Digestive System 04 21 2011 The Digestive System Functions Ingestion is taking in food Propulsion is moving foods from one region of the digestive system to another o Peristalsis are alternating waves of contraction and relaxation that squeezes food along the GI tract o Segmentation moves materials back and forth to aid with mixing in the small intestine Digestion is breaking food down both physically mechanical and chemically Absorption is movement of nutrients into the bloodstream o End products of digestion are absorbed in the blood or lymph o Food must enter mucosal cells and then into blood or lymph Defecation rids the body of indigestible waste Functions of the Digestive System Food breakdown as mechanical digestion capillaries o Examples Mixing food in the mouth by the tongue Churning food in the stomach Segmentation in the small intestine o Mechanical digestion prepares food for further degradation by enzymes Food breakdown as chemical digestion o Enzymes break down food molecules into their building blocks o Each major food group uses different enzymes Carbohydrates are broken to simple sugars by enzymes such as amylase lactase fructase Proteins are broken to amino acids by proteases such as Fats are broken to fatty acids and glycerol alcohols by Nucleic acids are broken down into nucleotides by trypsin lipases nucleases Organs of the Digestive System Two main groups o Alimentary canal gastrointestinal or GI tract is a continuous coiled hollow tube Mouth Pharynx Esophagus Stomach Small intestine Large intestine Anus o Accessory digestive organs Layers of the Alimentary Canal Organs Four layers o Mucosa o Submucosa o Muscularis externa o Serosa viseral peritoneum Layers of Alimentary Canal Organs Mucosa o Innermost moist membrane consisting of Surfaceepithelium Small amount of connective tissue lamina propria Small smooth muscle layer Submucosa o Just beneath the mucosa o Soft connective tissue with blood vessels nerve endings and lymphatics Layers of Alimentary Canal Organs o Circular layer o Outer longitudinal layer Muscularis externa is composed of smooth muscle had has a Serosa is the outermost layer of the wall contains fluid producing cells consists of the canal organs o Visceral peritoneum is the innermost layer that wraps the o Parietal peritoneum is the outer layer that lines the abdominopelvic cavity Accessory Digestive Organs Teeth Salivary glands Pancreas Liver Gallbladder Movement of the Digestive Materials Visceral smooth muscle shows rhythmic cycles of activity caused by pacemaker cells Peristalsis causes waves that move a bolus the ball of food Segmentation churns and fragments a bolus Control of the Digestive System Movement of materials along the digestive tract is highly regulated and controlled by contraction o 1 Neural mechanisms parasympathetic and local reflexes o 2 Hormonal mechanisms enhance or inhibit smooth muscle o 3 Local mechanisms coordinate response to changes in pH or chemical stimuli Control of Digestive Activity Mostly controlled by reflexes via the parasympathetic division o Neural and hormonal mechanisms coordinate glands o GI activity stimulated by parasympathetic innervation o Inhibited by sympathetic innervation Chemical and mechanical receptors are located in organ walls that trigger reflexes Stimuli include o Stretch of the organ o pH of the contents o Presence of breakdown products Reflexes include o Activation or inhibition of glandular secretions o Smooth muscle activity Mouth Oral Cavity Anatomy Lips labia protects the anterior opening Cheeks form the lateral walls Uvula is the fleshy projection of the soft palate speech direct food Hard palate forms the anterior roof Soft palate forms the posterior roof Mouth Oral Cavity Anatomy Vestibule is the space between lips externally and teeth and gums internally Oral cavity proper is the area contained by the teeth Tongue is attached at hyoid bone and styloid processes of the skull and by the lingual frenulum to the floor of the mouth o Tongue s primary functions include o Mechanical processing o Assistance in chewing and swallowing o Sensory analysis by touch temperature and taste receptors Tonsils o Palatine o Lingual Digestive Activities of the Mouth The mouth opens into the oral buccal cavity Mouth functions include o Analysis of material before swallowing o Mechanical processing by the teeth tongue and palatal surfaces o Lubrication o Limited digestion Mechanical breakdown o Mastication chewing of food food is physically broken down by chewing o Mixing masticated food with saliva o Initiation of swallowing by the tongue o Allows for the sense of taste works with smell Chemical digestion o Food is mixed with saliva o Starch is broken down into maltose by salivary amylase Teeth Function is to masticate chew food Humans have two sets of teeth o Deciduous baby or milk teeth o 20 teeth are fully formed by age two Permanent teeth o Replace deciduous teeth between ages of 6 and 12 o A full set is 32 teeth but some people do not have wisdom teeth 3rd molars o If they do emerge the wisdom teeth appear between ages of 17 and 25 Classification of Teeth o Incisors used for cutting o Canines used for tearing or piercing o Premolars used for grinding o Molars used for grinding Regions of a Tooth Crown is the exposed part o Enamel is the hardest substance in the body o Dentin is found deep to the enamel and forms the bulk of the tooth nerve fibers o Pulp cavity contains connective tissue blood vessels and o Root canal is where the pulp cavity extends into the root Neck Root o Region in contact with the gum o Connects crown to root o Cementum covers outer surface and attaches the tooth to the periodontal membrane Salivary Glands Three pairs of salivary glands empty secretions into the mouth o Parotid glands o Submandibular glands o Sublingual glands Saliva o Mixture of mucus and serous fluids o Helps to form a food bolus o Contains salivary amylase to begin starch digestion o Dissolves chemicals so they can be tasted Pharynx Anatomy Nasopharynx is not not part of the digestive system Oropharynx is posterior to oral cavity Laryngopharynx is below the oropharynx and connected to the esophagus Pharynx Physiology food liquids and air assist in swallowing Serves as a passageway for air and food common passageway for Lined with stratified squamous epithelium Pharyngeal muscles o Pharyngeal constrictor muscles o Palatal muscles Food is propelled to the esophagus by two muscle layers o Longitudinal
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