The stomach then churns the food and releases enzymes to breakdown the food.
The gut wall then excretes the enzymes and most of the nutrients in the food are absorbed in the small intestine. What remains is stored and concentrated into faeces where it’s then egested through the large intestine.
Structures
The structures that are important in the digestive system are: Mouth, Oesophagus (Gullet), Liver, Stomach, Gall Bladder, Bile Duct, Duodenum, Pancreas, Pancreatic Duct, Ileum (Small Intestine), Large Intestine.
When food is swallowed its moved down the Oesophagus by the action of muscles into the Stomach.
Digestion starts in the Stomach as the food mixes with enzymes and strong acids. After several hours the food is transported to the Small Intestine and more enzymes are added to complete the process of digestion.
After all the nutrients have been absorbed, the indigestible parts pass into the Large Intestine and egested through the Anus.
The Liver has many functions like storing minerals and vitamins and making Bile, which is stored in the Gall Bladder until needed for digesting Fats. The Pancreas supplies the enzymes.
Even though the appendix should be listed it has no function in the human body.
Balanced diet
(These are the main food groups we need for a balanced diet)
Starch Glucose (Polysaccharide)
Fats Amino Acids (Energy store, Insulation, cell membrane)
Protein Amino Acids (Growing)
Carbohydrate Glucose Fat
Structures and what the do
Stomach
Food stays here for up to five hours and is mixed with enzymes and acids made by glands in the stomach wall.
The acid helps the enzymes digest any protein in the food.
The acid helps the enzymes to work properly, and also kills bacteria, that could have been eaten with food.
The strong muscles in the stomach walls contracts and churns and mixes the food with enzymes and acid until it’s like porridge.
It then passes into the small intestine and digestion continues there.
Pancreas
This is an important organ, which is close to the small intestine and has two functions:
- It makes digestive enzymes for the body to digest food.
- It makes hormones to control the blood sugar level (Insulin and Glucagon) inside the body.
Gall bladder
A muscle walled sac attached to the liver, bile is made in the liver and passes on into the gall bladder for storage and concentration.
It passes the contents into the small intestine where the salts inside the bile lower surface tension and aid digestion and absorption.
Small Intestine
Inside the small intestine food is mixed with enzymes made up of the pancreas and gut wall, and protein, carbohydrates and fats are digested.
In the small intestine food is absorbed into the blood. The wall of the Ileum (small intestine) is covered in finger like spikes called Villi, which gives it a large surface area, which means absorption very efficient.
The walls of the Ileum also include many red blood vessels, which are ready to pickup the digested food. This is then taken directly to the liver to be processed.
Liver
This is the largest internal organ in the human body.
It processed absorbed food, which comes inside the liver, where it is changed into food groups.
E.g. Carbohydrates changed into fats, and minerals stored.
It makes bile for breakdown of fats and destroys poisons like alcohol and drugs.
The excess protein is made into Urea in the liver. It also contains stored Carbohydrates, which are used to keep the blood sugar level steady.
Large Intestine
Once food reaches the large intestine all useful substances have been digested and absorbed, so only the faeces remain.
As they pass through the large intestine water is absorbed and faeces is stored inside the rectum before being pushed outside the body through the anus.
Describing absorption (Conclusion)
Absorption is when small food molecules move through the gut wall and into the blood.
E.g. Proteins, Carbohydrates, and Fats. Which have to be digested before they can be absorbed, but some are by now small and don’t require to be digested.
E.g. Vitamins, minerals, and various sugars.
Absorption occurs in the Ileum (Small intestine).
The finger like spikes called the Villi; provide surface area to enlarge the effectiveness of absorption.
Food is absorbed into the blood, and then it is taken straight to the liver to be processed into food groups.
