DIGESTIVE SYSTEM.docx

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Department
Cellular, Anatomical and Physiological Sciences
Course
CAPS 391
Professor
Bruce Matheson
Semester
Winter

Description
DIGESTIVE SYSTEM Digestive tract > from mouth to anus (alimentary tract), through head, neck, thorax, abdomen, pelvis GI tract > stomach and intestines Oral cavity > mouth, teeth, salivary glands, tonsils Pharynx > throat Esophagus Stomach Small intestine > duodenum, jejunum, ileum, liver, gallbladder, pancreas * Large intestine > cecum, colon, rectum, anal canal Anus Swallowing Tongue forms food in bolus, pushes into oropharynx, contraction of pharyngeal constrictors moves through laryngopharynx, esophagus, stomach. Peristalsis > moves material through digestive tract, waves of smooth muscle contraction, relaxation of muscles in front of bolus and contraction of muscles behind bolus to move it along controlled by vagus nerve. 3 physiological sphincters: cardiac sphincter prevents reflux of food back into esophagus. Mechanical Digestion Chewing, mix saliva w/ food (saliva has salivary amylase > breaks down amylose sugar or starches), stomach muscles churn bolus into “chime” Chemical Digestion Digestive enzymes, acids, bases secreted along GI tract. Large organic molecules (macromolecules) digested into component parts before absorbed by digestive tract. Minerals, water, vitamins NOT broken down before being absorbed. Absorption Mainly in small intestine (increased SA), actively/passively absorbed, vitamins, fat = fatty acids/cholesterol, Carbs = simple sugars, proteins = peptides/amino acids Defacation Feces are formed in large intestine, absorbs water/salts to make it semi solid, stored in rectum, regulated by contraction/relaxation of anal and rectal sphincters. Tongue Attached posteriorly, free anteriorly, attached at bottom by LINGUAL FRENULUM. Intrinsic muscles > within tongue, change shape during communication, elevating/flattening during drinking/swallowing Extrinsic > outside tongue, but attached, protrude/retract tongue, change shape, move side to side Terminal Sulcus > groove in the middle, divides in 2, anterior to this is covered by papillae* (some w/ taste buds). Posterior tongue has a few scattered taste buds, small glands, lymphatic tissue to form lingual tonsils** Stratified Squamous ET covers tongue Taste buds on fungiform: sweet, salty, sour, bitter, meaty Salivary Glands 3 pairs of large, multicellular > parotid, submandibular, sublingual Small, coiled, tubular salivary glands > deep to tongue epithelium (lingual), palate (palatine glands), cheeks (buccal glands), lips (labial glands) Acinar Glands >major large salivary glands, branching glands w/ clusters of acini, produce thin serous secretions or thick mucous secretions. Parotid > largest, serous, produce watery saliva, anterior to ear on each side of head. Parotid ducts exit glands on anterior margin, crosses lateral masseter muscle, pierces bucinator muscle and enters oral cavity by second upper molar. Mumps can inflame/swell parotid glands. Submandibular > mixed glands w/ more serous than acini. Soft lump on inferior border of posterior half of mandible. Submandibular duct exits each gland, passes anteriorly deep to mucosal membrane on the oral cavity floor, opens into oral cavity beside frenulum of tongue. Sublingual > smallest, mixed serous/mucous acini, lie on floor of oral cavity, opens onto floor of oral cavity through 10-12 small ducts. Saliva > keeps oral cavity moist, tastes food molecules/speech, begins digestion, prevents bacterial infections, bicarbonate ions neutralize acids by oral bacteria, protects tooth enamel Serous part of saliva > contains salivary amylase, breaks covalent bonds between glucose molecules in starch/polysaccharides to produce dissacharides maltose and isomaltose (makes starch taste sweet) Lysozome prevents bacterial infection Mucin > proteoglycan that lubricates secretions of salivary glands Stimulated by parasympathetic nervous system mainly***, brainstem has salivary nuclei, sends AP’s through facial and glossyopharyngeal nerves in response to tastes, tactile stimulation. Mucosa Epithelium > moist stratified squamous ET in mouth, oropharynx, esophagus, anal canal and simple columnar ET in remainder of digestive tract, goblet cells, enzyme secreting cells, endocrine cells Lamine Propria > loost CT, lymphoid tissue, capillary networks (in absorptive areas like small intestine) Muscularis Mucosae > outer smooth muscle layer, increases SA for absorption, creates folds* Epithelium extends deep into lamina propria to form intestinal glands/crypts. Mechanoreceptors >peristaltic reflexes Chemoreceptors > detect chemical composition of food Submucosa Beneath mucosa, thick CT la
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