large bowel Flashcards
what does the Large bowel consists of
the colon, caecum, appendix, rectum and anal canal.
what is the caceum
The caecum is a blind pouch just distal to the ileocecal valve- larger in herbivores.
what is the appendix
The appendix is a thin, finger-like extension of the caecum - not physiologically relevant in humans.
function of the large bowel
the reabsorption of electrolytes & water, and the elimination of undigested food and waste.
how many parts to the colons
4 ascending transverse descending sigmoid
what is the transverse colon attached to
Hangs off the stomach, attached by a wide band of tissue called the greater omentum (posterior side, mesocolon).
the middle colic artery is a branch off which artery
superior mesenteric artery
what is the proximal trasberse colon supplied with
middle colic artery
Distal third of transverse colon is perfused by
the inferior mesenteric artery.
how many logitudinal bands do the muscles have in the colon
and the muscle coat has 3 thick longitudinal band
Structural or functional purpose of appendices epiploica
unknown- suggested to have a protective function against intra-abdominal infections.
function of Taenia coli
necessary for large intestine motility.
what is the special secondary lymph tissue in the small intestines
payers patches
and in the large
solitary nodules
how is the haustra formed
by the teania coli
Cause the formation of pouched ovoid segments called haustra
what is the function of the colon
reabsorption
Colon absorbs electrolytes & water. (More in proximal colon)
Na+ and Cl- absorbed by exchange mechanisms and ion channels.
Water follows by osmosis.
K+ moves passively into lumen.
what structure follows teh sigmoid colon
rectum
what is the rectum a portion of
Dilated distal portion of the alimentary canal.
how can you distinguish between the colon and rectus
but distinguished by transverse rectal folds in its submucosa and the absence of taenia coli in its muscularis externa.
what strcuture follows the rectum
anal canal
what are the sorrounding structures to the anal canal
internal and external anal sphincters
what is the internal anal sphincter
circular muscle
and external
striated muscle
how many layers to the mucosal stucture of the large bowel
4 (order from most internal to external) mucousa (glands in it) submucousa (glands in it) muscularis serosa (blood vessels and nerve ending)
what is the most deep layer
mucosa
and most external layer
serosa
what strcutures are similar in the large bowel and the small intestines
Enterocytes and goblet cells are abundant.
Abundant crypts
Stem cells are found in the crypts.
why is the mucosa smooth
no villi
what do the enterocytes (of the large bowel) have
short, irregular microvilli - primarily concerned with resorption of salts.
how is water absorbed
Water is absorbed as it passively follows the electrolytes, resulting in more solid gut contents
what is more numerous cypts or goblets
goblet cells
do the number of goblet cell increase along the large bowel
yes increases distally towards the rectum
function of the mucus
- facilitates the passage of the increasingly solid colonic contents and covers bacteria & particulate matter.
how are they stimulated
(parasympathetic and enteric nervous system) stimulates Goblet Cell secretion.
how are new cells made in LB
crypt stem cells
what cells are found in the SB and not in the LB
No Paneth cells & enteroendocrine cells are rarer than in small bowel
do the glycocalyx contain digestive enzymes
nope
what makes up the brush border
microvilli
what does the glycocalyx control
regulates rate of absorption from intestinal lumen
similarly to SB what do the musclaris externa consit of
inner circular and outer longitudinal layer
what do the longitudinal muscles have
3 bands formed by the taenia coli
how do the teania coli look like when h and e stained
round long circular blobs on the end of the muscles
what are the ovoid segments in the circular muscle layer called
haustra
what can they do
cintract individually
what are the haustra and tenia coli not found
rectum and anal canal
what is the colonic contarctions like
kneading process which is minimally propulsive
5-10cm/hr
what does the colonic contraction do
promotes absorption of lectrolytes and water
what pattern/contraction occurs at the proximal colon
antipropulsive pattern
why
to retain chyme
what pattern/contraction in transverse and descending colon
localised segmental contractions of circular muscle called Haustral contractions cause back and forth mixing
does it increase in frequency
yes during meal
how often do you see mass movement in the LB
1-3x daily
like peristaltic wave
what promotes rapid trasnport through colon
Food that contains fibre (indigestible material)
how are the ascending colon and travsevrse colon innervayed
vagus nerve
parasympthetic
and how is sympathetic innervation done
lower thoracic and upper lumbar spinal cord.
how is the external anal sphincter controlled
controlled by somatic motor fibres in the pudendal nerves.
what do the afferent sensory nuerons detect
pressure
where is the Myenteric plexus ganglia concentrated
below taenia coli
hoe is the rectum filled with feaces
by mass movement
how is defeaction reflex controlled normally
by sacral spinal cord
ref;ex and voluntray actions
describe the nervous pathway for defecation
Reflex to sudden distension of walls of rectum.
Pressure receptors send signals via myenteric plexus to initiate peristaltic waves in descending, sigmoid colon and rectum. Internal anal sphincter inhibited.
Weak intrinsic signal augmented by autonomic reflex.
External anal sphincter under voluntary control.
Urge resisted, sensation subsides
what are the last few c, of the rectum known as
social part
what can it do
Can distinguish between solid, liquid and gas.
why is it important
That perceptual ability is important in knowing what can be passed appropriately in what circumstance.
what gives it colour
bile pigment
what smell
bacterial fermentatation
what has more bacteria stomach, SB or LB
Stomach and small bowel have few bacteria- protected.
Large bowel contains many
Essential to normal function.
function of teh interstinal flora
Synthesize and excrete vitamins e.g. Vitamin K- germ-free animals can have clotting problems.
Prevent colonization by pathogens by competing for attachment sites or for essential nutrients.
Antagonize other bacteria through the production of substances which inhibit or kill non-indigenous species.
Stimulate the production of cross-reactive antibodies. Antibodies produced against components of the normal flora can crossreact with certain related pathogens, and thereby prevent infection or invasion.
Stimulate the development of certain tissues, including caecum and lymphatic tissues
how are fibres broken down
Fibre (indigestible carbohydrate) can be broken down by colonic bacteria.
what do they form once broken down
Produces short chain fatty acids which can regulate gut hormone release, or be absorbed to be used as an energy source or to influence functions such as food intake or insulin sensitivity directly
what are the most prevelant bacteria in the normal flora
Most prevalent bacteria are the Bacteroides-
what are bacteriodes
Gram-negative, anaerobic, non-spore forming bacteria. Implicated in the initiation colitis and colon cancer.
what are bifidobacteria
are Gram-positive, non-sporeforming, lactic acid bacteria. Have been described as “friendly” bacteria. Thought to prevent colonization by potential pathogens
