What does the basic electrical rhythm (BER) of the small intestine relate to?
What is the consequence of the frequency gradient of intestinal slow waves?
What is countercurrent blood flow in the GI tract?
What role do interstitial cells of Cajal (ICCs) play in the GI tract?
Which neurotransmitters are classified as excitatory in the enteric nervous system?
When does the swallowing sequence become automatic?
What causes high basal tone in the upper and lower esophageal sphincters?
What is the difference between primary and secondary peristalsis?
What are the roles of the stomach in digestion?
What factors affect the rate of gastric emptying?
What is segmentation in the small intestine?
What is the migrating motility complex (MMC)?
What is the gastroileal reflex?
What distinguishes colonic motor activity during mass movement?
What triggers reflexive defecation?
What are the major phases of GI tract regulation?
What components of saliva are important for oral hygiene?
What are the major components secreted by the pancreas?
How is chyme neutralized in the duodenum?
What role does CFTR play in pancreatic secretion?
What are the main components of bile as secreted by the liver?
What role does secretin play in bile production?
What is the function of CCK in relation to the gallbladder?
How does the amphipathic structure of bile acids assist fat digestion?
What is the difference between primary and secondary bile acids?
Define enterohepatic circulation.
How are bile acids reabsorbed in the small intestine?
What happens to bile secretion when hepatic portal vein bile acid concentration increases?
What are the functions of somatostatin and histamine in gastric secretion?
How do Na+, K+, and Cl- concentrations in gastric secretion compare to plasma?
What is the protein component of chief cell secretions?
Pepsinogen
What causes an 'alkaline tide' in the hepatic portal venous system after a meal?
Bicarbonate secretion from gastric parietal cells after meal ingestion
What role does HCl play in gastric digestion?
Aids in protein digestion and has little effect on carbohydrates and fats
What stimulates pepsinogen release and how is pepsinogen activated?
Stimulated by gastric distension and acidic pH; activated by HCl
How is the gastric H+-K+ ATPase regulated during acid secretion?
Activated by gastrin and histamine via vesicular fusion with the plasma membrane
Which factors increase and which inhibit gastrin release?
Increased by food intake; inhibited by low gastric pH
What is the mechanism of gastric H+ generation?
Involves carbonic anhydrase, H+-K+ ATPase, and Na+-K+ ATPase
How do ECL cells modulate gastric acid secretion?
ECL cells release histamine which potentiates acid secretion in response to vagal stimulation and gastrin
What effect do acid and fat in the duodenum have on gastric secretion?
They inhibit gastric secretion through feedback mechanisms
What is the role of intrinsic factor in vitamin B12 absorption?
Intrinsic factor is necessary for absorption of vitamin B12 in the small intestine
What causes changes in stomach pH after a protein meal?
Ingestion of protein increases acid secretion, lowering pH
What are common causes of peptic ulcer disease?
H. pylori infection, excessive NSAID use, and stress
How does the stomach help prevent pernicious anemia?
By secreting intrinsic factor necessary for vitamin B12 absorption
What is steatorrhea and how does it affect vitamin absorption?
Steatorrhea is excess fat in stool and causes malabsorption of fat-soluble vitamins
What is the role of the endoplasmic reticulum in enterocytes during lipid absorption?
Processes lipids absorbed across the apical membrane of enterocytes
Define dietary fiber and name common sources.
Plant material that is not digested; common sources are fruits, vegetables, and whole grains
How are sodium and water absorbed in the GI tract?
Sodium is absorbed via active transport and water follows osmotically
What is the approximate normal daily volume of fluid entering the GI tract?
About 7-8 liters per day
What is absorption in the gastrointestinal tract?
Processes by which nutrients, minerals, and water are absorbed and enter the bloodstream
What is the primary function of elimination in the GI tract?
Elimination of non-digestible materials or toxic products
List the major structures of the gastrointestinal tract.
What are the associated organs of the gastrointestinal tract?
What hormone is secreted by G cells and what stimulates it?
Gastrin is secreted by G cells; stimulated by protein digestion products, stomach distention, and vagal stimulation
What are the actions of gastrin?
Stimulates H+ secretion by parietal cells and promotes growth of gastric mucosa
What hormone is secreted by I cells and what stimulates it?
Cholecystokinin (CCK) is secreted by I cells; stimulated by monoglycerides, fatty acids, small peptides, and amino acids
What are the actions of cholecystokinin (CCK)?
Contracts gallbladder, relaxes sphincter of Oddi, stimulates pancreatic enzyme secretion, and inhibits gastric emptying
What hormone is secreted by S cells and what stimulates it?
Secretin is secreted by S cells; stimulated by H+ ions and fatty acids
What are the actions of secretin?
Increases pepsin secretion and stimulates pancreatic and biliary bicarbonate secretion
What stimulates secretion of secretin?
Name three actions of secretin on the digestive system.
What is the role of gastric inhibitory peptide (GIP)?
Which hormone is secreted during fasting?
What is the primary function of motilin in the GI tract?
Which stomach cells secrete ghrelin?
What does ghrelin stimulate and regulate?
What are the actions of glucagon-like peptide-1 (GLP-1)?
How does leptin regulate body weight in the hypothalamus?
What is the effect of pancreatic polypeptide on pancreatic secretions?
What common orientation do surfaces of the gastrointestinal tract have?
List the main histological layers of the gastrointestinal tract.
What is the primary function of the enteric nervous system?
Give the typical morphology of GI smooth muscle cells.
What are slow waves in intestinal smooth muscle?
What happens when slow waves reach threshold in GI smooth muscle?
How does GI smooth muscle contraction differ from skeletal muscle?
Which protein initiates contraction in smooth muscle and which enzyme does it activate?
What is the energy source for myosin activation in smooth muscle?
Define phasic versus tonic contractions in the GI tract.
Name three features of the splanchnic circulation.
How much can GI blood flow increase after a meal during active absorption?
Which systems regulate splanchnic blood flow?
What can trigger anticipatory increases in GI blood flow?
Name vasodilator substances that increase GI blood flow during digestion.
What is the villus countercurrent blood flow mechanism?
