Diet and Digestion
The entire process that the food undergoes from the time it is eaten to its excretion is known as metabolism of food. Nutrients are obtained from food by the process of metabolism that takes place in the following steps:
It begins at the mouth and comprises the esophagus stomach, small intestine, large intestine and it ends at the anus. The liver, gall bladder, salivary gland and pancreas are associated with the porkers of digestion.
The functions of each of the organs of the digestive system in brief are
- Mouth – Chewing the food (Mastication) and mixing with saliva coming from salivary gland.
- Oesophagus – Passage for the food from mouth to stomach.
- Stomach – storage and churning of food along with various secretion such as HCI, Pepsin renin.
- Small intestine – Made up of 3 parts
- Duodenum – receives pancreatic juice, bile juices.
- Jejunum and ileum – Complete digestion and absorbs the digested product through the villi.
Pancreas – It secretes digestive enzymes and also insulin which is responsible for carbohydrate metabolism.
Liver – It secretes bile which is stored in the gallbladder. The lives also stores sugar in the form of glycogen.
Gall Bladder – It is the storage gland for the bile secreted by the liver. It has several functions.
- Strongly alkaline – The acidic food parsing into the duodenum on mixing with bile becomes alkaline. This change from the acidic state to alkaline is essential for the action of enzymes in the small intestine.
- Prevents growth of bacteria
- Emulsifies fat.
The reabsorption of water and certain B Vitamins takes place in the large intestine. The waste products pars down into the colon and are stored in the rectum till they pass out as stools from the anus.
The food moves through the GI tract (Gastro-intestinal) by the regular contractions of the smooth muscles of the system. These movements are wave – like and called peristaltic movements and the process, peristalsis Digestion of carbohydrate takes the least time. Proteins the next and fat takes the longest. Food take about 12-24 her to travel from mouth to rectum.
Process of Digestion – Digestion in the Mouth
Food is chewed in the mouth where it mixes with saliva. Saliva contains and enzyme ptyalin which has amylase or starch digesting enzymes. It helps to partially digest the starch present in the food. If food is not hewed properly or is swallowed hastily then sufficient amylase is not mixed with it and also big pieces of food enter the stomach. This results in incomplete digestion. Saliva contains mucous secretions that wet food and make its passage easy into the stomach through the food pipe.
Digestion in The Stomach
In the stomach, muscular contractions churn the food, break it up and mix it with the gastric juices. The gastric juice contains a lot of water, HCI and enzyme pepsin. The acid enhances hydrolysis and food breaks down into micro fragments. Pepsin acts on protein to form polypeptides. While digestive actions continues in the stomach, the food is prevented from moving on through the alimentary canal by a muscular valve, the pylorus. From time to time the pylorus relaxes, allowing semi – digested food (Chyme) to pars into the small intestine.
Digestion in the Small Intestine
Here the chyme is mixed with the bile juices released from the gall bladder. It contains no digestive enzymes. It is strongly alkaline. Next, the alkaline mars is mixed with pancreatic juice. This juice contains several enzymes that act upon carbohydrates, fats and proteins. They are amylase, lipase, trypsin, polypeptides.
Amylase concert them to maltose.
Lipase emulsified fats to form glycerol and fatty acids.
Trypsin convert protein to polypeptides which are further broken down into aminoacids by peptidases. Small intestine also secretes digestive juices. The enzymes found in the intestinal juices are lipase, peptidase, lactose, maltose and sucrose. They convert them to glycerol and fattyacids, aminoacids and simple monosaccharidses (galactose, glucose and fructose) respectively. These final products of digestion are now ready for absorption.
Nearly, the whole process of absorption of digested materials occurs in the lower portion of the small intestine. The intestine lined with small fingers like projections called the villi Through these aminoacids simple sugars diffuse from the intestines into the bold. In the sameway, the fatty acids and glycerol are absorbed into lymph which is the another fluid of circulatory system.
Digestion and Absorption in the Large Intestine
Here absorption of water is the major task, hers absorption of water results in loose stools. Where as greater absorption of water results in dry stools. Along with water, sodium, other minerals, vitamins and aminoacids are also absorbed. The colon bacteria synthesize vitamins and some vitamins of the B-Complex group especially biotin and folic acid which are absorbed from the colon in sufficient amounts to meet the daily requirement. The resulting mass is now made up of indigestible matter ie undigested food, mucus, bacteria, cellular debris and metabolic waste products. The faeces are expelled from the alimentary canal through the anus.
It is the process whereby already digested food stuffs are absorbed and utilized by the tissues.