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Gastrointestinal 1 > Physiology of Ingestion and Propulsion > Flashcards

Physiology of Ingestion and Propulsion Flashcards

1
Q

What are the 4 functions of the gastrointestinal tract (alimentary tract)?

A
  1. movement of food through the alimentary tract
  2. secretion of digestive juices and digestion of foods
  3. absorption of water, various electrolytes, vitamins, and digestive products.
  4. control of all these functions by local, nervous and hormonal systems.
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2
Q

What comprises the walls of the GI wall?

A
  • outer wall= serosa
  • deep to that= LONGITUDINAL smooth muscle
  • deep to that= MYENTERIC (Auerbach’s) nerve plexus and CIRCULAR smooth muscle (involved in movements of GI tract).
  • deep to that= MEISSNER’S nerve plexus and submucosa
  • deep to that= mucosa and glands (muscularis mucosa for secretion and absorption).
  • deep to that= epithelium (for secretion and absorption).
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3
Q

What electrically connects the smooth muscle fibers of the GI tract?

A

gap junctions

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4
Q

What are the 2 types of electrical activity of GI smooth muscle?

A
  1. slow waves= Na+ entering cells, with a little Ca2+ but not crossing threshold (therefore no AP).
  2. spike potentials= membrane potential crosses threshold leading to large influx of Ca2+ (AP generated).
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5
Q

What stimulates spike potentials?

A
  • stretch
  • acetylcholine released from parasympathetic nerves
  • specific GI hormones
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6
Q

What causes HYPERpolarization of GI smooth muscle?

A
  • norepinephrine or epinephrine

- stimulation of sympathetic nerves that secrete norepinephrine at their endings.

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7
Q

What is the enteric nervous system (“little brain”)?

A

functions independently of extrinsic nerves, but stimulation by parasympathetic and sympathetic systems can greatly enhance or inhibit GI functions, respectively.
*myenteric and meissner’s nerve plexus

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8
Q

What is the myenteric (Auerbach’s) nerve plexus?

A
  • linear chain of many interconnecting neurons that span the entire length of the GI tract to increase tone, intensity, rate, and velocity of rhythmical contractions.
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9
Q

Is the myenteric (Auerbach’s) nerve plexus entirely excitatory?

A

NO, it also has inhibitory functions via vasoactive intestinal polypeptide.

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10
Q

What is the Submucosal (Meissner’s) nerve plexus?

A
  • responsible for integration of sensory signals in the submucosa to help control local intestinal secretion, absorption, and contraction of submucosal muscle (causes infolding of GI mucosa). Also blood flow control.
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11
Q

What are the 2 components of the PARAsympathetic system to the GI tract?

A
  1. CRANIAL= VAGUS innervates esophagus, stomach, intestines (via celiac and mesenteric plexi), and pancreas (little to mouth/pharynx).
  2. SACRAL nerves= originate in 2-4 sacral segments of spinal cord and pass through pelvic nerves to distal half of large intestine to anus.
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12
Q

What is the SYMPATHETIC influence on the GI tract?

A
  • inhibits GI activity (originating between T5 and L2)
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13
Q

What is the one exception of the sympathetic system on the GI tract, in which it is excitatory rather than inhibitory?

A

mucosal muscle

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14
Q

** What is the role of GI reflexes that are integrated entirely within the gut wall ENTERIC nervous system?

A

controls GI secretion, peristalsis, mixing contractions, and local inhibitory effects.

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15
Q

** What are the 3 roles of GI reflexes from the gut to PREVERTEBRAL SYMPATHETIC GANGLIA and then back to the GI tract?

A
  1. signals from the stomach cause evacuation of colon (gastrocolic reflex).
  2. signals from the colon and small intestine inhibit stomach motility and secretion (enterogastric reflex).
  3. reflexes from the colon to inhibit emptying of ileal contents into colon (colonileal reflex).
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16
Q

** What are the 3 reflexes that come from the gut and then travel to the SPINAL CORD or BRAIN STEM and back to the gut?

A
  1. reflexes from the stomach to the duodenum to the brain stem, and back to the stomach via the vagus nerves to control gastric motor and secretory activity.
  2. pain reflexes that cause general inhibition of the entire GI tract.
  3. defecation reflexes that travel from the colon and rectum to the spinal cord and back again to produce powerful colonic, rectal, and abdominal contractions required for defecation (defecation reflexes).
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17
Q

Do hormonal effects on the GI tract persist longer or shorter than nervous connections?