What pathological consequence can exaggerated oxygen countercurrent exchange cause in the gut?
What is the role of the autonomic nervous system in the gastrointestinal tract?
What is the role of the autonomic nervous system in the gastrointestinal (GI) tract?
It regulates the GI tract through extrinsic and intrinsic components.
What components make up the extrinsic autonomic supply to the gut?
Parasympathetic and sympathetic innervation.
How is the enteric nervous system (ENS) described?
An intrinsic 'minibrain' in the gut that is an independent integrative system containing neurotransmitters found in the CNS.
Which nerve provides parasympathetic innervation to the GI tract?
The vagus nerve.
What are vago-vagal reflex circuits in digestion?
Reflex circuits that control moment-to-moment adjustments in the digestive tract.
What is the general effect of sympathetic nerves on gut function?
They generally exert an inhibitory influence on motor and secretory functions.
Where do sympathetic nerves supplying the gut originate?
In the thoraco-lumbar region of the spinal cord (T8-L2).
What neurotransmitter is primarily released by postganglionic sympathetic fibers in the gut?
Norepinephrine.
What are the two main plexuses of the enteric nervous system?
The submucosal plexus and the myenteric plexus.
What is the primary function of the myenteric plexus?
It is primarily concerned with the control of motor activity in the gut.
Where is the myenteric plexus located?
Between the longitudinal and circular muscle layers of the intestine.
What functions does the submucosal plexus control?
Motor functions of the muscularis mucosae and mucosal functions such as absorption and secretion.
How does the ENS receive signals?
From local receptors in muscle and mucosa and from the CNS via the autonomic nervous system.
What types of neurons are found in the myenteric plexus?
Both excitatory and inhibitory neurons.
Does the myenteric plexus receive input from extrinsic parasympathetic nerves?
Yes, it receives pre-ganglionic input from extrinsic parasympathetic nerves and also functions independently.
What role do Interstitial Cells of Cajal (ICC) play in gastrointestinal motility?
They are necessary for the normal propagation of slow waves and are responsible for generating them.
What does the submucosal plexus innervate?
The mucosal epithelium and the muscularis mucosae.
What neurotransmitter is primarily released by secretomotor neurons in the small intestine?
Acetylcholine.
What is the effect of postganglionic sympathetic nerves on the mucosal epithelium?
They inhibit secretomotor neurons and promote the absorption of Na+ and Cl-.
What are the three phases of swallowing (deglutition)?
Oral phase, pharyngeal phase, and esophageal phase.
What happens during the oral phase of swallowing?
The tongue separates a bolus and forces it back toward the pharynx, stimulating an involuntary swallowing reflex.
What are the roles of chewing (mastication) in digestion?
Reduces particle size, increases surface area, mixes food with saliva, and lubricates food for swallowing.
What components are involved in chewing?
Both voluntary and involuntary components.
What do sensory neurons in the mucosa detect?
They detect pH, osmolality, viscosity, and volume of chyme, influencing secretomotor neurons.
What is the significance of the muscularis mucosae in the intestine?
It assists epithelial secretion by contracting, although its innervation from submucosal neurons is not fully understood.
How are the myenteric and submucosal plexuses related?
They are interconnected, suggesting coordination of motility with epithelial function.
What is the role of serotonin (5HT) in the enteric nervous system as stated?
It influences secretomotor neurons.
What is the role of serotonin (5HT) in the enteric nervous system?
What effect does norepinephrine have on the myenteric plexus?
What is the primary function of the circular muscle layer in the intestine?
What significance does the muscularis have in the gastrointestinal tract?
What role do mast cells play in the mucosal layer?
What is the function of the muscularis mucosae?
Which neurotransmitters do submucosal neurons release toward secretory cells?
What happens during the pharyngeal phase of swallowing?
What occurs during the esophageal phase of swallowing?
What is the role of the swallowing center?
What prevents air entry into the esophagus?
What prevents gastric contents from refluxing into the esophagus?
What are the three muscle layers of the esophagus?
What type of muscle composes the upper one third of the esophagus?
What characterizes the middle one third of the esophagus?
What type of muscle is found in the lower one third of the esophagus?
What innervation do the striated muscle regions of the esophagus receive?
Where are the cell bodies of nerves projecting to the upper esophagus located?
Which spinal segments give rise to sympathetic fibers to the esophageal body?
What neurotransmitters are released by intrinsic nerves in the myenteric plexus?
What initiates a primary peristaltic wave in the esophagus?
What triggers a secondary peristaltic wave in the esophagus?
What is the primary driving force moving a bolus toward the stomach during peristalsis?
How is peristalsis coordinated in the skeletal muscle region of the esophagus?
What controls peristalsis in the smooth muscle portion of the esophagus?
What contraction does the longitudinal muscle show in response to electrical stimulation?
What is the onset response of circular muscle to stimulation?
What causes LES relaxation during swallowing?
What produces the tone of the LES?
What neurotransmitter mediates relaxation of the lower esophageal sphincter (LES)?
What molecule is implicated in LES relaxation alongside VIP?
What primarily determines the resting tone of the LES?
What is the effect of calcium channel blockers on LES tone?
Which neurotransmitter increases LES pressure?
Name a hormone that increases LES pressure.
Give one agent that decreases LES pressure.
What is Achalasia?
What can accumulate in the esophagus due to Achalasia?
What condition is characterized by uncoordinated contractions of the esophagus?
What is Nutcracker Esophagus?
What is Gastroesophageal Reflux Disease (GERD)?
Name common symptoms of GERD.
What major risk is associated with Barrett's esophagus?
What is a major risk factor for developing Barrett's epithelium?
What diagnostic test involves visual examination of the esophagus?
What does manometry measure in the esophagus?
What are the three primary motor functions of the stomach?
Which sphincters separate gastric contents from the intestinal tract?
What is the resting membrane potential trend in stomach smooth muscle toward the pylorus?
What is the role of gastric pacemaker cells?
What is receptive relaxation of the stomach?
What reflex type mediates receptive relaxation?
What detects gastric distention during receptive relaxation?
What are the two types of innervation in the stomach?
