The Digestive System Section 30.3

What is the main purpose of the digestive system? The digestive system converts food into small molecules, that can be used by the cells of the body There are four stages Ingestion - eating Digestion – Mechanical and chemical Absorption – occurs in intestines, absorbed into circulatory system Elimination – all waste material removed as feces

Why is the mouth important? Teeth do most of the mechanical digestion Incisors, cuspids and bicuspids grind at food Molars grind and crush food Tonuge moves food around Saliva triggered by the scent of food (controlled by nervous system) Contains Amylase – breaks down starch Also contains Lyzosome – helps prevent infection by breaking down bacteria Tongue and throat muscles force clumps of food (bolus) down into throat Flap of connective tissue – (epiglottis) prevents food entering trachea

What is the esophagus? The esophagus connects the mouth to the stomach Does gravity force food down? If so, how would astronauts eat in space? Peristalsis provides the force that drives food into the stomach Cardiac Sphincter closes the esophagus from the stomach What is heartburn?

What is the pH of the stomach? What is it designed to digest? Very acidic due to hydrochloric acid Enzyme pepsin breaks down proteins Glands produce mucus which protects the stomach wall - if it fails, can lead to a peptic ulcer Stomach also causes mechanical digestion due to alternating contractions – essentially churning Chyme produced (oatmeal conistency) After a few hours, the pyloric valve opens up, and chyme is released into small intestine

What are the roles of the pancreas, liver and gallbladder in digestion? The pancreas produces hormones that regulate blood sugar level, It also produces enzymes to help break down carbohydrates, proteins, lipids and nucleic acids It also produces a sodium bicarbonate – a base. Why do you think a base is needed at this stage of the digestive system? Enzyme would be destoryed by stomach acid – it needs to be neutralized The Liver assists in fat digestion Liver produces bile, a fluid loaded with lipids and salt, which is stored in the gallbladder When fat is present in the duodenum, the gallbladder releases bile into the small intestine Fat globs together, making digestion difficult. Bile breaks up these globs

So where are different enzyme found in the digestive system So where are different enzyme found in the digestive system? What do they do?

How does absorption from the small intestine work? Most nutrients from food are absorbed through the small intestine After leaving the duodenum, most chemical digestion is finished Small intestine designed for absorption of food – how? Villi and microvilli move move and absorb food particles Products of carbohydrates and proteins absorbed by capillaries in the villi Fats and fatty acids are absorbed by lymph vessels At the end of the small intestine, only water, cellulose and other indigestible substances are left behind

What does the large intestine do? Before entering the large intestine, material passes by the appendix. What is the role of an appendix? Chyme then enters the large intestine/colon Primary function is to remove water from undigested material - this process happens quickly Colonies of bacteria help produce compounds that the body can use, such as vitamin K Antibiotics can inadvertently destroy these colonies Feces eliminated through the anus Issues with water removal can lead to diarrhea or constipation

Key points What is the function of the digestive system? What is the difference between mechanical and chemical digestion? What structures does food travel through during digestion? What are their functions? What would happen if your stomach could not contract and churn food? How are nutrients absorbed? Why are villi folded?