Alimentary tract

The four main roles of digestive system

.

Organs in the digestive system

Starting at the top - INGESTION

● Physical digestion takes place in the mouth

● Salivary glands release saliva

• water & mucous

• the enzyme amylase

● Amylase breaks down starch to maltose

going down - DIGESTION & SECRETION● The oesophagus is a muscular tube

where food is pushed down to the

stomach

● Peristalsis=muscular contractions

propelling the food along the tract.

● The internal surface of the oesphagus

has mucous layer to assist food

movement.

● Further chemical digestion of starch

into the stomach -digestion continues

● Circular muscles regulate movement of

food in and out of the stomach

● (eg pyloric sphincter)

● Muscular contractions of the stomach

churn and mix the food and enzymes etc

● Gastric juices containing pepsin and

protease in the stomach wall are released

● Protease breaks down proteins into amino

acids

into the small intestine - digestion goes on● The pancreas secretes pancreatic juice via the

pancreatic duct which enters the duodenum at the

top of the small intestine

● Pancreatic juice contains lipase and amylase

which act on lipids and carbohydrates respectively.

● Bile is produced by the liver but is stored in the

gall bladder

● Bile mechanically (physically) breaks down fats into

smaller globules to increase surface area

● Lipase then chemically breaks down

fat into glycerol and fatty acids

at last - ABSORPTION● The products of digestion are small enough to be

absorbed through the walls of the small intestine

transported to cells.

● Villi are structures which increase the surface area for more

efficient uptake

● Within the villi are capillaries - where glucose and amino

acids are absorbed.

● The capillaries are interconnected with the lymphatic system

- water absorption also takes place here

● Glucose and amino acids move from the small intestines

into the blood circulation by diffusion and active transport

● Glycerol and fatty acids move into a parallel circulation

called the lymphatic circulation Absorption of molecules in the villi

and now for - egestion• The small intestine connects with the large

intestine which consists of two main parts:

1. the colon

2. rectum

• Function of the large intestine is to compact

undigested food and absorb water and

salts back into the body

• Faeces are eliminated from the body through

the anus

Overview of Digestion Nat Geog

BIOMACROMOLECULES

Carbohydrates amylase maltose maltase

glucose

Protein pepsin

peptides peptidase

amino acids

Lipids(Triglycerides)

lipase

glycerol + fatty acidsGlucose

Enzymes and the break down of biomacromolecules