Which nerve fibers are more numerous in the vagus and splanchnic nerves?
What is the primary function of the stomach fundus?
What is the primary function of the stomach antrum?
Which neurotransmitters cause relaxation of the stomach wall?
What happens to the upper one third of the stomach after food entry?
What is the significance of the latency gradient in the smooth muscle esophagus?
What is the difference between primary and secondary peristaltic waves?
What roles do vagal and sympathetic nerves play in esophageal function?
Which neurotransmitters mediate relaxation of the stomach wall?
Nitric Oxide (NO) and Vasoactive Intestinal Polypeptide (VIP)
How do the upper one third stomach contractions move contents after food entry?
Slow sustained contractions gradually push contents from proximal to distal stomach
What is retropulsion in gastric motility?
Backward movement of antral contents toward the body, important for mixing stomach contents
How does the pyloric sphincter affect gastric emptying of liquids versus solids?
Its narrow diameter allows liquids to empty more rapidly than solids
What are migrating motor complexes (MMC) in the stomach?
Periodic gastric contractions occurring about every 90 minutes during fasting to clear remaining food
Name key factors that influence gastric emptying.
How does duodenal acid affect gastric emptying?
Acid in the duodenum releases secretin, which decreases gastric emptying by inhibiting antral contractions and stimulating pyloric sphincter contraction
What is the effect of hypertonic or hypotonic solutions on gastric emptying?
They empty slower than isotonic solutions due to duodenal osmoreceptor activation that inhibits gastric motility
Which hormones are listed as regulating gastric emptying?
Gastrin, cholecystokinin (CCK), and gastric inhibitory peptide (GIP)
What is gastroparesis?
A condition of delayed gastric emptying, often due to mechanical obstruction, diabetes, or surgical procedures
What causes dumping syndrome?
Sudden delivery of hypertonic fluid to the duodenum, leading to nausea and dizziness
What are the three sections of the small intestine?
Duodenum Jejunum Ileum
What is the role of the myenteric plexus in the small intestine?
It coordinates the motor function of the longitudinal and circular muscle layers
How does the mucosal layer of the small intestine enhance absorption?
By providing a large surface area through folds, villi, and crypts
What is the function of the submucosal plexus?
It regulates the function of the muscularis mucosae and epithelial cells
What is the significance of the gastric motility 'brake' mechanism?
It protects the duodenum from harmful acid and prevents rapid gastric emptying that could overwhelm pancreatic enzymes
How does meal composition affect gastric emptying rates for glucose, protein, and fat?
Glucose empties faster than protein, which empties faster than fat due to inhibitory responses to duodenal contents
What triggers gastrin release in the stomach?
Peptides and amino acids in the stomach and duodenum trigger gastrin release from G cells
How must gastric emptying be regulated relative to nutrient absorption?
It must be regulated to allow adequate time for neutralization of gastric acid and absorption of nutrients
What occurs during vomiting (emesis)?
Forced expulsion of stomach and intestinal contents, usually preceded by nausea and retching
What is the effect of pain on gastric motility?
Pain depresses gastric contractions, inhibiting gastric motility
How does duodenal distension affect gastric motility?
Distension of the duodenum inhibits gastric peristalsis and slows gastric emptying
What role does CCK play in gastric emptying?
CCK slows gastric emptying to ensure adequate time for digestion and absorption of fats
How does gastric volume impact emptying rate?
The stomach empties in proportion to the volume of gastric contents
What is the primary opposing relationship between stomach and duodenum regarding emptying?
The stomach promotes gastric emptying but the duodenum inhibits emptying
What is the primary function of the stomach in relation to gastric emptying?
The stomach promotes gastric emptying but the duodenum opposes it by inhibiting emptying.
What structures at the tip of each villus increase surface area?
Microvilli, which increase surface area a further twenty-fold.
What are slow waves in the small intestine?
Rhythmic episodes of spontaneous depolarization of 5–15 mV lasting 1–5 seconds, also called basal electrical rhythm (BER).
What initiates slow waves in the small intestine?
Interstitial Cells of Cajal initiate slow waves.
What is the frequency of slow waves in the duodenum?
Approximately 12 per minute.
What is the frequency of slow waves in the ileum?
Approximately 8 or 9 per minute.
What role do slow waves play in small intestinal motility?
They establish the frequency, direction, and velocity of rhythmic peristalsis.
Which hormone is secreted during fasting that increases smooth muscle contraction?
Motilin is secreted during fasting and increases smooth muscle contraction.
What characterizes Phase I of the migrating motor complex (MMC)?
A period of relative quiescence lasting about 70 minutes.
What occurs during Phase II of the MMC?
Intermittent motor activity with 1–5 contractions occurring with each slow wave.
What is the function of Phase III of the MMC?
To clear the small intestine of undigested residue and debris ('Housekeeper activity').
What is segmentation contraction in the small intestine?
A contraction that mixes chyme and facilitates its exposure to the absorptive surface.
What is peristalsis in the intestine?
A motility pattern in an oral to aboral sequence that propels chyme through the intestine.
State the Law of the Intestine.
Stimulation at one locus induces contraction above and relaxation below the point of stimulation.
What are the primary functions of the large intestine?
To store fecal material, extract water from luminal contents, and move fecal material toward the rectum.
What is ileus?
A state of no muscle contractility resulting in a partial or complete non-mechanical obstruction.
What is spasm of the circular muscle?
Maximal contraction due to lack of activity of inhibitory neurons.
What is the role of the ileocecal junction?
To control the flow of chyme between the small and large intestine through a sphincter and valve.
How does ileal distension affect the ileocecal sphincter?
Distension of the ileum relaxes the ileocecal sphincter, allowing chyme to pass into the large intestine.
What happens to motilin levels after a meal?
Motilin levels fall after a meal.
What is the primary type of contraction following a meal?
Segmentation contractions are the primary type following a meal.
What is the significance of a BER gradient along the intestine?
A BER gradient causes a higher frequency of segmentation in the proximal intestine.
How do autonomic nerves affect intestinal smooth muscle excitability?
