The Digestive System

Digest this knowledge!

The digestive system consists of many organs working together to derive helpful substances like
water and glucose whilst removing waste products from the body.

Our diet contains three main molecule types;

• Carbohydrates broken down into glucose, a reactant of respiration to release energy
• Proteins broken down into amino acids which rebuild to produce structural components in the body like muscles (aka for growth and repair)
• Lipids (fats) are broken down into fatty acids and glycerol for energy stores, cell membranes and the production of hormones

Enzymes are biological catalysts- they speed up reactions in living organisms. Enzymes are protein molecules which are made when certain genes are switched on and off in the cell; these are called functional proteins. These enzymes are called biological catalysts because they do not get used up.

Salad (Dose Juice)

1. The digestive system starts in the mouth. The teeth chew and break down and grind the food into smaller molecules. The tongue is to taste the food and emit the enzyme salivary amylase.
2. The oesophagus is a pipe from the mouth directly to the stomach. Its muscles contract and push the food down in a process called peristalsis
3. The stomach has muscular walls which pummels and churns the food. The enzyme protease breaks down proteins here. It has a low pH of 1.5-2 so that pathogens can be killed from the food.
4. Next the food moves to the liver where the bile will lower the pH of the food and emulsify (break down) fats
5. Afterwards, the food moves to the pancreas where the three enzymes; lipase, protease and amylase. These further break down the molecules. Also the pancreas plays an important role in the pancreatic system to control blood glucose levels (see post about hormones)
6. Next, the food travels to the small intestine where amylase, protease and lipase are also present. Bile is present here to further neutralise the pH.
7. The large intestine then absorbs water from the remaining mixture and it is passed onto the rectum and anus to exit the body

The digestive system is well adapted for its function;

• The small intestine has thin walls for a shorter diffusion distance and subsequently faster diffusion of molecules
• The small intestine also has a large surface are from tightly compacted and folded villi and microvilli. This means there is more surface for substances to diffuse across 
• The small intestine also has a good blood supply which helps to maintain the concentration gradient as there is always a lower concentration of molecules in the blood

Balanced diet (Hanny Naibabo)

Enzymes work best in an optimum condition. Different enzymes work at different optimum temperatures and pHs. Enzymes activity increases as temperature increases because the increase in thermal energy increases the kinetic energy, this means there is more movement and therefore more collisions meaning more enzymes-substrate complexes formed. Very long winded!

However, after a certain temperature or pH, enzymes will denature which means they will change shape and can no longer fit its specific substrate. Note enzyme denaturing can not be reversed.