large intestine anatomy and histology Flashcards
what are the 3 general divisions of the lrge intestine
- caecum
- colon (ascending, transverse, descending)
- rectum
what are the functions of the large intestine
- hindgut fermentations (horses and rabbits)
- microbial enzymes digesting remaining CHO and proteins from SI
- major site of water absorption and ion balance
- feces production
describe the species differences of the large intestine
list histological differences between different segemtns of the intestines
what major histological difference identifies the large intestine from small
- no villie
- villie replaced by mucus cells
describe the histological appearance of the large intestine
- microscopic anatomy of caecum, colon and rectum all very similar
- same 4 tunics as small (tunica mucosa, submucosa, muscularis, serosa)
- no villi
- only crypts (tubular mucus glands) which are deeper than in small intestine
- no enzymes
- numerus goblet cells (density rectum>colon>caecum)
- variable lymphoid tissue within mucosa and submuscoa (GALT)
what features histologically of the large intestine relate to function
- more goblet cells as need to produce mucus (chyme is drier here)
describe blood supply to the large intestine
- crainial mesenteric artery (does everything from duodenum to descending colon)
- caudal mesenteric artery = descending colon and most of rectum
- internal pudendal artery does caudal part of rectum
most veins from the large intestine drain into ……..
hepatic portal vein
veins of the caudal rectum and anal region drain into ……..
caudal vena cava
describe innervation to the large intestine
smooth muscle controled by ENS
- submucosal layer = submucossal plexus (meissners)
- mucosal layer = myenteric (auerbachs) plexus
- plexi are connected to the CNS by fine netwrok of nerve fibres
describe the caecum
- large blind viscus in herbivores
- small in carnivores
- only rabbits have appendix
- well developed in hind gut fermenters
- birds hav TWO
where will you find the caecum in the abdomen
right side (except in pigs left)
what is the role of the caecum
- blind ending sac with 2 muscular valves controlling entry and exit of ingesta
- major site for microbial digestion of cellulose and absorption of water and electrolytes (esp in horses)
-source of bacteria for repopulating GIT after illness
compare the caecum in dogs vs cats
- cats have smaller caecum as they are obligate carnivores
- dog = short and spiral shaped
- cat = comma shaped
describe the caecum in bovidae
- relatively small
- has no taenia or haustra
- no clear junction between caecum and ascending colon
describe the caecum in the pig
- cylindrical blind sac laying on the left half of the abdomen with its apex pointing caudoventrally
- has 3 taenia (lateral, medial, ventral)
describe the caecum in the horse
- huge (30 L, 1m long)
- has a base (dorsally located), a body and a blind ending apex pointing vranioventrally (close to xiphoid on ventral abdo floor)
what are taenia
- visible bands of smooth muscle and elastic fibres on the external surface
what are haustra
sacculations caused by muscle activity , there fore dynamic not fixed
how many taenia does the horse caecum have
4
medial, lateral, dorsal and ventral
discuss the caecal valves of the horse
- equidae are unique in that the ileum discharges into the caecum whereas other animals the ileal ingesta goes into the ascending colon
- ileocaecal valve at base of caecum raised as papillae
- caecocolic valve is slit like valve
what are the segments of the carnivore colon
- ascending
- transverse
- descending
discuss the ruminant colon
- long ascending colon with 2 sigmoid flexures and a double spiralled area
- short transverse colon followed by straight descending colon
