Alimentary term 2

Alimentary term 2

1. Teeth

   • Tooth Development
     • teeth form from epithelium and neural crest cells
       • tooth development relies on interaction between epithelium and mesenchyme cells. NCC/ mesenchyme produces shape but not form
     • 1-formation of dental lamina- focal thickening of oral epithelium medial to labiogingival groove
     • 2-formation of dental bud. dental lamina invaginates
     • 3-formation of enamel organ- dental bud expands and branches= enamel organ (wine glass shape)
     • 4-formation deciduous tooth- enamel organ surrounds dental papillae made of NCC. combination enamel organ and dental papillae= deciduous tooth
     • 5- mass of cell buds off the dental lamina= primordium of perm tooth
     • 6- inner cells enamel organ differentiate= ameloblasts make enamel
     • 7- neighbouring cells in dental papillae become odontoblasts- make dentine surround pulp
     • 8-epithelial cells in distal part of the tooth form cementoblasts. secrete cementum around the tooth root
   • Eruption
     • temporary tooth- crown fully formed but root not yet complete. gives space for root development. removes epithelium on eruption exposing enamel
     • Permanent tooth- moves to tooth socket left by temporary tooth, resorb the roots of the temporary tooth. temporary tooth is shed and replaced. metabolic activity in peridontal ligaments provides eruptive force
   • tooth structure
     • enamel- only in crown. ameloblasts lost on eruption= no repair of enamel. enamel is mineralised= enamel + amelogenins
     • Dentine- produced continually, mineralised matrix like bone but it's acellular
     • gingiva- adheres to tooth between gum and crown
     • alveolus/ peridontal ligaments- PL suspends tooth in alveolus. fibres bridge alveolar bone and cementum. orientation PL depends on tooth function. Alveolus lined compact bone
     • Cementum-mostly acellular surrounds root contains type 1 collagen
   • Classifying species
     • Brachydont- "shallow" roots. once tooth has erupted it stops- no continuous eruption
     • Hypsodont- Deep. there is tooth below gum identical to tooth above. good for wear and tear diet. continuous eruption*
       • radicular- have closed roots will eventually stop erupting
       • aradicular- no true root continuous eruption and continuous growth
     • heterodont- different teeth do different jobs
     • homodont- all teeth do the same job (shark)
     • monophydont- one planting of teeth
     • polyphydont- lots of different plantings of teeth- shark again
     • interesting species differences
       • Dog- incisors are single root so are canines (canine root longer than crown) molars broader than premolars. tooth root generally match tooth points. GUMS RECEDE WITH AGE
       • Horses- deal with wear and tear. continuous surface- high crowns. delayed root development and complex enamel folding. maesseter wider than mandible.
         • incisors. roots converge. wear and tear. 5 years infundibulum visable. 9 years the tooth has worn to the same level so dental mark and star visible. 15 years just star
       • OX no upper canines or incisors instead fibrous dental pad. incisors don't erupt continually. P/M do erupt continuously similar to horse
       • Rodents + Lagomorphs- fewer teeth. no canines. no pulp cavity teeth insesitive
       • Pig- incisors project rostrally. canines continuously erupt "tusks" p/m rounded cusps
   • Jaw articulation
     • Temporomandibular joint- temporal bone and chondylar process of mandible. fibrocartilage disc separates. upper compartment latero-medial movement. lower rotation. disk needs to be greater in herbivores chewing all the time side to side
       • carnivore chondylar process lower than coronoid generates a larger moment arm more leverage to shut jaw
       • mandibular symphsis in dogs and ruminants allows independant rotation of each mandibular bone
   • Sinuses
     • external nose- rostral end of the nasal cavities. flexible and cartiliginous. extends into vestibule and is covered by mucosa
       • nasolacrimal duct opens here
     • Nasal Cavities
       • twinned pair of cavities
       • contain tubernate bones covered in mucous called CONCHAE
       • size of the cavities impacted by cheek teeth, paranasal sinuses and size of conchae
       • conchae project medially produce air spaces called MEATUS
         • divide into dorsal, medial and ventral meatus
           • dorsal- olfactory mucosa
           • medial- access to paranasal sinuses
           • ventral leads to pharynx
       • most caudal conchae are ethmoid tubernates- more complex important in sense of smell
     • paranasal sinuses
       • diverticula of nasal cavity that excavate the bone
         • diverticulum= blind ended sac 
       • connected to nasal cavity
       • allows bone to big and light
       • separated into frontal and maxillary. frontal opens into nasal cavity with ethmoid meatus
       • maxillary opens to caudal and lateral upper jaw associated with hard pallate.
         • horse extensive- split into caudal and rostral connected to medial meatus

