Digestion

The process of digestion has 5 functions: The Digestive System The process of digestion has 5 functions: Ingestion: taking food into the body Digestion: breakdown of insoluble substances into soluble ones Absorption: uptake of soluble substances into cells Assimilation: how cells use food Egestion: removal of undigested waste

Digestion Egestion faeces Ingestion Absorption

Food is broken down into smaller pieces by biting, chewing, churning, bile action. These pieces are not soluble but have a large surface area for enzymes to work on.

Surface area = 24 cm2 Volume = 8 cm3 SA : V ratio = 24:8 = 3:1

Enzymes break chemical bonds to make insoluble food particles soluble. Carbohydrases break down carbohydrates into sugars Proteases break down proteins into amino acids Lipases break down fats (lipids) into fatty acids and glycerol

model gut experiment boiling tube

What do you remember

Add gall bladder, bile duct, sphincter Buccal cavity Salivary gland Oesophagus Liver Stomach Duodenum Pancreas Worksheet to go with this Ileum Colon Appendix Rectum Anus

The ball of food is called a bolus The Mouth Mechanical: chewing, biting Chemical: Saliva from the salivary glands contains the enzyme CARBOHYDRASE. Starch + carbohydrase  sugar (maltose) The ball of food is called a bolus

NO FOOD IS BROKEN DOWN HERE The oesophagus NO FOOD IS BROKEN DOWN HERE Muscles in the wall of the oesophagus contract, pushing food down to the stomach. This is called PERISTALSIS

peristalsis

Muscles in wall contract Oesophagus wall FOOD Food moves forwards PERISTALSIS

The stomach The strong muscle walls contract to churn and mix food with stomach juices called GASTRIC JUICES. Cells in the stomach wall produce a protease enzyme that digests proteins, breaking them down into amino acids.

The stomach cells also produce hydrochloric acid HCl, which Lowers the pH for the protease enzyme to work Kills bacteria Stops salivary amylase from working A circular, sphincter muscle at the exit of the stomach opens to allow food into the small intestine. It controls release of food from the stomach.

This is called emulsification. The liver Bile, made in the liver and stored in the gall bladder passes along the bile duct into the duodenum. Bile breaks fats into very small droplets, increasing the surface area for enzymes to work on. This is called emulsification. Bile is alkaline and therefore also neutralises acid from the stomach.

passes into the gall bladder bile made in the liver passes into the gall bladder gall bladder digestive enzymes produced in pancreas pancreatic duct bile duct duodenum

The duodenum ENZYMES are added to the duodenum from: The pancreas The wall of the duodenum Carbohydrases break down starch to sugars Proteases break down protein to amino acids Lipase breaks down fat to fatty acids and glycerol

Main function is absorption. The ileum Main function is absorption. The walls are adapted for efficient diffusion of the soluble products of digestion.

villus muscle layer ridge covered with villi network of blood capillaries lacteal absorbs fatty acids villus muscle layer arteriole venuole

A villus ileum wall blood capillaries lacteal sugar amino acids fatty acids lacteal to liver

how the ileum is adapted for absorption Long length (5m), folds and villi increase the surface area for absorption Villi contain blood vessels to carry away absorbed nutrients Villi contain lacteals to carry away absorbed fats The walls are thin, one cell thick, and permeable to form a short diffusion distance

The absorbed nutrients, amino acids and sugars are carried in the blood to the liver in the HEPATIC PORTAL VEIN.

NO DIGESTION OCCURS HERE the colon NO DIGESTION OCCURS HERE The colon has a large surface area for the absorption of water from the fluid we drink, food we eat, mucus and digestive juices. It also absorbs mineral salts.

the rectum & anus Solid waste made up of undigested food, bacteria and cells from the gut forms faeces, which is stored in the rectum before passing out of the body through the anus.

transverse colon descending colon ascending colon rectum appendix anus

Summary bbc learning zone clip 4180

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