Digestion © PDST Home Economics

Physical and Chemical Digestion Digestion is: the process by which nutrients are broken down into simple molecules that can be absorbed into the bloodstream. There are two types of digestion Physical and chemical Physical digestion : No new substance is formed Chewing, melting, mixing churning Chemical digestion: New substances are formed Enzymes (biological catalysts) are needed to control the reactions. Example starch is change into sugar in the mouth with the help of the enzyme salivary amylase. Proteins are changed into amino acids Fats are changed into fatty acids and glycerol Carbohydrates are changed into simple sugars like glucose

Digestive system/ alimentary canal MOUTH food chewed and melted mixed with saliva starch changed to maltose by amylase in saliva. OESOPHAGUS Tube (25cm) from mouth to stomach Muscle contract and relax to push food down (peristalsis)

Digestive system STOMACH pouched shape bag with walls made of muscle top left of abdomen under diaphragm lining makes gastric juice which contains HCl and enzymes pepsin & rennin Food is churned into chyme fat melts HCl kills bacteria Enzymes change protein into peptides

Digestive system SMALL INTESTINE joins stomach to large intestine 6m long, coiled up in centre of abdomen. Food moves by peristalsis. Bile made in liver and stored in gall bladder flows into intestine and emulsifies fat. Pancreatic juice made in pancreas flows into the intestine contains enzymes that change peptides into amino acids, and starch into sugar. Intestinal juice is made by the intestine wall. It contains enzymes that finish of the digestion of protein, fat and carbohydrate. Digestive system

Absorption Absorption is the passing of digested food into the bloodstream. Happens mainly in the small intestine. The inside of the small intestine is covered with tiny hairlike projections called villi. The villi give a large surface area through which food can be absorbed. The blood carries the digested food to every body cell where it is used for energy & growth

The Large Intestine 2m long , also called the bowel or colon. Joins the small intestine to the anus. It passes up the right side of the abdomen, across under the stomach and down the left side. The start is called the caecum and the last few cms. are called the rectum Functions: 1. completes absorption, 2. absorbs water, 3. makes Vits B & K, 4. eliminates waste. This solid waste is called faeces A high fibre diet is important for the health of the large intestine The Large Intestine