2. Headgut stuff

   • Tongue
     • Extrinsic muscles
       • styloglossus- retract tongue
       • genioglossus- stick out tongue
       • hyoglossus- depress/ retract tongue
       • geniohyoideus- moves mandible and assists in swallowing
       • sternohyoid- depress hyoid bone and elevate tongue
     • intrinsic- change shape of tongue, longitudinal on top and bottom, transverse under dorsal longitudinal, vertical ventral to these (see pic below)
     • papillae. Filiform= spikey. circumvalate= round. foliate papillae
       • filiform- grip food circumvalate- taste and grip foliate- taste
       • cat lots of filiform
       • circumvalate on caudal third of dog tongue
       • taste buds- sensory microvilli. basal cells are connected to afferent nerve- cauda tympani
     • Innervation in relation to development
       • develops from different phrangeal arches so has different innervation
       • rostral 2/3 from arch1- lingual branch of V3 trigeminal nerve + facial nerve
       • caudal third- arch 2/3. somatic afferent and taste glossopharyngeal nerve
       • motor control of all- hypoglossal nerve (XII)
     • species differences in tongue
       • dog- median groove
       • cat- lots of filiform papillae
       • pig- foliate papillae caudally
       • cow- torus linguale (v big bump)
         • followed rostrally by lingual fossa
       • horse- smaller torus and two very prominant valate papillae
   • Hyoid
     • series of bones which suspend the tongue and larynx from the underside of the skull- move cranially when we swallow
       • basihyoid, epihyoid, stylohyoid, ceratohyoid and thyrohyoid
         • muscle sling attached to basihyoid 
         • basihyoid unpaired
   • Pharynx
     • innervated by vagus nerve, lymphoid tissue tonsils
     • common area for food, water and air
     • split into nasopharynx, oropharynx and larygopharynx
     • pharyngeal constrictors attach between pharynx and larynx
     • pharyngeal dilators attach between pharynx and skull
     • pharyngeal shortners go from the skull to the vertebrae
   • deglutition
     • 1-Buccal phase- voluntary tongue moves upwards and backwards
     • 2-pharygeal phase- involuntary, food pushed through the pharynx to oesophagus. soft palate closes nasopharynx, epiglottis closes larynx
     • 3-oesphageal phase- peristalsis moves bolus down oesophagus
   • mastication
     • muscles of mastication from first pharngeal arch- innervated by mandibular branch trigeminal nerve
     • Temporalis- like a headband- origin cranium lateral surface. insertion on coronoid process. jaw closing- v large in carnivores
     • Masseter- origin maxillary region and zygomatic arch insert on caudal mandible. unilateral and bilateral contraction possible also protrude jaw. huge in herbivores
     • Medial Pterygoid- origin pterygopalatine region insert on medial aspect of mandible. close jaw and lateral movement
     • lateral pterygoid- same origin- closes and protrudes jaw
       • both huge on carnvivores- work with masseter for lateral translation of jaw
     • digastricus- open jaw- origin paracondylar process insert onto mandible
   • general oral cavity extras
     • lips and cheek- muscles of facial expression innervated by facial nerve. obicularis oris circles the mouth keeps it shut. obicularis oculi circles the eye. nasolabial levator flairs nostrils. buccinator in cheek keeps food in oral cavity proper
     • oral cavity proper lies inside the teeth. vestibule is the space between cheeks and teeth. histology- stratifies squamous epithelium to deal with wear and tear and a little epithelium. on aboral surface a little more interrupted
     • palate- hard palate 2/3, soft 1/3. soft is muscular and mobile allow for breathing and swallowing. horse soft pallete extends to the epiglottis- put a stomach tube and the horse can't breath. histo stratified squamous epithalim and palatine glands
     • salivary glands- parotid are ventral to the ear duct drains to fourth premolar. mandibular more round ventral to parotid drains under the tongue. sublingual shares gland with mandibular gland under tongue. *in carnivored zygomatic gland.
       • serous= watery dark staining small cells mucous= big light staining cells often a mix of the two
       • minor glands- palatine and buccal. mucous

