Nutrients, Digestion, and Your Body
Core Concepts in Nutrition and Digestion
Key Definitions
- Feeding: The ingestion of food selected from the environment, making up our diet.
- Food: Any substance (solid or liquid) usually ingested for living, nutritional, and psychological purposes.
- Nutrition: An involuntary process by which our body extracts the nutrients our cells need from food and transforms them into its own structures.
- Nutrients: Food substances that provide matter and energy for our cells to perform vital functions.
- Basal Metabolism: The amount of energy needed to maintain vital functions when the body is at rest.
- Mastication (Chewing): The process where food is fragmented in the mouth. Its presence stimulates saliva secretion by the salivary glands.
- Bolus: A mixed mass of crushed food and saliva.
- Deglutition (Swallowing): Once the bolus is formed, it passes from the mouth to the esophagus.
- Chyme: The pulpy acidic fluid which passes from the stomach to the small intestine, consisting of gastric juices and partly digested food.
- Chyle: A milky fluid consisting of lymph and emulsified fats, formed in the small intestine during digestion.
- Portion Size: The amount of a food typically consumed at one time.
- Calorie: A unit of heat energy, often used to measure the energy content of food required by the body.
Classification of Nutrients
Carbohydrates (Sugars)
These are primary energy nutrients. The simplest forms are sugars like:
- Glucose: The major energy component of the cell.
- Sucrose: Common table sugar.
More complex forms, known as polysaccharides (complex sugars), are a main component of our diet. Examples include:
- Starch (from cereals and potatoes)
- Fiber (from vegetables)
Lipids (Fats)
There are different types of lipids with various functions:
- Some form part of the structure of cell membranes.
- Others, like fats, serve as an important energy reserve.
- Waxes are lipids that waterproof surfaces (e.g., plant leaves).
- Cholesterol is a lipid that is part of cell membranes and also aids in producing substances like hormones or bile.
Proteins
Proteins are formed from simpler molecules called amino acids. Some amino acids are essential, meaning they cannot be produced by our bodies and must be obtained from the diet. Proteins are involved in almost all biological functions:
- Transporting oxygen from the lungs to tissues.
- Enabling muscle contraction.
- Forming structural fibers like collagen and elastin.
Vitamins
These are essential nutrients whose deficiency can cause illness. The thirteen known vitamins are classified into two groups:
- Water-soluble: Vitamin B complex and Vitamin C.
- Fat-soluble (Lipid-soluble): Vitamins A, D, E, and K.
Minerals
Minerals are also essential nutrients. They have various roles:
- Structural: Part of bone composition (e.g., phosphorus, calcium).
- Regulatory: Involved in vital processes like muscle contraction (e.g., sodium, potassium).
Water
Water is the major component of the body, making up about 60% of an adult’s weight. Water intake needs vary depending on factors like climate and health to compensate for losses.
The Digestive System
The digestive system is the set of organs responsible for the digestion process – processing food so it can be absorbed and utilized by the body’s cells. These organs include the mouth, pharynx, esophagus, stomach, small intestine, and large intestine. The system consists of the digestive tract and associated digestive glands.
The Digestive Tract
The Mouth
The roof of the mouth is the palate (hard at the front, soft at the rear), which separates the mouth from the nasal cavities. The uvula hangs from the soft palate. Inside the mouth:
- Teeth grind the food.
- The muscular tongue moves the food, mixing it with saliva to form the bolus.
The Pharynx
This connects the mouth to the esophagus. At its lower part, a flap called the epiglottis closes over the airway during swallowing to prevent food from entering it.