Flashcards in this deck (153)

• What intrinsic drive primarily determines how much food a person ingests?

  • Hunger
  ingestion hunger
• What determines the type of food a person preferentially seeks?

  • Appetite
  ingestion appetite
• Which teeth provide cutting and which provide grinding during mastication?

  • Incisors: cutting
  • Molars: grinding
  mastication teeth
• What maximum force can jaw muscles produce on incisors and molars during chewing?

  • Incisors: 55 pounds
  • Molars: 200 pounds
  mastication forces
• Which nerve motor branch innervates most chewing muscles and where is chewing controlled?

  • Motor branch of cranial nerve V (trigeminal); control by brain stem nuclei
  mastication neuroanatomy
• Describe the basic chewing reflex sequence that produces rhythmic chewing.

  • Bolus in mouth → reflex inhibition of jaw muscles → jaw drops → stretch reflex → rebound contraction → jaw closes and compresses bolus → inhibition repeats
  mastication reflex
• Name three reasons chewing is important for digestion.

  • Breaks cellulose membranes of fruits/vegetables
  • Increases surface area for enzymes
  • Prevents GI tract excoriation and eases stomach emptying
  mastication digestion
• List the three general stages of swallowing (deglutition).

  • Voluntary stage
  • Pharyngeal stage (involuntary)
  • Esophageal stage (involuntary)
  swallowing deglutition
• Why is swallowing a complicated mechanism in relation to respiration?

  • Pharynx also serves respiration, so it must function as a food tract only for a few seconds without compromising breathing
  swallowing respiration
• How can the provided stomach diagram be used when studying food propulsion and mixing?

  • Use the diagram as an illustration of gastric anatomy and regions involved in mixing and emptying
  stomach diagram
• What action of the tongue propels a food bolus into the pharynx?

  • The tongue presses upward and backward against the palate, propelling the bolus into the pharynx.
  swallowing mastication physiology
• What happens to swallowing after the bolus enters the pharynx?

  • Swallowing becomes entirely or almost entirely automatic and ordinarily cannot be stopped.
  swallowing reflex physiology
• What happens during the pharyngeal stage of swallowing?

  • Trachea is closed
  • Esophagus is opened
  • A fast peristaltic wave forces the bolus into the upper esophagus
  • Entire process occurs in less than 2 seconds
  swallowing pharynx
• How does the soft palate contribute to swallowing?

  • Soft palate is pulled upward to close the posterior nares and prevent reflux into the nasal cavities
  swallowing softpalate
• What is the role of the palatopharyngeal folds during swallowing?

  • Palatopharyngeal folds are pulled medially to form a sagittal slit that selectively allows well-masticated food into the posterior pharynx
  swallowing palatopharyngeal
• Which actions prevent food from entering the trachea during swallowing?

  • Tight approximation of the vocal cords plus epiglottis swinging backward over the laryngeal opening prevent food entry into the trachea
  swallowing larynx
• What changes occur at the upper esophageal sphincter during swallowing?

  • Upper esophageal (pharyngoesophageal) sphincter relaxes as the larynx is pulled upward, allowing food to enter the upper esophagus
  esophagus sphincter
• How does pharyngeal muscle contraction propel the bolus into the esophagus?

  • Entire pharyngeal muscular wall contracts starting superiorly then spreading downward, producing peristalsis that propels the bolus into the esophagus
  pharynx peristalsis
• Which sensory nerves initiate the pharyngeal swallowing reflex and where do they project?

  • Sensory portions of the trigeminal and glossopharyngeal nerves transmit impulses to the medulla oblongata, into or near the tractus solitarius
  nervous swallowing
• Where are the most sensitive tactile areas for initiating the pharyngeal stage located?

  • The most sensitive tactile areas lie in a ring around the pharyngeal opening, with greatest sensitivity on the tonsillar pillars
  sensory pharynx
• Where are the neuronal areas that constitute the swallowing (deglutition) center located?

  • In the reticular substance of the medulla and the lower portion of the pons
  anatomy swallowing
• Which cranial nerves transmit the motor impulses from the swallowing center to the pharynx and upper esophagus?

