Human physiology is the study of how the human body functions. It encompasses a wide range of topics, including the structure and function of cells, tissues, and organs, as well as the mechanisms that regulate physiological processes. In this lesson, we will focus on the digestive system, which is responsible for breaking down food and absorbing nutrients.
The Structure of the Digestive System
The digestive system is composed of a series of organs that work together to break down food and extract nutrients. These organs include the mouth, esophagus, stomach, small intestine, large intestine, rectum, and anus. Each organ has a specific function in the digestive process, and they are connected by a long, muscular tube called the gastrointestinal tract.
The Function of the Digestive System
The primary function of the digestive system is to break down food into smaller molecules that can be absorbed by the body. This process begins in the mouth, where food is chewed and mixed with saliva. The food then travels down the esophagus and into the stomach, where it is further broken down by stomach acid and enzymes. From there, it enters the small intestine, where most of the nutrients are absorbed into the bloodstream. The remaining waste products then pass into the large intestine, where water is absorbed and the waste is prepared for elimination.
The Regulation of Digestion and Absorption
The digestive system is regulated by a complex network of hormones and nerve signals. These signals control the release of digestive enzymes and the movement of food through the gastrointestinal tract. For example, the hormone gastrin stimulates the release of stomach acid, while the hormone cholecystokinin stimulates the release of digestive enzymes from the pancreas. Nerve signals also play a role in regulating digestion, such as the vagus nerve, which stimulates the release of digestive enzymes and increases blood flow to the digestive organs.
The Metabolism of Nutrients
Once nutrients are absorbed into the bloodstream, they are transported to the liver, where they are metabolized and either stored or used for energy. Carbohydrates are broken down into glucose, which can be used immediately for energy or stored as glycogen. Fats are broken down into fatty acids and glycerol, which can also be used for energy or stored as adipose tissue. Proteins are broken down into amino acids, which are used to build new proteins or can be used for energy.
The Role of the Digestive System in Energy Balance
The digestive system plays a crucial role in maintaining energy balance in the body. When we consume more calories than we need, the excess energy is stored as fat. When we consume fewer calories than we need, the body breaks down stored fat to use for energy. The digestive system also responds to changes in dietary intake, such as when we consume a high-fat meal. This can affect the release of hormones and enzymes, which can impact how the body processes and stores nutrients.
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⇦ 4 The cardiovascular system