Nutrients and the Digestive System: Functions, Sources and Key Concepts
Nutrients
Nutrients are small organic and inorganic molecules that make up food. They provide energy and are the building material our cells need to maintain their functions.
Carbohydrates
Carbohydrates provide immediate energy to the cell and are involved in the production of metabolic reactions. They form part of plasma membranes.
Sources: sugar, pasta, bread, rice.
Lipids
Lipids provide energy to cells and are stored as reserve energy, making them a complementary source to carbohydrates. They form part of the plasma membrane (phospholipids) and regulate reproductive functions (sexual hormones).
Sources: animal fats, vegetable oils, margarine, peanuts, nuts.
Proteins
Proteins form part of cells. They catalyze chemical reactions (enzymes) and are involved in defending our body (antibodies).
Sources: meat, legumes, eggs.
Vitamins
Vitamins regulate the operation of cells and are involved in the regulation of cellular metabolism.
Sources: fruit, vegetables, principally eggs.
Mineral Salts
Mineral salts participate in many activities of the body, such as the formation of bones and teeth (calcium and phosphorus), the synthesis of hemoglobin (iron and copper), the production of thyroid hormones (iodine), and the transmission of nerve impulses (sodium and potassium).
Other sources: salt, fruits, vegetables, eggs.
Water
Water is the most powerful solvent of organic and inorganic molecules. It stabilizes temperature and regulates mineral balance. It also causes changes in the body such as sweating, and helps maintain normal body temperature.
Sources: most foods, especially fruit and vegetables.
BMI: weight / height²
Glucose
Glucose is a simple sugar (monosaccharide) and the main source of energy. Glycogen is a large molecule (a polysaccharide of about 100 glucose units) stored in the liver and muscles. Blood glucose is the amount of sugar in the blood; the normal range is 60–120 mg/100 ml of blood.
Hypoglycemia: a low amount of sugar in the blood.
Hyperglycemia: a high amount of sugar in the blood, which may cause diabetes.
Digestive System: the process by which food is broken down so nutrients can reach the cells.
Components of the System
1. Digestive tube: oral cavity, pharynx, esophagus, stomach, small intestine, large intestine, rectum, anus.
2. Accessory glands: salivary glands (2 parotid, 2 sublingual, submaxillary), liver, pancreas.
Important Concepts
Ingestion: taking food into the system through the mouth.
Digestion: the process of breaking down complex food into simpler substances.
Transport: moving nutrients to where they are needed; absorption occurs mainly in the small intestine.
Egestion: eliminating the substances the system cannot assimilate.
Oral Cavity
The oral cavity contains the tongue and the palate.
Teeth: 28 in children, 32 in adults.
Types: incisors, canines, premolars, molars.
Tongue: a voluntary muscular organ. Its functions include perceiving flavors (sour, salty, sweet, bitter), speech, and helping to shape food into a bolus.
Types of Digestion
Digestion is divided into mechanical and chemical digestion. Mechanical digestion physically transforms food through the action of the teeth, tongue, and palate. Chemical digestion occurs through the action of enzymes and saliva in the mouth.