Alimentary Flashcards
what does the intraembryonic coelom become?
the peritoneal cavity
what is a mesentery?
a double layer of peritoneum
what develops into the parietal peritoneum?
somatic lateral plate mesoderm
what develops into the gut muscle and visceral peritoneum?
splanchnic lateral plate mesoderm
what is the peritoneum?
a serosal membrane ‘mesothelium’, single squamous epithelium which secretes small amount of fluid
what are the 4 fetal membranes in reptiles, birds and mammals?
allantois, chorion, amnion, yolk sac
how many fetal membranes are there in reptiles, birds and mammals?
4
what does the allantois form in doemstic mammals?
placenta with chorion
what does the chorion develop from?
trophoblast
what do the allantois and chorion form together?
placenta
what contains and protects the yolk sac?
the amnion
what membrane breaks down to form the mouth?
buccopharyngeal membrane
what breaks down to form the anus?
the cloacal plate
what germ layer are the buccopharyngeal membrane and cloacal plate missing?
mesoderm
what are the lungs derived from?
ventral gut
what germ layer forms the lungs?
endoderm
what does the hindgut connect to?
the allantois
what does the midgut connect to?
the yolk sac
what forms the upper mediastinum?
dorsal mesentery in the thorax
what does the ventral mesentery of the hindgut become?
ventral ligament of the bladder
what distorts the ventral mesentery of the foregut?
ventral pancreatic bud and liver biliary tree growing within it
what is the falciform ligament?
the bit between the liver and ventral body wall
how do the 2 pancreatic buds fuse?
ventral bud grows round to join dorsal bud
how does the stomach move to the left hand side?
by rolling around its own axis
how many times does the gut rotate around the root of the mesentery?
3
what does the gut rotate around?
the root of the mesentery
what shape does the gut end up as after rotation?
2 intertwined hooks
what direction does food in the stomach move from?
left to right
what is the greater curvature of the stomach?
the old dorsal edge of the stomach before it rolled
what is the lesser curvature of the stomach?
the old ventral edge of the stomach before it rolled
what does the stomach empty into?
the duodenum
what side does the colon descend on?
left
what does the colon empty into?
the rectum
what is the boundary of the foregut/midgut?
where the duodenum starts to descend
what is the boundary of the midgut/hindgut?
about 3/4 along the transverse colon
what is the lesser omentum?
the ventral mesentery of the stomach
what is the greater omentum?
the dorsal mesentery of the stomach
what does the pancreas drag with it as it burrows through the gut?
the opening of the billowing system of the liver
what does the bile duct run through?
the free edge of the lesser omentum then the dorsal wall of the duodenum
what are mesenteric fusions?
when gut regions end up near each other and their adjacent leaves of mesenteric peritoneum may fuse
what is the ileocaecal fold useful for?
orientation as it attaches the ileum to the caecum
what are the rumen and equine stomachs/RDC/caecums directly attached to?
the dorsal body wall with the mesentery ‘shortened to nothing’
what is the function of the oesophagus?
conveys food, drink and salvia to stomach, conveys vomit, regurgitated food and eructated gas in other direction
what nerves run with the oesophagus?
the vagal nerves
what makes up most of the outer layer of the oesophagus?
loose ‘adventitial’ connective tissue coat
how many layers of muscle does the oesophagus have?
2
what part of the oesophagus is smooth muscle in most species?
the caudal 1/3
what part of the oesophagus is striated muscle in most specie?
the cranial 2/3
in which species is all of the oesophageal muscle striated?
dog and ox
what does the arrangement of the 2 layers of muscle in the oesophagus become as it nears the stomach?
inner circular and outer longitudinal layer
what is the lining of the oesophagus formed from?
keratinised stratified squamous mucosa
which species has the most goblet cells in the oesophageal lining?
dogs
which species has more goblet cells in the oesophageal lining than other species except for dogs?
pigs
what attaches the oesophagus to the larynx?
a 1cm crico-oesophageal tendon
what does the caudal 1/3 of the cat oesophagus have?
distinctive ridges by circular muscle bands
what is the nerve supply to the cranial oesophagus?
somatic fibres of vagus nerve X
what is the nerve supply to the caudal oesophagus?
parasympathetic fibres of vagus
what arteries run alongside the trachea?
the common carotid arteries
what is the peritoneum separated into?
parietal, visceral and mesentery
what does the mesentery of the oesophagus form?
the dorsal part of the mediastinum
what are the pleuropericardial folds?
ventral ingrowths on either side of the pleural+pericardial cavities with common cardinal veins and phrenic nerves
which is dorsal the pleural cavity or the pericardial cavity?
the pleural cavity
which is ventral the pleural cavity or the pericardial cavity?
the pericardial cavity
how does the heart end up in the pericardial cavity?
migrates from cephalic location caudally and squishes into the pericardial cavity
why does the heart have 2 layers of pericardium?
it impinges on the pericardial cavity and displaces the pericardium so there are 2 layers
why do the mediastinum and pleuroparietal folds fuse?
the pleuroparietal folds grow dorsomedially towards the mediastinum
which pericardium forms the shiny ‘epicardium’ stuck to the outside of the heart?
visceral pericardium
what is surgeon’s pericardium a combination of?
mediastinal pleura, connective tissue and parietal pericardium
what is the more superficial layer of pericardium?
parietal pericardium
what causes pleuroperitoneal hernias?
pleuroperitoneal folds don’t form properly so end up with hole which guts wiggle through
what causes a peritoneo-pericardial hernia?
a hole into the pericardial sac which intestines crawl through
what is the stomach tube inserted via in most species?
the mouth
what is the stomach tube inserted via in the horse?
the nose
what is a good way to feed cats in the medium term?
oesophageal tube via nose
what is the benefit of transoesophageal echocardiography?
there is no rib cage in the way
what are the signs of oesophageal disease?
regurgitation, ballooning of neck (especially if abdomen compressed)
what is the difference between regurgitation and retching/vomiting?
retching/vomiting is active contraction of stomach, regurgitation is delayed ejection of undigested food, quite passive
what can oesophageal disease lead to? (5)
inhalation pneumonia, broncho-oesophageal fistula, mediastinitis, pleurisy, pleurisy can develop into pyothorax/pneumothorax
what is inhalation pneumonia caused by?
inhaling ingested food/saliva
what is a fistula?
a rupture
what is mediastinitis?
inflammation of mediastinum
what is pleurisy?
rupture into the pleural cavity
what is megaoesophagus?
a large, floppy, dilated oesophagus
what are the causes of megaoesophagus?
congenital or acquired
what are most foreign bodies in dog oesophagi?
bones in dogs
what may be evidence of functional valves in oesophagi?
usual sites of foreign body obstruction reflect points of external narrowing of oesophagus
what are the sites of external narrowing of the oesophagus?
cricopharyngeus muscle, thoracic inlet, heart base, oesophageal hiatus
what dog breeds does vascular ring anomaly normally occur in?
