Large Intestine …

★anatomy★function

The large intestine comes after the small

intestine in the digestive tract and measures

approximately 1.5 meters in length in adult

humans.

ANATOMY

➢cecum➔ is the proximal end of the large intestine and is where

the large and small intestines meet at the ileocecel junction.

➔ it is located in the right lower quadrantof the abdomen near the iliac fossa.

➔ is a sac that extends inferiorly about 6cm past the ileocecal junction.

➔ Appendix is attached to the cecum is a tube about 9 cm long.

➢colon

➔ is the last part of the digestive system in most

vertebrates. It extracts water and salt from solid wastes

before they are eliminated from the body and is the site

in which flora-aided (large bacterial) fermentation of

unabsorbed material occurs. Unlike the small intestine,

the colon does not play a major role in absorption of

foods and nutrients. However, the colon does absorb

water, sodium and some fat soluble vitamins.

The colon consists of four sections:● Ascending colon - extends

superiorly from the right colic flexure near the liver, where it turns to the left.

- is a small caliber than cecum❖ to remove the water and other key

nutrients from waste material and recycle it back into the body.

● Transverse colon- extends from the right colic flexure to the left colic flexure near the spleen, where the colon turns inferiorly.

- longest and most movable colon❖ serve as a reservoir for liquid that comes

from the small intestine and also the absorption of water and other substances

● Descending colon- extends from the left colic flexure to the pelvic.

❖ is to store faeces that will be emptied into the rectum.

● Sigmoid colon- forms an S-shaped tube that extends medially and then inferiorly into the pelvic cavity and ends at the rectum.- forms a loop which average is

about 40 cm in length, and normally lies within the pelvis.❖ is to store fecal matter until the body is

ready to expel it.

➔ Crypts - mucosal lining of the colon contains numerous straight tubular glands

- contain many mucus- producing goblet cells➔ Tenia coli - the longitudinal smooth muscle layer of the colon does not

completely envelope the intestinal wall but forms three bands

- is a straight , muscular tube that begins at the termination of the sigmoid colon and ends at the anal canal. The muscular tunic is smooth muscle and it is relatively thick in the rectum compared with the rest of the digestive tract.

- is continuous above with the sigmoid colon, while below it ends in anal canal. From its origin at the level of the third sacral vertebral its passes downward, lying in the sacrococcygeal curve and extends for about 2.5 cm in front of and a little below, the tip of the coccyx as far as the apex of the prostate.

➢Rectum

Anal Canal- the last 2-3 cm of the digestive tract. It can begins at the inferior end

of the rectum and ends at the anus. - the smooth muscle of the anal canal is even thicker than that of the

rectum and forms the internal anal sphincter at the superior end of the anal canal. The external anal sphincter at the inferior end of the anal canal is formed by skeletal muscle.

FUNCTION★ Absorbing water★ Absorption of vitamins★ Reducing acidity and protecting from infections★ Producing antibodies

The large intestine takes about 16 hours to finish the digestion of the food. It removes water and any remaining absorbable nutrients from the food before sending the indigestible matter to the rectum. The colon absorbs vitamins which are created by the colonic bacteria - such as vitamin K (especially important as the daily ingestion of vitamin K is not normally enough to maintain adequate blood coagulation), vitamin B12, thiamine and riboflavin. It also compacts feces, and stores fecal matter in the rectum until it can be discharged via the anus in defecation. The large intestine also secretes K+ and Cl-. Chloride secretion increases in cystic fibrosis. Recycling of various nutrients takes place in colon. Examples include fermentation of carbohydrates, short chain fatty acids, and urea cycling.

Defecation is the final act of digestion by which organisms eliminate solid, semisolid or liquid waste material (feces) from the digestive tractvia the anus. Waves of muscular contraction known as peristalsis in the walls of the colonmove fecal matter through the digestive tract towards the rectum. Undigested food may also be expelled this way; this process is called egestion.

Normal Functioning Defecation ReflexA normal functioning defecation reflex produces a muscular contraction that serves as a signal to the body that it is time to move the bowels and eliminate stools. Prompt response to the defecation reflex by going to the bathroom when it is activated, prevents stool from drying out and becoming difficult to pass. The defecation reflex may be triggered about 45 minutes to an hour upon rising from sleep, after drinking a hot beverage, or after eating a meal. The defecation reflex will disengage after about 15 minutes of being ignored. Like any other muscle that is not used, it will breakdown and fail to function if continuously ignored. When the defecation reflex is ignored, constipation will result as the stool that is retained in the colon becomes dried out, hard and difficult to pass. Retained waste can stretch out the rectal sack. A stretched out rectal sack requires more and more stool to fill the rectal sack before the reflex will be activated. This causes even more stool to dry out as it collects behind the previously retained stool.