Parasympathetic nerves enhance excitability; sympathetic nerves inhibit excitability.
What is the primary purpose of segmentation contractions?
To thoroughly mix chyme with digestive juices and facilitate contact with the absorptive surface.
What is the typical distance propagated by intestinal peristaltic waves?
Peristaltic waves typically propagate short distances of 3–5 cm.
What is the intestino-intestinal reflex?
A reflex that inhibits contractile activity in other intestinal segments when one segment is overdistended.
Does the colon secrete digestive enzymes?
No; the colon does not secrete digestive enzymes.
What role does mucus play in the colon?
The colonic epithelium secretes mucus to aid the movement of fecal material.
What are teniae coli?
Three bands of longitudinal muscle in the colon.
What are haustra in the colon?
Bulges in the circular muscle of the colon caused by the teniae coli.
What effect does vagal stimulation have on the proximal colon?
Vagal stimulation produces segmental contractions in the proximal colon.
What type of contractions do pelvic nerves induce in the distal colon?
Pelvic nerves induce tonic propulsive contractions in the distal colon.
How do sympathetic and parasympathetic stimulation affect colonic muscle tone?
Parasympathetic stimulation leads to contraction; sympathetic stimulation causes relaxation.
What are the three main motility patterns in the colon?
What is the primary characteristic of mixing movements in the colon?
There is no net movement; contents are shuttled back and forth.
What is haustral migration in the colon?
A motility pattern that results in net movement of chyme in an aboral direction.
What is mass movement in the colon?
The least frequent motility pattern that moves luminal contents over long distances in an aboral direction.
How does transit time in the colon compare with the small intestine?
Transit time in the colon is days, while in the small intestine it is hours.
What is the gastrocolic reflex?
Distension of the stomach by food increases the motility of the colon.
What composes the internal anal sphincter and what is its resting state?
Circular smooth muscle that is tonically contracted.
What causes the internal anal sphincter to relax?
Activation of parasympathetic nerves via the release of VIP.
What type of muscle composes the external anal sphincter?
Skeletal muscle.
What is the role of the pudendal nerve regarding the external anal sphincter?
It provides excitatory innervation to the external anal sphincter.
What initiates the defecation reflex?
Mild distension of the rectum activates the rectosphincteric reflex.
Define constipation as given in the text.
Slow transit of chyme through the colon resulting in excess water removal.
What is Hirschsprung's disease?
A congenital disorder resulting from the absence of intrinsic innervation of the colon.
What characterizes diverticular disease?
Herniation of the mucosa and submucosa through the muscularis propria.
How is irritable bowel syndrome (IBS) characterized?
Altered bowel function and abdominal pain without detectable structural abnormality.
What conditions are included under inflammatory bowel disease (IBD)?
What is the primary symptom pattern of IBD?
Symptoms consistent with altered motility, such as abdominal pain and diarrhea.
What role does slow wave frequency play in the colon?
It governs the rate of colonic contractions.
How does slow wave frequency change as it moves distally in the colon?
It increases in the ascending and first half of the transverse colon.
How does Crohn's disease differ from ulcerative colitis?
Crohn's disease is associated with transmural inflammation and more frequent anal lesions.
What is the colon's primary defensive mechanism against microorganisms?
Microbial ecology due to massive normal flora.
What is dysbiosis?
Disturbances in normal levels or localization of local microflora that can lead to pathologic conditions.
What can prolonged antibiotic treatment cause in the gut?
Pseudomembranous colitis due to proliferation of Clostridium difficile.
Approximately how much flatus does a normal human expel per day?
About 150 cc.
What are the sources of gases in the gastrointestinal tract?
What is the role of the gut microbiome established after birth?
It is essential for immune cell differentiation and maintenance and alters with diet and environment.
What are the major components of saliva?
Water, electrolytes, mucins, and enzymes such as amylase and lipase.
What is the function of salivary amylase?
It helps in the digestion of carbohydrates.
What are the two types of acinar cells in salivary glands?
Serous acinar cells and mucous acinar cells.
How does saliva assist in oral hygiene?
By washing away food particles that bacteria feed on.
What is the salivon?
The functional unit of the salivary gland.
What is the salivon in salivary glands?
What is the primary role of the acinus in salivary glands?
What is the function of myoepithelial cells in salivary glands?
How does saliva help with oral hygiene?
Which inorganic constituents are found in saliva?
Which organic constituents are found in saliva?
What is the significance of mucous in saliva?
What is the primary antibacterial function of lactoferrin in saliva?
What antibacterial role does muramidase play in saliva?
How does increasing salivary flow rate affect electrolyte composition?
How does salivary HCO3- change with increased flow rate?
During ductal modification of saliva, which ions are secreted and which are absorbed?
How does the Na+/K+-ATPase pump contribute to saliva production?
How do parasympathetic and sympathetic stimulation affect salivary secretion?
What are the differences between parasympathetic and sympathetic salivary stimulation?
How does parasympathetic stimulation increase salivary blood flow?
What is xerostomia and its effects?
What is Sjogren's Syndrome?
What condition is characterized by inflammation of the parotid glands?
What is the primary function of the pancreas?
What are the two main constituents of pancreatic juice?
What are acinar cells in the pancreas?
What is the function of pancreatic ductal cells?
How is bicarbonate (HCO3-) secreted into pancreatic juice?
What is the role of enterokinase in pancreatic secretion?
What stimulates pancreatic secretion neurologically?
What are the Islets of Langerhans in the pancreas?
What major factor influences the number of bacteria in the colon?
What stimulates HCO3- and water secretion from pancreatic duct cells?
Secretin
What triggers release of cholecystokinin (CCK)?
Presence of amino acids and fats in the duodenum
What effect does CCK have on pancreatic secretion?
Stimulates enzyme secretion from acinar cells
What is the role of enterokinase in pancreatic secretion?
Activates trypsinogen to trypsin, which then activates other proenzymes
How do vago-vagal reflexes affect pancreatic secretion?
Increase enzyme secretion from acinar cells and HCO3- secretion from duct cells
What is the composition of pancreatic juice relative to plasma at different secretion rates?
