Gastrointestinal Nursing A Lifespan Approach PDF
The human body is made up of trillions of cells, each of which requires access to nutrients to survive. These include carbohydrates, proteins, fats, vitamins and minerals. These nutrients provide energy for metabolic processes and are the building blocks for cell growth and repair, existing within the food we eat (macromolecules). For the cells to be able to gain access to these nutrients, the food material must be broken down into much smaller micromolecules (amino acids, fatty acids, glucose) that are absorbed via the small intestine and transported via the circulatory system to the cells. Conversion of large molecules to small molecules is achieved through the action of two interrelated processes: mechanical digestion and chemical digestion.
This is carried out by the gastrointestinal tract, which can be defined as a hollow tube running from the mouth to the anus.
• Mechanical digestion is the use of muscles to mix and break up food to increase the surface area for the action of enzymes. Mechanical digestion starts with chewing where the teeth and the tongue break up the food material. This is assisted by saliva that helps dissolve the nutrients within the food.
Mechanical digestion continues in the stomach where a churning action, generated by smooth muscle contractions, pushes the gastric contents in different directions. Mechanical digestion is also assisted by the process of segmentation, which consists of localised rhythmic constrictions of the intestines which helps mix the food material with enzymes.
• Chemical digestion is provided by the action of enzymes that break the chemical bonds from complex food materials, helping to produce the small micromolecules ready for absorption.
Chemical digestion begins in the mouth with the action of the enzymes amylase and lipase, continues in the stomach with the action of pepsin and is then completed in the small intestine with the assistance of enzymes from the pancreas.