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197 Cards in this Set
- Front
- Back
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How does the parasympathetic pathway innervate the GI?
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stimulates activity
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Whast is the vagovagal reflex?
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information from receptors in mucosa and smooth muscle relayed to CNS via vagus afferents, then efferents from vagus are sent back to GI tract
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What does the sympathetic pathway do?
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inhibits activity; usually fibers synapse outside the GI tract
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What are the myenteric and submucosal plexuses part of?
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intrinsic/enteric innervation system; relay info via extrinsic system
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what are neurocrines?
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synthesized in cell bodies of neurons nadn released by AP's
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where is gastrin secreted from
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G cells in stomach
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what is gastrin released in response to
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peptides and amino acids from protein digestion, distension of the stomach and vagal stimulation
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what does gastrin stimulate
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HCl secretion
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what inhibits gastrin secretion
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acid in stomach
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what is zollinger-ellison syndrome
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people who hypersecrete gastrin and develop ulcers, diarrhea and steatorrhea
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where is CCK released from
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I cells of small intestine in response to peptides, aa, fatty acids and monoglycerides
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what does CCK stimulate
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gallbladder contraction and pancreatic enzyme secretion and also potentiates HCO3 secretin with secretin
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what does CCK inhibit
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gastric emptying
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what does secretin stimulate
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HCO3 and H2O secretion in pancreas and liver; also increases bile production
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what does secretin inhibit
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gastric acid secretion
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where is secretin released from
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S cells of small intestine in response to acid
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what does gastric inhibitory peptide stimulate
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insulin release; released in response to fat, protein and carbs
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what is gastric inhibitory peptide stimulated by
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proximal small intestine
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when is motilin released
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every 90 minutes during fasting
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what does motilin stimulate
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migrating myoelectric complex in stomach and small intestine
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When is somatostatin stimulated?
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secreted in response to acid in lumen
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what does somatostatin inhibit?
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gastric acid secretion and release of gastrin and release of all GI hormones
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what is histamine's function
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increase gastric acid secretion directly and by potentiating effects of gastrin and Ach
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whats the function of vasoactive intestinal peptide?
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relaxation of smooth muscle and stimulates intestinal and pancreatic secretion
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what are the role of enkephalins
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stimulate contraction of GI smooth muscle and inhibit intestinal secretion of fluid and electrolyte
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what are the neurocrines
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VIP, GRP and enkephalins; all released from nerves in mucosa
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what are slow waves
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periodic changes in resting membrane potential of smooth muscle cells
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what generates a slow wave
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intersitial cells of Cajal
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are slow waves action potentials
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no but they do determine the pattern of AP's
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what are the two phases of slow waves
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upstroke and plateau phase
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when can contraction occur during a slow wave
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when plateau phase exceeds threshold
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what happens when threshold is reached
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voltage gated Ca channels open and Ca comes in causing an AP
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what do AP's do to slow waves
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increase strength and duration of contraction
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can contractions occur in the absence of action potentials?
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only in the stomach
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how can neural or hormonal input influence contraction
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nerves increase probablity that membrane potential will cross threshold but will not affect frequency
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what sets max frequency for contraction for any part of the GIU
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frequency of slow waves
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can you have contractions without slow waves
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no but can have slow waves without contractions
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3 functions of salivary secretion
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digestion of starch and fat, lubrication and protection from bacteria
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3 major glands
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parotid, sublingual and submandibular
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which one contributes to salivation the most
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submandibular
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what is the acinus of a duct
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blind end, lined with acinar cells that secrete initial saliva
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what connects acinus and striated duct
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intercalated duct
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what is the striated duct
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modifies inorganic composition of saliva
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specialized contractile cells
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myoepithelial cells
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what contols saliva
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autonomic nervous system, parasympatheic and sympathetic nerves increase saliva
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which one, PSNS or SNS provides stronger input for saliva release
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PSNS
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what is the role of PSNS in saliva realease
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increase transport processes of acinar and ductal cells, stimulates vasodilation of blood vessels and stimulates glandular metabolism and growth
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what is the role of SNS on saliva secretion
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transiently increases production and growth of salivary glands, contraction of myoepithelial and constriction
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what would lesioning PSNS nerves do to salivary glands
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atrophy them, SNS would have little effect
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what increases production of saliva
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food, smells, conditioned reflexes and nausea
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what decreases production of saliva?