Pancreatic juice is isotonic to plasma at all rates of secretion
Which cation is primary in pancreatic juice?
Sodium (Na+)
What are the principal anions in pancreatic juice?
What is the role of trypsin inhibitor in pancreatic juice?
Binds free trypsin to prevent premature activation of proenzymes
What is autodigestion regarding pancreatic enzymes?
Pancreatic enzymes digesting each other in the intestinal lumen after substrates are used
What is basal pancreatic enzyme secretion during the interdigestive phase?
About 10% of maximal secretion
How does sympathetic stimulation affect pancreatic secretion?
Inhibits vagal- and secretin-induced secretion and may reduce blood flow
What is the effect of combining different stimulants on pancreatic secretion?
Potentiation: combined stimulants produce a greater effect than the sum of individual effects
What does the basic electrical rhythm (BER) of the small intestine relate to?
What is the consequence of the frequency gradient of intestinal slow waves?
What is countercurrent blood flow in the GI tract?
What role do interstitial cells of Cajal (ICCs) play in the GI tract?
Which neurotransmitters are classified as excitatory in the enteric nervous system?
When does the swallowing sequence become automatic?
What causes high basal tone in the upper and lower esophageal sphincters?
What is the difference between primary and secondary peristalsis?
What is segmentation in the small intestine?
What is the migrating motility complex (MMC)?
What is the gastroileal reflex?
What distinguishes colonic motor activity during mass movement?
What triggers reflexive defecation?
What components of saliva are important for oral hygiene?
What are the major components secreted by the pancreas?
What role does CFTR play in pancreatic secretion?
What are the main components of bile as secreted by the liver?
What is the function of CCK in relation to the gallbladder?
How does the amphipathic structure of bile acids assist fat digestion?
What is the difference between primary and secondary bile acids?
Define enterohepatic circulation.
How are bile acids reabsorbed in the small intestine?
What happens to bile secretion when hepatic portal vein bile acid concentration increases?
What are the functions of somatostatin and histamine in gastric secretion?
How do Na+, K+, and Cl- concentrations in gastric secretion compare to plasma?
What causes an 'alkaline tide' in the hepatic portal venous system after a meal?
Bicarbonate secretion from gastric parietal cells after meal ingestion
What role does HCl play in gastric digestion?
Aids in protein digestion and has little effect on carbohydrates and fats
What stimulates pepsinogen release and how is pepsinogen activated?
Stimulated by gastric distension and acidic pH; activated by HCl
How is the gastric H+-K+ ATPase regulated during acid secretion?
Activated by gastrin and histamine via vesicular fusion with the plasma membrane
Which factors increase and which inhibit gastrin release?
Increased by food intake; inhibited by low gastric pH
What is the mechanism of gastric H+ generation?
Involves carbonic anhydrase, H+-K+ ATPase, and Na+-K+ ATPase
How do ECL cells modulate gastric acid secretion?
ECL cells release histamine which potentiates acid secretion in response to vagal stimulation and gastrin
What effect do acid and fat in the duodenum have on gastric secretion?
They inhibit gastric secretion through feedback mechanisms
What is the role of intrinsic factor in vitamin B12 absorption?
Intrinsic factor is necessary for absorption of vitamin B12 in the small intestine
What causes changes in stomach pH after a protein meal?
Ingestion of protein increases acid secretion, lowering pH
What are common causes of peptic ulcer disease?
H. pylori infection, excessive NSAID use, and stress
How does the stomach help prevent pernicious anemia?
By secreting intrinsic factor necessary for vitamin B12 absorption
What is steatorrhea and how does it affect vitamin absorption?
Steatorrhea is excess fat in stool and causes malabsorption of fat-soluble vitamins
What is the role of the endoplasmic reticulum in enterocytes during lipid absorption?
Processes lipids absorbed across the apical membrane of enterocytes
Define dietary fiber and name common sources.
Plant material that is not digested; common sources are fruits, vegetables, and whole grains
How are sodium and water absorbed in the GI tract?
Sodium is absorbed via active transport and water follows osmotically
What is the approximate normal daily volume of fluid entering the GI tract?
About 7-8 liters per day
What is absorption in the gastrointestinal tract?
Processes by which nutrients, minerals, and water are absorbed and enter the bloodstream
What is the primary function of elimination in the GI tract?
Elimination of non-digestible materials or toxic products
List the major structures of the gastrointestinal tract.
What are the associated organs of the gastrointestinal tract?
What hormone is secreted by G cells and what stimulates it?
Gastrin is secreted by G cells; stimulated by protein digestion products, stomach distention, and vagal stimulation
What are the actions of gastrin?
Stimulates H+ secretion by parietal cells and promotes growth of gastric mucosa
What hormone is secreted by I cells and what stimulates it?
Cholecystokinin (CCK) is secreted by I cells; stimulated by monoglycerides, fatty acids, small peptides, and amino acids
What are the actions of cholecystokinin (CCK)?
Contracts gallbladder, relaxes sphincter of Oddi, stimulates pancreatic enzyme secretion, and inhibits gastric emptying
What hormone is secreted by S cells and what stimulates it?
Secretin is secreted by S cells; stimulated by H+ ions and fatty acids
What are the actions of secretin?
Increases pepsin secretion and stimulates pancreatic and biliary bicarbonate secretion
Name three actions of secretin on the digestive system.
What is the role of gastric inhibitory peptide (GIP)?
What is the primary function of motilin in the GI tract?
What does ghrelin stimulate and regulate?
What are the actions of glucagon-like peptide-1 (GLP-1)?
How does leptin regulate body weight in the hypothalamus?
What is the effect of pancreatic polypeptide on pancreatic secretions?
What common orientation do surfaces of the gastrointestinal tract have?
List the main histological layers of the gastrointestinal tract.
What is the primary function of the enteric nervous system?
Give the typical morphology of GI smooth muscle cells.
What are slow waves in intestinal smooth muscle?
What happens when slow waves reach threshold in GI smooth muscle?
How does GI smooth muscle contraction differ from skeletal muscle?
Which protein initiates contraction in smooth muscle and which enzyme does it activate?
