The Digestive System
University of Hawai‘i at Mānoa Food Science and Human Nutrition Program and Human Nutrition Program
The process of digestion begins even before you put food into your mouth. When you feel hungry, your body sends a message to your brain that it is time to eat. Sights and smells influence your body’s preparedness for food. Smelling food sends a message to your brain.
Once you have eaten, your (Figure 2.4 “The Human Digestive System”) starts the process that breaks down the components of food into smaller components that can be absorbed and taken into the body. To do this, the digestive system functions on two levels, mechanically to move and mix ingested food and chemically to break down large molecules. The smaller nutrient molecules can then be absorbed and processed by cells throughout the body for energy or used as building blocks for new cells. The digestive system is one of the eleven of the human body, and it is composed of several hollow tube-shaped including the mouth, pharynx, esophagus, stomach, small intestine, large intestine (colon), rectum, and anus. It is lined with mucosal tissue that secretes digestive juices (which aid in the breakdown of food) and (which facilitates the propulsion of food through the tract). Smooth muscle tissue surrounds the digestive tract and its contraction produces waves, known as , that propel food down the tract. Nutrients, as well as some non-nutrients, are absorbed. Substances such as get left behind and are appropriately excreted.
Figure 2.4 Digestion Breakdown of Macronutrients
3 molecules of Glucose, Lipids becomes 1 molecule of fatty acids and and one molecule of glycerol, and Proteins become 3 molecultes of Amino Acids” class=”alignnone wp-image-77″ width=”438″ height=”234″>
Digestion converts components of the food we eat into smaller molecules that can be absorbed into the body and utilized for energy needs or as building blocks for making larger molecules in cells.
Everyday Connection
There has been significant talk about pre- and probiotic foods in the mainstream media. The World Health Organization defines as live bacteria that confer beneficial health effects on their host. They are sometimes called “friendly bacteria.” The most common bacteria labeled as probiotic is lactic acid bacteria (lactobacilli). They are added as live cultures to certain fermented foods such as yogurt. Prebiotics are indigestible foods, primarily soluble fibers, that stimulate the growth of certain strains of bacteria in the large intestine and provide health benefits to the host. A review article in the June 2008 issue of the Journal of Nutrition concludes that there is scientific consensus that probiotics ward off viral-induced diarrhea and reduce the symptoms of .[1]
Expert nutritionists agree that more health benefits of pre- and probiotics will likely reach scientific consensus. As the fields of pre- and probiotic manufacturing and their clinical study progress, more information on proper d