  • Fifth (V)
  • Ninth (IX)
  • Tenth (X)
  • Twelfth (XII)
  • Also a few superior cervical nerves
  neuroanatomy cranialnerves
• Is the pharyngeal stage of swallowing voluntary or reflexive?

  • Principally a reflex act
  physiology swallowing
• How is the pharyngeal swallowing reflex usually initiated?

  • By voluntary movement of food into the back of the mouth, which excites involuntary pharyngeal sensory receptors
  physiology reflex
• What effect does the pharyngeal stage of swallowing have on respiration?

  • It momentarily interrupts respiration
  physiology respiration
• How long does the entire pharyngeal stage of swallowing usually take?

  • Usually occurs in less than 6 seconds
  physiology timing
• Is the sequence and timing of the swallowing reflex variable between swallows?

  • No — the sequence is the same and the timing of the entire cycle remains constant from one swallow to the next
  physiology consistency
• What happens to respiration during swallowing?

  The swallowing center inhibits the medullary respiratory center, briefly halting respiration for a fraction of the respiratory cycle.
  swallowing respiration
• What are the two types of esophageal peristalsis?

  • Primary peristalsis
  • Secondary peristalsis
  esophagus peristalsis
• What is primary peristalsis in the esophagus?

  Continuation of the peristaltic wave that begins in the pharynx and spreads into the esophagus, passing to the stomach in about 8–10 seconds.
  primary peristalsis
• How does gravity affect transit of swallowed food when upright?

  Gravity helps transmit food to the lower esophagus faster than the peristaltic wave, about 5–8 seconds.
  gravity transit
• What triggers secondary peristalsis in the esophagus?

  Distention of the esophagus by retained food, producing waves until the esophagus is emptied.
  secondary peristalsis
• Which muscles control the upper third of the esophagus and how are they activated?

  Striated muscle in the pharyngeal wall and upper third of the esophagus; controlled by skeletal nerve impulses from glossopharyngeal and vagus nerves.
  muscle upperesophagus
• How is the lower two-thirds of the esophagus controlled?

  Smooth muscle controlled strongly by vagus nerves acting via the esophageal myenteric nervous system.
  muscle loweresophagus
• What happens to esophageal peristalsis after vagus nerve cut and why can food still pass?

  After vagal cuts the myenteric plexus becomes excitable and generates strong secondary peristaltic waves, allowing food to pass despite loss of brain stem swallowing reflexes.
  vagus myenteric
• What is receptive relaxation of the stomach during swallowing?

  A wave of relaxation via myenteric inhibitory neurons precedes the esophageal peristaltic wave, relaxing the stomach and duodenum to receive food.
  receptive stomach
• What is the normal intraluminal pressure of the lower esophageal (gastroesophageal) sphincter?

  About 30 mm Hg of tonic constriction at the lower esophageal sphincter.
  les pressure
• What occurs at the lower esophageal sphincter when a peristaltic swallowing wave arrives?

  Receptive relaxation of the lower esophageal sphincter occurs ahead of the peristaltic wave, allowing easy propulsion of swallowed food into the stomach.
  les relaxation
• What is achalasia in relation to the lower esophageal sphincter?

  A condition in which the lower esophageal sphincter rarely fails to relax satisfactorily, causing impaired relaxation.
  esophagus pathology
• Describe the acidity and enzyme content of stomach secretions.

  Stomach secretions are highly acidic and contain many proteolytic enzymes.
  stomach secretion
• Which part of the esophageal mucosa resists gastric secretions best?

  The lower one-eighth of the esophagus is the part capable of resisting the digestive action of gastric secretions better than the rest.
  esophagus mucosa
• How does the tonic constriction of the lower esophageal sphincter (LES) protect the esophagus?

  Tonic constriction of the LES helps prevent significant reflux of stomach contents into the esophagus except under abnormal conditions.
  les reflux
• What valvelike mechanism helps prevent esophageal reflux at the distal esophagus?