GSD, Irish setter, greyhound, Boston terrier
what is vascular ring anomaly?
entrapment of oesophagus in ring formed by right aorta, ligamentum arteriosum, or left aorta if present, pulmonary artery, heart
what is the surgical approach for vascular ring anomaly, thoracic foreign bodies and PDA?
via left intercostal space 5
what is the part of the stomach directly after the oesophagus opens into it?
the cardia
what is the output of the stomach?
pyloric canal
what does the old dorsal edge of the stomach become after it rolls?
greater curvature
what does the old ventral edge of the stomach become after it rolls?
lesser curvature
what is the angular incisure?
very sharp kink in lesser curvature present in stomach of some species
what is the left side of stomach like in general?
floppier and less muscular than the right
what is the right side of the stomach like in general?
narrower lumen, thicker muscle, less distensible
which surface of the stomach faces the liver?
parietal
which surface of the stomach faces the intestine, pancreas, right kidney?
the visceral surface
what does the dorsal greater omentum connect?
the greater curvature of the stomach to the epiploon
what is the epiploon?
line on dorsal wall that the dorsal greater omentum connects the stomach to
what does the dorsal greater omentum enclose?
capacious bursa in carnivores, pig and horse
what is the bursa that the dorsal greater omentum encloses accessible via?
the epiploic foramen under free edge of the ventral lesser omentum
what does the ventral lesser omentum connect?
the lesser curvature of the stomach to the liver
what does the ventral lesser omentum convey?
bile duct to duodenum, hepatic artery, portal vein and vagus to liver
how many layers of muscle does the stomach have?
3
what are the layers of muscle in the stomach?
outer longitudinal, middle circular, inner oblique
which layers of stomach muscle are continuous with the oesophagus and duodenum?
outer longitudinal, middle circular
what does the inner oblique muscle of the stomach not cover?
lesser curvature and pylorus
what are the 3 regions of glands in the stomach?
cardiac, proper gastric, pyloric
what glands does the cardiac region of the stomach have?
mucus
what glands does the proper gastric region of the stomach have?
pepsin, HCl, mucus
what is the darker gland region of the stomach?
proper gastric
what glands does the pyloric region of the stomach have?
mucus
what does the stomach have instead of goblet cells?
foveolar cells
what is the foregut artery (coeliac) derived from?
vitelline arteries of the yolk sac
what does the coeliac artery run between?
the 2 layers of mesentery, to under the visceral peritoneum of organs
what does the coeliac artery branch into?
splenic, gastric and common hepatic arteries
what does all gut between the cardia and the distal rectum drain into?
the hepatic portal vein
what is the hepatic portal vein derived from?
vitelline veins
what forms the ventral margin of the epiploic foramen?
the hepatic portal vein
what forms the dorsal margin of the epiploic foramen?
the caudal vena cava
what does the common mesenteric vein form in?
the great mesentery
what veins does the common mesenteric vein receive (in order) to form the hepatic portal vein?
gastrosplenic vein, gastroduodenal vein
what does the hepatic portal vein pass to the porta of the liver via?
the lesser omentum
what does lymphatic drainage of the stomach drain to?
collection of nodes, the coeliac nodes, around the coeliac artery
how does the parasympathetic innervation of the stomach reach the stomach?
vagus enters via oesophageal hiatus, ventral branch follows lesser curvature, dorsal mainly from coeliac plexus and then along artery
what do nerves to the stomach branch in?
submucosal plexi
what are differences between the cat and dog stomach?
cat has narrower lumen, less distensible, extravagant vomiting behaviour
what is the difference between the pig and dog stomach?
pig has diverticulum ventriculi and extensive cardiac gland region, torus pyloricus, shorter greater omentum
what are the diverticulum ventriculi in the pig stomach?
helical ridges of mucosa
what is the torus pyloricus?
an erectile ‘valve’ which may control flow through pyloric canal
what is the difference between the horse and dog stomach?
surprisingly small, sharp angular incisure, blind-ending ‘saccus caecus’, gastrophrenic ligament from proximal greater curvature to crura, extensive keratinised region, dilate proximal duodenal ‘cap’
what is location of the abrupt transition from the keratinised region to the glandular epithelium in the horse stomach called?
margo plicatus
what is the difference between the rabbit and dog stomach?
surprisingly large, holds fermenting caecotrophs
what is the only simple-stomached domestic species in which the stomach can be palpated in healthy individuals?
rabbit
what are caecotrophs?
ingested soft faecal pellets
which are usually better for imaging the stomach, plain radiographs or contrasts?
contrasts
what is gastric dilation/volvulus?
an acute, life-threatening condition where stomach swells without stopping
what are the secondary complications of gastric dilation/volvulus?
post-op sepsis, gastric necrosis, myocardial depression
what are the functions of the liver?
storage, metabolism of C, L, P, vitamins and hormones, detoxification, excretion, immunological function
what is the largest gland in the body?
liver
what is the exocrine function of the pancreas?
digestion of fat, protein and carbohydrate
what is the endocrine function of the pancreas?
produces key hormones for regulation of blood sugar levels- insulin and glycogen
what surface of the liver is visible in the left lateral view?
diaphragmatic (parietal) surface
what are the visceral surface impressions of the dog liver?
stomach, duodenum, R kidney
what are the visceral surface impressions of the pig liver?
stomach, duodenum
what are the visceral surface impressions of the ox liver?
omasum, reticulum, R kidney
what are the visceral surface impressions of the horse liver?
stomach, apex of caecum, diaphragmatic flexure, RDC, R kidney
what species does not have a right kidney impression on the liver?
the pig as the kidneys are further back
what does the coronary ligament of the liver surround?
caudal vena cava to caval hiatus
what is the falciform ligament the remnants of?
the umbilical vein
what does the liver attach to?
duodenum, gallbladder, stomach, spleen, lesser omentum
what cups the cranial pole of the right kidney? (dog)
the caudate process of the liver
what marks the division of the quadrate and right lobes of the liver?
gall bladder
what are the differences between the pig and dog liver?
pig has no papillary process, R kidney doesn’t reach caudate process, less obvious division of quadrate, marked surface lobulation
what is the difference between the horse and dog liver?
horse has no papillary process, has scalloped quadrate lobe, no division of right lobe, no gall bladder
what is the difference between ruminant and dog liver?
ruminant has no division of left lobe, no division of right lobe, clockwise rotation to right, lies almost entirely to right of midline
what are signs of portal hypertension in humans?
portal vein enlargement, portal venous thrombosis, splenomegaly, enlarged superior mesenteric vein and splenic vein, enlarged paraumbilical vein, portosystemic collaterals
how much of the liver blood supply does the hepatic artery provide?
1/5th
how much of the liver oxygen supply does the hepatic artery provide?
3/5ths
where is the ventral lobe of the pancreas found?
in the mesoduodenum
where is the dorsal lobe of the pancreas found?
in the deep leaf of the greater omentum
is the ventral lobe of the pancreas left or right?
right
is the dorsal lobe of the pancreas left or right?
left
do dogs have the main pancreatic duct?
some do, some don’t
which species have the main pancreatic duct?
cat, horse, sheep, most ox, some dogs
which species don’t have the main pancreatic duct?
rabbits, pig, some ox, some dogs
where does the main pancreatic duct come from?
the ventral (right) lobe
which species don’t have the accessory pancreatic duct?
sheep and most cats
what is triaditis in cats?
simultaneous inflammation of the liver, SI and pancreas
why do cats get triaditis?
anatomical adaptations in the feline GI tract increase the risk of bacteria ascending from the duodenum into the liver + pancreas
what percentage of porto-sytemic shunts are congenital?
