up of myofibres and striations related to sarcomeres
what is the structure of smooth muscle?
made of single cells with single nucleus as don’t require as much energy
what is striated muscle under control of?
vagus nerve
what is smooth muscle under control of?
ENS (enteric nervous system)
describe the skeletal Muscular variation in the oesophagus between species
- dogs, cattle and sheep the entire length of the oesophagus is striated
- In horses, primates and cats a portion of the oesophagus is smooth muscle
what are oesophagus sphincters
bands of muscle which are tightly controlled and constricted when deglutition is not taking place
Upper (mouth end) and lower (stomach end) sphincter at each end of oesophagus
how is the lower sphincter aided by the anatomical attachment to the stomach?
tight bend in the oesophagus just as it goes towards the stomach and the pressure from this structural link helps keep the sphincter closed. Reflux otherwise.
describe how peristalsis occurs/ is carried out
- Comes in primary and secondary waves; primary waves are much stronger, secondary waves much weaker in force
- Circular and longitudinal muscles are paired.
- Circular muscle contracts while longitudinal muscle is relaxed which pushes the bolus (propulsion), the circular muscle is relaxed and longitudinal contracted where the bolus is
