Describe the anatomy of the digestive system:
Describe the muscle bit of the digestive tract wall?
-two layers of smooth muscle, in different orientations inner= circular so contraction = decrease in diameter or increase if relaxed outer= longitudinal= shorten or lengthen the tube = that's how we get movement in the digestive tract moving things inside= shortening and changing diameter
Describe the layers in the digestive tract wall? (part 2)
mesentry=connected to serosa= aslso to the body wall= prevents the tubes from tangling --way the nerves and blood vessels can access the intestines serosa=outer layer, continuos with mesentry, rich with lymphatic cells and covers the entire thing submucosa=glands in there
What is peritonisis?
peritonisis= inflamation of the peritonium, but typically it is also of serosa
What is the Autonomous smooth muscle function in the digestive system?
-GIT motility=Propels food from mouth to anus =Mechanically mixes & breaks down food -GIT contains layers of single unit smooth muscle fibres =Specific cells noncontractile maintain oscillating resting potentials=drive the regular cycling behaviour of the cycling contractions of the gut -slow wave activity= below threshold then hit threshold= lot of activity -the strength of contraction depends on how many AP
What are the systems regulating digestion in general?
-Local changes in digestive tract leads to a response from Receptors in digestive tract
What is the enteric nervous system, what does it use to control the digestive system?
enteric nervous system= ENS= one big subdivision of the autonomic nervous system -sensory afferent neurons -interneurons -motor (efferent) neurons = =Stimulatory neurons,mainly cholinergic ie acetylcholine = Inhibitory neurons - neurotransmitters eg nitric oxide, vasoactive intestinal peptide=also effects on blood flow
What are the extrinsic nerves involved in the regulation of the digestive system?
-nerve from the brain or spinal chord -part of the autonomic nervous system -both Parasympathetic (mainly vagus nerve) and Sympathetic =their main role is to modify enteric nervous system -modifying activity, even without its input the digestive system works well (during sleep etc)
What are the three things involved in digestion in the mouth?
-prehension= getting the food to the mouth(hands for us) -mastication= chewing=mechanical breakdown -saliva= contains amylase =no nutrition absorption here! only processing
What secretes saliva?
-sublingual -submandibular -and parotid glands
How much saliva do ruminants produce per day?
What is the difference in saliva contents in ruminants and monogastrics?
-Monogastrics (Low [NaCl], low [HCO3-]) -Ruminant (High [HCO3-] & [PO4-] =ruminants= the components important for what happens in the stomach
What is the deal with amylase?
-some species have it and some don't have it, the ones who eat more starch more likely to have it
What is lingual lipase?
-break down fat=thought to help cats determine the nature of the food -medium-chained fats in cats
What is the composition of a tooth?
-enamel, dentin, cementum -no cells within the hard tooth structure (no living cells)unlike bones enamel= sharp and hard crystals= tough edge brittle dentin= more flexible cementum= protective layer
What is the difference between a homodont and a heterodont?
homodont= just one type of teeth heterodont= more types =incisors, canine, premolar, molar =incisors= cutting, prehension(grasping) canine= fighting, tearing premolar and molar= solid big teeth, crunching breaking bones and grass(shearing)
What is an elodont and an anelodont?
elodont= continue growing )rabbits= continues to grow if not enough chewing in horses huge root= so continues coming out anelodont= limited period of growth
What is a brachydont and a hypsodont?
brachydont=Short crown (dogs /cats)=brachydont= short crown= crunching hypsodont= continual eruption, seen in herbivores
What is a Diphyodont / polyphyodont?
diphydont= have disiduous teeth 2 polyphyodont: more than two sets of teeth
What are ruminant teeth like?
-ruminants= only upper incisors and down= a plate, hold onto food by action of head
In which animals is amylase and in which it isn't?
-Present in ominvores eg pig, rat, human - Absent in carnivores eg dog, cat - Absent in some herbivores eg sheep
What does amylase do?
-amylase starts the process of breakdown (ominvores= usually have amylase) herbivores have different system as they also need to break them down
What can stimulate salivation?
-pressure receptors and chemoreceptors in the mouth=when food is in the mouth -cerebral cortex -also the Conditioned reflex(remember pavlov= salivating with the bell = conditioned reflex= anticipation of food) =all these stimulate the Salivary center in medulla which via autonomic nerves stimulates salivary glands= salivation!
What is swallowing?
-also called deglutition -it is sequentially programmed=all-or-nothing reflex(can't do half a swallow, all or nothing can't stop once started) -Respiratory centres are inhibited during swallowing
What are the three phases of swallowing?
-Buccal=back of oral cavity stimulated -Pharyngeal=pharyx modifies itself to allow the material to roll back -Oesophageal= opens so it can go into the oesophagus
What is reverse peristalsis?
bringing food back into the mouth cats and dogs= it comes up if unhappy with the food, useful ruminants= different role, the ability to chew the fibrous material to smaller bits again horses= don't have either do have to be careful
What is the purpose of the stomach?
storage, regulates the amount coming into the small intestine (duodendum)
Describe the anatomy of the stomach:
phyloric sphincter=held shut most of the time controls how much gets in
What are the four stages of stomach motility and where does it take place in the stomach?
-Gastric filling=Plasticity and Receptive relaxation(similar to the bladder, increase in volume without increasing the tension too much) -Gastric storage= Body & fundus region of stomach, Less smooth muscle -Gastric mixing=further down,continual movement of the posterior part of the stomach -Gastric emptying=via the phyloric sphincter
How big is the stomach in monogastrics?
-In monogastrics from 50ml to 10L (horse) -not large in comparison to th eanimal. can expand in cats and dogs, lot of plasticity but stomach has a limit= if reached can rupture