Q. Describe the process of digestion by taking human as an example.
Answers
Answer:
Humans have holozoic nutrition, that means the food is consumed as a whole and the digestion occurs internally. It can be described as:
1. Ingestion of food- The food is taken in the oral cavity in the process called the ingestion. The teeth help in grinding of the food, salivary amylase helps in partial breakdown of the starch and the tongue helps in mixing the food with saliva and helps in swallowing it. The food is now called bolus.
2. Digestion- The process of break-down of complex substances into simpler substances is called digestion and it starts with the mouth where physical break-down occurs along with some chemical digestion. The bolus is swallowed in and it arrives in stomach where the digestion of proteins occurs due to presence of the enzyme pepsin. Bolus is now called the chyme. This chyme now moves into the small intestine where rest of the process of digestion will be completed. The pancreatic juice, the intestinal juice and the bile will result in breakdown of carbohydrates, fats and the rest of the proteins. The chyme is now called the chyle and it moves to the large intestine where the water is absorbed.
3. Absorption- The digested food is absorbed via the finger-like projections present on the inner surface of the small-intestine and the reach the blood stream.
4. Assimilation- The absorbed food is then used by different tissues for the energy generation. The excess food is stored as glycogen in the liver and s fats in adipose tissue.
5. Excretion- The undigested material passes from the small-intestine to the rectum of the large-intestine, from where it is removed from the body through anus.
Answer:
The various processes involved in the digestion of human beings are:
(i) Ingestion: Through the help of mouth human beings ingest food.
(ii) Digestion: The teeth helps in physical digestion of food. In mouth there are salivary glands, which secretes saliva, in which salivary amylase enzyme is present which digest the starch present in food into maltose sugar, i.e., the digestion of carbohydrate starts from mouth itself . Mouth opens into a small funnel-shaped area called pharynx which leads to a long tube called oesophagus, whose wall is highly muscular. When the slightly digested food enters into oesophagus the contraction and expansion movement of its wall, takes place, which is known as peristaltic movement. This movement helps the food to move towards the stomach. Usually, in oesophagus there is no digestion of food. From the oesophagus the food enters into the stomach. In the stomach there is secretion of gastric juices which is a mixture of hydrochloric acid, pepsin (protein digesting enzyme) and mucus. Now, the partially digested food enters from stomach into the small intestine's wider part which is known as duodenum and the remaining part of the small intestine is termed as ileum. The duodenum, receives secretions of two glands, i.e., liver and pancreas. Liver secretes bile pigments and pancreas secretes pancreatic juice which digestes the proteins, carbohydrates and emulsified fats. Here the digestive enzymes are amylase, maltose and invertase for digesting the carbohydrates, trypsin for proteins and lipase for fats. Thus, food is completely digested in ileum part of small intestine.
(iii) Absorption: Now, the food enters from duodenum into ileum part of small intestine where millions of finger-like projections known as villi are present which absorb the food.
(iv) Assimilation: The blood carries the digested and dissolved food to all parts of the body, where it is assimilated into the cells which is used for obtaining energy as well as for growth and repair of the body.
(v) Egestion: The undigested food enters into the large intestine's wider part, where water is absorbed from the undigested food and the food becomes solid. Now, this solid undigested food enters the last part of large intestine known as rectum through which it moves out from the body.
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