Functional anatomy of Large Intestine .
Large intestine or colon extends from ileocecal valve up to anus .
Parts of Large Intestine .
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| Large intestine Dissection . |
Large intestine is made up of the following parts:
1. Cecum with appendix .
2. Ascending colon .
3. Transverse colon .
4. Descending colon .
5. Sigmoid colon or pelvic colon .
6. Rectum .
7. Anal canal.
Structure of Wall of Large Intestine .
Wall of large intestine is formed by four layers of structures like any other part of the gut.
1. Serous layer .
It is formed by peritoneum
2. Muscular layer .
[1]. Smooth muscles of large intestine are distributed in two layers, namely the outer longitudinal layer and inner circular layer.
[2]. The longitudinal muscle fibers of large intestine are arranged in the form of three long bands called tenia coli.
[3]. The length of the tenia coli is less when compared to the length of large intestine. Because of this, the large intestine is made into series of pouches called haustra .
3. Submucus layer .
It is not well developed in large intestine
4. Mucus layer .
[1]. The crypts of Leiberkühn are present in mucosa of large intestine.
[2]. But the villi, which are present in mucus membrane of small intestine are absent in the large intestine.
[3]. Only mucus-secreting glands are present in the mucosa of large intestine.
Secretions of Large Intestine .
Large intestinal juice is a watery fluid with pH of 8.0.
Composition of Large Intestinal Juice .
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| Composition of large intestinal juice . |
[1]. Large intestinal juice contains 99.5% of water and 0.5% of solids .
[2]. Digestive enzymes are absent and concentration of bicarbonate is high in large intestinal juice.
Functions of Large Intestinal Juice .
1. Neutralization of Acids .
[1]. Strong acids formed by bacterial action in large intestine are neutralized by the alkaline nature of large intestinal juice.
[2]. The alkalinity of this juice is mainly due to the presence of large quantity of bicarbonate.
2.Lubrication Activity .
[1]. Mucin present in the secretion of large intestine lubricates the mucosa of large intestine and the bowel contents, so that, the movement of bowel is facilitated.
[2]. Mucin also protects the mucus membrane of large intestine by preventing the damage caused by mechanical injury or chemical substances.
Functions of Large Intestine .
1. Absorptive Function .
Large intestine plays an important role in the absorption of various substances such as:
1. Water .
2. Electrolytes .
3. Organic substances like glucose .
4. Alcohol .
5. Drugs like anesthetic agents, sedatives and steroids.
2. Formation of Feces .
After the absorption of nutrients, water and other substances, the unwanted substances in the large intestine form feces. This is excreted out.
3. Excretory Function .
Large intestine excretes heavy metals like mercury, lead, bismuth and arsenic through feces.
4. Secretory Function .
Large intestine secretes mucin and inorganic substances like chlorides and bicarbonates.
5. Synthetic Function .
[1]. Bacterial flora of large intestine synthesizes folic acid, vitamin B12 and vitamin K.
[2]. By this function, large intestine contributes in erythropoietic activity and blood clotting mechanism.
Dietary Fiber .
[1]. Dietary fiber or roughage is a group of food particles which pass through stomach and small intestine without being digested and reach the large intestine unchanged.
[2]. Other nutritive substances of food are digested and absorbed before reaching large intestine.
[3]. Characteristic feature of dietary fiber is that it is not hydrolyzed by digestive enzymes. So, it escapes digestion in small intestine and passes to large intestine.
[4]. It provides substrate for microflora of large intestine and increases the bacterial mass.
[5]. The anaerobic bacteria, in turn, degrade the fermentable components of the fiber.
[6]. Thus, in large intestine, some of the components of fiber are broken down and absorbed and remaining components are excreted through feces.
Components of Dietary Fiber .
[1]. Major components of dietary fiber are cellulose, hemicelluloses, D-glucans, pectin, lignin and gums.
[2]. Cellulose, hemicelluloses and pectin are partially degradable, while other components are indigestible.
[3]. Dietary fiber also contains minerals, antioxidants and other chemicals that are useful for health.
Sources of Dietary Fiber .
Sources of dietary fiber are fruits, vegetables, cereals, bread and wheat grain (particularly its outer layer).
Significance of Dietary Fiber .
Diet with high dietary fiber has health benefits since dietary fiber:
1.Delays emptying of stomach
2. Increases formation of bulk and soft feces and eases defecation
3.Contains substances such as antioxidants and other useful substances.
[1]. When high dietary fiber food is taken, other foods, which may cause some diseases may be decreased in quantity or completely excluded from diet.
[2]. Diet with high fiber content tends to be low in energy and it may be useful in reducing the body weight.
[3]. Some components of dietary fiber also reduce blood cholesterol level and thereby decrease the risk for coronary heart disease and gallstones.
[4]. Dietary fiber is suggested for treating or to prevent constipation and bowel syndrome.
[5]. It is also useful in treatment of some disorders such as diabetics, cancer, ulcer, etc.
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