70%
what breed of dogs get congenital porto-systemic shunts?
small/miniature breeds
what are the symptoms of congenital porto-systemic shunts?
poor growth and response to anaesthesia, post prandial neurological signs
what type of porto-systemic shunt is often possible to treat with surgery?
extra-hepatic
what percentage of porto-systemic shunts in dogs are acquired?
30%
what causes acquired porto-systemic shunts?
microvasculature opens under back-pressure
what is the external landmark for percutaneous liver biopsy in dogs?
caudal to xiphoid process into left lobe
what is the external landmark for percutaneous liver biopsy in ox?
right 10th/11th intercostal space on line between tuber coxae and point of shoulder
what is the external landmark for percutaneous liver biopsy in horse?
right 12th intercostal space- on line between tuber coxae and point of shoulder
what increases the SA of the intestines?
they are tortuous and have mucosal folding
how much longer is the dog intestine than the length of the animal?
3-4x
how much longer is the sheep intestine than the length of the animal?
25x
how much greater is the internal SA of a dog’s SI compared to a featureless tube of same proportions?
around 600x
how much do folds increase SI SA in dogs?
3x
how much do villi and crypts increase SI SA in dogs?
10x
how much do microvilli increase SI SA in dogs?
20x
what is the right-most region of the gut?
the duodenum
what do the glands in the duodenum resemble?
pyloric glands
what is the cranial part of the duodenum, foregut or midgut?
foregut
what is the cranial part of the foregut attached to?
lesser omentum
why do most parasites live in the duodenum?
more nutrients available
what do bile and pancreatic ducts open via in the duodenum?
2 papillae
what are Peyer’s patches?
aggregated lymphoid follicles scattered in small intestine
how many Peyer’s patches are there in the dog SI?
around 22
what are the Peyer’s patches found under?
SI endothelium
what is the ileum defined as?
short stretch with ileocaecal fold and anti-mesenteric artery
what is the difference between the jejunum and ileum?
ileum is firmer and narrower, no abrupt transition
where does the ileum open into the colon?
at ileal papilla (ileocolic sphincter)
what is a common site of impaction in the small intestine?
the ileal papilla/ileocolic sphincter (where ileum opens into colon)
what does the caecum come off?
the colon
what does the caecum open into the colon via?
caecocolic orifice
why is the caecum tortuous in dogs?
due to the ileocaecal fold growing slowly
what are the parts of the caecum?
base, body, apex
does the colon have villi?
no
what is the left-most region of the gut?
descending colon
does the colon have Peyer’s patches?
no
does the colon have lymphoid follicles?
yes
what is the dog rectum defined as?
region of intestine caudal to pelvic brim
where does the rectum run?
down the midline
which way does the distended bladder deviate the rectum?
to the left
which way do the fibres of the rectococcygeus muscle run?
longitudinal smooth muscle fibres pass caudally to attach on Cd5/6
what is the function of the rectococcygeus muscle?
retractor
what does the epithelium transition to in the dog from cranial to caudal anal sphincter?
columnar to cutaneous
what are the characteristics of the ‘internal’ (cranial) anal sphincter?
thickened circular smooth muscle
what are the characteristics of the ‘external’ (caudal) anal sphincter?
striated, ventral to Cd4, fibres blend with genitalia muscles
what supplies the parasympathetic innervation to the midgut?
dorsal vagus
what supplies the parasympathetic innervation to the hindgut?
pelvic plexus (sacral outflow from S1 and 2)
what is the main artery of the midgut?
cranial mesenteric artery
what does the cranial mesenteric artery give off?
jejunals, right colic artery, middle colic artery, ileocolic artery
what does the ileocolic artery branch to?
ileal and antimesenteric artery
what does the hepatic portal vein initially form from?
cranial and caudal mesenteric veins
what do lacteals drain to?
mesenteric nodes which drain to cisterna chyli
where are the mesenteric nodes in dogs?
near to the mesenteric root
what is the difference between the cat and dog intestine?
cat caecum is straight and often palpatable in mid-abdomen
what is the difference between the ferret and dog intestine?
ferret has no caecum
what is the difference between the pig and dog intestine?
pig has some regions elaborated as fermentation chambers, ascending colon lengthens into long hairpin loop which coils into conical helix, caecum drawn to left side, caecum sacculated into haustra, which are ruched up by taenia, mesenteric nodes lie halfway between root and gut
what are haustra?
sacs divided by taenia
what are taenia?
2 thickened strands of longitudinal muscle in to pig caecum that ruche up the haustra
where do the mesenteric nodes lie in pigs?
halfway between the root and gut
what is the only species where the caecum is drawn to the left side?
pig
where is the lesser omentum positioned in the ruminant with respect to duodenum?
dorso-cranially
where is the greater omentum positioned in the ruminant with respect to duodenum?
caudally
what parts of the ruminant duodenum are similar to carnivores?
the descending and ascending parts
where do the mesenteric nodes lie in ruminants?
near to the gut
what % of fermentation takes place in ruminant stomach (rumen)?
75%
what % of fermentation takes place in ruminant caecum + first part of ascending colon?
25%
what is the ileum attached to the caecum by?
ileocaecal fold
what is the caecum like in ruminants?
long featureless tube which sticks far back caudally into pelvic cavity to lie alongside rectum
what is the difference between the opening into the caecum from the colon in ruminants and dogs?
ruminants have no obvious caecocolic sphincter, imperceptible transition
what are the 3 parts to the ascending colon in the ruminant?
ansa proximalis, ansa spiralis, ansa distalis
what is the ansa proximalis?
big dilate S-end of ruminant ascending colon
what does the ansa proximalis empty into?
ansa spiralis
what is the ansa spiralis?
narrow tube in ruminant ascending colon where absorption occurs, spirals into centre then out again
what does the ansa spiralis empty into?
ansa distalis
what is the ansa distalis?
loop in ruminant ascending colon that leads into transverse colon
what species are caecocolic fermenters?
horses and rabbits
what fills the ventral half of the horse abdomen?
caecum and colon
what is the shape of the caecum in the horse?
inverted comma shape
what does the base of the horse caecum attach to?
directly to the right dorsal body wall
what is the body of the horse caecum like?
long, sacculated by 4 taenia
what does the apex of the horse caecum reach?
reaches the xiphisternum
what does the horse ileum appear to open into?
caecal base
what is the caecal base in the horse?
a region of colon ‘stolen’ by the caecum during development
what are the 2 fermenting zones in the horse caecum/colon?
caecum + right and left ventral colon; right descending colon
what are the characteristics of the descending colon?
long, tortuous, sacculated, intermingled with jejunal coils
what is the site of parasite larvae in horses?
cranial mesenteric artery
what does the pelvic flexure act as in the horse?
a valve and site of impaction
where do the mesenteric nodes lie in the horse?
near the root of the mesentery
what is the only domestic mammal with an appendix caeci?
rabbit
what is expanded in the rabbit intestine?
ascending colon, especially caecum
how does double fermentation occur in the rabbit?
by re-ingestion
what secretes the enzymes that digest food in ruminants?
microbes in the rumen and colon
what does the host ruminant digest?
metabolites and dead microbes, products of microbe digestion
how much of the ox stomach is rumen?