A

longer

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18
Q

What are the 2 functional types of movement in the GI tract?

A
  1. propulsive

2. mixing

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19
Q

What is the splanchnic blood flow?

A

blood that flows through the gut, spleen, and pancreas, and then the liver. This empties into the inferior vena cava.

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20
Q

What arteries supply the walls of the small and large intestine?

A

superior and inferior mesenteric arteries

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21
Q

What artery supplies the stomach?

A

celiac artery

22
Q

To what is blood flow directly related?

A

local gut activity. During active absorption of nutrients, blood flow in villi and adjacent regions of the submucosa is increased (up to 8-fold).

23
Q

What VASODILATORS are released from the mucosa to enhance local blood flow?

A
  • peptide hormones
  • cholecystokinin
  • vasoactive intestinal peptide
  • gastrin
  • secretin
  • kallidin and bradykinin (from GI glands)= powerful
24
Q

How does O2 concentration affect blood flow?

A

decreases in O2 increases blood flow

25
Q

Is there countercurrent blood flow in the intestinal villi?

A

YES. Arterial flow into the villus and venous flow out are in opposite directions.

26
Q

What is the effect of the parasympathetic and sympathetic nervous systems on blood flow, respectively?

A
  • parasympathetic= vasodilation and increased blood flow.

- sympathetic= vasoconstriction and decreased blood flow.

27
Q

What is auto-regulatory escape?

A

local metabolic vasodilator mechanisms elicited by ischemia (overrides sympathetic vasoconstriction).

28
Q

What happens during heavy exercise or circulatory shock?

A

sympathetic vasoconstriction shuts off GI and other splanchnic blood flow for short periods of time.

29
Q

What are the important components of mastication?

A
  • teeth (incisors cut, molars grind)
  • jaw muscles (innervated by 5th cranial nerve)
  • chewing process controlled by nuclei in the brain stem.
30
Q

What happens when a bolus of food enters the mouth?

A

it initiates reflex inhibition of muscles of mastication, allowing lower jaw to drop. This in turn initiates a stretch reflex of rebound contraction, raising the jaw to close teeth. The compression of bolus against linings of mouth inhibits jaw muscles again to repeat the cycle…

31
Q

What is the importance of the salivary glands (parotid, submandibular, and sublingual; also tiny buccal glands in cheeks)?

A

lubricates the mouth and food, and begins the digestion process.

32
Q

What does the parotid gland secrete?

A

serous secretion containing ptyalin (a-amylase) to digest starches

33
Q

What do the submandibular and sublingual glands secrete?

A

both ptyalin (for starch digestion) and mucus (contains mucin for lubrication).

34
Q

What do buccal glands secrete?

A

just mucus for lubrication

35
Q

What happens in the salivary DUCT?

A

Na+ is actively absorbed leading to passive Cl- absorption. K+ and HCO3- are actively secreted.

36
Q

What stimulates salivary secretion?

A
  • taste and tactile stimuli via parasympathetics

- higher centers in nervous system (i.e. smell).

37
Q

Do sympathetics increase or decrease salivation?

A

actually INCREASE slightly

38
Q

What does salivation do to local blood vessels of the salivary glands?

A

dilates them. Kallikrein (protease) is also secreted by activated salivary cells, which splits a2-globulin to form bradykinin.

39
Q

What happens generally during deglutition (swallowing)?

