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50 Cards in this Set
- Front
- Back
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Two types of motility
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Propulsive
Mixing |
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What are the 4 digestive processes?
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Motility
Absorption Digestion Secretion |
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What % of food is available as energy?
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95%
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Carb digestion
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-Most are ingested as polysaccharides such as starch and glycogen
-Less are ingested as disaccharides like sucrose and lactose |
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Simplest carb?
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Monosaccharide
-usually the end product of digestion -EG: glucose, fructose, |
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Sucrose is...
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glucose and fructose
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Lactose is...
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glucose and galactose
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Protein digestion
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-Cleavage of protein into amino acids and small peptides
-Done by: chymotrypsin, carboxypeptidase, pepsin, trypsin |
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Fat digestion
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-Enter as triglycerides: glycerol and three fatty acids
-Digestive processes remove 2 fatty acids -Done by lipase |
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Digestive tract wall
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1. Serosa-external covering
2. Muscularis externa-outer longitudinal m. and inner circular m. 3. Submucosa 4. Mucousa-mucosa membrane, lamina propia, muscularis mucosa Also has two plexuses: myenteric and submucous |
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Mucosa Features
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-Composed of 3 layers
-Mucous membrane has 3 cell type -Lamina propria plays a role in defense -Muscularis mucosa is the outermost muscle layer |
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Cells in mucous membrane
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Exocrine cells: secrete GI enzymes
Endocrine cells: secrete GI hormones Epithelial cells: absorption of digestive nutrients |
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What does serosa secrete?
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Serous fluid to lubricate from surrounding viscera
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What is the mesentery's role?
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To suspend digestive organs from wall and allow for a relatively fixed position
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Regulation of digestive fxn involves...
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1. Autonomous smooth m. fxn
2. Intrinsic nerve plexuses 3. Extrinsic nerves 4. GI peptides |
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Autonomous smooth muscle fxn involves...
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-Pacesetter cells: found between longitudinal and cicrcular smooth muscle. Responsible for slow wave potentials
-These cells determine the rate of rhythmic contractions. |
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Intrinsic nerve plexuses do what?
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Contain neurons that release both ACh and VIP.
-ACh promotes smc contraction -Vasoactive intestinal peptide (VIP) promotes smc relaxation -Found as both myenteric and submucous plexuses -This is the enteric nervous system |
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Role of ACh in digestive tract?
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-Acts on cholinergic neurons
-Contracts smc in the walls -Relaxes sphincters -Increases salivary secretion, gastric secretion, and pancreatic secretion |
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Role of NE in the digestive tract?
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-Acts upon adrenergics
-Relaxes smc in wall -Contracts sphincters -Increases salivary secretions |
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Vasoactive Intestinal Peptide
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-Acts upon on mucosa and smooth muscle
-Relaxes smc -Increases intestinal, pancreatic secretions |
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Enkephalins role in the digestive tract?
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-Act upon mucosa and smooth muscle
-Contracts smc -Decreases intestinal secretion |
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Neuropeptide Y's role in the diestive tract?
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-Acts upon mucosa and smooth muscle
-Relaxes smooth muscle -Decreases intestinal secretion |
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Substance P's role in the digestive tract?
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-Secreted along with ACh
-Contracts smc -Increases salivary secretion |
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What do the extrinsic nerves do?
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Both branches affect motility and secretion
-PNS: Vagus and Pelvic; tends to increase motility and secretion; long preganglionic fibers -SNS: tends to decrease GI motility; preganglionics are short |
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What do GI peptides do?
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-Contraction/relaxation of smc wall & sphincters
-Secrete enzymes for digestion -Secrete fluids & electrolytes -Eg: hormones, paracines, neurocrines |
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Hormones
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CCK, gastrin, secretin
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Paracrines
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Somatostatin
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Neurocrines
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ACh, NE, VIP
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Purpose of chewing?
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1. Grind/mix food with saliva
2. Stimulate taste buds 3. Reflexively increase salivation, gastric, pancreatic, and biliary secretions |
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What kind of spit do serous glands make?
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Aqueous
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What type of fluid do mucus glands make?
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Mucousy
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Saliva composition?
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99.5% water
.5% electrolytes Salivary proteins: amylase, mucus, lysozyme |
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What does amylase do?
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-Breaks polysaccharides into maltose (2 glucoses)
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What does mucus do?
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Facilitates swallowing by lubing food up
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What does lysozyme do?
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Antibacterial
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What does kallikrien do?
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Cleaves kininogen into bradykinin
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What is bradykinin?
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A vasodilator that increases bloodflow to salivary glands when secretion increases.
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What are the fxns of saliva?
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1. Solvent for molecules to stimulate taste buds.
2. Aids in speech by facilitating movement 3. Keeps teeths clean 4. Contains bicarb buffers-protects teeths from decay |
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What is the role of myoepithelial cells in saliva secretion?
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They contract to eject spit
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What is saliva secretion stimulated by?
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-Pressure receptors/chemoreceptors in mouth
-External cues (Pavlov) -Eating acidic foods -PNS is stim by food/smells and inhibited by fear, sleep, dehydration |
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What is PNS spit like?
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Watery, enzyme-rich; this type is dominant normally
-ACh, muscarinic receptors release IP3 which increase [Ca] |
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What is SNS spit like?
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Less volume, mucus rich; more common with stress
-NE, B-adrenergic, stim adenylyl cyclase, increase [cAMP] |
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How much spit is made/day?
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1-2 L/day basal (.5ml/min)
-up to 5ml/day |
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Xerostomia
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-Decreased spit production
-Causes: dz (infections, stones, mumps), radiation/chemo, meds S/sx: dry mouth, difficulty chewing, difficulty speaking, increase cavities, facial px Tx: no etoh, tobacco, caffiene, more water, brush teeths |
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Achalasia
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-Occurs when the lower sphincters fails to relax during swallowing and food does not enter stomach
-Tx involves surgery, drugs to inhibit tone (botox, ca channel blockers) |
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Phases of swallowing
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1. oral
2. pharyngeal 3. esophageal |
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Oral phase of swallowing
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-The swallowing reflex is initated when a bolus of food hits the rear of the pharynx
-This stimulates tactile receptors which send a signal to the swallowing center in the brainstem; efferent signals leave via vagus/glossopharyngeal nn. |
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Pharyngeal phase of swallowing
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-Soft palate moves upward to prevent reflux of food into nasopharynx
- Vocal cords pulled together, larynx moves forward & upward against epiglottis –prevents food entering trachea -Pharyngeal muscles contract & peristaltic wave begins |
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Esophageal phase of swallowing...
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-Primarily controlled by swallowing center
-Begins after bolus passes UES -Peristalsis moves food down -Once started, it can't be stopped - |
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Swallowing disorders
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S/Sx: frequent choking on food, food takes a long time to move, px w/ swallowing
Dx: Cineradiography (swallow barium prep, X-ray & videotape movement), Upper endoscopy (direct visualization), manometry Tx: monitor amts/rate of food, drink plenty of fluids -Degenerative neurological disorders can also cause these problems ( als, myasthenia gravis) |
