The Digestive System The Digestive System Functions o Peristalsis o Segmentation Ingestion is taking in food Propulsion is moving foods from one region of the digestive system to another Absorption is movement of nutrients into the bloodstream end products of digestion are absorbed in the blood or lymph of food that was chemically and physically broken down Defecation rids the body of indigestible waste Movement of Digestive Materials Visceral smooth muscle shows rhythmic cycles of activity caused by pacemaker cells Peristalsis causes waves that move a bolus food chewed up and swallowed Segmentation churns and fragments a bolus Control of Digestive Activity Mostly controlled by reflexes via the parasympathetic NS o Neural and hormonal mechanisms coordinate glands o GI activity stimulated by parasympathetic and 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 Developmental Aspects of the Digestive System problems of the digestive system o gastroenteritis is inflammation of the GI tract o appendicitis is inflammation of the appendix metabolism decreases with old age activity of the digestive tract in old age o fewer digestive juices o peristalsis slows o diverticulosis and cancer are more common o alimentary canal gastrointestinal or GI tract is a continuous coiled hollow tube Organs of the Digestive System two main groups mouth pharynx esophagus stomach small intestine large intestine o Accessory digestive organs Accessory Digestive Organs teeth salivary gland pancreas liver gallbladder Mouth Oral Cavity Anatomy tonsils o palatine o lingual Digestive Activities of the Mouth 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 o lubrication the mouth opens into the oral buccal cavity 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 o Replace deciduous teeth between ages of 6 to 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 17 and 25 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 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 Salivary Glands o Parotid glands o Submandibular glands o Sublingual glands Saliva o Mixture of mucus and serous fluids o Helps to form a Pharynx Physiology Three pairs of salivary glands empty secretions into the mouth Serves as a passageway for air and food common passageway for food liquids and air Lined with stratified squamous epithelium Pharyngeal muscles assist in swallowing o Pharyngeal constrictor muscles o Pala Deglutition Swallowing Buccal phase o Voluntary and occurs in the mouth o Food is formed into a bolus and forced into the pharynx by the tongue Pharyngeal esophageal phase o Involuntary transport of the bolus o All passageways except to the stomach are blocked Tongue blocks off the mouth Soft palate and uvula blocks the nasopharynx Epiglottis blocks the larynx Peristalsis moves the bolus toward the stomach The cardioesophageal sphincter is opened when food presses against it Esophagus Anatomy and Physiology Anatomy o About 10 inches long o Runs from pharynx to stomach through the diaphragm o Functions of the Stomach Bulk storage of undigested food Mechanical breakdown of food Disruption of chemical bonds via acids and enzymes Delivers chyme processed food to the small intestine Production of intrinsic factor Temporary storage tank for food Chemical breakdown of protein begins Site of some food breakdown Stomach Anatomy Located on the left side of the abdominal cavity Food enters at the cardioesophageal sphincter Food empties into the small intestine at the pyloric sphincter valve Regions of the stomach o Cardiac region is near the heart o Fundus is the expanded portion lateral to the cardiac region o Body is the midportion o Pylorus is the funnel shaped terminal end Rugae are internal folds of the mucosa External regions o Lesser curvature concave medial surface o Greater curvature convex lateral surface Acid reflux heart burn Structure of the Stomach Mucosa Mucosa is simple columnar epithelium Mucous neck cells produce a sticky alkaline mucus Gastric glands are situated in gastric pits and secrete gastric juice Chief cells produce protein digesting enzymes pepsinogens Parietal cells produce hydrochloric acid Enteroendocrine cells produce gastrin and somatostatin hormones Peptic Ulcers Peptic ulcers are most common in the lower half of the stomach gastric ulcer or in the upper part of the duodenum duodenal ulcer Ulcers can affect all ages and about 1 in 10 Americans develops a peptic ulcer at some point Ulcers are the result of damage to the cells that produce a layer of mucus and other factors that neutralize any acid Cells lining the stomach and intestines are constantly renewed with normal turnover occurring every 72 hours Problems arise cell function is disrupted by Helicobacter pylori infection aspirin or other non steroidal anti inflammatory drugs NSAIDs alcohol nutrient deficiencies long term hunger and stress Digestion and Absorption in the Stomach Preliminary digestion of proteins Permits digestion of carbohydrates Very little absorption of nutrients Enteroendocrine cells o G cells secrete o D cells secrete somatostatin Food Breakdown in the Stomach o Some drugs may be absorbed aspirin alcohol o Mucous secretion containing several hormones Presence of food or rising pH causes the release of the hormone gastrin Gastric juice is regulated by neural local and hormonal factors Gastrin causes stomach glands to produce o Protein digesting enzymes o o
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