80%
how much of the ox abdomen is taken up by rumen?
50%
how much of the ox stomach is reticulum?
5%
how much of the ox stomach is omasum?
8%
how much of the ox stomach is abomasum?
7%
what is the ruminant forestomach?
rumen, reticulum and omasum
what epithelium does the rumen forestomach (rumen, reticulum, omasum) have?
stratified squamous
what part of the rumen stomach is like a carnivore stomach?
the abomasum
what is the first chamber of the ruminant forestomach?
the reticulum
what is the rumen partially separated into?
2 major portions- the dorsal ruminal sac and ventral ruminal sac
what is the left longitudinal groove?
external groove alongside where partial separation is in rumen
what does the spleen sit on in ruminants?
cranially on left of stomach
what is the parietal side of the ruminant stomach?
the left side
what is the visceral side of the ruminant stomach?
the right side
what is the shape of the omasum?
circular
what does the abomasum run along?
ventral midline
what contacts the left flank in ruminants?
spleen, stomach and omentum
what was a common cause of death in cows when straw was tied with wire?
traumatic reticulitis (punctured reticular wall and diaphragm leading to septic pericarditis)
what do dense materials do in the ruminant stomach?
fall into the reticulum
where is the reticulum positioned relative to the opening of the oesophagus?
ventral
what is the atrium in the rumen?
entrance to the cranial sac
what does the atrium in the rumen open into?
dorsal ruminant sac
what does the right dorsal coronary pillar separate?
the dorsal ruminant sac from the caudal dorsal blind sac
what does the right ventral coronary pillar separate?
the ventral ruminant sac from the caudal ventral blind sac
what does the cranial pillar separate in the rumen?
ventral sac from dorsal sac
what is the oesophageal orifice?
entrance from oesophagus into rumen
what is the reticulo-omasal orifice?
exit from the reticular rumen into the omasum
what is between the oesophageal orifice and reticulo-omasal orifice?
oesophageal groove
when does the oesophageal groove close in ruminants?
in infants to divert milk directly into the omasum and bypass the rumen
what lines the rumen?
flat, rounded papillae for absorption
what are the papillae near the reticulum like in the rumen?
filiform
what are the papillae on the pillars like in the rumen?
flat and scale-like
what are the rumen papillae like in terms of blood supply?
very vascular with central supply and marginal drainage
what is the pattern of the epithelium in the reticulum?
epithelial ridges forming polygonial ‘cells’
what shape are the polygonial ‘cells’ in the reticulum of small ruminants?
hexagonal
what shape are the polygonial ‘cells’ in the reticulum of cattle?
quadrilateral
what are the polygonial ‘cells’ in ruminant reticulum covered with?
conical papillae
what is the reticulum the master controller of?
motility
what is the master controller of motility in the ruminant stomach?
reticulum
what is the omasum largely filled with?
epithelial leaves (small, intermediate and large) with conical papillae
what is the epithelium in the abomasum?
columnar
what characteristics does the abomasum share with the carnivore stomach?
columnar epithelium, glandular (same arrangement of glands), rugose
what characteristic does the abomasum share with the pig stomach?
torus pyloricus
how many muscle layers does the ruminant stomach have?
3
how many layers does the ruminant stomach have in any 1 place?
2
which arteries to the rumen stomach have canine equivalents?
arteries to the abomasum
what is the sympathetic supply to the ruminant stomach?
from the coeliac ganglion
what is the parasympathetic supply to the ruminant stomach?
dorsal and vagus nerves, both directly and via coeliacomesenteric plexus
what attaches the ruminant stomach dorsally (in development)?
dorsal mesentery (will become greater omentum)
what attaches the ruminant stomach ventrally (in development)?
ventral mesentery (will become lesser omentum)
what is the shape of the early ruminant stomach?
spindle shaped
what is the bulge that grows out of the top of the spindle in ruminant stomach development destined to become?
reticular rumen
why is the reticular rumen innervated by the dorsal vagus?
it is a dorsal structure to begin
what distorts the line of attachment of the dorsal mesentery in ruminant stomach development?
1) the bulge of the reticular rumen growing
2) the bulge of the reticular rumen rotating 90 degrees
3) the rotation of the abomasum 180 degrees
which parts of the ruminant stomach are large at birth?
omasum + abomasum
what are the 2 leaves of the continuous greater omentum in the ruminant stomach?
deep and superficial
where does the deep leaf of the greater omentum in the ruminant stomach attach?
right longitudinal groove to dorsal body wall
where does the superficial leaf of the greater omentum in the ruminant stomach attach?
left longitudinal groove to greater curvature of abomasum
which use dietary hexose sources directly, foregut or midgut fermenters?
midgut
do ruminants use dietary hexose sources directly?
no
do horses use dietary hexose sources directly?
yes
can horses digest microbes like ruminants?
no
how many bacteria per gram do ruminants have in rumen?
10^10
why can ruminants be considered to have roughly equivalent amounts of bacteria and protozoa even though they have fewer individual protozoa per gram?
protozoa are much bigger so have similar mass of bacteria and protozoa
is the rumen aerobic or anaerobic?
anaerobic
what do cellulolytic microbes digest?
plant structural compounds (cellulose)
what do amylolytic microbes digest?
starch and sugars
what do methanogenic microbes do?
reduce CO2 to methane
what do proteolytic microbes digest?
proteins
what do ureolytic microbes digest?
urea to ammonia
what does fermentation in the rumen produce?
microbes of good biological values and volatile fatty acids/SCFAs
what percentage of energy do VFAs supply to ruminants?
70%
what is the rumen pH range?
5.5-7
what threats do VFAs pose?
osmotic threat, and threat of metabolic acidosis due to low pK
what percentage of gross energy is lost as gas in ruminants?
8-10% as methane etc.
what % of greenhouse gases do ruminants contribute?
20%
what characteristics of rumen food will produce acetate (good for milk fat)?
high fibre, low solubility carbon substrates
what characteristics of rumen food will produce more butyrate and proprionate?
low fibre, high solubility
what is the risk when a grazing ruminant suddenly gets access to grain?
highest rates of B and P production reached, pH drops, lactic acid producing microbes take over- risk of acidosis as half of lactate produced is d-lactate which liver can’t absorb
up to how much saliva a day can cattle produce?
200 litres
what % of total body water in ruminants does saliva make up?
50%
what % of water reaching the rumen comes from saliva?
70%
what does 30% of water reaching the rumen come from?
rumen secretions and drinking
how much water/day does a dry cow need?