  A short portion of the esophagus that extends slightly into the stomach forms a valvelike closure that caves inward with increased intra-abdominal pressure, preventing reflux.
  reflux mechanics
• What are the three main motor functions of the stomach?

  • Storage of large quantities of food
  • Mixing food with gastric secretions into chyme
  • Slow emptying of chyme into the small intestine at a suitable rate
  stomach motility
• How is food arranged inside the stomach after entering (orientation of newest vs oldest)?

  • Food forms concentric circles
  • Newest food lies closest to the esophageal opening
  • Oldest food lies nearest the outer wall of the stomach
  stomach storage
• What reflex reduces gastric wall tone to allow stomach storage when food stretches the stomach?

  • The 'vagovagal reflex' from the stomach to the brain stem and back reduces tone
  reflex vagus
• What is the relaxed stomach volume limit for accommodation during storage?

  • About 0.8 to 1.5 liters in the completely relaxed stomach
  stomach volume
• Where are gastric glands that secrete digestive juices located in the stomach body?

  • Present in almost the entire wall of the body of the stomach except along a narrow strip on the lesser curvature
  gastric anatomy
• What initiates the stomach's peristaltic mixing waves and how often do they occur?

  • Initiated by the gut wall basic electrical rhythm ('slow waves')
  • Occur about once every 15 to 20 seconds
  electrical motility
• Where do mixing waves begin and toward where do they move?

  • Begin in the mid to upper portions of the stomach wall
  • Move toward the antrum
  mixing peristalsis
• How do peristaltic constrictor rings in the antrum contribute to propulsion?

  • They become more intense in the antrum and provide powerful peristaltic action potential-driven constrictor rings that force antral contents toward the pylorus
  antrum propulsion
• Why does each peristaltic wave expel only a few milliliters into the duodenum?

  • The pyloric opening is small so only a few milliliters or less pass with each wave; pyloric muscle often contracts and further impedes emptying
  pylorus emptying
• What is 'retropulsion' and what role does it play in gastric mixing?

  • 'Retropulsion' is squeezing of antral contents upstream through the peristaltic ring toward the body
  • It is an important mixing mechanism in the stomach
  retropulsion mixing
• What is chyme and what determines its fluidity?

  • Chyme is the thoroughly mixed stomach contents that pass down the gut (murky semifluid or paste)
  • Fluidity depends on amounts of food, water, stomach secretions, and degree of digestion
  chyme digestion
• What are hunger contractions and when do they occur?

  • Intense rhythmic peristaltic contractions in the body of the stomach
  • Often occur when the stomach has been empty for several hours or more
  hunger contractions
• How long can a continuing tetanic contraction sometimes last?

  2 to 3 minutes
  muscle contraction
• In whom are hunger contractions most intense?

  • Young, healthy people
  • People with high gastrointestinal tonus
  hunger physiology
• What factor greatly increases hunger contractions related to blood chemistry?

  Lower than normal blood sugar levels
  hunger metabolism
• What are hunger pangs and where are they felt?

  Mild pain felt in the pit of the stomach
  hunger symptoms
• When do hunger pangs usually begin after the last ingestion of food?

  12 to 24 hours after the last ingestion of food
  hunger timing
• How do hunger pangs change in people in a state of starvation?

  They reach greatest intensity in 3 to 4 days and then gradually weaken in succeeding days
  hunger starvation
• What promotes stomach emptying?

  Intense peristaltic contractions in the stomach antrum
  stomach emptying
• What opposes passage of chyme at the pylorus during stomach emptying?

  Varying degrees of resistance to passage of chyme at the pylorus
  stomach pylorus
• What is the 'pyloric pump' in stomach physiology?

  • The pyloric pump is the pumping action produced by strong peristaltic waves that force chyme from the stomach into the duodenum.
  stomach pyloric
• When do stomach contractions become intense and cause emptying?

  • For about 20% of the time while food is in the stomach, contractions become intense beginning in midstomach and spreading caudally, causing stomach emptying.
  motility peristalsis
• How much pressure can the intense peristaltic contractions generate compared with usual mixing waves?