Define phasic versus tonic contractions in the GI tract.
Name three features of the splanchnic circulation.
Which systems regulate splanchnic blood flow?
Name vasodilator substances that increase GI blood flow during digestion.
What is the villus countercurrent blood flow mechanism?
What pathological consequence can exaggerated oxygen countercurrent exchange cause in the gut?
What is the role of the autonomic nervous system in the gastrointestinal tract?
What is the role of the autonomic nervous system in the gastrointestinal (GI) tract?
It regulates the GI tract through extrinsic and intrinsic components.
What components make up the extrinsic autonomic supply to the gut?
Parasympathetic and sympathetic innervation.
How is the enteric nervous system (ENS) described?
An intrinsic 'minibrain' in the gut that is an independent integrative system containing neurotransmitters found in the CNS.
What are vago-vagal reflex circuits in digestion?
Reflex circuits that control moment-to-moment adjustments in the digestive tract.
What is the general effect of sympathetic nerves on gut function?
They generally exert an inhibitory influence on motor and secretory functions.
Where do sympathetic nerves supplying the gut originate?
In the thoraco-lumbar region of the spinal cord (T8-L2).
What neurotransmitter is primarily released by postganglionic sympathetic fibers in the gut?
Norepinephrine.
What are the two main plexuses of the enteric nervous system?
The submucosal plexus and the myenteric plexus.
What is the primary function of the myenteric plexus?
It is primarily concerned with the control of motor activity in the gut.
Where is the myenteric plexus located?
Between the longitudinal and circular muscle layers of the intestine.
What functions does the submucosal plexus control?
Motor functions of the muscularis mucosae and mucosal functions such as absorption and secretion.
How does the ENS receive signals?
From local receptors in muscle and mucosa and from the CNS via the autonomic nervous system.
Does the myenteric plexus receive input from extrinsic parasympathetic nerves?
Yes, it receives pre-ganglionic input from extrinsic parasympathetic nerves and also functions independently.
What role do Interstitial Cells of Cajal (ICC) play in gastrointestinal motility?
They are necessary for the normal propagation of slow waves and are responsible for generating them.
What neurotransmitter is primarily released by secretomotor neurons in the small intestine?
Acetylcholine.
What is the effect of postganglionic sympathetic nerves on the mucosal epithelium?
They inhibit secretomotor neurons and promote the absorption of Na+ and Cl-.
What are the three phases of swallowing (deglutition)?
Oral phase, pharyngeal phase, and esophageal phase.
What happens during the oral phase of swallowing?
The tongue separates a bolus and forces it back toward the pharynx, stimulating an involuntary swallowing reflex.
What are the roles of chewing (mastication) in digestion?
Reduces particle size, increases surface area, mixes food with saliva, and lubricates food for swallowing.
What do sensory neurons in the mucosa detect?
They detect pH, osmolality, viscosity, and volume of chyme, influencing secretomotor neurons.
What is the significance of the muscularis mucosae in the intestine?
It assists epithelial secretion by contracting, although its innervation from submucosal neurons is not fully understood.
How are the myenteric and submucosal plexuses related?
They are interconnected, suggesting coordination of motility with epithelial function.
What is the role of serotonin (5HT) in the enteric nervous system as stated?
It influences secretomotor neurons.
What is the role of serotonin (5HT) in the enteric nervous system?
What effect does norepinephrine have on the myenteric plexus?
What is the primary function of the circular muscle layer in the intestine?
What significance does the muscularis have in the gastrointestinal tract?
What role do mast cells play in the mucosal layer?
Which neurotransmitters do submucosal neurons release toward secretory cells?
What happens during the pharyngeal phase of swallowing?
What occurs during the esophageal phase of swallowing?
What is the role of the swallowing center?
What prevents gastric contents from refluxing into the esophagus?
What are the three muscle layers of the esophagus?
What characterizes the middle one third of the esophagus?
What innervation do the striated muscle regions of the esophagus receive?
Where are the cell bodies of nerves projecting to the upper esophagus located?
What neurotransmitters are released by intrinsic nerves in the myenteric plexus?
What initiates a primary peristaltic wave in the esophagus?
What triggers a secondary peristaltic wave in the esophagus?
What is the primary driving force moving a bolus toward the stomach during peristalsis?
How is peristalsis coordinated in the skeletal muscle region of the esophagus?
What contraction does the longitudinal muscle show in response to electrical stimulation?
What causes LES relaxation during swallowing?
What produces the tone of the LES?
What neurotransmitter mediates relaxation of the lower esophageal sphincter (LES)?
What primarily determines the resting tone of the LES?
What condition is characterized by uncoordinated contractions of the esophagus?
What is Gastroesophageal Reflux Disease (GERD)?
What is a major risk factor for developing Barrett's epithelium?
Which sphincters separate gastric contents from the intestinal tract?
What is the resting membrane potential trend in stomach smooth muscle toward the pylorus?
What is the role of gastric pacemaker cells?
What is receptive relaxation of the stomach?
What are the two types of innervation in the stomach?
Which neurotransmitters cause relaxation of the stomach wall?
What happens to the upper one third of the stomach after food entry?
What is the significance of the latency gradient in the smooth muscle esophagus?
What is the difference between primary and secondary peristaltic waves?
What roles do vagal and sympathetic nerves play in esophageal function?
Which neurotransmitters mediate relaxation of the stomach wall?
Nitric Oxide (NO) and Vasoactive Intestinal Polypeptide (VIP)
How do the upper one third stomach contractions move contents after food entry?
Slow sustained contractions gradually push contents from proximal to distal stomach
What is retropulsion in gastric motility?
Backward movement of antral contents toward the body, important for mixing stomach contents
How does the pyloric sphincter affect gastric emptying of liquids versus solids?
Its narrow diameter allows liquids to empty more rapidly than solids
What are migrating motor complexes (MMC) in the stomach?
Periodic gastric contractions occurring about every 90 minutes during fasting to clear remaining food
Name key factors that influence gastric emptying.
How does duodenal acid affect gastric emptying?
