Digestive System. Flashcards
Food taken into the body goes through 4 different stages during its passage through the alimentary canal: Name them.
- Ingestion.
- Digestion.
- Mechanical digestion.
- Chemical digestion. - Absorption.
- Assimilation.
- Egestion.
Define ingestion.
The taking of substances, e.g. food and drink, into the body through the mouth.
Define mechanical or physical digestion.
The breakdown of food into smaller pieces without chemical change to the food molecules.
Define chemical digestion.
The breakdown of large, insoluble molecules into small, soluble molecules that can be absorbed.
Define absorption.
The movement of small food molecules and ions through the wall of the intestine into the blood.
Define assimilation.
The uptakes and use of nutrients by cells
Define egestion.
The removal of undigested food from the body as faeces.
Define digestion.
The breakdown of food.
What is the role of physical digestion?
Physical digestion increase the surface area of food for the action of enzymes in chemical digestion.
What are three ways in which mechanical digestion is mainly carried out?
It is mainly carried out by the chewing action of the teeth, the churning action of the stomach, and the emulsification of fats by bile in the duodenum.
The differing shapes and sizes of teeth enable them to perform slightly different functions:
Incisors - chisel-shaped and sharp for biting and cutting.
Canines - pointed for tearing and ripping.
Premolars - Bicuspid, two roots, flat surfaces with ridges at the edges for chewing and grinding up food.
Molars - Tricuspid, three roots, flat surfaces with ridges at the edges for chewing and grinding up food.
Teeth are held firmly in the bone of the jaw and the gums. What is the use of teeth?
They are used for chewing to increase the surface area of the food so that it can be exposed to saliva and other digestive juices and broken down more quickly.
Bile (physical digestion) is secreted into the small intestine where it has two effects:
It is alkaline to neutralize the hydrochloric acid which comes from the stomach providing the alkaline conditions needed in the small intestine.
It emulsifies fat turning large droplets of fat into lots of smaller droplets, thus providing a larger surface area over which the lipase enzymes can work.
Where is amylase secreted?
Amylase is secreted into the alimentary canal in the mouth and the duodenum (from the pancreas).
What is the function of the following enzymes:
- Amylase.
- Proteases.
- Lipase.
- Amylase breaks down starch to simple reducing sugars (glucose).
- Proteases break down protein into amino acids in the stomach and small intestine.
- Lipase breaks down fats and oils (lipids) into fatty acids and glycerol.
Where is protease (trypsin) produced and secreted?
Trypsin is produced in the pancreas and secreted into the duodenum
Where is lipase produced and secreted?
Lipase enzymes are produced in the pancreas and secreted into the duodenum.
The stomach produces several fluids which together are known as gastric juice and one of the fluids produced is hydrochloric acid.
Describe the functions of hydrochloric acid in gastric juice.
The hydrochloric acid produced in the stomach ensures that conditions in the stomach remain within the optimum range for enzymes to work at their fastest rates.
How does a low pH in the stomach kill bacteria in food?
The low pH kills bacteria in food that we have ingested as it denatures the enzymes in their cells, meaning they cannot carry out any cell reactions to maintain life.
Describe the digestion of starch in the digestive system.
Amylase breaks down starch to maltose → maltase breaks down maltose to glucose on the membranes of the epithelium lining the small intestine.
Describe the digestion of protein by proteases in the digestive system.
Pepsin breaks down protein in the acidic conditions of the stomach → trypsin breaks down protein in the alkaline conditions of the small intestine.
Explain the use of bile.
Bile is an alkaline mixture that consists of bile salts that emulsify fats, increasing the surface area for lipase action, and neutralize the acidic mixture of food and gastric juices entering the duodenum from the stomach, to provide a suitable pH for enzyme action.
NOTE - Bile does not contain any enzymes, it contains bile salts.
Where is water absorbed?
Water is absorbed in both the small intestine and the colon, but most absorption of water also happens in the small intestine.
Where does absorption take place?
Absorption takes place in the second section of the small intestine, the ileum.
