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
What are the movements in the stomach during gastric mixing?
-peristaltic contraction in the down bit (ANTRUM)
What are the movements in the stomach during gastric emptying?
-contraction in the body and then the antrum
How is the gastric emptying regulated in the stomach?
-volume of food= more volume(more food) stimulates motility -fluidity= increase in fluidity=more rapid emptying (more easily passed into the duodendum if fluid)
How is the gastric emptying regulated in the duodenum?
-"stretch" in the duodenum initiates the enterogastric reflex=decrease in gastric motility and emptying (feedback mechanism if lot of volume in stomach= slows down movement of the stomach from the duodenum= slows pushing in of the material) -Presence of fat, acid or hypertonicity triggers release of enterogastrones (cholecystokinin, secretin, gastric inhibitory peptide) =decrease in gastric motility and emptying
How does emotion and pain regulate the gastric emptying?
-increase of sympathetic activity=decrease in gastric motility and emptying -overriding factors= if upset etc
What are the stomachs in ruminants called?
-Rumen, reticulum, omasum, abomasum -four sections of a stomach not four stomachs -biggest made of two chambers closely connected greatest proprtion of volume in here -125 L (cattle) / 53% of digestive tract
What happens in the stomach in ruminants?
-Fermentation of fibre -we don't get any nutrition -Rumen microbes:break down cellulose / starch into volatile fatty acids= energy molecules (glucose) -Volatile Fatty Acids (acetate, butyrate, propionate)
What is rumination?
-after reticular contraction -vomit it into mouth and chew again
What does the reticulum do?
-reticulum= lowest part of the stomach -heaviest bits coming in (not well chewed material) goes there -periodically it contracts and pushes the material up towards the oesaphagus= reverse peristalsis can chew again
What happens in the omasum and abomasum?
-then material go through the omasum= small but large surface area, probably water reabsorption occuring here and some minerals then goes into abomasum= basically like the stomach of all the other animals, but most of the stuff going in here is fermented, mixed so modified and lot of the nutrients are released by microbes and here the microbes are broken down here and proetin comes from them
How do ruminants get rid of the gas produced in rumination?
-gases produced in the stomach= gets out via the secondary contactions= burping/eructation
What is the oesophageal groove and who has it and why?
newborn ruminants= don't do the fermentation as milk fermentation not advantageous -can bypass the rumen by a structure called oesophagal groove so it goes straight into the abomasum, when the animals sucks it causes the groove to contract and become apparent to bypass the rumen
Why is it wasteful to feed ruminants high quality food?
-ruminants= feeding them high quality feed can be wasteful as the microbes get it not the animal
What are the primary and secondary contractions for in ruminants?
-primary= 1-3 a minute = mixing of the matter -secondary= eructation(vomiting)
What is ruminal tympany?
-if they don't release gas, feed with lot of protein, the gases prevented from rising up= bloating = ruminal tympany= life threatening= have to release the gas= puncture
How much do adult cattle and sheep eructitate=burping in an hour?
-30-50 l 5 liters an hour in sheep -green house gases: methane CO2
What is gastric ulceration in horses?
-animals devlop ulceration, not clear why. -can see and hear it -believed to be due to stress(even us), trying to reduce the effects of the autonomic nervous system during stress -now due to a bacteria heliobacteri pilori = causes it in humans -what about horses?-not sure what causes it...
What is the cost of rumination?
cost of this: weight and size= slow running, 25liters