3. GIT development

   • stomach development
     • foregut supplied by celiac artery
     • primitive gut tube. embedded in dorsal mesogastrium is spleen which is attached to stomach by gastrosplenic ligament. ventral mesogastrium is liver, attached to stomach by lesser omentum
     • gut tube streatches and rotates, dragging mesogastrium with it, spleen ends up on LHS, liver on RHS
   • midgut/ intestine develpment
     • supplied by cranial mesenteric artery
     • 1-primitive gut tube expands/ elongates around the cranial mesenteric artery herniates into the umbilical stalk
     • 2-causes tube to fold and rotate (aprox 360) around the artery. cranial grows faster than caudal. mesentry folds too
     • 3- distal part of the loop develops bulge- caecum. rotates again caecum ends up on RHS in most animals bar pig bc it rotates an extra 180
     • ascending colon- grows faster in horse dragging the mesentry and artery with it. wrapping round small intestine forms 2 U shapes. cow similar problem instead forms spiral (ansa spiralis)
   • Hindgut
     • Supplied by caudal mesenteric artery
     • transverse colon, descending colon and rectum
     • initially common opening with urinary and reproductive tract. separate tubes form and distinct exits form.

4. Canine Abdomen

   • boundaries- cranial diaphragm. lateral= lateral abdominal walls. caudal pubic brim. cavity lined with peritoneum- serous membrane allows organs move without friction. parietal peritoneum in contact with body wall. visceral peritoneum facing organs
     • retro peritoneal- organ behind peritoneum think wallpaper intra periotneal almost surrounded by peritoneum
     • abdominal wall- external abdominal oblique (caudoventral fibres) internal abdominal oblique, fibres at 90 degrees to that of external. transversus abdominus fibres transverse. rectus abdominus parallel with linea alba embedded in rectus sheath
   • TOPOGRAPHY
     • RHS-duodenum (short mesentery) liver, pancreas,
       • caecum too
     • LHS- stomach- greater omentum- spleen,
   • peritoneum- reflects off caudal boarder liver attach to stomach via lesser omentum. then reflects off stomach forming greater omentum which folds back on itself (omental bursae) attaches to pancreas. mesentery of the intestines comes from the root mesentery attached to dorsal body wall
   • ileocaecolic junction- easy to identify ileum, has blood supply from ileum and ileocaecal fold
   • liver structure
     • caudal vena cava runs through midline
     • hepatic portal vein also at midline brings deoxgynated blood from gut
       • hepatic artery supplies oxygenated blood in same space
         • bile duct drains to the duodenum
     • renal fossa on caudate lobe- right lobe
   • blood supply and innervation
     • celiac artery- branch to liver stomach and spleen
     • cranial mesenteric- SI, ascending colon and part of transverse
     • caudal mesenteric- part of transverse, decsending colon and rectum
     • nerves- enteric NS, parasypathetic vagus nerve. sympathetic splanchnic nerves

