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Digestion in Animals. Digestion. Digestion is the chemical decomposition of food into simple substances which the body of cells of an animal can absorb. Food particles need to be broken down so they can be transported to all parts of the body.
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Digestion • Digestion is the chemical decomposition of food into simple substances which the body of cells of an animal can absorb. • Food particles need to be broken down so they can be transported to all parts of the body. • To be absorbed by blood, the particles need to soluble and small enough to pass through the walls of blood vessels and cell membranes.
Digestion • The whole process of taking in and using food particles is called nutrition. • In animals nutrition involves five stages. • Ingestion – the intake of complex organic foods into the body. • Digestion – the breaking down of food into simpler, soluble substances inside the organism. • Absorption – the taking in of soluble substances into the bloodstream. • Assimilation – the movement of soluble substances from the bloodstream into the cells. • Egestion – the elimination from the body of undigested food and wastes.
The digestive system • Many animals have a digestive system to process food material. • These systems consists of a series of organs connected to a tube, called the alimentary canal that runs from the mouth to the anus. • Glands along the alimentary canal secrete chemicals, which help digest the food. • Food is moved along the alimentary canal by a muscular action called peristalsis.
The human digestive system • Food enters through the mouth. • Here it is chewed (mastication) into smaller pieces. • Then swallowed down part of the alimentary canal called the oesophagus. • The oesophagus takes the food to the stomach, where chemicals break down the food further into a sludge. • Food is then moved into the small intestine, where more chemicals act on it. • Soluble food particles are absorbed through the walls of the small intestine into the bloodstream. • Undigested food travels through the large intestine and is eliminated through the anus.
The Mouth • Describe the involvement of the mouth in the digestive process
The stomach • The stomach is a muscular organ situated in the left side of the abdominal cavity just below the diaphragm. • It has a capacity of about 1.5 litres. • Contraction of the stomach muscles churns the food into a sludge. • Glands in the lining of the stomach secrete a gastric juice which breaks down the food further. • Gastric juice contain three main substances: • The enzyme pepsin which breaks down long chains of proteins into shorter chains of amino acids called peptides. • The enzyme rennin which coagulates milk, causing its to stay in the stomach until pepsin breaks down the milk proteins. • Hydrochloric acid, which provides a suitable pH for pepsin activity. It also dissolves minerals and kills bacteria. • In addition gastric juices also contains lipase (which digests fats to fatty acids and glycerol) and mucus (to protect the lining of the stomach from the acid. • The stomach is a temporary store of food. • It delivers food in small amounts at a time to the duodenum. • Mineral ions and simple sugars, also drugs and alcohol, are absorbed through the stomach wall into the bloodstream.
Duodenum • What role does the Duodenum play in digestion?
Small Intestine • Summarise the function of the small intestine’s role in digestion. – Remember to talk about its structure.
Summary of Chemical Digestion • Copy the Summary of chemical digestion of page 113.
Large Intestine • Undigested material from the small intestine passes along the alimentary canal into the large intestine. • The main part of the large intestine is the colon. • The main function of the colon is to absorb water from the undigested matter. • Remaining semi-solid waste (faeces) is moved into the rectum by peristalsis. • The rectum stores faeces until they are egested through the anus by muscular action.
Important things to realize • Humans lack certain enzymes to digest some substances, such as plant cellulose. However indigestible substances are important because they help move food through the alimentary canal. • Herbivorous mammals are able to digest plant cellulose and convert it into glucose. Rats, cows and koalas are examples of mammals that do this in an area called the caecum. This large sac contains cellulose-digesting bacteria and is situated between the small and large intestines. • The elimination of faeces by the anus is not the same type of process as the elimination of metabolic wastes by the kidneys, lungs and skin.
Questions • What is digestion? Why is it necessary? • Summarise the five main stages of nutrition in an animal. • What is the alimentary canal? • How is food moved along this canal? • Draw a labelled diagram of the human digestive system. Identify these parts on a human torso. • In which part of the digestive system is most food absorbed into the bloodstream? • What is the role of the villi? How does their structure suit their function? • What does bile do? Where is it produced and stored? • Which of the following organs do not secrete digestive enzymes? (Stomach, oesophagus, liver, small intestine, large intestine) • Name two important functions of the large intestine. • Where does the digestion process begin? • Account for the fact that stomach juice is acidic, and juice in the small intestine is alkaline.
