- begins as a long tube from mouth(stomodeum) to anus(proctodeum)
- growth and development of the tube form the digestive system
- especially special in horse is the caecum
Midgut starts with the 2 half of duodenum
a)comprises: - 2nf half of duodenum . duodenum is pretty constant in position in all species. Hangs of
the mesodeum of the dorsal body wall. Prox is retroperitoneal, distal is intraperitoneal.
- jejunum- in human. 60% of Si
-ileum – in human is 40 % of SI. in horse only 10 to 12 inches
-caecum- site of microbial fermentation. So its called midgut fermenter
-1 half of transverse colon
- hindgut starts 2/3 the way of the transverse colon.
2)equine gut- relative sizes.
Mesocolon/descending mesocolon- provides ability to move arm around ruring rectal
Blood supply differentiates all of them
3) equine surface projections
a) caecum on right- human also right side.(bottom right) . in mammals, mostly on the right side.
Horses- it is pressed up against right abdominal wall. So can put a needle in to let out gas
b) small intestine displaced to the left of caecum
- much busier on the left side of the body. Spleen, liver, stomach, left limbs of descending colon.
Ox- left kidney is intraperitoneal
3) small intestine
- parietal peritoneum is reflected off the kidney then known as visceral peritoneum.
- midline- caudal vena cava and aorta. - the kidney ispresssed up against the dorsal body wall. The parietal peritoneum when reflected off is
known as the visceral peritoneum.
-When reach to base of aorta- it is known as the root of mesentery.- is a stout stalk of mesentery caring
blood vessels & nerves from vagus and lymphatic channels going back goes through the root of
- descending duodenum is retroperitoneal(reflected peritoneum that covers it) or suspended by
mesentery(just like small intestine)
- the spleen- space btwn ventrolateral wall of spleen
-left colon entrapment- the large intestine on left side can migrate and get hooked on the spleen shelf
dorsal to it.
-blood vessels is sandwiched between the mesentery
- the arterial arcades- big long loopy anastomic branches that form loopy structure
- the straight arteries- is the vasa recta
- some species-
that has larger ileum- before the ileum-u get short arcades and longer vasa recta
- ileum gets longer arcades and shorter vasarecta.
a) suspended from dorsal abdominal wall/aorta by ‘root’
b) mesentery allows some mobility of small intestine
c) mesentery of Si contains branches of Cranial mesenteric artery tributaries of Cran mesentery vein( to
portal vein), autonomic nerves and lymphatic channels
-celiac trunk supply foregut. Cranial mesenteric artery.
Caudal mesenteric artery supply hindgut.
Anastomotic braches – fore- mid and hind gut blood vessels
d) Histology: four tunics
- since its one tube – get the standard 4 layers.
- esophagus. – more mucosa- stratified squamous epithelium.
- glandular in SI more like that of stomach- mucus secreting glands, acid secreating glands and bicard
secreting gland to protect SI from acid., enzyme secreting gland. i) mucosa: glandular epithelium and muscularis mucosa. Only real difference.
ii) submucosa: nerves, blood & lymph vessels, elastic tissue
iii) muscle layers: inne