Download Mass movement Colon

Mass movement
occur to move the contents of large intestine over long distances, occur
1-3 me s per day.
Water absorption occur in distal colon, making the fecal contents
semisolid. Mass movement propels the fecal contents into rectum
where they are stored until defecation occurs.
Colon;
Apical membrane contains Na and K channels which responsible for Na
absorption and K secretion, induced by aldosterone which lead to
increase in Na absorption and to increase in K secretion.
Figure (15)electrolyte transport in the colon
The colon mucosa is simple columnar epithelium except in the anal canal
where it is stratified squamous epithelium.
There are no circular folds and a reduced number of villi. The mucosa is
thicker, with a larger number of globet cells.
The colon mucosa is simple columnar epithelium except in the anal canal
where it is stratified squamous epithelium.
There are no circular folds and a reduced number of villi. The mucosa is
thicker, with a larger number of globet cells.
Defecation:
As the rectum fills with feces, the smooth muscle wall of rectum
contracts and the internal anal sphincter relaxes, called rectosphincteric
reflex.
The smooth muscle of rectum contract to create pressure, and feces are
forced out through anal canal.
Gastrocolic reflex: Distension of the stomach by food increases the
motility of the colon and increases the frequency of mass movement in
large intestine.
This reflex is called the gastrocolic reflex, has afferent limb in the
stomach which is mediated by parasympathetic nervous system.
The efferent limb of the reflex produces increased motility of colon and
mediated by CCK (cholecystokinin) and gastrin. hormone increased
motility of colon .
As well as the afferent signals entering the spinal cord initiate other
effects ,such as taking a deep breath, closure of the glottis ,and
contraction of the abdominal muscles
to force the fecal contents of the colon downward ,at the same time
causing the pelvic floor to extend downward to pull out ward on the
anus to evaginate the feces
Secretion of the large intestine: Mucus which is regulated by direct
tactile and by local nervous reflexes to mucous cells. Stimulation of
pelvic nerve which carry parasyrspathetic to distal two third of large
intestine increase secretion of mucus and mol ity (ever y 30 m
i nut es ).
Mucus protect the intestinal wall against excoriation, from the great
amount of bacterial activity and provide the adherent medium for
holding fecal matter together
Absorption in large intestine:
The colon ( proximal half) absorbs 2-3 L of water per day, Na and Clions, secretes K ions, and bicarbonate ions to neutralize the acidic end
products of bacterial action in colon
.. In colon the hormone control regulate Na and K absorption is
aldosterone. The function of distal half of colon is storage.
Bacteria:
Intestinal bacterial flora is harmless unless it enter the blood. The
function of bacteria are:
1-Ul ize vi tami n C, B 12, synt hes i s vi tami n K and B pl ex.
2- Brown color of stool due to metabolism of bile pigment.
3- Acidity of stool due to formation of organic acid from carbohydrate by
bacteria
4- Play role in cholesterol metabolism.
5- Formation of toxic substances (histamine and tyramine).
6- Formation of indole, in addition to sulfide gives the odder of stool.
7- Formation of ammonia.
The antibodies which are produced by lymphocyte cells (proliferate and
differentiate by intestinal antigens) coat the mucous and prevent
bacteria from penetrating intestinal wall.
Bacterial action in the colon: numerous bacteria such as colon bacilli are
present in the absorbing colon. The substances formed as result of
bacterial activity are vitamin K, vitamin B12, thiamin, riboflavin and
various gases that contribute to flatus in colon
especially carbon dioxide, hydrogen gas, N2 and methane. The gases
produced due to breakdown of undigested nutrients that reach the
colon.
bile pigment, sloughed epithelial cells and undigested roughage of food.
The brown color of feces is caused by sterobilin and urobilin which are
derivatives of bilirubin. The odor is caused by products of bacterial
action
The function of colon
1-Storage of fecal materials.
2- Absorption of water and electrolytes.
Constipation- longer than usual time between bowel movements
and there is difficulty, pain, or discomfort when having a bowel
movement. Each person’s GI tract responds differently to food,
digestion, absorption, and transport.
Diarrhea- characterized by frequent loose, watery stools.
Indicating that the intestinal contents have moved too rapidly
through the intestines for fluid absorption to take place. This can be
a symptom of a variety of medical conditions.