5C-the digestive system

Bio unit 1

digestion overview

1. ingestion of food

2. mechanical breakdown of ingested food

3. secretion of various digestive enzymes into the food (chemical digestion)

4. absorption of digested food

3 main types of digestive enzyme

• amylases -act on carbohydrates

• proteases -act on proteins

• lipases -act on lipids

(different enzymes are released in the saliva, stomach, and gut lining as they all have different optimal pH conditions)

difference between mechanical and chemical digestion

mechanical digestion breaks the food into smaller pieces, increasing the SA:V ratio, whereas chemical digestion uses enzymes to change the chemical structure of the food molecules so it is able to be absorbed

mouth function

teeth mechanically digest by chewing causing an increase in the foods SA:V ratio

amylase in saliva chemically digests complex carbohydrates

swallowing

tongue pushes food backward from the mouth

the soft palate and the epiglottis move to prevent food entering the airway

oesophagus

site of peristalsis, which is the coordinated muscular contraction and relaxation of the gut wall that moves food along the digestive tract

stomach

food is turned to chyme through:

mechanical digestion -stomach churning

chemical digestion -hydrochloric acid, gastric lipase, and pepsin (in it’s ideal low pH)

Liver

regulates metabolism by storing excess glucose as glycogen

produces bile

gall bladder

stores, concentrates, and distributes bile (mainly to the small intestine as that is where majority of fats are broken down)

pancreas

produces the digestive enzymes that are released into the small intestine

neutralises the acidity of food coming from the stomach

small intestine

absorbs over 90% of the body’s water and nutrients through villi

duodeum (first part) - food enters and mixes with digestive juices

jejunum (middle part) - absorbs most of the nutrients

illeum (final, longest part) - absorbs remaining nutrients

large intestine

final absorption of water and soluble compounds, with the undigested material leaving the body as feaces

consists of cecum (where appendix is attached) colon, and rectum

alimentary canal

(passage for food to travel through)

mouth, oesophagus, stomach, small and large intestine, and anus