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27 Cards in this Set
- Front
- Back
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What are the basic components of the Digestive System?
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GI tract (Alimentary canal):
-mouth, oropharynx, laryngopharynx, esophagus, stomach, large intestine, and small intestine Accessory digestive organs: -teeth, tongue, salivary glands, pancreas, liver, and galbladder |
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What are the primary mechanisms of the Digestive System?
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Ingestion:
-process of taking complex food into mouth Digestion: -breaks down large particles and complex nutrients into small absorbable molecules which can be absorbed into circulation Motility: -movement by muscular contractions Secretion: -digestive juices released through ducts into alimentary canal Absorption: -movement of digested nutrients, water, electrolytes etc from alimentary canal through mucosa into blood or lymph Elimination: -excretion of feces through rectum; defecation Regulation |
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What are the 4 layers of the GI wall?
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1. Mucosa:
-Epithelium: nonkeratinized stratifed squamous = mouth, pharynx, esophagus, and anal canal simple columnar = stomach, large and small intestines goblet cells in mucosa secrete mucus enteroendocrine cells secrete hormones -lamina propria: loose CT containing collagen and elastic fibers contains lymphoid tissue (MALT) = protective function, blood and lymphatic capillaries supports epithelium -muscularis mucosae: thin layer of smooth mm. formation of small folds in GIT, increases absorptive surface area 2. Submucosa: -highly vascularized layer of loose CT -contains glands and submucosal (Meissner's) nerve plexus which provides autonomic nerve supply to muscularis mucosae 3. Serosa: -areolar connective tissue, simple squamous epithelium -binding and protecting layer 4. Muscularis: -longitudinal muscle, circular muscle -contains myenteric (Auerbach's) plexus located between two muscular layers; fibers and ganglia of both PSNS and SNS |
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What are characteristics of GI Innervation?
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-Striated muscles of mouth, pharynx, upper esophagus and external rectal sphincter innervated by somatic nervous system
-GIT and accessory structures by ANS and ENS |
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What is the Enteric Nervous System?
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3rd division of the ANS
semiautonomous - can integrate motor and secretory activities of GIT in absence of extrinsic innervation; modulated by ANS located in gut wall includes submucosal and myenteric plexuses and other neurons of GIT Contains: Sensory neurons - connected to mucosal chemoreceptors (gut lumen), stretch receptors (wall by food and chyme), thermo and pain receptors Interneurons - provide excitatory and inhibitory connections in secretomotor, motor, and vasomotor pathways Efferent neurons - innervate smooth msucle fibers, blood vessels, epithelial and gland cells Neurotransmitters - Ach, NAdr and NANC |
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What are the Plexuses of the ENS?
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Myenteric Plexus:
*mostly controls GI tract motility* Includes: excitatory neurons (release Ach) - increase muscle tone, intensity and rate of rhythmic contractions and velocity of conduction of excitatory waves along GIT wall inhibitory neurons (release VIP and NO) - relaxation of smooth muscles Submucosal Plexus: *mainly regulates GI secretion and blood flow* -controls secretion, local blood flow, absorption, contractions of villi and folding of GIT mucosa, activity of GI endocrine cells |
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How is the GI Innervated by the PSNS?
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Preganglionic neurons:
Cranial divison -Vagus = innervates esophagus, stomach, small and proximal part of large intestine Sacral Division -S2-S4, pelvic nerves = innervate distal part of large intestine Postganglionic neurons: -Location = the myenteric and submucosal plexuses Effects: -Ach has direct excitatory effect on increase in GIT motility and secretion -relaxation of sphincters (indirect effect dude to release of peptide neurotransmitters) NO effect on GI blood vessels |
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How is the GI innervated by the SNS?