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sleep, fatiuge, dehydration, fear and anticholingeric drugs
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what is saliva composed of
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water, electrolytes and organic compounds, bactericidal compounds; acidic pH
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what proteins are in saliva
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amylase-starches
lipase-fats mucin-lubrication and protection |
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what is the ionic composition of saliva
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ultrafiltrate of plasma and hypotonic to plasma
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how do the striated ducts modifiy the ionic composition of fluid
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reabsorb Na and Cl, secrete K and HCO3 into plasma
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how does flow rate affect concentrations
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higher flow rate= less time for reabsorbtion and saliva more isotonic
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what ion is increased with increasing flow rate
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HCO3 (secretion into plasma) because its secretion is stimlulated when salivation stimulated
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when does flow rate increase
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eating
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what is xerostomia
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lack of salivary secretion
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what can cause xerostomia
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chronic infection of buccal mucoas and dental caries, antidepressants and Sjogrens
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what are the 2 phases of swallowing
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oral (voluntary) and pharyngeanl (involuntary)
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what initates the oral phase of swallowing
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collecting bolus of food and forcing it into oropharynx by pushing it up and back against hard palate
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what is the process of the pharyngeal phase of swallowing
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1. nasopharynx closed by soft palate and breating inhibited
2. laryngeal muscles contract to close glottis and elevate larynx 3. peristalsis begins to propel food toward esophagus 4. upper esophageal sphincter relaxes and allows contraction of contstrictor muscles in pharynx to move mater into esophagus |
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dysphagia
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difficulty in swallowing; caused by neurological disorders
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structure of esophagus
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upper 1/3 striated muscle, lower 1/2 smooth muscle
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function of upper esophageal sphincter
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separates esophagus from oral cavity and prevents entry of air
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function of lower esophageal sphincter
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separates esophagus from stomach and prevents entry of gastric acid
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what initates primary peristaltic contraction
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swallowing, it creates a zone of increased pressure behind bolus
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what happens as bolus reaches LES
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sphincter relaxes, allows bolus into stomach and then contracts preventing reflux
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what initiates the secondary peristaltic contraction
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presence of food in esophagus which stretches mechanical receptors, continues until all food is removed
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what is GERD caused by
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decreased tone of LES-reflux of stomach acid
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what does GERD cause
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heartburn and esophagitis
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how is GERD treated
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lifestyle changes, medications, surgery
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what will long term exposure to acid lead to
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Barrett's esophagus causing metaplasia
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what is achalasia
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neuromuscular disorder of lower 2/3 of esophagus leading to absence of peristalsis and failure of LES to relax
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what is the outcome of achalasia
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food accumulates in esophagus and takes hours to enter stomach
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what do patients with achalasia experience
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dysphagia, regurgitation of ingested food and weight loss
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how is achalasia treated
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drugs, surgery to relax LES and endoscope
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what causes bleching (eructation)
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air swallowed during eating or drinking; when LES relaxes during swallowing, air/gas enters esophagus and is regurgitated
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what are the 2 function areas of the stomach and their functions
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orad- receives ingested meal
caudad- responsible for contractions that mix food and propel it into duodenum |
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receptive relaxation
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food enters the orad region and stomach opens and allows food in without increasing pressure; mediated by vagovagal reflex
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when does mixing occur in the stomach
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presence of food causes caudad stomach to increase contractions therefore mixing food with gastric acids
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chyme
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food mixed into a pasty consistency
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where do peristaltic contractions originate in the stomach
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midstomach and proceed caudally; velocity and force of contraction increases as moved distally
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where do slow waves originate
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in pacemaker near border of orad and caudad
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retropulsion
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wave of contraction closes antrum and pyloric sphincter before chyme reaches there and this causes chyme to be propelled back into stomach to be mixed
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migrating myoelectric complex
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contractions that occur every 90 minutes during fasting to clear the stomach of any residual food
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what type of foods leave the stomach faster
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carbohydrate faster than protein faster than fats
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what controls the rate of food leaving the stomach
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inversely proportional to pressure in orad stomach; increase pressure longer it takes food to leave stomach (increases during digestive period)
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what inhibits gastric emptying
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1. high fat or protein digestion products
2. increased distension of orad stomach 3. increased pressure in small intestine 4. decreased frequency and force of peristaltic contractions in caudad |
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gastroparesis
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impaired or delayed emptying; produces symptoms of fullness, loss of apppetite and nausea
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dumping syndrome
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occurs when lower end of small intestine fills too quickly with undigested food from the stomach; usually a result of stomach surgery
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oxyntic gland mucosa
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region of stomach for secretory function; located in proximal 80% and secretes acid, pepsinogen, intrinsic factor and mucus
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pyloric gland mucosa
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distal 20% of stomach and secretes gastrin
