Lesson 86 - Anatomy & Microanatomy of Large Intestine

What does the large intestine lack?

villi

What cells are lacking in the large intestine?

paneth cells

What type of tissue is substantial and scattered in the cecum?

lymphatic nodules

Where are cecum lymphatic nodules more concentrated in pigs, ruminants, and dogs?

ileal ostium

Where are cecum lymphatic nodules more concentrated in horses and cats?

apex of cecum

How does the mucosa of the colon compare to the mucosa of the small intestine?

substantially thicker because the glands are longer, more goblet cells

What is the mucosal surface like in the colon, cecum, and rectum?

smooth

What layer of the large intestine do the lymphatic nodules interrupt?

lamina muscularis and submucosa

What species have taenia coli and taenia ceci?

pigs and horses

What makes the taenia coli and ceci?

outer longitudinal layer of the tunica muscularis forms flat large muscle bands with elastic fibers

What component of the taenia coli and ceci is more predominant in horses?

more elastic fibers than smooth muscle cells

How does the wall of the colon and rectum compare in horses and ruminants?

rectum wall is thicker than the colon

What layer is thickened in the carnivore rectum?

longitudinal layer of tunica muscularis

What species have more elastic fibers in the rectum?

horses and cattle

What species have little elastic fibers in the rectum?

sheep and goats

What covers the cranial portion of the rectum?

serosa

What covers the retroperitoneal portion of the rectum?

adventitia

What structures can be seen near the junction of the anal canal and rectum?

rectal columns

What structures are very prominent in the rectum of dogs?

lymphatic nodules which are grossly seen because of pit-like depressions called rectal pits

Where does the outer longitudinal layer of the tunica muscularis end?

anorectal junction

Where does the inner circular layer of the tunica muscularis end?

internal anal sphincter muscle

What happens to the epithelium at the anorectal junction?

simple columnar epithelium changes abruptly to nonkeratinized stratified squamous epithelium

What animals lack glands in the mucosa of their anal canal?

ruminants and horses

What animals is the anal mucosa divided into three zones?

pigs and carnivores

What does the columnar zone contain?

rectal columns

What spaces form between the rectal columns?

anal sinuses

What lines the intermediate and columnar zone?

nonkeratinized stratified squamous epithelium

What are the zones of the anal canal?

columnar, intermediate, cutaneous

What lines the cutaneous zone?

keratinized stratified squamous epithelium

What type of glands are the anal glands?

tubuloalveolar sweat glands

What layer are the anal glands in?

propria-submucosa

What do cat and dog anal glands produce?

lipid secretion

What do pig anal glands produce?

mucous secretion

Where do the ducts of the anal glands open in carnivores?

junction of intermediate and cutaneous zones

What other glands do dogs have in their cutaneous zone?

sebaceous glands called circumanal glands

Where are the circumanal glands?

cutaneous zone near the junction with the skin

What are the four segments of the ascending horse colon?

right ventral colon, left ventral colon, left dorsal colon, right dorsal colon

What are the three flexures of the ascending horse colon?

sternal flexure, pelvic flexure, diaphragmatic flexure

What is the shape of the horse cecum?

comma shaped

Where does the horse colon extend to?

from pelvic inlet to diaphragmatic area

What are the parts of the cecum?

base, body, apex

How many taenia coli does the horse cecum have?

four

What opens into the cecum?

ileum and right ventral colon

Where is the base of the horse cecum located?

dorsal right of the midline, attached to the sublumbar region and right kidney

Where does the body of the horse cecum run?

ventral on right flank then lies on the ventral wall

What attaches the cecum to the right ventral colon?

cecocolic fold

Where is the horse cecum apex located?

ventral wall between the right and left ventral colons

What part of the cecum is palpable?

base of cecum

If you were performing a rectal palpation and feel a structure on the right side, what would it possibly be?

cecum base

What is the function of the cecum?

fermentation, water and electrolyte absorption, microbial protein synthesis, gas production & expulsion, motility and mixing

What is the ascending colon as known as?

large colon

What is the first segment of the ascending colon?

right ventral colon

What is the second segment of the ascending colon?

left ventral colon

What is the third segment of the ascending colon?

left dorsal colon

What is the last segment of the ascending colon?

right dorsal colon

What is the flexure between the right and left ventral colons?

sternal flexure

What is the flexure between the left ventral and dorsal colons?

pelvic flexure

What is the flexure between the left and right dorsal colons?

diaphragmatic flexure

How many taenia coli are present on the right ventral colon?

four

What segments of the ascending colon have haustra?

right and left ventral colon

What organs in the horse have haustra other than ascending colon?

cecum and descending colon

Where does the left ventral colon run?

caudally on abdominal floor left of the body and apex of the cecum

Where does the right ventral colon run?

from junction at base of last rib, ventrally and cranially on right body wall and abdominal floor

What parts of the ascending colon are palpable?

left dorsal and ventral colon and pelvic flexure

How many taenia coli does the left ventral colon have?

four

Where does the left dorsal colon run?

cranially over the left ventral colon

What is cranial to the left dorsal colon?

diaphragm and left liver

How many taenia coli does the left dorsal colon have?

one

Where is the right dorsal colon?

mostly within the thoracic cage

What is the shortest but widest segment of the ascending colon in horses?

right dorsal colon

How many taenia coli does the right dorsal colon have?

three

Where is the transverse colon in horses?

cranial to the root of the mesentery crossing the median plane

What is the transverse colon attached to in horses?

roof of body cavity

How many taenia coli does the transverse colon have in horses?

two

How many taenia coli does the descending colon have in horses?

two

What is the descending colon also called?

short colon

Where is the descending colon in horses?

left dorsal part of abdominal cavity and in pelvic region

What is present within the descending colon?

fecal balls

What is the function of the ascending colon?

continued fermentation, water and VFA absorption, motility and transit of digesta

What are the two arteries supplying the cecum in horses?

medial and lateral cecal artery