digestive anatomy of HORSE Flashcards
describe oral cavity
- small entrance
- long and narrow
- dark; gag and flashlight needed to examine
horses lips are v
mobile; graze close to ground
horse incisors are what kind of teeth
hypsodont
do horses have a dental pad
no
hypsodont teeth in horses have ____ crown
high crown in relation to roots
horse hypsodont teeth; how long to fully erupt
can take a long time to fully erupt; large proportion of tooth body can lie under gum line, enables more wear and tear
what teeth in horses are brachydont
the canines; often not present/ erupted in females
what are canine teeth in horses for
fighting now chewing
what teeth in horse are brachydont
incisors and cheek teeth
as the tooth surface wears, pulp cavity may become exposed, sealed with _____ formed as result of odontoblast activity
secondary/tertiary dentine
what allows us to age the animal
enamel crests
wolf teeth
rudimentary upper first premolar, sits immediately rostral to PM2
horse dental formula
2(I3/3, C1/1, P3(4)/3, M3/3) = 40(42)
baby teeth:
2(Di3/3, Dc0/0, Dp3/3) = 24
temporary teeth eruption
i1= 6 days
i2= 6 weeks
i3= 6 months
permanent teeth eruption
I1= 2.5-3 years
I2= 3.5-4 years
I3= 4.5=5 years
canine= 4-5 years
describe cups and stars
infundibulum as teeth wear creates cups: like a dark circle on the tooth
as tooth wears more the pulp cavity becomes exposed and you can see stars
infundibulum is filled with
cementum
There is the outer layer of enamel, then the dentine, then the inner ring of enamel that is the edge of the infundibulum, and then the cementum in the centre, which is darker
wear of permanent teeth
cups gone (smooth):
- I1= 6 years
- I2= 9 years
- I3= 8 years
start to see stars
- I1= 8 years
- I2= 10 years
- I3= 11 years
round
- I1= 9 years
- I2- 10 years
- I3= 11 years
triangular
- I1= 16 years
- I2= 17 years
- I3= 18 years
rectangular
- 18-20+ years
diastema
space in between incisors and premolars
what may be present in diastema in males
canine tooth
for the molar teeth the upper arcade sits ____ to lower arcade
lateral (so upper and lower teeth have a slope like a pyramid ^)
where will sharp edges occur on the maxillary (upper) teeth and on the mandibular (lower) teeth
buccal surface in upper/maxillary
lingual surface in lower/ mandibular
wave mouth
Some teeth will be worn away excessively, while others grow too long. This leads to a wave‐
like appearance of the molar teeth
what is dental procedure called on horses where sharp edges are filed away
floating
in young horses the molars and occasionally last premolar project into the
maxillary sinus
(but as horse ages and teeth grow amount of tooth in sinus decreases)
tooth root access and dental fractures can result in
sinus empyema (collection of pus)
are growth bumps of deciduous teeth normal
yes
tongue is velvety due to the many fine
filiform papillae
where do you find vallate papilla
dorsal surface of root of tongue
where do you find foliate papillae
lateral surfaces of root of tongue
root of tongue has diffuse ____ tonsils
lingual
parotid salivary gland location
extend from base of ear to ventral neck behind mandible
mandibular gland location
medial to the parotid
what is the largest salivary gland in horse
parotid
parotid duct lies
ventral to mandible
lampas
condition when incisor teeth are erupting where the hard palate swells, normal
soft palate is ____ in horse
longest
soft palate completely separates the
oropharynx from laryngopharynx
EXCEPT during swallowing
the epiglottis rests within the
nasopharynx
horse is an ______ nose breather
obligate
why is the horse an obligate nose breather (3 reasons)
- The tongue rests against the hard palate when the mouth is closed.