5. disease

   • Diarrhoea
     • normal function. in jejunum villi are taller but fewer. in ileum villi are shorter but more numerous. stem cells formed in crypts migrate to villus tip and develop. takes 3-5 days
       • 98% fluid secreted in the lumen must be reabsorbed
         • crypt cells are leaky allow sodium into lumen. enterocytes are tight and absorb- net absorption at villus tip should be higher than excretion at crypt base
     • 1- altered epithelial cell transport. e.g. e coli. inject toxin into enterocyte prevents sodium pump activity and activley promotes sodium excretion. water follows. self limiting no destruction of cells and they are replaced after 3-5 days
       • maintain on fluid support
     • 2- altered structure of permeability of mucosa- most common
       • cytotoxins. e.g. salmonellosis. toxins which damage or kill cells allow blood and fluid to leak out of villus core. villus no longer absorptive. nutrients remain in lumen and water follows
       • infiltration of cells in villus due to neoplasia/ inflammation/ infection e.g. johnes disease. make villus short and fat decrease SA for absorption. enterocytes flatten loss brush boarder "cobblestone gut" less absorption nutrients remain in lumen, water follows
       • lytic infection of villus epithelial cells by virus. e.g. coronavirus or rotavirus. villus atrophy can't absorb products of digestion- stay in lumen water follows
       • lytic infection of villus crypt cells by virus e.g parvo virus. replicate in crypts result in mucosal collapse
     • 3-osmotic diarrhoea- lack of brush boarder enzymes needed for final stage digestion accumulation of small osmotic solutes. draw water into lumen. E.G. LACTOSE INTOLLERANCE
     • 4- disruption of segmental movement in intestine. hypermotility- no time to absorb nutrients so accumulate in lumen- water follows. hypomotolity- bacteria accumulate in lumen
   • malabsorption
     • food digested but not absorbed
     • primary- structural disease of gut e.g. IBD
     • secondary- metabolic disease making absorption difficult- e.g. hepatic disease decreasng bile acid production
     • clinical signs- weight loss, diarrhoea, sometimes corporophagia
   • maldigestion
     • food can't be broken down properly to aborbable products. causes =exocrine pancreatic insufficiency/ secondary enzymatic deficiency/ pancreatic neoplasia/ pancreatic hypoplasia
       • secondary enzymatic deficiency- enzymes secreted but luminal environment is not optimum e.g. deficiency of bile acids so lipases can't function. loss brush boarder enzymes
     • exocrine pancreatic insufficency
       • causes
         • pancreatic acinar atrophy- autoimmune disease phase 1 pancrease inflamed and T lymphocytes infiltrate. phase 2 end stage atrophy.
           • just affects exocrine pancreas- islets of langerhans remain in tact
         • pancreatitis- inflammation of pancreas- affects both exocrine and endocrine pancreas- progressive destruction with fibrosis
       • clinical signs- weight loss, increased appetite, increased faecal volume, abnormal faeces, flatulence, coprophagia
       • diagnosis- test for trypsin and trypsinogen. trypsinogen leaks into blood from pancreas- if low EPI. high trypsin indicates inflamed pancreas be careful
         • treatment- avoid high fat diet. put on high calorie low fibre diet. treate with pancreatic enzyme replacement perhaps combined with antimicrobial therapy to avoid secondary infections. look for enzyme mix with highest lipase conc

6. Ruminant Abdomen

   • Topography LHS- RUMEN ventral sack shielded by omentum. Reticulum most cranial, ventral to rumen atria. abomasum ventral to reticulum
   • Topography RHS- omasum (very round) abomasum at midline. abomasum exit to duodenum. lesser omentum attaches to lesser curvature of the abomasum.
   • OMENTA- LHS reflects of longitudinal groove of rumen and goes round to the dorsal body wall on rhs= superficial greater omentum
     • Deep sheet of greater omentum from the RHS of the longitudinal groove round to the dorsal body wall- space between the two sheets is the omental bursae. intestines sit in supraomental recess
   • Intestines- RHS in supraomental recess. ascending duodenum attached by mesenery. Caecum apex points caudally out of recess into pelvic inlet.
     • ascending colon is S shaped- ansa proximalis, then ansa spiralis, then U shaped- transverse crosses the body to the LHS and continues as descending colon
   • Associated Abdominal Organs- liver on RHS because rumen takes up so much space. spleen attached to stomach by gastrosplenic ligament much shorter in ruminants. 1 duct from pancreas- in sheep this drains with the bile duct. in cows there is a separate duct

