Large Intestine:
Last part of G.I.T.
Length is about 5 Foot and diameter increases from Caecaum to Anus.
In fact length is very less as compared to small intestine but called as Large intestine because of its bigger diameter.
It is present around the small intestine and forms a frame around it.
It is divided into following parts;
Caecum.
Ascending Colon.
Transverse Colon.
Descending Colon.
Sigmoid Colon.
Rectum.
Anal Canal.
Caecum:
First part of the large intestine.
Starts at “Ileocaecal Junction”.
Ileocaecal sphincter is present in caecum.
Caecum has a small twisted coiled tubule called “Appendix”.
It ends at “Ascending Colon”.
Ascending Colon:
Remaining part of the large intestine after caecaum is called “Colon”.
Ascending colon is the first part of the colon.
It moves upwards till the lower surface of Liver.
From the liver it turns to the left.
The turn is called “Right Colic Flexure (Hepatic Flexure)”.
Transverse Colon:
It starts from Hepatic Flexure and runs left toward Spleen.
Just below the spleen it turns downwards.
The turn is called “Left Colic Flexure (Splenic Flexure)”.
Descending Colon:
At Splenic Flexure the colon turns and runs downwards till the iliac crest.
This part is called a descending colon.
Descending colon ends at Sigmoid Colon.
Sigmoid Colon:
It starts from the descending colon and ends in rectum.
Rectum:
Starts from sigmoid colon and ends in anal canal.
13 cm long.
Storage site for fecal material before excretion.
Contains rich blood supply.
Anal Canal:
Last part of GIT that opens in an external environment.
Around 4 cm in length.
Mucous membrane is arranged in folds called “Anal columns” it contains rich blood supply.
Opening to an external environment is called “Anus”.
Anus is guarded by two sphincters,
Internal Anal Sphincter.
External Anal Sphincter.
Internal anal sphincter is made up of smooth muscles hence is involuntary in nature.
External anal sphincter is made up of skeletal muscles hence is voluntary in nature.
These sphincters allow defecation of feces.
Functions of Large Intestine:
Absorption:
Large intestine mainly deals with absorption of water.
It also absorbs many minerals, certain vitamins and alkaline drugs.
Microbial Flora:
Large intestine provides a friendly environment for growth of many microbes and hence is heavily colonized by many bacterias.
These microbes are called “Normal Microbial Flora”.
Normal microbial flora synthesizes certain vitamins like folic acid, cyanocobalamin etc.
The microbial flora also prevents infections from pathogenic microbes found in food.
The microbes when they enter other parts of the body may cause infection e.g. E. coli.
Defecation:
The “mass peristalsis” movement rises in the sigmoid colon and pushes fecal material into rectum.
Stretched rectum produces an urge for defecation.
Sphincters are opened and fecal material is expelled out.
Commonly Asked Questions.
Draw a neat labelled diagram of digestive system and explain the functions of large intestine.
Write in detail about the large intestine.