- The soft palate position below the epiglottis,
- the palatopharyngeal arches complete the sphincter around the opening of the larynx
palatopharyngeal arches help seal off
the oropharynx from the nasopharynx
DDSP (dorsal displacement of soft palate)
- flipped soft palate
- soft palate displaced dorsally over epiglottis
- upper airway pathology that can contribute to poor performance in horses
at the opening of the trachea what kind of cartilage can you see almost lining the top of it
arytenoid cartilage
esophagus is dorsal or ventral to trachea
dorsal (above)
guttural pouches
large diverticula, extending from the eustachian (auditory) tubes that connect the nasopharynx to the ear
in horses esophagus where can you find submucosal glands
only near pharynx
in horse esophagus, cranial 60% is
skeletal muscle
similar to other species, esophagus starts dorsal to trachea and then moves to
LHS
describe the passing of a nasogastric tube (in the nose)
- Insert tube to level of pharynx and wait for horse to swallow tube
- View tube progress down LHS of neck as it passes down the oesophagus
- Can “rattle” the underside of neck to hear if in trachea
choke
- esophageal obstruction; common equine emergency
- commonly occurs when horse eats concentrated feed to quickly without chewing properly
- food bolus lodged in esophagus
- sedate and pass nasogastric tube, flush w water
the simple stomach is bent sharply so the ____ and ____ are close
esophagus and duodenum (ie esophagus and pylorus are close together)
makes a C shape
why does stomach shape make it difficult for horses to vomit
The oesophagus enters obliquely, and the cardiac sphincter is well developed, so it’s really difficult for the contents of the stomach to enter the oesophagus
stomach has enlarged fundus, called the
saccus caecus
where does stomach lie
deeply under ribs, almost entirely to LHS and never contacts ventral abdominal wall
where is spleen and liver in relation to stomach
spleen to left
liver cranially and to right
describe internal morphology of horses stomach
more extensive non‐glandular mucosa than other species. It covers nearly half of the total area, and extends into the saccus caecus. The cardiac
glandular region is a narrow zone running along the border of the non‐glandular mucosa. This border is thrown up into a thickened ridge, the margo plicatus. The fundic and the pyloric gland area are about equal size
margo plicatus
border between cardiac (glandular) and non glandular regions, thickened ridge
are cardiac sphincter and pyloric sphincters well developed in horse
yes
describe non glandular mucosa of stomach
- Whitish
- Stratified squamous epithelium
- Often folded, may be thick and cornified
- Involved with storage
describe glandular muscosa of stomach
- Reddish to yellow
- Covered with simple columnar epithelium
- May have folds (rugae)
- Involved with digestion
where are gastric ulcers more commonly found in horse stomach
non glandular region bc not protected from acidic contents
normally non glandular region is full of ____ to buffer stomach acid
fiber
non glandular region of horse stomach is extensive and extends from _____ to _____
esophageal sphincter to margo plicatus
describe epithelium and lamina propria of non glandular stomach
- keratinized stratified squamous epithelium
- dense irregular connective tissue
equine gastric ulcer syndrome (EGUS) is subdivided into
- equine squamous gastric ulcer syndrome (ESGUS). (common! non glandular mucosa)
- equine glandular gastric ulcer syndrome (EGGUS) which is less recognized, has high prevalence in some pops, and is less responsive to traditional treatments
- these are unrelated to each other
how does equine squamous gastric ulcer syndrome occur, what are some risk factors
A horses’ stomach produces acid continuously, creating up to 42L of acid a day. When the stomach isn’t full, acid can splash onto the
vulnerable upper portion of the stomach – the squamous mucosa, or non‐glandular mucosa, causing acid burn.
Risk factors include heavy training or competition schedules, low roughage or high grain diets, extended travel, so the stomach is empty for prolonged periods of time, and stabling horses, so they’re unable to graze.
in small intestine what is extremely long and why
mesentery is extremely long; allows jejunum to be v mobile
where does most of jejunum lie
left dorsal quadrant, rest of SI in unremarkable
is there taenia or haustra in the small intestine
no!
what can occur to make the SI die/ become necrotic
SI gets twisted/ blood flow gets cut off
how does a small intestinal volvulus occur
segment of SI rotates more than 180 degrees around its mesentery
acute and severe, painful abdominal pain
where are brunners glands found
entire length of duodenum
what do brunners glands open into
base of crypts of lieberkuhn
secretion of brunners glands
alkaline, mucous, viscous
protects duodenum from gastric secretions
where are paneth cells found
at base of crypts of lieberkuhn
small intestine in horses contains what 4 cells
- absorptive cells (enterocytes),
- goblet cells,
- enteroendocrine cells,
- paneth cells
what do paneth cells secrete
secrete dense granules which contain antimicrobial peptides and proteins to keep the microbial population in check
where is the major site for bacterial fermentation
caecum
where is caecum
very large, comma shaped, fills most of RHS of abdomen
base of ceacum is bulbous and lies doral in right
paralumbar fossa
base of caecum has
greater curvature (dorsal) and lesser curvature (ventral)
describe caecum curving
has curved body that extends ventrally and then cranially and medially to an apex, when full the apex can reach level of xiphoid process at end of sternum
can auscultate apex of caecum for
sand colic
large intestine taenia and haustra
- taenia; longitudinal muscle bands providing support
- haustra; sacculations in the intestine wall
caecum has how many taenia
4
the 4 taenia divide the caecum into 4 haustra separates by deep folds, describe them
- The dorsal band attaches to the ileocaecal fold.
- The lateral band attaches to thecaecocolic fold.
