16-01-2013, 04:51 PM
ANATOMY & PHYSIOLOGY OF COLON
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Anatomy of The Colon
It is about 1.5 m long & extends from ileocecal valve up to the anus.
The colon is a cylindrical tube that is lined by moist, soft pink lining called mucosa; the pathway is called the lumen and is approximately 2-3 inches in diameter
It consists of seven portions.
Caecum
Ascending colon
Transverse colon
Descending colon
Sigmoid colon or Pelvic colon
Rectum
Anal Canal
In the angle between caecum & terminal part of the ileum there is narrow diverticulum called the vermiform Appendix.
Structure of the wall of Colon
The wall of colon is formed by 4 layers of structures like any other part of the gut.
1).Serosa layer – this is formed by peritoneum.
Small bags of peritoneum filled with fat and called appendices epiploicae, scattered over the surface of the colon except appendix, the caecum & the rectum
2).Muscular layer- The smooth muscle of colon distributed in to two layers namely
Outer longitudinal layer
Inner circular layer.
The longitudinal muscle fiber of colon arranged in the form of three line bands called taeniae coli.
Secretions of the colon
The large intestine juice is a watery fluid with PH of 7-8.
There is a fall in pH on the entry into the colon due to the presence of short chain fatty acids arising from bacterial fermentation of polysaccharides.
It contains 99.5% of water and 0.5% of solids.
Organic substances :-
Albumin, globulin, mucin, urea & debris of
epithelial cells.
Inorganic substanes :-
Sodium, potassium, chloride, bicarbonate (high conc.)
Functions of The colon secretion
Neutrilization of acids –
Strong acids formed by bacterial action are neutralized by the alkaline nature of the colon.
The alkanity of this juice is mainly due to the presence of large qnty of bicarbonates.
Lubrication Activity –
The mucin present in secretion of the colon lubricates mucosa of colon & bowel contents. The mucin also protects mucus membrane of colon by preventing the damage caused by mechanical injury or chemical substances.
Transit of material in the colon
The movement of materials through the colon is slow (long transit time ) and tends to be highly variable and influenced by a number of factors such as diet, dietary fiber content, mobility, stress, disease and drugs.
In healthy young and adult males, dosage forms such as capsules and tablets pass through the colon in approximately 20-30 hours, although the transit time of a few hours to more than 2 days can occur .
Functions of the colon
1). Absorptive Function :-
Play an important role in absorption of various substances like water, electrolytes, organic substances like glucose, alcohol and some drugs like anesthetics agents, sedative & steroids.
2). Formation of feces :-
After the absorption of nutrients, water & other
substances , the unwanted substances excreted out.
3) Excretory Function :-
Large intestine Excretes heavy metals like mercury, lead, bismuth and arsenic through feces.