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The pathway of food through the digestive system.

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Introduction

Assignment 1 The pathway of food through the digestive system The first phase is ingestion. This is when food enters the mouth and is chewed into small pieces. Saliva from the salivary gland pours into the mouth. This contains the enzyme amylase, which begins the process of digestion by breaking down starch into simple sugars. The tongue rolls the food into a ball called a bolus, which is pushed to the back of the throat. The food passes through the throat into the Oesophagus. The bolus is squeezed down the Oesophagus by muscular walls. The gut contracts above the bolus and relaxes below the bolus so that the food is passed down through the Oesophagus into the stomach by waves of contractions called peristalsis. ...read more.

Middle

Bile also emulsifies fats so that they are mixed up with the churned up liquid food. Bile is stored in the gall bladder before it is poured in to the small intestine. The digestive enzymes, protease, carbohydrase, and lipase are also produced in the pancreas. The food passes from the stomach into the small intestine. The inside of the small intestine is covered with thousands of villi. They greatly increase the surface area of the small intestine for maximum absorption to take place. Villi are tiny finger shaped projections about 0.5mm long. They have microvilli, which further increases the surface area. The walls of the villi are very thin so that fluids can pass quickly through them. ...read more.

Conclusion

The hepatic portal vein caries blood from the small intestine to the liver where some of the products of the digestion are stored or changed. These products are released from the liver when they are needed into the blood circulatory system. The products defuse out of the blood cells where they are needed. The material that passes through the large intestine is mainly water and digested food and this is mainly fibre. No enzymes are secreted here. The bile salts are absorbed and returned to the liver in the blood. The colon absorbs the water from the undigested food so that the body does not to become dehydrated. Elimination occurs when the semi solid waste passes to the rectum by peristalsis and is passed out of the body at intervals-this is egestion. ...read more.

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