March 3 Lecture - March 3, 2009 The Digestive System...

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March 3, 2009 The Digestive System Passage of the Digestive System - Mouth and oral cavity lead back to the pharynx - Esophagus passes through the respiratory diaphragm into the stomach - From the Stomach, the small intestine emerges - The small intestine will give rise to the large intestine - The large intestine unites with the rectum and then the terminal portion of the digestive tract; the anus Accessory Structures of the Digestive System - Most are in the form of glands - Accessory organs: o Salivary glands o Liver o Gall bladder o Pancreas Islets of langerhan (endocrine portion) Mostly acini (exocrine portion) The Digestive System as a Whole - Function of digestive system is to digest food we take in, breaking down the food into simple derivatives - This is accomplished by two types of processes o Mechanical processes From mastication (biting and crushing) of the food o Chemical processes Chemicals used to break down food into derivatives - The particles are usually broken down and absorbed by the blood vascular system - Carbohydrates are ultimately broken down into molecular sugars such as glucose - Proteins will be broken down into poly peptides and eventually amino acids - Products of carbohydrate and protein breakdown are taken across the wall of the gut into the blood vascular system where they are taken to various regions across the body - Triglycerides and monoglycerides are broken down into fatty acids, which will not be taken up by the blood vascular system, but rather by the lymphatic system (absorbed by the lacteals of the lymphatic system within the wall of the gut and drain back to the thorax as part of the lymph) - Remainder of material which is passed into the digestive tract are passed into the digestive tract and become part of the fecal material which will eventually be expelled to the lower parts of the system Is the digestive tract part of the organism or the environment? - A simpler organism (like an earthworm) reveal a simple tube-like structure - Gill tract of human is containuous with the environment (much like the earthworm), although it is more complex
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- Digestive tract may be considered as part of the organism or the environment - Digestive tract is approximately 15 feet in length - Various portions of the digestive tract have been modified into serval structures (organs) to assist in the digestive process or the absorption process of the system - Despite the fact that various regions have been modified into performing particular
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March 3 Lecture - March 3, 2009 The Digestive System...

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