The human body: a nutrition perspective

Merely eating food won't nourish you. You must first digest the food - break it down into usable forms of the essential nutrients that can be absorbed into the bloodstream. Once nutrients are taken into the bloodstream, they can be distributed to and used by body cells. We rarely think about, let alone control, digesting and absorbing foods. Except for a few voluntary responses - such as deciding what and when to eat, how well to chew food and when to eliminate the remains - most digestion and absorption processes control themselves. As suggested in the cartoon in this chapter, we don't consciously decide when the pancreas will secrete digestive substances into the small intestine or how quickly foodstuffs will be propelled down the intestinal tract. Various hormones and the nervous system mostly control these functions. Your only awareness of these involuntary responses may be a hunger pang right before lunch or a 'full' feeling after eating that last slice of pizza. In this chapter we examine digestion and absorption as well as other aspects of human physiology that support nutritional health. In the process you will become acquainted with the basic anatomy (structure) and physiology (function) of the circulatory system, nervous system, endocrine system, immune system, digestive system, urinary system and storage capabilities of the human body.