7. Horse Abdomen

   • and pig stuff
   • specialisations
     • Small stomach because it's a trickle feeder
     • glandular and non glandular regions of stomach divided by margo picatus (non glandular region near fundus lots of rugae)
     • cardiac and pyloric sphincter really close and muscle tone makes it difficult for horse to vomit
     • really enlarged caecum
       • everything must pass through the caecum at ileocaecolic junction
     • complex ascending colon
     • 2 duodenal papillae- large is for the greater pancreatic duct and bile duct to drain, accessory is for the smaller pancreatic gland
   • Caecum- base on RHS apex midline near sternum. teni coli= white bands of longitudinal muscle causing haustra- slows down transit and increase surface area
   • Colon- complex ascending colon like 2 u's on top of each other. RVC- sternal flexure- LVC- pelvic flexure- lDC- diaphragmatic flexure- RDC- transverse colon- descending colon
   • Rectal- what can you feel?
     • Caudal pole left kidney
     • caudal boarder spleen
       • nephrosplenic ligament
     • faeces in descending colon
       • pelvic flexure
     • root of mesentery
     • base of caecum and teni coli
     • only feel small intestine if distended
   • Colic- causes
     • stretch of gut wall
     • tension in mesentery
     • blood supply cut off
     • inflammation
     • build up of gas
     • torsion
     • can't vomit
     • pelvic flexure- stuff likely to get impacted. goes against gravity- 180 degree turn and lumen narrows
     • LDC and jejunum both very mobile can get stuck
   • Gut Development
     • caecum and ascending colon grow so quickly they wrap around the root mesentery- colon forms double U shape
     • LHS dorsal and ventral colon attached bu just intercolic ligament so they are more mobile
   • Acessory abdominal organs- liver is less lobed and has no gall bladder, spleen has an elongated hilus
   • Pig abdomen stuff
     • Pharynx- soft palate and epiglottis make contact like in horse- also has pharyngeal diverticulum
     • Stomach- fundic region has a diverticulum body is aglandular
     • development- ascendinc colon grows fast and forms a conical spiral. caecum does an extra 180 degree turn so on left hand side

8. Small animal abdomen*

   • Rabbits
     • dentition
       • herbivores
       • constantly growing incisors and cheek teeth which need to be worn down (aradicular hypsodont)
         • hypsodont lie @shakira 
       • No canines- has more incisors on top "peg teeth" 3 premolars and 3 molars on top- one fewer PM on bottom
       • if diet doesn't have enough fivre the teeth don't wear down- spurs.
     • GI tract
       • Stomach- well developed sphincters- can't vomit. must have some food in stomach at all times can't starve them
       • short small intestine - sacculus rotundus near end full of lymphoid follicles
       • Colon- proximal- contractions separate fibrous and non fibrous material
         • where proximal and distal colon meet- fusus coli controls large gut motility and is stimulated by fibre in diet
       • caecum- microbes break down indigestible fibre into fatty acids- produce ceacotrophs covered in muucous. caecotrophs eaten- ceacotrophy. mucous can pass through stomach so more microbial protein and vitamin B/K can be absorbed second time round
       • problems- hypomotility "gut stasis" or flora problems
   • Hystricomorphs-
     • SMALL HERBIVORES
     • similar dentition to rabbits but no peg teeth and slightly fewer cheek teeth
     • v similar GI tract too since they eat a similar diet
     • same problems as rabbits- spurs, gut stasis ad flora imbalance
   • Myomorphs
     • OMNIVORES
     • only incisors constantly grow. much fewer cheek teeth since there is less grinding in diet
     • GI tract varies with diet- generally much simpler and smaller ceacum
   • Carnivores
     • e.g. ferret
     • typical carnivore dentition- curved incisors
     • strong muscles of mastication especially temporalis- keep mouth closed
     • really fast gut transit time 3-4 hrs so can't starve or will get hypoglyceamia
   • Avian digestion
     • must be light
     • crop= dilation in oesophagus to store food
     • proventriculus- normal stomach first one
     • ventriculus- very muscular crushes food
     • not used to store food- very short transit time
   • reptile digestion
     • adapted for diet
       • e.g. tortoise very hard beak
     • crocodile lots of teeth
     • snake has extra arcades of teeth and they are hooked backwards

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