Alimentary System

The processes of digestion include six activities: ingestion, propulsion, mechanical (physical) digestion, chemical digestion, absorption, and defecation. **Ingestion** refers to the entry of food into the alimentary canal through the mouth. There, the food is chewed and mixed with saliva, which contains enzymes that begin breaking down the food. Food leaves the mouth when the tongue and pharyngeal muscles propel it into the esophagus. This act of swallowing, the last voluntary act, is an example of **propulsion**, which refers to the movement of food through the digestive tract. **Mechanical digestion** is a purely physical process that does not change the chemical nature of the food. It includes chewing, as well as tongue movements that help break food into smaller bits and mix food with saliva. In **chemical digestion**, starting in the mouth, digestive secretions break down complex food molecules into their chemical building blocks (for example, proteins into separate amino acids). Food that has been broken down is of no value to the body unless it enters the bloodstream and its nutrients are put to work. This occurs through the process of **absorption**, which takes place primarily within the small intestine. There, most nutrients are absorbed from the lumen of the alimentary canal into the bloodstream. In **defecation**, the final step in digestion, undigested materials are removed from the body as feces.



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## Keywords
digestive system oral cavity teeth tongue sublingual salivary gland parotid submandibular pharynx esophagus diaphragm gallbladder liver stomach pancreas colon small intestine rectum appendicitis structure of the digestive system digestion of food intake absorption of nutrients removal of undigested substances