50 litres
how much water/day does a high yielding milker cow need?
150-200
what are the main salivary glands in the ruminant?
parotid, buccals, sublinguals, submandibular/submaxillary
which salivary gland supplies 50% of saliva in ruminants?
parotid
what are the characteristics of the parotid gland?
serous, dense cytoplasm
what are the characteristics of the submandibular and most other salivary glands?
mixed, discontinuous for protein, mostly mucin, foamy appearance
where are mechanoreceptors involved in salivation?
on buccal/oesophageal mucosae
what stimulates the mechanoreceptors on the buccal/oesophageal mucosae?
chewing, rumination, oesophageal distension
where are the chemoreceptors for low pH involved in salivation found?
in the mouth
what nerves are involved with salivation?
glossopharyngeal and vagus
what inhibits efferent discharge of the parasympathetic nerves involved in salivation?
mechanoreceptors that detect distension of rumen and reticulum
is saliva hypertonic or hypotonic to plasma?
hypertonic, perhaps near isotonic at high flow
what are the main components of saliva (5)?
water, buffers, cations, urea, protein
what % of saliva is water?
about 99%
what percentage of rumen HCO3 does saliva provide?
about 20%
what is the pH of saliva?
around 8.2
what do urea levels in saliva follow?
levels in plasma
what proteins does saliva not contain in ruminants?
enzymes
why does ruminant saliva contain mucin?
to stop frothy bloat
which has higher HCO3- levels, ruminant at rest or human saliva at peak flow?
ruminant
what does loss of saliva cause in ruminants?
hypovolaemia and metabolic acidosis
what pH do buffers work best at?
pH near their pK
when pH = pK of a buffer, what proportion of the buffer are proton acceptor/donor?
50/50
which cells are responsible for salivary secretion in monogastrics?
acinar cells
which cells are responsible for saliva modification in monogastrics?
duct cells
what keeps intracellular Na+ low in acinar cells in monogastrics and ruminants?
Na+/K+ pump
what stimulates NKCC1 in monogastrics?
Ca2+
what exchangers do duct cells in monogastrics have?
Cl- for HCO3- and Na+ for K+
what do ruminants not have that monogastrics have for salivary secretion?
NKCC and ducts cell modification
what is the risk of prolonged general anaesthesia in ruminants?
metabolic acidosis
what is a portosystemic shunt?
something which bypasses the system of sinusoids (connection between central vein and hepatic artery/portal vein without passing through sinusoid)
where are extrahepatic portosystemic shunts?
before entering liver
where are intrahepatic portosystemic shunts?
after entering liver, beyond hilus, before passing through sinusoids
how many general lobes does the liver have?
4
how many liver lobes does the dog have?
6
what are the liver lobes in the dog?
caudate, quadrate, right medial, right lateral, left medial, left lateral
what are the visceral surface impressions on the dog liver?
stomach, duodenum, right kidney
what are the visceral surface impressions on the pig liver?
stomach and duodenum
what are the visceral surface impressions on the ox liver?
omasum, reticulum, right kidney
what are the visceral surface impressions on the horse liver?
stomach, apex of caecum, diaphragmatic flexure, RDC, right kidney
which species don’t have a right kidney impression on the liver?
pigs
where is the impression of the stomach on the dog liver?
left lobes
where is the impression of the duodenum on the dog liver?
right lobes
where is the impression of the kidney on the dog liver?
caudate process of caudate lobe
what are the liver attachments?
right and left triangular ligaments, falciform ligament, lesser omentum, coronary ligament
what doe the right and left triangular ligaments attach the liver to?
diaphragmatic crura
what are the diaphragmatic crura?
sheets that attach diaphragm to dorsal body wall
what does the falciform ligament attach the liver to?
ventral body wall
what does the lesser omentum attach the liver to?
stomach
what does the coronary ligament of the liver surround?
hepatic vein leaving liver which immediately joins caudal vena cava and the attaches around caval hiatus
which species have no papillary process on the liver?
pig and horse
in which species does the right kidney not reach the caudate process?
pig
which species has marked surface liver lobulation?
pig
what is the difference in the lobes of the liver in pigs and dogs?
pig has less obvious division of quadrate
which species has a scalloped quadrate liver lobe?
horse
what is the difference of lobation of the horse and dog liver lobes?
no division of right lobe in horse, scalloped quadrate in horse
what is the difference between the ruminant and dog liver lobation?
ruminant has no division of left or right lobes
which species has no gall bladder?
horse
which species has clockwise rotation of the liver to the right?
ruminant
in which species does the liver lie almost entirely to the right of the midline?
ruminant
what are the steps to identify species of liver?
gallbladder, lobulation, right kidney impression, left and right lobe division
what is the function of the reticulorumen?
digests, absorbs VFAs, water and ions, synthesises B vitamins and microbial protein
what is the function of the omasum?
further absorption of water and VFAs
what is the function of the abomasum?
similar function to simple stomachs: delays and controls passage, stable pH, stable temperature, anaerobic environment, removal of gas by eructation, physical grinding by mixing breaks lignin
what do gas bubbles create in the rumen?
ruminal gas cap
where is the ruminal gas cap?
around top 5% of rumen
why does ingesta sink to the liquid zone in rumen?
fibres shorten and gas bubble rise
what is the ruminal fibre mat full of?
gas bubbles
how many types of contractile movement does the RR show?
2
what are the 2 types of contractile movement in the RR?
A and B waves in which smooth muscle contractions run across the viscus
how can the contractile movements of the RR be felt?
by leaning on/auscultation at the left paralumbar fossa
where is the left paralumbar fossa?
last rib, lumbar transverse processes, IAO bundle
what is the contractile motility of the RR measurable by?
balloon manometers, strain gauges, electrodes
what is the contractile motion of A waves?
churning contraction
how much more frequent are A waves than B waves in fasted ruminants?
2-3x
what does B wave contraction often follow?
an A wave
which has more symmetrical propagation A or B waves?
B waves
which way do B waves push gas?
towards cardia
which way do B waves push dense ingesta and short fibres?
towards reticulum to be sent towards omasum
what happens in the reticulorumen initially during feeding?
A frequency increases from 50-90s to 15-25s, duration, complexity, force and resting tone increase
what happens in the reticulorumen as feeding continues?
B frequency increases until as frequent as As, A to B interval increases, dorsal ruminal contraction force decreases
what is phase 2 of reticulorumen motility?
rumination
what happens in rumination?
regurgitation for further chewing, ingesta stimulate craniodorsal reticulorumen, reticular contraction, inspiratory effort against closed glottis, oesophageal antiperistalsis, reticular relaxation -> chewing -> swallowing
what is phase 3 of reticulorumen motility?
eructation
what happens in eructation?
belching of gases, B wave + craniodorsal rumen relaxation, reticular relaxation, empties craniodorsal rumen
what is eructation inhibited by?
liquids and foams (bloat)
what is the motor control of reticulorumen motility?
vagus: muscarinic ACh causes contraction and VIP causes relaxation
what does vagotomy stop in the reticulorumen?
all movements: rumination, eructation
what does dorsal vagotomy stop in the reticulorumen?
rumen, oesophageal groove, +/- reticulum
what does ventral vagotomy stop in the reticulorumen?
strangely variable: can range from death to no effect
what is the effect of cutting splanchnic nerve supply to the reticulorumen?
little effect
what restores post-vagotomy motility?
intrinsic control from intramural nerves within wall of rumen
what are present in the brainstem that drive R-R activity?
cyclically active neural circuits
what is vagal indigestion?
a dysautonomia, often with an identifiable lesion (e.g. abscess) in cattle
what external sign does vagal indigestion cause?
