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IHST 1002 – Exam Review Digestive System
• Overview o Takes in food, breaks it down into nutrients, absorbs, releases leftovers o Two Different Aspects ▪ GI Tract (Gastrointestinal)
• continuous muscular tube – runs through the mouth to the anus
• digestion (breakdown of molecules) and absorption occurs
• mouth (oral cavity), pharynx, esophagus, stomach, small intestine, large intestine, anus ▪ Accessory Digestive Organs
• Help GI tract
• Produce secretions that help breakdown food
• Organs involved: teeth, tongue, salivary glands, pancreas, liver, gallbladder
• Gastrointestinal Tract Activities o 1.Ingestion – putting the food in your mouth o 2. Propulsion – move the food along the GI tract (swallowing, peristalsis) happens all the way through o 3 Mechanical Breakdown – physical breakdown (chewing, churning – stomach, segmentation -small intestine) o 4. Chemical breakdown – digestive enzymes will be released from the accessory digestive organs, or from the GI tract, they will break down the food in their molecular components o 5.Absorption – in small intestine – nutrients cross the intestinal wall and absorb into the blood vessels, and lymph vessels o 6. Defecation – feces
• Peristalsis and Segmentation o Peristalsis: Part of propulsion, in GI tract, starts at esophagus ▪ Lumen – space ▪ Smooth muscle – causes subconscious movement ▪ Closer to mouth – proximal; closer to anus – distal o Segmentation: Part of mechanical breakdown ▪ Happens mainly in small intestine ▪ Mixes food/bolus/chime back and forth with digestive enzymes ▪ Slow process
• Regulation of Digestive System o Stimulation of Digestive System activity: ▪ Mechanical and chemical stimuli in walls of GI tract ▪ Have receptors that detect changes; initiate reflexes that affect releases of enzymes and movement of walls i.e. stretching, pH, solute concentration o Controls of Digestive System activity: ▪ Intrinsic: nervous system (short reflexes), helps with releasing digestive enzymes, getting peristalsis and segmentation going ▪ Extrinsic: through Central Nervous System (long reflexes), sends ques for when to eat, continues blood flow ▪ Hormonal: released by cells in GI tract; travel to target organs in bloodstreams
• Histology of the Alimentary Canal o Lumen is relativity; depends on where you are o Layers referred to as tunics o 1.lumen is in the center o 2. Is mucosa – inner most layer, involves in secretion of mucus, digestive enzymes, hormones, and helps absorb o 3. Is submucosa – veins, arteries, lymphatic capillaries, nerves are all there o 4.is muscularis externa – smooth muscle layer – responsible for peristalsis and segmentation o 5.serosa – outer most layer – holds GI tract in place, made of connective tissue
• Enteric Nervous System o Located in the submucosa – nerve supply o Converse with the CNS o Regulates digestive system activity
• The Oral Cavity o Runs from the palate – between oral cavity and nasal cavity; formed by bone in the front, and muscle in the back o Teeth, and tongue contribute to mechanical breakdown o Bolus – food smashed up
• The Salivary Glands o Parotid gland ▪ In front of the ear ▪ Largest o Sublingual gland ▪ Underneath the tongue o Submandibular Gland ▪ Inferior to the sublingual gland; just lower