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paritel cells
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secrete acid and intrinsic factor
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chief cells
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secrete pepsinogen
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mucous neck cells in oxyntic gland
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secrete mucus
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gastric juice has 4 components
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1. HCl
2. pepsin 3. mucus 4. intrinsic factor |
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functions of HCl
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begins digestion of protein, converts pepsinogen to pepsin and provide optimal pH, kills bacteria that enter stomach
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function of pepsin
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digests protein; stimulated by vagus and acid
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function of mucus
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protective coating for stomach and lubricant and barrier between cells and ingested material
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what is the soluble form of mucus
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mixes with other secretions of glands and lubricates chyme; not present in resting stomach; secreted by mucus neck cells
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what secretes insoluble form of mucus
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surface epithelial cells in resting stomach in response to chemical or physical irritation
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what forms the unstirred layer
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insoluble mucus
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function of unstirred layer
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traps dead cells and forms protective coat; HCO3 also trapped maintaining neutrality of stomach surface
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what happens to insoluble mucus
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on contact with acid passes into duodenum with chyme
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functin of intrinsic factor
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necessary for absorption of B12
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what does an absence of intrinsic factor lead to
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pernicious anemia
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function of paritel cells
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secrete HCl into lumen of stomach and HCO3 into bloodstream
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how is H formed in paritel cells
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from dissociation of water; it is secreted into the lumen in exchange for K
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what enzyme forms HCO3
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carbonic anhydrase
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what is exchanged for HCO3
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Cl enters the cell and HCO3 leaves
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alkaline tide
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created by HCO3 in venous blood; increases pH; presence of so much HCO3 in blood by paritel cells
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what happens at low(basal) rates?
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gastric juice primarily NaCl from nonparitel secretion
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What 3 things stimulate acid secretion
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Ach
histamine gastrin all 3 required for production |
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how does Ach stimulate acid secretion
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binds to muscarinic receptors, activates phospholipase C and causes release of Ca
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how does histamine cause acid release
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binds to H2 receptors on paritel cells and activates adenylate cyclase
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how does gastrin stimulate gastrin release
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binds to gastrin receptors on paritel cells, activates phospholipase C and causes release of Ca
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what is potentiation?
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when response to simulataneous administration of 2 stimulants greater than sum of responses to either agent given alone
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what potentiates the actions of gastrin and Ach
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histamine
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what is the function of histamine receptor blockers
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can inhibit acid secretion because they block action of histamine therefore blocking action of Ach and gastrin
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what does Ach potentiate
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histamine and gastrin
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what stimulates the synthesis of histamine
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gastrin and Ach but gastrin more
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what inhibits acid secretion in the stomach
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low pH and chyme in duodenum
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what hormone inhibits acid secretion when pH gets too low in the stomach
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somatostatin
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what occurs in the basal phase of acid secretion
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occurs in absence of all gastric stimulation, circadian rhythm (highest at night)
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what initates the cephalic phase
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thought, sight, taste and smell of food
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how does vagus nerve increase acid secretion during the cephalic phase
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Ach directly stimulates paritel cells and Ach causes release of GRP
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what initates the gastric phase of acid secretion
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entry of food into stomach
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during what phase is the largest amount of gastrin secreted
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gastric phase
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how does food entering the stomach cause acid release
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1. stomach distends
2. stretch receptors activated 3. initate vagovagal reflexes 4. gastrin release stimulated and acid secretion stimulated via Ach |
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what nutrient stimulates gastric secretion
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protein
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what other substances stimulate acid secretion
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Ca and caffeine
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what inhibits secretion of acid in the stomach
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acid itself
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what initates the intestinal phase
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presence of protein digestion products in duodenum; duodenum secretes gastrin which then stimulates acid secretion
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when does a gastric ulcer occur
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when protective barrier of stomach breaks down, injuring of mucosa by acid
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what are more common, duodenal or gastric ulcers
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duodenal
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when does pain during eating occur
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gastric ulcers
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what is the pathophysiology of duodenal ulcers
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too much acid, gastrin and pepsin; no control mechanism for acid production
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what can cause ulcers
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H. pylori, NSAIDS and alchol
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what is the Tx for ulcers
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proton-pump inhibitors, antibiotics and pepto-bismol
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what is another word for vomiting
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emesis
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definition of vomiting
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forceful expulsion of gasric and intestinal contents through mouth
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where does vomiting begin?
