DIGESTIVE SYSTEM - DIGESTIVE SYSTEM Digestive System-Uses...

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DIGESTIVE SYSTEM Digestive System : -Uses mechanical and chemical methods to break food down into nutrient molecules that can be absorbed into the blood. Once in the blood, the food molecules are routed to every cell in the body. -Converts food into nutrient molecules that can be used and stored by the body -Involves 5 functions: movement, secretion, digestion, absorption, elimination. 1. Movement : propels food through the digestive system 2. Secretion : releases of digestive juices in response to a specific stimulus: the presence of food 3. Digestion : breaks down food into molecular components 4. Absorption : the products of digestion are transferred into the body's internal environment where they enter the cells of the body 5. Elimination : removal of undigested food and wastes The human digestive system called the Digestive Tract is a coiled, muscular tube (6-9 meters long when fully extended) stretching from the mouth to the anus. Structures/Order/ Organs of the Digestive System 1 st -Mouth 2 nd -Pharynx 3 rd -Esophagus 4 th -Stomach 5 th -Small Intestine 6 th -Large Intestine 7 th -Anus Accessory Digestive Organs (Are connected to the main system by a series of ducts: -Salivary Glands - Pancreas -Liver -Gall Bladder
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The Mouth and Pharynx Mechanical Breakdown: (begins in the mouth) -In the mouth our teeth, jaws and the tongue begin to mechanically breakdown food into smaller particles. -Humans have teeth for tearing, grinding and chewing food. -The tongue manipulates food during chewing and swallowing; mammals have taste buds clustered on their tongues. Chemical Breakdown -Chemical breakdown of startch begins by production of saliva (salivary amylase) -Salivary glands secrete salivary amylase , an enzyme that begins the breakdown of complex sugars and starch into glucose. - Bicarbonate ions in saliva neutralize the acids in foods. Pharynx and Esophogus -This mixture of food and saliva is then pushed into the pharynx which is the passage way to the esohpagus -The Esophagus is a muscular tube whose muscular contractions ( peristalsis ) propel food to the stomach. - Mucus moistens food and lubricates the esophagus. Swallowing -Moves food from the mouth through the pharynx into the esophagus and then to the stomach. Step 1: A mass of chewed, moistened food, is moved to the back of the moth by the tongue. In the pharynx, the food mass triggers an involuntary swallowing reflex that prevents food from entering the lungs, and directs it into the esophagus. Step 2: Muscles in the esophagus propel the food by Peristalis waves of involuntary contractions of smooth muscle in the walls the esophagus (stomach, and intestines too) that propel food along the digestive tract. Peristalis in the esophagus propels food from the oral cavity to the stomach Step 3: The food passes through the gastro-esophogeal sphincter ( A ring of muscle at the junction of the esophagus and the stomach that remains closed except during swallowing to prevent the stomach contents from entering the esophagus) into the stomach. Heartburn results from irritation of the esophagus by gastric juices that leak through this sphincter.
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