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Preganglionic:
-located in thoraco-lumbar (T5-L2) Postganglionic: -celiac and superior and inferior mesenteric ganglia innervates essentially ALL of GIT Effects: -INHIBITORY effect on enteric neurons and smooth muscles -Vasoconstriction to digestive tract --> inhibitory effect of GIT -has some excitatory effects --> contraction of muscularis mucosae via alpha1 receptors |
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What are the Salivary Glands?
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Major:
Parotid glands - 60 - 65 % Submandibular - 2-30 % Sublingual - 2 - 65 % -release saliva through ducts into oral cavity Minor: -lingual, buccal, labial etc -open directly or via short ducts into oral cavity |
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Where are each of the major glands located and what are some of their functional classifications?
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Parotid:
Duct - opens into vestibule opposite 2nd maxillary molar Gland - inferior and anterior to ear; between skin and masseter -purely serous Sublingual: Glands - beneath tongue, superior to submandibular glands ducts - open into floor of mouth -mixed, predominantly mucous (viscous secretion containing mucin) Submandibular: Gland - floor of mouth Duct - opens laterally to the lingual frenulum -mixed, predominantly serous (watery secretions) |
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What is Gut Motility?
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movement of the alimentary canal mediated by muscular contractions
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What are the different types of Gut Motility?
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1. Peristalsis - coordinated contraction of circular and longitudinal layer of gut wall, results in prokinetic movement
-contraction of circular muscle layer behind a food bolus -contraction of longitudinal muscle layer ahead of food bolus (receptive relaxation) -proximal-distal gradient --> propulsion of content 2. Mixing Movements: A. non propulsive peristalsis and retropulsion -forward propulsion of content blocked by sphincter -function to churn and grind content -takes place in esophagus, stomach, small and large intestine B. Rhythmic Segmentation -contraction of circular layer -new contractions at other segments mixing the luminal content -takes place in small and large intestines C. Oscillations -contraction of longitudinal muscles cause shortening, widening, elongation, then narrowing of lumen --> mixing of luminal content -takes place in small and large intestines 3. Tonic Contractions -sustained contractions of smooth muscles, espeically sphincters funct: decrease lumen size and increase pressure --> facilitation of mixing and propulsion -receptive relaxtion: lower muscular tone to accommodate food |
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What is Mastication?
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ingestion and mechanical digestion of food, resulting in formation of food bolus and initiation of swallowing
is a reflex (involuntary) activity that can be voluntary facilitated by presence of saliva opening and closing of jaw --> biting protrusion and retraction of jaw --> cutting lateral movements --> grinding |
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What is an important property of saliva?
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has a MUCH LOWER osmolarity than plasma: 100 compared to 300
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What are the organic components of saliva?
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alpha amylase (ptyalin):
-from submandibular and parotid gland -hydrolyzes cooked starch to maltose -activated by Cl-, inactivated by pH 4 Lipase: -from lingual glands -hydrolyzes triglycerides containing long chain FA -value in neonates and decreased pancreatic secretion -able to act in absence of bile acids and acidic pH Lysosome: -in submandibular and parotid -hydrolyzes bacterial wall -inhibition of mucosal colonization mucus: -sublingual and submandibular -lubricates food |
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What are some functions of saliva?
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Protective:
acid neutralization (bicarbonate) preventing Ca2+ loss from teeth general cleansing antibacterial activity: -IgA -lysozyme contribution to sensation of taste aiding in bolus formation, chewing, swallowing facilitation of speech and promotion of oral comfort sensation of thirst oral absorption |
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How is saliva regulated?
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neural regulation is more important than humoral
involves conditioned and unconditioned reflexes receptors --> afferents and higher brain centers --> superior and infereior salivatory nuclei in brain stem --> preganglionic parasympathetic --> otic and submandibular ganglia --> posganglionic fibers or nuclei --> T1-T3/4 preganglionic sympathetic fibers --> superior cervical ganglia --> postganglionic sympathetic fibers sympathetic --> viscous saliva with high concentration of organic molecules parasympathetic --> large amounts of serous saliva with low concentration of organic molecules, provides physiological tone, controls activity of salivary glands both act synergistically to provide salivary secretion |
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What is the structure of the pharynx?
