The Human Digestive System The Digestive System The Four Stages of Food Processing 1. Ingestion the taking in or eating of food 2. Digestion the breakdown of food by mechanical and chemical processes into molecules small enough for cells of the body to absorb Mechanical Digestion chewing, chopping, and grinding of food into smaller pieces, increasing its surface area done by teeth, beak or other similar structures, and by contractions and churning motions in the stomach 1
Chemical Digestion the chemical breakdown of nutrient molecules into smaller molecules by enzyme action; called hydrolysis Carbohydrates simple sugars Lipids glycerol + fatty acids Proteins amino acids 3. Absorption the transport of the products of digestion from the digestive system into the circulatory system the molecules are transported in the blood to the body cells in the cells they are joined to make bigger molecules or broken down to provide energy 4. Elimination the removal of undigested solid waste matter from the body 2
Oral Cavity (The Mouth) The primary functions of the oral cavity (mouth) is to... to break up food particles mechanical digestion to lubricate food particles saliva begin digestion of complex carbohydrates (starches and glycogen) chemical digestion The mouth is also used for tasting food (using the tongue) to help determine if it should be ingested or not. Mechanical Digestion: Oral Cavity The Mouth Mechanical digestion in the oral cavity (mouth) involves... Teeth to break up food particles (mastication) Tongue position food particles Salivary Glands lubricate food particles 3
Tooth Decay What do you think causes tooth decay? Saliva is normally slightly alkaline. When we eat, bacteria in our mouth feed on sugar and turn it into acid. The acid starts to attack the enamel and wear it away. Chemical Digestion: Oral Cavity The Mouth Chemical digestion in the mouth involves the enzyme amylase. 4
Oral Cavity The Mouth http://health.howstuffworks.com/human body/systems/nose throat/adam 200089.htm The Movement of Food: Peristalsis is a distinctive pattern of smooth muscle contractions that propels foodstuffs distally through the esophagus and intestines. 5
Segmentation contractions are a common type of mixing movement seen especially in the small intestine. Segmental rings of contraction chop and mix the ingested food. Alternating contraction and relaxation of the longitudinal muscle in the wall of the gut also provides effective mixing of its contents. The Esophagus STRUCTURE: Location: neck / thoracic cavity Physical description: a muscular tube with a mucus lining 6
FUNCTION: The Esophagus The primary function of the esophagus is to transport food from the mouth to the stomach by the process of swallowing. This is done using a powerful, synchronized set of muscle contractions called Peristalsis. mouth stomach The Esophagus Between swallows, the esophagus usually does not contract. There is a sphincter muscle separating the esophagus from the stomach (called the lower esophageal sphincter) which normally stays tightly closed to prevent acid in the stomach from washing up into the esophagus. However, when we swallow, this sphincter muscle opens up (relaxes) so that the food we swallow can enter the stomach. sphincter 7
The Esophagus The most common symptom that occurs in the esophagus is heartburn (acid reflux), which is caused when acid washes up into the esophagus repeatedly (gastroesophageal reflux) and irritates the lining of the esophagus. This happens when the sphincter separating the stomach from the esophagus does not work properly; the function of this sphincter is to prevent reflux from occurring when the stomach contracts. 8