  • Intense peristaltic contractions often create 50 to 70 centimeters of water pressure, about six times as powerful as usual mixing waves.
  pressure peristalsis
• What is the structural difference of the pylorus compared to earlier portions of the antrum?

  • The pyloric circular muscle thickness becomes 50% to 100% greater than in earlier portions of the stomach antrum.
  anatomy pylorus
• How does the pyloric sphincter behave most of the time?

  • The pyloric sphincter remains slightly tonically contracted almost all the time, though it is usually open enough for fluids to empty easily.
  pyloric sphincter
• How does stomach food volume affect the rate of emptying?

  • Increased food volume promotes increased emptying by stretching the stomach wall, which elicits local myenteric reflexes that accentuate the pyloric pump and inhibit the pylorus.
  regulation volume
• What effect does the hormone gastrin have on stomach emptying?

  • Gastrin has mild to moderate stimulatory effects on gastric motor functions and seems to enhance activity of the pyloric pump, thus promoting stomach emptying.
  hormone gastrin
• Which intestinal region provides the most potent signals to inhibit stomach emptying?

  • The duodenum provides far more potent signals to inhibit stomach emptying than the stomach, controlling emptying to match digestion and absorption rates.
  duodenum regulation
• What reflexes are initiated when food enters the duodenum?

  • Multiple enterogastric nervous reflexes are initiated from the duodenal wall that pass back to the stomach to slow or stop stomach emptying when duodenal chyme volume is excessive.
  enterogastric reflex
• What are the three neural pathways mediating enterogastric inhibition from the duodenum to the stomach?

  • Enteric nervous system in the gut wall
  • Extrinsic nerves via prevertebral sympathetic ganglia and inhibitory sympathetic fibers
  • Vagus nerves to the brain stem that reduce vagal excitatory signals
  physiology gi neuro
• What are the two main effects of enterogastric inhibitory reflexes on stomach motility?

  • Strong inhibition of the pyloric pump propulsive contractions
  • Increased tone of the pyloric sphincter
  physiology stomach motility
• Name five types of duodenal factors that can initiate enterogastric inhibitory reflexes.

  • Duodenal distention
  • Irritation of the duodenal mucosa
  • Acidity of duodenal chyme
  • Osmolality of the chyme
  • Breakdown products of chyme (especially protein breakdown products)
  duodenum feedback gi
• How quickly can enterogastric inhibitory reflexes become strongly activated in response to irritants or acids?

  • Often in as little as 30 seconds
  timing physiology gi
• At what duodenal chyme pH do enterogastric reflexes frequently block further release of acidic stomach contents?

  • When duodenal chyme pH falls below about 3.5 to 4
  ph duodenum regulation
• Why does the enterogastric reflex block further acidic stomach emptying when duodenal pH is very low?

  • To prevent more acid entering the duodenum until the chyme can be neutralized by pancreatic and other secretions
  function protection gi
• Which chyme components especially elicit inhibitory enterogastric reflexes?

  • Breakdown products of proteins and, perhaps to a lesser extent, of fats
  nutrients duodenum feedback
• What duodenal stimulus is the most potent trigger for release of hormones that inhibit gastric emptying?

  Fats entering the duodenum
  gi hormones
• Which hormone from the jejunal mucosa is the most potent inhibitor of stomach motility and pyloric pump?

  Cholecystokinin (CCK)
  cck gi
• How do hormones released from the upper intestine inhibit gastric emptying?

  They travel via the blood to the stomach, inhibit the pyloric pump, and increase pyloric sphincter contraction
  physiology feedback
• Name two other intestinal hormones that can inhibit stomach emptying besides CCK.

  • Secretin
  • Glucose-dependent insulinotropic peptide (GIP)
  hormones gi
• What mainly stimulates release of secretin from the duodenal mucosa?

  Gastric acid entering the duodenum
  secretin gi
• What is the primary physiological effect of GIP at normal concentrations?

  Stimulation of insulin secretion by the pancreas
  gip endocrine
• List duodenal conditions that slow gastric emptying via inhibitory feedback.