‘papple’ distension
what is papple distension?
bloat in left dorsal quadrant and sag in right ventral quadrant
what stimulates vagus sensory fibres?
tactile stimulation of craniodorsal region of RR and oesophagus, reticulum and RR fold distension, abomasal acidification
what inhibits splanchnic sensory fibres to the RR?
abomasal or ruminal distension
what stimulates splanchnic sensory fibres to RR?
manipulation of pylorus
what is the small controlling outlet of the adult RR?
the reticulo-omasal orifice
what is the oesophageal groove?
a muscular spiral groove running from oesophageal to omasal orifice
what does the oesophageal groove do in infants?
seals into a tube to divert milk past reticulorumen
how does the oesophageal groove seal into a tube?
1) longitudinal shortening pulls orifices near each other, 2) ‘lips’ fold in to create sealed tube
what supplies motor control to the oesophageal groove?
dorsal vagus
what inhibits the oesophageal groove?
reticulum or abomasum stretch (a CNS mediated effect)
how is the oesophageal groove peripherally inhibited?
by stimulation of sensory fibres in splanchnic nerves and adrenal adrenaline release
what pumps ingesta between leaves in the omasum?
muscular sulcus
what do the leaves of the omasum absorb?
water, Na+ and K+, exchange Cl- and HCO3-
what is abomasal filling dependent on?
omasal filling
what does abomasal distension inhibit and why?
RR contractions to prevent overfilling
what are abomasal contractions linked to?
reticular contractions, emptiness of duodenum (stimulates), duodenal acidity (inhibits)
which is more common, left or right abomasal displacement?
left
which is more severe RDA or RTA?
RTA- rapidly fatal
why is the first month postpartum a greater risk for abomasal displacement?
low Ca2+, concentrate diets so lots of VFAs, fetus gone
how can low Ca2+ increase risk of abomasal displacement?
no parts of stomach contract at same time, abomasum becomes slightly floppy
how does the postpartum diet of dairy cows increase risk of abomasal displacement?
produces large amounts of VFAs which make abomasum slacker and produce gas, means rumen is small as smaller amounts of feed when diet is concentrate
why does the lack of fetus mean postpartum cows are at greater risk of abomasal displacement?
means rumen smaller from when fetus was there and lots of space in abdomen for abomasum to move into
what can predispose cows to abomasal displacement?
long lesser omentum as lesser omentum holds abomasum in place- if unusually long it has more flexibility to move
what are the signs of LDA?
cyclical inappetence, reduced yield, ketosis, loose faeces, occasional discomfort, metallic tinkling ping halfway between tuber coxae and elbow
what is the non surgical treatment for LDA?
non-surgical rolling
what are the signs of RDA?
similar to LDA but right ping, more fluid than gas
what are the signs of RTA?
shock, pain, distension, ping higher on right
what % of ruminant energy is supplied by VFAs?
70%
what are the eating habits of wild rabbits?
graze large amounts of low-quality forage 6-9 hours a day, circadian pattern- graze at night, eat caecotrophs in day
when do rabbits start to wean from?
2-4 weeks
how much grass hay/grass should a rabbit be fed per day?
its own volume
what should a rabbit on a recovery diet eat?
grass hay/grass only
how many greens should rabbits eat per day?
an adult handful
what greens should rabbits not eat?
tomato leaves, potato, rhubarb
what food should only be given to rabbits as a treat?
carrots, fruit, dandelions
what does eating too many dandelions cause in rabbits?
diarrhoea
how much water should rabbits drink per day (and how does this compare to carnivores)
50-100ml/kg, more than carnivores
what is ingestion based on in rabbits?
smell and touch (with whiskers)
what is the technical term for whiskers?
vibrissae
what is a defining feature of lagomorphs vs rodents?
rabbits have distinctive upper second incisor ‘peg teeth’
what is a diasema? (rabbits)
gap between front teeth and cheek teeth
what is a common site of disease in rabbit mouth?
teeth roots impinging on tear drainage duct
how much do rabbit teeth grow per week?
1-2mm
what % of GIT volume is the rabbit stomach?
around 15%
what is the emptying time of the rabbit stomach?
around 4 days
why can’t rabbits vomit?
muscular cardia
what are the main functions of saliva?
lubrication, source of fluid, evaporation, buffering, microbial nitrogen source, provision of anti-foaming fluid
what is the composition of saliva?
high levels of bicarbonate and phosphate, similar amounts of chloride to plasma, high Na+ unless its being conserved (then high K+), high levels of urea, about 99% water, low protein, contains mucin
what happens to Na+ in saliva when Na+ is being conserved by the ruminant?
aldosterone secretion switches K+ for Na+
what causes reflex stimulation of salivation?
mechanical stimulation of mouth, oesophagus, cardia, reticulo-omasal orifice
what happens to protein and non-protein nitrogen in ruminant digestion?
converted to microbial proteins for digestion in more distal GI tract
what happens to fats, B vitamins and vitamin K in ruminant digestion?
synthesised by microbes and available through digestion
what happens to particulate matter in ruminant digestion?
regurgitated, re-chewed, swallowed and further fermented. smaller particles sifted through omasum and passed on to distal GI tract
how much CO2 can be converted to methane in cattle per hour?
up to 50 litres
what does nitrite caused by fermentation lead to?
methaemoglobinaemia
what does 3-methylinodole cause?
fog fever
what is the rabbit stomach pH?
1-2
what is the pH in the stomach of kits and why?
3-4 so microbes can seed in distal regions
what is a common impaction site in rabbit stomach?
tight bend in pylorus
what lobes are fused in the rabbit liver?
right medial and right lateral
what does the rabbit liver mainly secrete?
biliverdin
what is the cranial swelling of the rabbit and horse duodenum?
the ampulla
what is the ampulla?
cranial swelling of duodenum in horse and rabbit
which carbohydrates mostly reach the caecocolon in rabbits?
glucose and starch
what is rabbit milk low in?
lactose
where does much lipid reach in rabbits?
caecocolon
what can lipid do in the rabbit caecocolon?
inhibit cellulose digestion
what % can protein digestion be up to in rabbits?
up to 90%
where is the sacculus rotundus (rabbits)?
starts at ampulla, sends food either into caecum or ascending colon
how long does it take long fibres to pass in rabbits?
around 4 hours
how long do short fibres take to pass in rabbits?
around 24 hours
where does the ampulla send long fibres in rabbits?
into ascending colon
where does the ampulla send short fibres in rabbits?
caecum
what % of GIT volume is carbohydrates in rabbits?
