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Digestive System Divisions
• Alimentary Canal (Gastrointestinal Tract)– These are all the structures that food passes
through during digestion– One, long, tube open at both ends– Starting with the mouth, ending with the anus
• Accessory Organs– These are the structures that aid in digestion
of food, but in which no food passes– Liver, gallbladder, pancreas, salivary glands
Dentition• Function: Mastication (chewing)• Diphyodont = two sets (20 primary/32 permanent)
• Forms: – Incisors (8) Cutting and shearing – Canines (4) Gripping and tearing– Premolars (8) Crushing– Molars (12) Grinding
Palates
• • Palatum Durum (hard palate): Upper, anterior roof of the mouth, covered with rugae (folds) to allow backwards movement of food
• Palatum Velum (i.e. “Soft Palate”): Upper, posterior roof of the mouth. Closes off access to nasopharynx during swallowing
Anatomy of Tongue
• Tongue: Muscle that mixes food with saliva, pushes food into the oropharynx, and contains gustatory papillae (taste receptors)
• Lingual frenulum: Fold of mucous membrane that attaches the tongue to the floor of the mouth
Tonsils
• Lymphoid tissue = first line of immune defense for aerodigestive tract
• Largest pre-puberty; atrophy after puberty
Deglutition and Pharyngeal-Esophageal Anatomy
• Deglutition = swallowing• Food enters into the
oropharynx, then passes into the laryngopharynx
• Closure of the epiglottis allows passage of food into the esophagus and prevents aspiration (particulates in lungs)
Peristalsis
• Alternating contractions between circular and longitudinal muscle of the pharynx and esophagus
• Physically separates food into small spheres (bolus) and moves it through the esophagus
STOMACH
• Initial site of protein hydrolysis/digestion
• Primary site of mechanical digestion via rumination
• Absorption of water and alcohol
Cardiac Sphincter(antrum cardiacum)
• Food enters the stomach through this muscle via the esophagus
• Accidental opening of this structure may lead to Gastro-Esophageal Reflux Disorder (GERD)
Fundus
• Means “bottom” in Latin but is the left anterior curvature of the stomach
• Stores food for appx. 1 hour
• Digestive gases collect here
Anatomy of Stomach Body
• Greater and lesser curvature
• Gastric canal – can hold appx. 1 gallon of food
• Rugae (increase surface area)
Pyloric Antrum & Sphincter
• Muscular terminus of stomach
• Involved in rumination of food
• Food exits the gastric canal via passage through the pyloric sphincter
DUODENUM
• First section of small intestine
• Drastic rise in pH due to addition of bile salts
• Receives secretions of pancreas
Peptic Ulcers
• Most common site of ulcers is 5cm distal to pyloric spincter
• Only 4% of ulcers are stomach
• Caused by actions of Heliobacter pylori
• Exacerbated by stress & diet
VILLI
• Small (1mm) projections of small intestine that drastically increase surface area of small intestine
• Cells lining villi die and are consumed!
• Contain capillaries for transport of material
• Contain lacteals to transport fats
Colonic Form and Function
• 1.5m divided into– Ascending– Transverse– Descending– Sigmoid
• Involved in conduction of solid waste
• Reabsorption of water via standing gradient osmosis
Anal Sphincter
• Muscular bands that control expulsion of feces
• Regulated via recto-anal inhibitory reflex (RAIR)
• Flatuaria is a loss of control over RAIR
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