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ANATOMY & PHYSIOLOGY OF COLON Prepared by - Nilesh Makwana Guided by – Dr.A.N.Mishra


Contents Anatomy of Colon Parts of colon Structure of wall of Colon Physiology Of Colon Secretion of Colon Function of Colon Secretion Colonic Microbial flora Enzymes In Colon Function of Colon Disease of colon

Anatomy of The Colon:

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 . . Structure of the wall of Colon

Layers of the wall of colon:

Layers of the wall of colon

Structure of Wall of The colon:

Structure of Wall of The colon Since the taeniae are shorter than the muscular coat, the colon is made in to the series of pouches called haustra. 3).Submucosa Layer – This is not well developed in colon. 4). Mucosa layer – The villi and leiberkuhn are absent in the colon. Only mucus secreting glands are present in the colon.

Secretions of the colon:

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:

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 :

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 .

Colonic micro flora :

Colonic micro flora Over 400 distinct bacterial species have been found, 20-30% of which are of the genus of Bacteroides. The concentration of bacteria in the human colon is 10 11 -10 12 CFU/ml. Fundamentally anaerobic in nature. Predominant species: Bacteroides, Bifidobacterium and Eubacterium . Major metabolic processes occurring in the colon are hydrolysis and reduction .

Enzymes In Colon:

Enzymes In Colon Reducing enzymes Nitroreductase Azoreductase N-oxide reductase Sulphoxide reductase Hydrolytic enzymes Esterases Amidases Glycosidases Glucuronidase Sulfatase Azoreductases, which reduces azo-bonds selectively. Polysaccharidases, which degrades the polysaccharides.

Functions of the colon:

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.

Functions of the colon:

Functions of the colon 4). Secretory function - The Colon secrets mucin and inorganic substances like chlorides and bicarbonates, 5). Synthesize function - The bacterial flora of the colon synthesizes folic acid, vitamin B 12 and Vitamin K,

Diseases Related to The colon:

Diseases Related to The colon FUNCTIONAL DISORDERS: Irritable bowel syndrome Mega colon INFLAMMATORY BOWEL DISEASE Ulcerative colitis Crohn’s disease Inflammatory bowel disease NEOPLASTIC DISORDERS Colonic polyps Colorectal carcinoma

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