Because we know that you may not have a background in biology, we start with a tour through the human body, from the single cell to the full organism, we set up for a discussion about the processes of digestion and absorption, followed by explorations of the other organ systems. After that, we discuss the concept of energy and calories. We also discuss some disorders and diseases related to nutritional health.
- 3.1: Chapter Introduction
- “Let food be thy medicine and medicine be thy food.” These words, espoused by Greek physician Hippocrates over two thousand years ago, bear much relevance on our food choices and their connection to our health. Today, the scientific community echoes Hippocrates’ statement as it recognizes some foods as functional foods.
- 3.2: The Basic Structural and Functional Unit of Life: The Cell
- The cell is the basic structural and functional unit of life. Cells are independent, single-celled organisms that take in nutrients, excrete wastes, detect and respond to their environment, move, breathe, grow, and reproduce. The macromolecules carbohydrates, proteins, lipids, and nucleic acids make up all of the structural and functional units of cells. In complex organisms, cells are organized into five levels so that an organism can conduct all basic processes associated with life.
- 3.3: Digestion and Absorption in the Gastrointestinal Tract (GI tract)
- The breakdown of complex macromolecules in foods to absorbable components is accomplished by the digestive system. These components are processed by cells throughout the body into energy or are used as building blocks. The digestive system is composed of the mouth, pharynx, esophagus, stomach, small intestine, large intestine (or colon), rectum, and anus. There are four steps in the digestion process: ingestion, the breakdown of food, nutrient absorption, and elimination of indigestible food.
- 3.4: Nutrients Are Essential for Organ Function
- Metabolic homeostasis occurs when the amount of nutrients consumed matches the energy required to carry out life’s biological processes. The circulatory system transports nutrients to cells and transports wastes from them. The essential minerals sodium, potassium, calcium, and chloride, and the macronutrients protein and carbohydrates, are required for central nervous system function. Fat is also critical for central nervous system function (see the Discussion Starter below).
- 3.5: Energy and Calories
- Energy is vital to life and is categorized into two types—kinetic and potential. There are also different forms of energy such as thermal, chemical, and electrochemical. Calories are a measurement of a specific quantity of energy contained in foods. The number of calories contained in a commercially prepared food is listed on the Nutrition Facts panel.
- 3.6: Disorders That Can Compromise Health
- Unbalanced diets can cause diseases and, conversely, certain disorders and diseases can cause an inadequate intake and absorption of nutrients simulating the health consequences of an unbalanced diet. Unbalanced, high-fat diets can exacerbate the symptoms of GERD and IBS. Celiac disease and anorexia can lead to nutritional deficiencies, which compromise functioning of the organ systems and decrease health.
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