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oro and laryngopharynx seve as common passageway for food and air
3 sphincters: superior constrictor mm - contraction helps closure into nasopharynx, prevents bolus from entering nasal cavities middle and infereior constrictor mm - direct bolus into esophagus, prevent back-movement of bolus |
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What is the structure of the esophagus?
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collapsible muscle, tube length
has thoracic part and abdominal part muscle layers: upper third - striated muscular layers middle third - skeletal and smooth muscle fibers lower third - smooth muscle fibers Sphincters: Upper esophageal sphincter (UES): -directs food bolus into esophagus -prevents air from entering esophagus -prevents regurgitation of food Lower Esophageal Sphincter (LES) directs a food bolus into stomach prevents regurgitation of acidic gastic contents |
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What is the innervation of the Esophagus?
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Glossopharyngeal nerves --> striated muscle fibers, stimulates contraction
Vagus Nerves (preganglionic): -innervates both striated and smooth effects: cholinergic fibers --> excitatory fibers non-cholinergic --> inhibitory effect |
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What are the events in swallowing?
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propel bolus from mouth into stomach
voluntary/involuntary stages: oral: -voluntary -separation of a food bolus and forcing it into the oropharynx pharyngeal: -rapid involuntary -sensory fibers of CN V, IX, and X -swallowing center - located in medulla and pons close to respiratory and vomiting center; afferentation from pharyngeal and esophageal receptors -efferent fibers of V, VII, X, and XII to pharyngeal and esophageal mm. -prevention of aspiration -entrance into esophagus -delutition apnea (no breathing while swallowing) -peristaltic wave --> proximo-distal gradient --> bolus goes from upper esophagus to relaxed UES Esophageal: -slow involuntary -closure of UES -peristalsis --> proximo-distal gradient -primary peristaltic wave (food goes down) and secondary wave (remnant particles) -receptive relaxation of LES and proximal stomach |
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How do you prevent Gastric Reflux?
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tonic activity of the LES
contraction of muscle fibers of the diaphragm valve-like closure of distal end of esophagus when intra-abdominal pressure rises Compression of terminal part of esophagus by positive intra-abdominal pressure |
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What is GERD and what are its causes?
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reason:
-incompetence of LES -weakness of diaphragm consequence of reflux of acidic gastric content in esophagus: -heartburn -asthmatic symptoms Compensation: -secondary peristalsis --> acid neutralization |
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What is Achlasia?
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increase resting tone of LES and failure to relax during swallowing
Pathogenesis: damage to myenteric plexus consequences: -megaesophagus |
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What are the functions of the stomach and its structure?
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functions:
-temporarily storage of ingested food -secretory function -motor function -endocrine structure: 1. cardia 2. fundus 3. body 4. antrum 5. pylorus rugae (large folds of mucosa) muscles: -longitudinal muscle -circular muscle -oblique muscle |
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What are the functions of some different gastric regions?
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"Orad" region:
-storage of food w/o increase in intraluminal pressure -2/3 of stomach (fundus and proximal body) "Caudal" portion: -formation of gastic chyme and evacuation -last 1/3 (body and antrum) Pyloric Sphincter: -emptying of chyme at rate consistent with duodenum ability to process it -prevention of regurgitation of duodenal content into stomach |
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What are characteristics of the mucosa of the stomach?
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Secretory cells:
Surface Epithelium (simple columnar) -secrete visible mucous (clumps on contact with acid), lysozyme -mucus covers surface of mucosa by alkaline coat Tubular glands: -chief or peptic cells (deep) - in fundus and body; pepsinogen secretion -parietal/oxyntic (walls of tubules) - acid and intrisic factor secretion -neck cells (between surface epithelial cells and glands) - soluble mucin -endocrine cells (G cells - gastrin) |