  • Too much chyme in the small intestine
  • Excessively acidic chyme
  • Chyme with too much unprocessed protein or fat
  • Hypotonic or hypertonic chyme
  • Irritating chyme
  regulation gi
• Which stomach factors moderately influence rate of gastric emptying?

  • Degree of stomach filling
  • Excitatory effect of gastrin on peristalsis
  stomach gastrin
• Into what two functional categories are small intestine movements commonly divided?

  • Mixing contractions (segmentation)
  • Propulsive contractions (peristalsis)
  motility smallintestine
• What triggers segmentation contractions in the small intestine?

  Stretching of the intestinal wall when the lumen becomes distended with chyme
  physiology intestine
• Describe the appearance produced by segmentation contractions in the small intestine.

  The intestine is divided into spaced segments that look like a chain of sausages
  physiology motility
• How do successive segmentation contractions change location along the intestine?

  As one set relaxes, a new set often begins mainly at new points between the previous contractions
  physiology motility
• At what rate do segmentation contractions 'chop' chyme and what is the purpose?

  They chop chyme two to three times per minute to promote progressive mixing with intestinal secretions
  physiology digestion
• What generates the basic electrical rhythm that controls intestinal segmentation contractions?

  The electrical slow waves of the intestinal wall (basic electrical rhythm).
  physiology intestinal
• What is the typical maximum frequency of segmentation contractions in the duodenum and proximal jejunum?

  About 12 contractions per minute (maximum under extreme stimulation).
  motility smallintestine
• What is the usual maximum frequency of contractions in the terminal ileum?

  Usually eight to nine contractions per minute.
  motility ileum
• How does blocking enteric excitatory activity with atropine affect segmentation contractions?

  Segmentation contractions become exceedingly weak when enteric excitatory activity is blocked by atropine.
  pharmacology enteric
• What is the normal velocity range of peristaltic waves in the small intestine?

  Approximately 0.5 to 2.0 cm/sec, faster proximally and slower terminally.
  peristalsis velocity
• How far do typical peristaltic waves in the small intestine travel before dying out?

  They usually die out after traveling only 3 to 5 cm and rarely farther than 10 cm.
  peristalsis distance
• What is the average net forward movement rate of chyme along the small intestine?

  About 1 cm per minute.
  transit smallintestine
• How long does passage of chyme from the pylorus to the ileocecal valve normally take?

  Approximately 3 to 5 hours.
  transit time
• Which nervous reflex increases small intestinal peristalsis after a meal?

  The gastroenteric reflex initiated by stomach distention and conducted mainly through the myenteric plexus.
  reflex gastroenteric
• Name hormones that enhance small intestinal motility according to the text.

  • Gastrin
  • CCK
  • Insulin
  • Motilin
  • Serotonin
  hormones motility
• Which hormones inhibit small intestinal motility according to the text?

  • Secretin
  • Glucagon
  hormones inhibition
• What triggers the gastroileal reflex that forces chyme through the ileocecal valve?

  Eating another meal increases the gastroileal reflex, intensifying ileal peristalsis and forcing chyme into the cecum.
  reflex ileocecal
• Do segmentation movements contribute to propulsion in the small intestine?

  Yes; they often travel ~1 cm analward during each event and help propel chyme down the intestine.
  segmentation propulsion
• What is a 'peristaltic rush' as described in the text?

  A powerful, rapid peristalsis caused by intense irritation of the intestinal mucosa (e.g., severe infectious diarrhea).
  peristalsis pathology
• What is the peristaltic rush in the small intestine?

  A powerful series of peristaltic contractions that travel long distances in the small intestine within minutes, sweeping intestinal contents into the colon.
  motility smallintestine
• Which neural mechanisms initiate the peristaltic rush?

  It is initiated partly by autonomic nervous system and brain stem reflexes and partly by intrinsic enhancement of myenteric plexus reflexes.
  neuro motility
• What effect does the peristaltic rush have on the small intestine contents?

  It sweeps chyme into the colon, relieving the small intestine of irritative chyme and excessive distention.
  physiology motility
• What action does the muscularis mucosae produce on the intestinal mucosa?