A
  • trachea is closed, esophagus is opened
  • fast peristaltic wave is initiated by nervous system as the pharynx forces the bolus of food into the upper esophagus (less than 2 seconds).
40
Q

** What are the detailed stages of swallowing?

A
  1. VOLUNTARY STAGE= food is voluntarily rolled posteriorly into pharynx by pressure of tongue upward and backward against palate.
  2. PHARYNGEAL STAGE (involuntary)= passage of food through the pharynx into esophagus stimulates epithelial swallowing receptor areas causing reflex autonomic pharyngeal muscle contractions (soft palate pulled upward to close the posterior nares, palatopharyngeal folds pulled medially, and vocal cords come close together as the epiglottis swings back over the opening of the larynx. The larynx moves upward to enlarge the opening to the esophagus and this also lifts the glottis out of the main stream of food, allowing it to pass on each side of the epiglottis rather than over its surface. Additionally, the upper esophageal sphincter/pharyngoesophageal sphincter relaxes. Food is then peristaltically moved into the esophagus.
  3. ESOPHAGEAL STAGE (involuntary)= transports food from pharynx to stomach via primary and secondary peristalsis (if first, primary fails). It is initiated by the MYENTERIC (Auerbach’s) plexus and reflexes of vagal afferents upward to the medulla and back to the esophagus (via IX and X CN efferent fibers).
41
Q

What is the peristaltic reflex?

A

at the same time as peristaltic movement pushes bolus towards the anus, the gut relaxes several cm down stream (receptive relaxation) via the myenteric plexus.

42
Q

What type of musculature makes up the pharyngeal wall and upper third of the esophagus?

A

striated voluntary skeletal muscle controlled via glossopharyngeal (IX) and vagus (X) nerves

43
Q

What type of musculature makes up the lower 2/3 of the esophagus?

A

smooth muscle innervated by vagus (X) nerve and connected via myenteric plexus

44
Q

Does secretion take place in the esophagus?

A

YES it is entirely mucous for lubrication and protection

45
Q

What happens when the esophageal peristaltic wave approaches the stomach?

A

a wave of relaxation (receptive relaxation) is transmitted through the myenteric inhibitory neurons causing the entire stomach and some of the duodenum to relax in preparation to receive food.

46
Q

What prevents the stomach contents from entering into the lower esophagus?

A

the lower esophageal sphincter (gastroesophageal sphincter). It is normally tonically constricted due to intraluminal pressure.

47
Q

Is the esophageal mucosa capable of resisting the digestive action of gastric secretions?

A

NO (except lower 1/8th)

48
Q

What additionally helps to prevent reflux?

A

valve-like mechanism of a short portion of esophagus that extends slightly into the stomach.

49
Q

What is vomiting?

A
  • when upper GI rids its contents (reverse peristalsis) due to irritation, over-distention, or over-excitation.
  • nerve impulses are transmitted by vagal and sympathetic afferents to “vomiting center” in brainstem causing motor impulses via vagus and sympathetics to induce strong intrinsic contractions in the duodenum and stomach.
50
Q

From where can sensory signals originate to induce vomiting?

A

pharynx, esophagus, stomach, or upper small intestine

51
Q

What happens once the vomiting center has been sufficiently stimulated?

A
  1. deep breath
  2. raising of the hyoid bone and larynx to pull the upper esophageal sphincter open
  3. closing of the glottis to prevent aspiration
  4. lifting of the soft palate to close the posterior nares.
  5. strong downward contraction of the diaphragm and contraction of abdominal muscles.
  6. building of intragastric pressure causes lower esophageal sphincter to relax, allowing expulsion of gastric contents.
52
Q

What are some disorders of swallowing?

A
  • esophageal obstruction or stenosis such as diverticulum (outpouching of hollowing tubing).
  • parkinsons, ALS, stroke, which will cause loss of voluntary control of swallowing.
  • Head or spinal injury
  • cancer of the head, neck, or esophagus
  • Esophagitis (inflammation of esophagus) such as GERD

Gastrointestinal 1 (21 decks)

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