40%
what do carbohydrates do in GIT in rabbits?
buffer and hydrate a reducing anaerobic environment for bacteria, archaea, protists, yeasts, microbes
what are the % VFA energy productions in rabbits, pigs, horses and ruminants?
14% in rabbits, 22% in pigs, 41% in horses, 44% in ruminants
what are fatty/carboxylic acids often saturated by in a reducing environment?
H2
what does the fusus coli do in the rabbit?
controls passage
what are the characteristics of the fusus coli in the rabbit?
muscular, vascular, densely innervated, goblet cells, longitudinal folds
what faeces do long indigestible fibres produce in the rabbit?
dry faecal pellets
what do long indigestible fibres produce in the fusus coli?
strong contractions
what are caecotrophs?
pasty caecal output, mucus capsule containing microbes, lysozyme, pH buffers, bacteriophage
what sort of fusus coli contractions do caecotrophs produce in the rabbit?
weak
what stimulate caecotrophs to be egested?
cortisol
what inhibits caecotroph egestion?
adrenaline
how does ingestion of caecotrophs work?
emerge in fused ‘loaves’, ingested directly from anus and swallowed without chewing, stay in fundus for 6-8h, fermented, continues distally and can cycle more than twice.
what can cause poorly formed caecotrophs, water diarrhoea, ileus (gut stasis) and enterotoxaemia (bacterial toxins) in rabbits?
poor diet, sudden diet change, dental disease, virus, bacteria, coccidia, liver disease, antibiosis
what can prevent poorly formed caecotrophs, water diarrhoea, ileus (gut stasis) and enterotoxaemia (bacterial toxins) in rabbits?
rehydration, high-fibre diet, pain relief, prokinetic drugs
what are the 3 main products of fermentation of carbon sources in rumen stomach?
acetate, butyrate, propionate
how % of ruminant energy is supplied by VFAs?
70%
what proportion of VFAs produced is acetate?
70%
what proportion of VFAs produced is propionate?
20%
what proportion of VFAs produced is butyrate?
10%
what generates the considerable reducing power of the rumen?
NADH and FADH2
what do microbial cells supply to the abomasum and SI?
vitamins, lipids, amino acids
what are the waste gases from fermentation?
CO2, CH4, a little H2 and H2S
what is the effect of the reducing environment on the gases produced by fermentation?
much CO2 -> CH4
how are gases removed from the rumen?
eructation
what happens if gases aren’t removed by eructation?
ruminal tympany (bloat) occurs and animal dies of asphyxia
what % of CH4, H2S and H2 is digestible?
8-10%
what % of H2S, CH4, H2 are metabolisable?
12%
what does a high fibre diet generate more of in ruminants?
more acetate and CH4
what does a high concentrate diet generate more of in ruminants?
more proprionate
what happens to most protein that enters the rumen?
degraded by microbes, amino acids either used by microbes to synthesise microbial proteins or deaminated to form ammonia
how do ruminants use non protein nitrogen such as urea or nitrate?
reducing environment of rumen converts them into ammonia, they are a N source for the microbes
what is the main protein source from ruminants?
microbial proteins that enter the lower GI tract
what is the nitrogen recycling cycle?
urea enters rumen via saliva/directly across ruminal epithelium, then converted into ammonia by microbes, can be regained as microbial protein
what is the nitrogen salvaging pathway?
if large amounts of N enter rumen excess ammonia will be absorbed by the host rather than converted to microbial protein. excess is then detoxified by the liver and converted to urea. if N supplies are high N absorbed as ammonia and if N supplies low N enters rumen as urea
what does excess glucose lead to in ruminant digestion?
energy losses in microbial maintenance
what does excess peptide lead to in ruminant digestion?
N loss as ammonia
what is the feed conversion ratio?
feed consumed/liveweight gained
what is the order of feed conversion efficiency of pig, cattle and sheep?
pigs > cattle=sheep
what is the order of the feed conversion ratio of pigs, cattle and sheep?
pigs < cattle=sheep
what is feed conversion efficiency?
liveweight gained/feed consumed
what is residual feed intake?
feed consumed/expected
how can ruminant productivity be increased?
matching N and C supply to reduce losses as urea and methane; buffers to prevent acidosis; selective breeding; manipulate microbes; rumen undegradable proteins
what would accumulation of VFAs in the rumen do?
stop further fermentation and lower pH
what is the epithelium of the rumen characterised as?
keratinised, stratified squamous, multilayered epithelium
what are the layers of the ruminal epithelium from luminal to basolateral side?
stratum corneum, stratum granulosum, stratum spinosum, stratum basale
is absorption of VFAs in the rumen faster at higher or lower pH? what does this suggest?
lower - suggests they are preferentially absorbed as undissociated acids
as undissociated acids what is the order of amount absorbed of the VFAs?
butyrate > propionate > acetate
what does absorption of VFAs across the rumen epithelium involve?
Na+/H+ exchangers, anion exchangers, monocarboxylate transporters
what is the fate of acetate?
partly absorbed in epithelium, mainly absorbed intact, used for fat synthesis
what is the fate of proprionate?
partly oxidised in epithelium, mainly absorbed intact, used for gluconeogenesis
what is the fate of butyrate?
forms β-hydroxybutyrate, a ketone body
what increases to aid absorption of VFAs and what stimulates this?
ruminal blood flow, stimulated by CO2 and butyrate
which vitamins must be provided by the ruminants diet?
A, D and E
which vitamins are synthesised in adequate amounts by microbes to meet ruminant requirements?
B vitamins and vitamin K
how can vitamin A be lost from herbage?
by oxidation
what vitamins are depleted in hay?
A, E and K
what does dicoumarol in mouldy sweet clover do?
inhibits vitamin K
what can thiaminase do and what is it present in?
can cause signs of vitamin B deficiency, present in bracken and fish livers
what happens to esterified fats in ruminant digestion?
hydrolysed to triglycerides and glycerol
what happens to the majority of unsaturated fats in the rumen?
they are hydrogenated
what are the main precursors of fat synthesis in the ruminant?
acetate, butyrate, lactate
what changes occur in ruminant digestion early in life?
reticulorumen increases in size, acquisition of microflora, VFAs stimulate papillae development, salivary secretion becomes continuous
how can rumen system be replicated in vitro?
using Ussing chambers to find net transport
what is acute acidosis?
life-threatening reduction in pH and bicarbonate levels
what is subacute ruminal acidosis?
mild and short-lived acidosis
what is the treatment for acidosis?
careful administration of bicarbonate buffers
how can ruminal acidosis be prevented?
gradual adaptation to new diets
what does subacute/chronic ruminal acidosis lead to?
thiamine deficiency causing cerebrocortical necrosis, poorly protected epithelium with discontinuities so microbes absorbed, bacteria produce liver abscesses, microbial endotoxins cause horn weakness and laminitis
why is ingestion of excess nitrate or urea more hazardous in ruminants than non-ruminants?
reducing atmosphere of rumen means microbes convert these to toxins substrates- nitrate to nitrite, urea to ammonia
why is nitrite toxic to ruminants?
causes formation of methaemoglobin which can’t carry O2
what are the signs of excess nitrite in ruminants?
mucous membranes become chocolate brown, respiratory rate and pulse increase, urea converted by microbial urease to ammonia.
what is fog fever?
excess tryptophan in lush regrowth grass fermented to indeoleacetic acid in rumen, which is decarboxylated to 3-MI- causes lung damage, respiratory distress and death
what method of digestion does the horse use?
hindgut fermenter
what is hindgut fermentation?
digesting food in similar fashion to other monogastrics and fermenting what is unabsorbed in the large intestine
how long do horses graze for per day?