  It can cause short folds to appear in the intestinal mucosa.
  histology mucosa
• How do muscle fibers of the villi affect lymph flow?

  Intermittent contraction of villous muscle fibers 'milk' the villi so lymph flows from central lacteals into the lymphatic system.
  lymphatics villi
• How do mucosal folds affect absorption in the small intestine?

  Mucosal folds increase the surface area exposed to chyme, thereby increasing absorption.
  absorption anatomy
• What triggers mucosal and villous contractions in the small intestine?

  They are initiated mainly by local nervous reflexes in the submucosal nerve plexus in response to chyme in the small intestine.
  neuro mucosa
• How does the ileocecal valve prevent backflow from the colon to the small intestine?

  The valve protrudes into the cecal lumen and is forcefully closed when excess cecal pressure pushes backward against its lips.
  anatomy ileocecal
• What reverse pressure can the ileocecal valve usually resist?

  The valve usually can resist reverse pressure of at least 50 to 60 centimeters of water.
  physiology ileocecal
• What is the ileocecal sphincter and where is it located?

  A thickened circular muscle in the ileal wall several centimeters upstream from the ileocecal valve.
  anatomy sphincter
• What are the two principal functions of the colon?

  • Absorption of water and electrolytes to form solid feces
  • Storage of fecal matter until expulsion
  colon physiology
• Which half of the colon is primarily responsible for absorption and which for storage?

  • Proximal half: absorption
  • Distal half: storage
  colon anatomy
• How much chyme normally empties into the cecum each day?

  • 1500 to 2000 ml per day
  ileocecal quantities
• What effect does resistance at the ileocecal valve have on chyme in the ileum?

  • Prolongs stay of chyme in the ileum, facilitating absorption
  ileocecal absorption
• What is the gastroileal reflex effect immediately after a meal?

  • Intensifies ileal peristalsis and promotes emptying of ileal contents into the cecum
  reflexes ileum
• How does cecal distension or irritation affect the ileocecal sphincter and ileal peristalsis?

  • Cecal distension/irritation intensifies ileocecal sphincter contraction and inhibits ileal peristalsis, delaying emptying
  cecum reflexes
• Through which pathways are reflexes from the cecum to the ileocecal sphincter and ileum mediated?

  • Myenteric plexus in the gut wall and extrinsic autonomic nerves, especially prevertebral sympathetic ganglia
  neural reflexes
• What are haustrations and how are they produced in the colon?

  • Haustrations: baglike sacs formed when circular muscle contracts in ~2.5 cm segments while teniae coli longitudinal strips contract, causing outward bulging
  haustration motility
• Describe the timing and movement characteristics of a typical haustration.

  • Timing: peaks in ~30 seconds, disappears over the next 60 seconds; may slowly move toward the anus providing minor forward propulsion
  haustration dynamics
• How is fecal material processed against the large-intestine mucosa to allow absorption?

  Fecal material is gradually exposed to the mucosal surface of the large intestine (like spading the earth), allowing progressive absorption of fluid and dissolved substances.
  colon absorption
• How much fecal volume is typically expelled daily after colonic absorption?

  About 80 to 200 ml of feces are expelled each day.
  colon physiology
• What term does the text use for propulsive movements in the colon?

  Propulsive movements are called 'Mass Movements.'
  motility colon
• What produces most propulsion in the cecum and ascending colon?

  Slow but persistent haustral contractions that move chyme over 8 to 15 hours.
  colon motility
• How long can haustral contractions take to move chyme from the ileocecal valve through the colon?

  As many as 8 to 15 hours.
  colon timing
• When do mass movements in the colon typically occur each day?

  Usually only one to three times each day, often about 15 minutes during the first hour after breakfast.
  massmovement colon
• Describe the sequence of events in a colonic mass movement.

  A constrictive ring forms (often in transverse colon), distal 20+ cm lose haustrations and contract as a unit, contraction increases for ~30 seconds, then relaxes over 2–3 minutes.
  massmovement physiology
• What triggers the gastrocolic and duodenocolic reflexes that facilitate mass movements after meals?

