Food and digestion, topics 4 and 5.

Ingestion

The taking of food and drink into the body

Mechanical digestion

The breakdown of food into smaller pieces without chemical change to the food molecules

Chemical digestion

The breakdown of large molecules in food into smaller molecules, so that they can be absorbed

Absorption

The movement of nutrients from the alimentary canal into the blood

Assimilation

The uptake and use of nutrients by cells

Egestion

The removal of undigested food from the body as faeces

Order of the food processes

Ingestion, digestion, absorption, assimilation, egestion

Route of food

Mouth, oesophagus, stomach, small intestine, large intestine, anus

Organs food does not pass through

Salivary glands, liver, gall bladder, pancreas

Mouth

Food is chewed (mechanical digestion) and mixed with saliva

Salivary glands

Make saliva containing amylase

Oesophagus

Muscular tube that moves food from the mouth to the stomach by peristalsis

Stomach

Churns food with gastric juice (pepsin and hydrochloric acid); protein digestion begins

Small intestine

Site of most digestion and most absorption of nutrients into the blood

Large intestine

Absorbs water and forms faeces

Anus

Where faeces leave the body

Liver

Produces bile; stores glucose as glycogen

Gall bladder

Stores bile and releases it into the small intestine

Pancreas

Produces digestive enzymes (amylase, protease, lipase) and the hormone insulin

Peristalsis

Longitudinal and circular muscle contractions used to move food through the digestive system

Villi

Tiny finger-like projections in the small intestine that increase the surface area for absorption

Microvilli

Even smaller projections on the villi that further increase absorption

Enzyme

A protein that speeds up chemical reactions (biological catalyst); not used up

Function of enzymes in digestion

Chemically break down large molecules into small molecules, ready for absorption

Amylase

Breaks starch into sugars (e.g. glucose); made in the salivary glands and pancreas

Protease

Breaks protein into amino acids; made in the stomach (pepsin) and pancreas

Lipase

Breaks lipids into fatty acids and glycerol; made in the pancreas

Enzymes and conditions

Each works on one type of molecule; affected by temperature (most stop above 45 °C) and pH (stomach enzymes best at pH 2)

Bile

Alkaline fluid made by the liver, stored in the gall bladder; neutralises stomach acid and emulsifies fat; not an enzyme

Emulsifying fat

Breaking large fat drops into small droplets, giving a bigger surface area for lipase

4-mark digestion answer

Enzyme, where it is made, what it digests, final products