18 hours or more
what are horse jaw movements like at grass?
relatively wide and long
what are horse jaw movements like when eating hay, cereals and pelleted feed?
reduced
what head position is the horse jaw designed for eating with?
lowered head
what salivary glands does the horse have?
paired parotid, mandibular and sublingual salivary glands
up to how much saliva may be secreted in 24 hours by a horse on a very dry hay diet?
100 litres
what is salivary enzyme concentration like in the horse?
low
what are the 2 zones of the equine stomach?
cardiac region and fundic region
what is the difference between the cardiac and fundic region of the horse stomach?
the epithelial types
what is the epithelium type in the cardiac region of the horse stomach?
non-secretory, keratinised, continuous with oesophagus epithelium
why does limited bacterial fermentation occur in the cardiac portion of the horse stomach?
bacteria are ‘shielded’ from gastric HCl
what is the pH range of the cardiac region of the horse stomach?
4-6
what is the function of salivary HCO3- in the horse stomach?
acts as a buffer
what are produced in the horse stomach and passed to the SI for absorption?
VFAs and lactic acid
what is the epithelium of the fundic region of the horse stomach?
gastric mucosa
where does ‘conventional’ monogastric digestion occur in the horse stomach?
in the fundic region
what is rate of transit of ingesta through the horse stomach dependent on?
particle size
what does the process of gastric emptying favour the movement and retention of in the horse stomach?
movement of smaller particles, retention of larger particles
how long does a single meal of hay/concentrates take to pass through the horse stomach?
3-4 hours
what are ‘slow waves’/’pacesetter potentials’ shown by intestinal smooth muscle cells?
cyclic changes in membrane potentiall, sub-threshold so don’t generate AP
how are slow waves in intestinal smooth muscle cells initiated and propagated?
initiated orally, propagate aborally
what are spiking potentials in intestinal smooth muscle cells?
where threshold is exceeded leading to contraction
what is the migrating myoelectric complex?
pattern of periods of spiking activity and quiescence in stomach and small intestine smooth muscle
what are the 4 phases of the MMC?
1) no spike potentials, no contractions, 2) intermittent spike potentials, 3) regular spiking activity, 4) rapidly diminishing contractile activity
which phases of the MMC are associated with propulsion of ingesta in horses?
mostly phase 3, but also phase 2
how long do liquid markers take to reach the caecum in the horse?
1 and 1/2 hours
how long do liquid markers take to pass completely in the horse?
8 hours
how long is a full meal estimated to take to pass in the horse?
10-12 hours
do MMCs occur in the horse caecum and large intestine?
no
when do short spike bursts occur in the horse caecum and large intestine?
during mixing
when do long spike bursts occur in the horse caecum and large intestine?
during propulsion
how many types of mass movement of the cranial portion of the base of the horse caecum are there?
2
what does the more frequent type of mass movement of the cranial portion of the base of the horse caecum result in?
transfer of ingesta
what does the less frequent type of mass movement of the cranial portion of the base of the horse caecum occur after?
the cranial sac has become dilated with gas and the caeco-colic orifice is exposed above the surface of the ingesta
what does the less frequent type of mass movement of the cranial portion of the base of the horse caecum involve?
gas transport with very little movement of ingesta
what is ileus?
impairment of transit of equine GI contents
what is one of the most commonly encountered complications of equine GI surgery?
ileus
where is equine pancreatic exocrine secretion added to ingesta?
just distal to pylorus
is a large or small volume of pancreatic exocrine secretion produced in horses?
large
what change in flow of pancreatic exocrine secretion results from horses eating and why?
5 fold increase via vagal stimulation
what does pancreatic juice contain in horses?
large amounts of NaCl and HCO3, low enzyme concentration. It’s isotonic
why is the total volume of enzyme delivery from pancreatic juice high in horses when the concentration is low?
large volume of pancreatic juice secreted
what does neural stimulation increase in most species, pancreatic juice volume or enzyme concentration?
mostly enzyme concentration
what does neural stimulation cause in the horse, increased pancreatic juice volume or enzyme concentration?
mostly increases volume
what does the lack of gallbladder in the horse mean for bile secretion?
bile secretion is continuous, increases after feeding
what does bile do?
alkalinises digesta and is involved in lipid digestion
what % of total dietary carbohydrate may reach the caecum in the horse?
around 70%
up to what % of soluble carbohydrate may reach the caecum in the horse?
50%
what is rapidly fermented in the horse large intestine?
carbohydrate, cellulose takes longer
what does digestion of residual carbohydrate rely on in the horse large intestine?
microbial fermentation and absorption of the products of this
where do the highest concentrations of VFAs produced in the horse caecum and large intestine occur?
in the ventral colon
when do VFA concentrations in the ventral horse colon peak after a meal?
around 14 hours after the meal
what happens to the VFAs produced in the horse caecum and large intestine?
either used by gut cells as energy source or absorbed and converted to glucose or fat
what % of total energy leads can VFAs absorbed in the horse caecum provide?
about 30%
what is the main end product of protein and urea broken down in the horse caecum and large intestine?
NH3
do horses get protein in the same way as ruminants?
very little microbial protein can be used by the horse
where is phosphorus primarily absorbed in the horse?
in the large intestine
what may phosphorus interfere with in the horse SI?
calcium absorption
where are most minerals, trace elements and vitamins absorbed in the horse?
in the small intestine
where are vitamin K and many water soluble vitamins synthesised in the horse?
in the large intestine
what do large concentrate meals fed infrequently cause in the horse?
a transient circulatory hypovolaemia due to increased secretion of GI fluids
what may the role of the large volume of fluid that reaches the ileocaecal junction in the horse be?
similar to parotid saliva in rumen as buffer and provider of electrolytes
what is HCO3- exchanged for in the ileum, caecum and large intestine of the horse?
Cl-
what are the sources of fluid entering the equine GI tract?
water ingested, parotid saliva, gastric secretions, pancreatic juice, bile
where does absorption of large amounts of water and Na+ occur in the horse?
in the caecum and ventral colon
where does absorption of water with Na+ and Cl- occur in the horse?
in the small colon and rectum
why should exercise be delayed for 1-3 hours following a meal in horses?
large amounts of material in the stomach or SI may make breathing in exercise harder, diversion of blood to splanchnic circulation can have implications for muscle blood flow, relative dehydration associated with feeding-induced hypovolaemia, post-feeding blood glucose may be reduced due to increased insulin secretion