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distal small intestine as a wave of reverse or anti-peristalsis
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what is retching
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involves all involunatary motions of vomiting without production of vomitus
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what accompanies vomiting
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increased salivation, sweating, rapid breathing and irregular heartbeat
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where is the vomiting center
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medulla
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what activates the afferents for vomiting
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tickling back of throat, distension of stomach or duodenum, vestibular stimulation and painful injury to genitourinary tract
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what does stimulation of second separate medullary area lead to
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retching without vomiting
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what does direct activation of the vomiting center cause
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vomiting without nausea or retching
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where is teh chemoreceptor trigger zone
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fourth ventricle
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what activates the CTZ?
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emetics, radiation and motion sickness
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what are some effects of protracted vomiting
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metabolic alkalosis
hypokalemia hyponatremia |
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where do the major parts of digestion occur
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duodenum and jejunum
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where are the fold of Kerckring?
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longitudinal folds on the surface of the small intestin
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purpose of villi
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increase surface area
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another name for microvilli
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brush border
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where are the crypts located
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project down into surface at base of each villus; 3 crypts/villus
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3 cells of the smaill intestin
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enterocytes, goblet cells and crypt cells
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function of enterocytes
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digestion, absorption and secretion
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function of goblet cells
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secrete mucus; interspersed with enterocytes
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function of crypt cells
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secrete fluids and electrolytes
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function of small intestine
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mix chyme with digestive juices and bile to facilitate digestion and absorption
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types of contraction in the small intestine
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segmentation, peristalitic and migrating motility complex
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most common type of contraction in small intestin
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segmentation
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how does segmentation work
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smooth muscle contracts pushing chyme toward stomach and colon, when muscle relaxes chyme returns to original segment to mix with digestive juices
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where is the higher frequency of contractions
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proximal intestine to propel it downward toward colon
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purpose of peristalsis in small intestine
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propel chyme down small intestine; only moves short distance
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how often does the migrating motility complex occur
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every 90 minutes to clear remaining chyme from small intestine
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do intestinal slow waves trigger contraction by themselves or through spike potentials
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through spike potentials
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what is the strength of the contraction proportional to
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frequency of spikes; greater slow wave amplitude, greater frequency therefore greater contraction
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does the frequency of slow waves increase distally
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no, decreases
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what affects the motility of small intestine
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higher centers of nervous systme
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peristaltic reflex
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contraction that moves intestinal contents along small intestine; initated by chyme
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intestinointestinal reflex
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overdistension of one segement inhibits contractile activity in the rest of the intestine; prevents movement of material into already distended segment of bowel
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gastroileal reflex
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gastric secretion and emptying triggers increased peristalsis in ileum causing relaxtion of ileocecal sphincter and movement of ileal contents into large intestine
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what do acinar cells secrete
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petidases, lipases and amylases
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what do ductule cells secrete
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pancreatic juice containing high HCO3
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is pancreatic juice alwasy isotonic with plasma
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yes
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what is higher in plasma
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HCO3
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what is lower in plasma
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Cl and K is equal
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what is pancreatic juice composed of at lowest flow rates
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Na and Cl
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what is pancreatic juice composed of at high flow rates
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Na and HCO3
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what enzymes are secreted in the active form
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lipase and amylase
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what are pancreatic proteases
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trypsin and chymotrypsin which are secreted as inactive precursors
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why is trypsin inhibitor secreted
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to protect pancreas from autodigestion
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what neurotransmitter acts on acinar and ductule cells
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Ach during gastric and cephalic phase
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what stimulates the intestinal phase in the small intestine
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acid and fat and protein digestion products in duodenum
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where is acid released from in the small intestine
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S cells in the duodenum
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where does secretin act on the small intestin
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acts on ductule cells to increase HCO3 release
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what triggers CCK release from I cells
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fata and protein digestion products
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what is CCK's function in the small intestin
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acts on acinar cells to increase enzyme secretion
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what else stimulates enzyme secretion from the pancreas
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vagovagal reflex that was initated by acid and fat and protein products
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what potentiates teh effect of secretin
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CCk and Ach
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what causes pancreatitis
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chronic alcoholism or gallstones
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acute symptoms fo pancreatitis
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severe abdominal pain, swollen and tender abdomen, nausea and vomiting, diarrhea and fever
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what are the serum amylase and lipase levels in pancreatitis
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greatly elevated
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