Nutrition function

We will begin, from this topic, to see the apparatus and systems that intervene in the vital functions of living beings (nutrition, relationship and reproduction).

The nutrition is the set of processes by which the body gets different substances necessary for life, providing energy and necessary elements for structures and proper functioning of the body.

The processes involved in nutrition are:

• Digestion. The digestive system is responsible for introducing food into the body, and transforming it into simple nutrients that can be used by cells.
• Breathing. The respiratory system is responsible for obtaining the oxygen necessary for the cells and eliminating CO₂ from cellular metabolism.
• Circulation. The circulatory system carries nutrients, gases, waste products and other substances, linking all the cells of the body together.
• Excretion. The excretory system eliminates waste products from cellular metabolism, transported by the circulatory system, filtering the blood and expelling them through the urine.

The foods contain matter and energy we need, but in our cells can only enter small molecules. Food is made up of complex molecules (polymers) made up of hundreds or thousands of simple molecules (monomers) that can be used by cells. Therefore, it is necessary to break down these polymers into monomers, and digestive enzymes are responsible for that, very specific proteins that are responsible for this simplification throughout the journey of food through our body.

Digestive enzymes are secreted by the walls of the intestine or by attached glands, which discharge them to the digestive tract as food passes, leaving it ready to be used by the cells.

Then, in the intestinal villi of the small intestine, absorption will take place, passing the digested food to the blood. Undigested substances will make their way through the large intestine, where water will be absorbed and feces will form.

Therefore, digestion is a process by which digestive enzymes break the bonds between monomers that make up polymers, leaving many free monomers. The enzymes digestive are specific for each polymer:

• The amylases or carbohydrases break the glycosidic bonds forming carbohydrates like starch, leaving free monosaccharides, such as glucose.
• The lipases separate the fat in fatty acids and glycerine.
• The peptidases or proteases break the peptide bonds which join the amino acids in proteins, leaving them free.