Anatomy Notes

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Western University
Anatomy and Cell Biology
Anatomy and Cell Biology 3319
Peter Merrifield

Anatomy NotesMar 1312 The GI tract is also called the alimentary canal The upper digestive GI tract consists of the mouth pharynx esophagus and stomach and these structures are involved in ingestion and digestion The lower digestive GI tract consists of the small intestine large intestine and rectumanus and these structures are involved in absorption and defecation Ingestion is the taking of food into the mouth Digestion is the breaking down of food and it can be mechanical chewing or chemical enzymes Absorption occurs mainly in the small intestine and it is the transportation of nutrients from food into the blood Defecation is the removal of indigestible substances from the body as feces Swallowing has three stages The oral stage involves the movement of food from the mouth to the oropharynx which is located right behind the oral cavity The pharyngeal stage moves food from the oropharynx to the esophagus The esophageal stage moves food from the esophagus to the stomach 1 Oral Stage The oral stage is voluntary The tongue elevates and this pushes the bolus against the hard palate and backwards into the oropharynx The superior longitudinal muscle intrinsic muscle and the styloglossus and palatoglossus muscles extrinsic muscles are involved and they help elevate the tongue 2 Pharyngeal stage The pharyngeal stage is involuntary The blockage of three openings and contraction of the pharynx forces the bolus into the esophagus The oral cavity is blocked by continued elevation of the tongue The nasocavity is blocked by elevation of the soft palate which is done by the levator palati and tensor palati muscles The larynx is blocked by elevation of the larynx which causes the epiglottis to fold over the laryngeal inlet The muscles involved are the suprahyoid thyrohyoid the vertical muscles of the laryngopharynx palatopharyngeus stylopharyngeus and salpingopharyngeus Contraction of the pharynx occurs through its three musclesthe superior middle and inferior constrictors 3 Esophageal stage The esophageal stage is involuntary and it involves the downward movement of the bolus through the esophagus and into the stomach The mechanism of this action occurs by contraction of skeletal muscle in the upper part of the esophagus and peristalsis Peristalsis is wavelike contraction of smooth muscles in the lower part of the esophagus and the rest of the alimentary canal The top 13 of the esophagus is composed of skeletal muscle and the bottom 13 is composed of smooth muscle Peristalsis Adjacent segments of the alimentary canal relax and contract and food is squeezed from one organ to the next Some mixing of food by segmentation occurs as well In segmentation nonadjacent segments of the alimentary canal alternately contract and relax moving the food forward then backward The purpose of segmentation is to mix food in any direction The purpose of peristalsis is to move food down in one direction Histology of the alimentary canal The walls of the alimentary canal from the esophagus to the anus have the same four distinct layers From internal lumen to external are the mucosa submucosa muscularis externa and serosaadventitia Mucosa The mucosa is the innermost layer and is located next to the lumen It is made up of three distinct layersthe epithelium highly differentiated along the several regions of the GI tract lamina propia and muscularis mucosae The epithelium is located right next to the lumen and it is involved in many functions related to digestion such as absorbing nutrients and secreting mucus The lamina propia is a loose areolar connective tissue that absorbs nutrients from the lumen and epithelium and sends it to the bloodstream The muscularis mucosae is involved in localized contraction of the mucosa Submucosa The submucosa contains blood vessels lymphatics and lymph nodes and nerves
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