- The medial and ventral bands join together near the apex
The openings to the ilium – the ileocaecal orifice ‐ and the colon ‐ the caecocolic orifice ‐ both open
into the
lesser curvature of the base of caecum
is ileum directly connected to colon
no
does all the food a horse eat pass through the caecum
yes
ascending and descending colon in horse are
very large; 3-5m long and 50-130 L
does colon have taenia and haustra
yes
describe acending colon aka the great colon
- long, double U‐shaped loop which is doubled on itself. It’s not technically ascending as it doubles
back on itself, but it’s analogous to the ascending region of the simple colon. - It’s got 4 main parts, which are joined by flexures.
- In order, there’s the right ventral colon, the
left ventral colon, the left dorsal colon, and the right dorsal colon
4 part of ascending colon (in order)
- Right ventral (attached to the caecum by the caecocolic fold) 25cm diameter
- Left ventral 25 cm diameter
- pelvic flexure; abrupt decrease in diameter 10cm
- Left dorsal 10 cm diameter
- diaphragmatic flexure
- Right dorsal 50cm diameter
how is right ventral part of ascending colon attached to caecum
attached to the caecum by the caecocolic fold
describe diqmeter from right dorsal colon (last part of ascending colon where diameter is 50cm ish) to transverse colon to descending colon
- transverse colon is short, right to left, cranial to the root of mesentery and abrupt decrease in diameter: 7-10cm
- descending colon (aka small colon) continues at this diameter and is very long 3-4 m, has a mobile loose mesocolon
right and left ventral colon have how many bands (ie taenia)
describe them
- 4; 2 dorsal and 2 ventral
- 2 dorsal bands of RVC and LVC form intercolonic mesenteric bands (lateral and medial mesocolic)
- attach to right and left dorsal colon respectively
- ventral bands of both colons (lateral and medial) are free
- both RVC and LVC are sacculated
describe taenia and haustra of levic flexure and left dorsal colon
- only 1 taenia (band)
- no haustra
- 2 new dorsal bands start at diaphragmatic flexure
describe taenia of right dorsal colon
3 bands
describe taenia and haustra of descending colon
- 2 bands, wide
- deep sacculations form fecal balls
summary of taenia of large intestine
- caecum 4
- right ventral colon 4
- left ventral colon 4
- left dorsal colon 1
- right dorsal colon 3
- small colon 2
colonic volvulus
same as SI; if colon revolves more than 180 degrees around mesenteric attachment
straight terminal part of LI
rectum
rectum passes through
pelvic cavity
does the anus have glands
no
liver lobes
L medial
L lateral
single R lobe
fluted quadrate lobe
caudate lobe
no papillary processes
NO gall bladder
abdominal muscles
external abdominal oblique
internal abdominal oblique
rectus abdominus
transverse abdominus
tunica flava
deep layer of fascia over the external abdominal oblique muscle, which is made of elastic tissue. This layer is yellowish in colour and is known as the tunica flava . It is thickest ventrally, where it helps to support the enormous weight of the GI tract.
The dental formula of an adult horse that does not have wolf teeth is 2(Ia/a, Cb/b, Pc/c, Md/d) = 40. Which of the following is CORRECT?
A.
a = 3; b = 1; c = 3; d = 3
B.
a = 3; b = 0; c = 4; d = 3
C.
a = 3; b = 1; c = 3; d = 4
D.
a = 3; b = 0; c = 3; d = 0
A.
a = 3; b = 1; c = 3; d = 3
As the surface of hypsodont teeth wears, the pulp of the tooth may become exposed. This is sealed with __________ and is visible as the dental star in the incisors.
B.
Secondary/tertiary dentine
Where can you view the passage of a stomach tube as it passes down the oesophagus of the horse?
left side of neck
What is the name given to the enlarged fundus of a horse
saccus caecus
The internal surface of a horses’ stomach is lined by two types of mucosa: non-glandular and glandular mucosa. Which type of mucosa appears reddish to yellow in colour?
Glandular mucosa
In the horse, there is a raised border between the glandular and non-glandular regions of the stomach. What is this ridge called?
A.
Margo plicatus
In which quadrant of the abdomen do the majority of the small intestines reside?
Left dorsal quadrant
The secretion from Brunner’s glands plays a role in protecting the duodenum from acidic gastric secretions. How far along the duodenum do Brunner’s glands extend in the horse?
Entire length of the duodenum
How many taenia does the caecum of the horse have?
4
Which part of the equine colon attaches to the caecum?
Right ventral colon
Which part of the equine colon connects to the transverse colon
Right dorsal colon
Which part of the equine colon has a single taenia?
Left dorsal colon
liver lobes
Left medial and lateral lobes; single right lobe; fluted quadrate lobe; caudate lobe with no papillary process
The 4 main abdominal muscles in the horse are:
External and internal abdominal oblique muscles, the rectus abdominus, and the transverse abdominus