Acid in the duodenum releases secretin, which decreases gastric emptying by inhibiting antral contractions and stimulating pyloric sphincter contraction
What is the effect of hypertonic or hypotonic solutions on gastric emptying?
They empty slower than isotonic solutions due to duodenal osmoreceptor activation that inhibits gastric motility
Which hormones are listed as regulating gastric emptying?
Gastrin, cholecystokinin (CCK), and gastric inhibitory peptide (GIP)
What is gastroparesis?
A condition of delayed gastric emptying, often due to mechanical obstruction, diabetes, or surgical procedures
What causes dumping syndrome?
Sudden delivery of hypertonic fluid to the duodenum, leading to nausea and dizziness
What is the role of the myenteric plexus in the small intestine?
It coordinates the motor function of the longitudinal and circular muscle layers
How does the mucosal layer of the small intestine enhance absorption?
By providing a large surface area through folds, villi, and crypts
What is the function of the submucosal plexus?
It regulates the function of the muscularis mucosae and epithelial cells
What is the significance of the gastric motility 'brake' mechanism?
It protects the duodenum from harmful acid and prevents rapid gastric emptying that could overwhelm pancreatic enzymes
How does meal composition affect gastric emptying rates for glucose, protein, and fat?
Glucose empties faster than protein, which empties faster than fat due to inhibitory responses to duodenal contents
What triggers gastrin release in the stomach?
Peptides and amino acids in the stomach and duodenum trigger gastrin release from G cells
How must gastric emptying be regulated relative to nutrient absorption?
It must be regulated to allow adequate time for neutralization of gastric acid and absorption of nutrients
What occurs during vomiting (emesis)?
Forced expulsion of stomach and intestinal contents, usually preceded by nausea and retching
What is the effect of pain on gastric motility?
Pain depresses gastric contractions, inhibiting gastric motility
How does duodenal distension affect gastric motility?
Distension of the duodenum inhibits gastric peristalsis and slows gastric emptying
What role does CCK play in gastric emptying?
CCK slows gastric emptying to ensure adequate time for digestion and absorption of fats
How does gastric volume impact emptying rate?
The stomach empties in proportion to the volume of gastric contents
What is the primary opposing relationship between stomach and duodenum regarding emptying?
The stomach promotes gastric emptying but the duodenum inhibits emptying
What is the primary function of the stomach in relation to gastric emptying?
The stomach promotes gastric emptying but the duodenum opposes it by inhibiting emptying.
What structures at the tip of each villus increase surface area?
Microvilli, which increase surface area a further twenty-fold.
What are slow waves in the small intestine?
Rhythmic episodes of spontaneous depolarization of 5–15 mV lasting 1–5 seconds, also called basal electrical rhythm (BER).
What role do slow waves play in small intestinal motility?
They establish the frequency, direction, and velocity of rhythmic peristalsis.
Which hormone is secreted during fasting that increases smooth muscle contraction?
Motilin is secreted during fasting and increases smooth muscle contraction.
What characterizes Phase I of the migrating motor complex (MMC)?
A period of relative quiescence lasting about 70 minutes.
What occurs during Phase II of the MMC?
Intermittent motor activity with 1–5 contractions occurring with each slow wave.
What is the function of Phase III of the MMC?
To clear the small intestine of undigested residue and debris ('Housekeeper activity').
What is segmentation contraction in the small intestine?
A contraction that mixes chyme and facilitates its exposure to the absorptive surface.
What is peristalsis in the intestine?
A motility pattern in an oral to aboral sequence that propels chyme through the intestine.
State the Law of the Intestine.
Stimulation at one locus induces contraction above and relaxation below the point of stimulation.
What are the primary functions of the large intestine?
To store fecal material, extract water from luminal contents, and move fecal material toward the rectum.
What is ileus?
A state of no muscle contractility resulting in a partial or complete non-mechanical obstruction.
What is spasm of the circular muscle?
Maximal contraction due to lack of activity of inhibitory neurons.
What is the role of the ileocecal junction?
To control the flow of chyme between the small and large intestine through a sphincter and valve.
How does ileal distension affect the ileocecal sphincter?
Distension of the ileum relaxes the ileocecal sphincter, allowing chyme to pass into the large intestine.
What is the primary type of contraction following a meal?
Segmentation contractions are the primary type following a meal.
What is the significance of a BER gradient along the intestine?
A BER gradient causes a higher frequency of segmentation in the proximal intestine.
How do autonomic nerves affect intestinal smooth muscle excitability?
Parasympathetic nerves enhance excitability; sympathetic nerves inhibit excitability.
What is the primary purpose of segmentation contractions?
To thoroughly mix chyme with digestive juices and facilitate contact with the absorptive surface.
What is the typical distance propagated by intestinal peristaltic waves?
Peristaltic waves typically propagate short distances of 3–5 cm.
What is the intestino-intestinal reflex?
A reflex that inhibits contractile activity in other intestinal segments when one segment is overdistended.
What role does mucus play in the colon?
The colonic epithelium secretes mucus to aid the movement of fecal material.
What are haustra in the colon?
Bulges in the circular muscle of the colon caused by the teniae coli.
What effect does vagal stimulation have on the proximal colon?
Vagal stimulation produces segmental contractions in the proximal colon.
What type of contractions do pelvic nerves induce in the distal colon?
Pelvic nerves induce tonic propulsive contractions in the distal colon.
How do sympathetic and parasympathetic stimulation affect colonic muscle tone?
Parasympathetic stimulation leads to contraction; sympathetic stimulation causes relaxation.
What are the three main motility patterns in the colon?
What is the primary characteristic of mixing movements in the colon?
There is no net movement; contents are shuttled back and forth.
What is haustral migration in the colon?
A motility pattern that results in net movement of chyme in an aboral direction.
What is mass movement in the colon?
The least frequent motility pattern that moves luminal contents over long distances in an aboral direction.
How does transit time in the colon compare with the small intestine?
Transit time in the colon is days, while in the small intestine it is hours.
What is the gastrocolic reflex?
Distension of the stomach by food increases the motility of the colon.
What composes the internal anal sphincter and what is its resting state?
Circular smooth muscle that is tonically contracted.
