Lecture 18- Digestion 1

Question 1

Describe the anatomy of the digestive system:

Answer 1

-

Question 2

Describe the muscle bit of the digestive tract wall?

Answer 2

-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

Question 3

Describe the layers in the digestive tract wall? (part 2)

Answer 3

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

Question 4

What is peritonisis?

Answer 4

peritonisis= inflamation of the peritonium, but typically it is also of serosa

Question 5

What is the Autonomous smooth muscle function in the digestive system?

Answer 5

-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

Question 6

What are the systems regulating digestion in general?

Answer 6

-Local changes in digestive tract leads to a response from Receptors in digestive tract

Question 7

What is the enteric nervous system, what does it use to control the digestive system?

Answer 7

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

Question 8

What are the extrinsic nerves involved in the regulation of the digestive system?

Answer 8

-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)

Question 9

What are the three things involved in digestion in the mouth?

Answer 9

-prehension= getting the food to the mouth(hands for us) -mastication= chewing=mechanical breakdown -saliva= contains amylase =no nutrition absorption here! only processing

Question 10

What secretes saliva?

Answer 10

-sublingual -submandibular -and parotid glands

Question 11

How much saliva do ruminants produce per day?

Answer 11

-100-200 liters

Question 12

What is the difference in saliva contents in ruminants and monogastrics?

Answer 12

-Monogastrics (Low [NaCl], low [HCO3-]) -Ruminant (High [HCO3-] & [PO4-] =ruminants= the components important for what happens in the stomach

Question 13

What is the deal with amylase?

Answer 13

-some species have it and some don’t have it, the ones who eat more starch more likely to have it

Question 14

What is lingual lipase?

Answer 14

-break down fat=thought to help cats determine the nature of the food -medium-chained fats in cats

Question 15

What is the composition of a tooth?

Answer 15

-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

Question 16

What is the difference between a homodont and a heterodont?

Answer 16

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)

Question 17

What is an elodont and an anelodont?

Answer 17

elodont= continue growing )rabbits= continues to grow if not enough chewing in horses huge root= so continues coming out anelodont= limited period of growth

Question 18

What is a brachydont and a hypsodont?

Answer 18

brachydont=Short crown (dogs /cats)=brachydont= short crown= crunching hypsodont= continual eruption, seen in herbivores

Question 19

What is a Diphyodont / polyphyodont?

Answer 19

diphydont= have disiduous teeth 2 polyphyodont: more than two sets of teeth

Question 20

What are ruminant teeth like?

Answer 20

-ruminants= only upper incisors and down= a plate, hold onto food by action of head

Question 21

In which animals is amylase and in which it isn’t?

Answer 21

-Present in ominvores eg pig, rat, human - Absent in carnivores eg dog, cat - Absent in some herbivores eg sheep

Question 22

What does amylase do?

Answer 22

-amylase starts the process of breakdown (ominvores= usually have amylase) herbivores have different system as they also need to break them down

Question 23

What can stimulate salivation?

Answer 23

-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!

Question 24

What is swallowing?

Answer 24

-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

Question 25

What are the three phases of swallowing?

Answer 25

-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

Question 26

What is reverse peristalsis?

Answer 26

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

Question 27

What is the purpose of the stomach?

Answer 27

storage, regulates the amount coming into the small intestine (duodendum)

Question 28

Describe the anatomy of the stomach:

Answer 28

phyloric sphincter=held shut most of the time controls how much gets in

Question 29

What are the four stages of stomach motility and where does it take place in the stomach?

Answer 29

-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

Question 30

How big is the stomach in monogastrics?

Answer 30

-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

Question 31

What are the movements in the stomach during gastric mixing?

Answer 31

-peristaltic contraction in the down bit (ANTRUM)

Question 32

What are the movements in the stomach during gastric emptying?

Answer 32

-contraction in the body and then the antrum

Question 33

How is the gastric emptying regulated in the stomach?

Answer 33

-volume of food= more volume(more food) stimulates motility -fluidity= increase in fluidity=more rapid emptying (more easily passed into the duodendum if fluid)

Question 34

How is the gastric emptying regulated in the duodenum?

Answer 34

-“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

Question 35

How does emotion and pain regulate the gastric emptying?

Answer 35

-increase of sympathetic activity=decrease in gastric motility and emptying -overriding factors= if upset etc

Question 36

What are the stomachs in ruminants called?

Answer 36

-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

Question 37

What happens in the stomach in ruminants?

Answer 37

-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)

Question 38

What is rumination?

Answer 38

-after reticular contraction -vomit it into mouth and chew again

Question 39

What does the reticulum do?

Answer 39

-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

Question 40

What happens in the omasum and abomasum?

Answer 40

-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

Question 41

How do ruminants get rid of the gas produced in rumination?

Answer 41

-gases produced in the stomach= gets out via the secondary contactions= burping/eructation

Question 42

What is the oesophageal groove and who has it and why?

Answer 42

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

Question 43

Why is it wasteful to feed ruminants high quality food?

Answer 43

-ruminants= feeding them high quality feed can be wasteful as the microbes get it not the animal

Question 44

What are the primary and secondary contractions for in ruminants?

Answer 44

-primary= 1-3 a minute = mixing of the matter -secondary= eructation(vomiting)

Question 45

What is ruminal tympany?

Answer 45

-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

Question 46

How much do adult cattle and sheep eructitate=burping in an hour?

Answer 46

-30-50 l 5 liters an hour in sheep -green house gases: methane CO2

Question 47

What is gastric ulceration in horses?

Answer 47

-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…

Question 48

What is the cost of rumination?

Answer 48

cost of this: weight and size= slow running, 25liters