  Distention of the stomach and duodenum.
  reflex gastrocolic
• Through which pathway are the gastrocolic and duodenocolic reflexes almost certainly transmitted?

  By way of the autonomic nervous system (they occur little or not at all when extrinsic autonomic nerves to the colon are removed).
  reflex autonomic
• What prevents continual dribble of fecal matter through the anus?

  Tonic constriction of the internal anal sphincter (circular smooth muscle) and the external anal sphincter (striated voluntary muscle).
  anatomy sphincter
• How is the external anal sphincter controlled?

  By nerve fibers in the pudendal nerve, part of the somatic nervous system, under voluntary or subconscious control.
  sphincter neuro
• What initiates the intrinsic defecation reflex in the rectum?

  Distention of the rectal wall when feces enter, triggering afferent signals in the myenteric plexus that start peristaltic waves.
  defecation reflex
• What happens to the internal anal sphincter as the peristaltic wave approaches the anus during defecation?

  The internal anal sphincter is relaxed by inhibitory signals from the myenteric plexus.
  defecation physiology
• How can irritation of the colon mucosa affect mass movements?

  Irritation can initiate intense mass movements that may persist almost all the time (e.g., ulcerative colitis).
  pathology colon
• What is the typical strength of the intrinsic myenteric defecation reflex when acting alone?

  The intrinsic myenteric defecation reflex is relatively weak when functioning by itself.
  physiology defecation
• Which secondary reflex usually fortifies the intrinsic defecation reflex to cause effective defecation?

  The parasympathetic defecation reflex involving the sacral spinal segments.
  physiology parasympathetic
• Describe the afferent-efferent pathway of the parasympathetic defecation reflex from rectal stimulation.

  • Afferent signals travel from rectal nerve endings into the spinal cord
  • Reflex signals return via pelvic parasympathetic nerves to descending colon, sigmoid, rectum, and anus
  neuroanatomy reflex
• What two main effects do parasympathetic signals have to intensify defecation?

  • Greatly intensify peristaltic waves
  • Relax the internal anal sphincter
  physiology mechanism
• What additional voluntary action is required along with sphincter relaxation for defecation to occur?

  Conscious, voluntary relaxation of the external anal sphincter is required for defecation.
  physiology volition
• What reflex actions accompany defecation signals entering the spinal cord?

  • Deep breath
  • Closure of the glottis
  • Contraction of abdominal wall muscles
  • Pelvic floor relaxation downward and outward
  defecation reflexes
• How does pelvic floor movement aid evacuation during defecation?

  The pelvic floor relaxes downward and pulls outward on the anal ring to evaginate the feces.
  pelvic defecation
• How can defecation reflexes be voluntarily activated?

  By taking a deep breath to move the diaphragm downward and then contracting the abdominal muscles to increase abdominal pressure and force fecal contents into the rectum.
  voluntary defecation
• How effective are purposely activated defecation reflexes compared with natural reflexes?

  Reflexes initiated purposely are almost never as effective as natural reflexes.
  efficacy defecation
• What consequence can occur from frequently inhibiting natural defecation reflexes?

  People who too often inhibit their natural reflexes are likely to become severely constipated.
  constipation behavior
• How do defecation reflexes behave in newborns and some people with transected spinal cords?

  They cause automatic emptying of the lower bowel at inconvenient times because of lack of conscious control of the external anal sphincter.
  newborns spinalcord
• What is the peritoneointestinal reflex and its effect on intestinal activity?

  Irritation of the peritoneum strongly inhibits the excitatory enteric nerves and can cause intestinal paralysis.
  peritoneum reflex
• What do the renointestinal and vesicointestinal reflexes do?

  They inhibit intestinal activity as a result of kidney irritation (renointestinal) or bladder irritation (vesicointestinal).
  reflex autonomic
• What region of the large bowel can be emptied by the reflexes described?

  They can be effective in emptying the large bowel all the way from the splenic flexure of the colon to the anus.
  colon defecation