What causes the internal anal sphincter to relax?
Activation of parasympathetic nerves via the release of VIP.
What is the role of the pudendal nerve regarding the external anal sphincter?
It provides excitatory innervation to the external anal sphincter.
What initiates the defecation reflex?
Mild distension of the rectum activates the rectosphincteric reflex.
Define constipation as given in the text.
Slow transit of chyme through the colon resulting in excess water removal.
What is Hirschsprung's disease?
A congenital disorder resulting from the absence of intrinsic innervation of the colon.
What characterizes diverticular disease?
Herniation of the mucosa and submucosa through the muscularis propria.
How is irritable bowel syndrome (IBS) characterized?
Altered bowel function and abdominal pain without detectable structural abnormality.
What conditions are included under inflammatory bowel disease (IBD)?
What is the primary symptom pattern of IBD?
Symptoms consistent with altered motility, such as abdominal pain and diarrhea.
How does slow wave frequency change as it moves distally in the colon?
It increases in the ascending and first half of the transverse colon.
How does Crohn's disease differ from ulcerative colitis?
Crohn's disease is associated with transmural inflammation and more frequent anal lesions.
What is the colon's primary defensive mechanism against microorganisms?
Microbial ecology due to massive normal flora.
What is dysbiosis?
Disturbances in normal levels or localization of local microflora that can lead to pathologic conditions.
What can prolonged antibiotic treatment cause in the gut?
Pseudomembranous colitis due to proliferation of Clostridium difficile.
What are the sources of gases in the gastrointestinal tract?
What is the role of the gut microbiome established after birth?
It is essential for immune cell differentiation and maintenance and alters with diet and environment.
What are the major components of saliva?
Water, electrolytes, mucins, and enzymes such as amylase and lipase.
What are the two types of acinar cells in salivary glands?
Serous acinar cells and mucous acinar cells.
What is the salivon in salivary glands?
What is the primary role of the acinus in salivary glands?
What is the function of myoepithelial cells in salivary glands?
How does saliva help with oral hygiene?
Which inorganic constituents are found in saliva?
What is the primary antibacterial function of lactoferrin in saliva?
What antibacterial role does muramidase play in saliva?
How does increasing salivary flow rate affect electrolyte composition?
How does salivary HCO3- change with increased flow rate?
During ductal modification of saliva, which ions are secreted and which are absorbed?
How does the Na+/K+-ATPase pump contribute to saliva production?
How do parasympathetic and sympathetic stimulation affect salivary secretion?
What are the differences between parasympathetic and sympathetic salivary stimulation?
How does parasympathetic stimulation increase salivary blood flow?
What is xerostomia and its effects?
What is Sjogren's Syndrome?
What condition is characterized by inflammation of the parotid glands?
What is the primary function of the pancreas?
What are the two main constituents of pancreatic juice?
What are acinar cells in the pancreas?
What is the function of pancreatic ductal cells?
How is bicarbonate (HCO3-) secreted into pancreatic juice?
What stimulates pancreatic secretion neurologically?
What are the Islets of Langerhans in the pancreas?
What is the role of enterokinase in pancreatic secretion?
Activates trypsinogen to trypsin, which then activates other proenzymes
How do vago-vagal reflexes affect pancreatic secretion?
Increase enzyme secretion from acinar cells and HCO3- secretion from duct cells
What is the composition of pancreatic juice relative to plasma at different secretion rates?
Pancreatic juice is isotonic to plasma at all rates of secretion
What is the role of trypsin inhibitor in pancreatic juice?
Binds free trypsin to prevent premature activation of proenzymes
What is autodigestion regarding pancreatic enzymes?
Pancreatic enzymes digesting each other in the intestinal lumen after substrates are used
What is basal pancreatic enzyme secretion during the interdigestive phase?
About 10% of maximal secretion
How does sympathetic stimulation affect pancreatic secretion?
Inhibits vagal- and secretin-induced secretion and may reduce blood flow
What is the effect of combining different stimulants on pancreatic secretion?
Potentiation: combined stimulants produce a greater effect than the sum of individual effects
Saliva - Major components: water, electrolytes (Na+, K+, Cl-, HCO3-), mucins, enzymes (amylase, lipase), antimicrobial agents (lactoferrin, muramidase). - Saliva flow changes composition: increased flow raises Na+ and Cl-; ductal modification secretes K+ and HCO3- while absorbing Na+ and Cl-. - Both parasympathetic (large sustained increase) and sympathetic (small transient increase) stimulation increase saliva; myoepithelial cells eject saliva.
Gastric secretions - Parietal cells: HCl and intrinsic factor; chief cells: pepsinogen (activated by HCl). - Acid secretion requires carbonic anhydrase, H+–K+ ATPase (regulated by gastrin and histamine) and Na+–K+ ATPase. - Somatostatin inhibits acid secretion; histamine from ECL cells potentiates acid release. - "Alkaline tide": postprandial bicarbonate increases in portal blood due to HCl secretion. - Intrinsic factor is essential for vitamin B12 absorption; lack causes pernicious anemia.
Pancreas - Exocrine pancreas secretes an isotonic fluid containing digestive enzymes and high HCO3-. - Ductal cells secrete HCO3- (neutralizes duodenal acid); acinar cells secrete enzymes (zymogens). - Secretin stimulates HCO3- secretion; CCK stimulates enzyme release; vagal reflexes potentiate both. - Trypsinogen activation by enterokinase (enteropeptidase) converts to trypsin, which activates other zymogens; trypsin inhibitor prevents premature activation.
Bile and liver - Bile contains water, ions, bile salts (amphipathic), and bilirubin. - Bile salts emulsify fats to aid lipase action and micelle formation for absorption. - Primary bile acids synthesized from cholesterol in liver; intestinal bacteria convert them to secondary bile acids. - Enterohepatic circulation recycles bile acids from intestine to liver. - Secretin increases hepatic bile production; CCK causes gallbladder contraction and sphincter of Oddi relaxation.
Are you sure you want to delete 0 flashcard(s)? This cannot be undone.
Select tags to remove from 0 selected flashcard(s):
Loading tags...