- have both afferent and efferent limbs - ACh and Substance P released from postganglionic neurons excites contraction - release of VIP and NO inhibit contraction

Basal electrical rhythm (rate of slow waves) - stomach=3/min - duodenum=12/min slows from duodenum to ileum colon does not have BER BER is set by pacemaker cells

Phys 1-2 Flashcards by Tiffany Reid

7 sphincters of the GI tract

UES
LES
Pyloric
Sphincter of Oddi
Ileocecal
Internal anal
External anal

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Contraction of the muscularis externa is primarily responsible for ___

Mixing and propulsion of luminal contents

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Collection of neurons in the GI tract

brain of the gut
can exert much of its function independent of the CNS

Enteric nervous system

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Examples of things the Enteric Nervous System controls

Motility
Exocrine/endocrine secretions
Microcirculation
Regulating immune and inflammatory responses

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Parasympathetic innervation to the GI tract is supplied by nerve fibers from ___

Vagus (above and including the transverse colon)

2. Pelvic sacral nerves (below and the distal end of the transverse colon)

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Preganglionic parasympathetic fibers terminate on ____, and the postganglionic neurons are shared with __
Mostly cholinergic

Ganglia of the intramural plexuses

- ENS

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Activation of parasympathetic nerves (vagus) is most often (inhibitory/excitatory), (decreasing/increasing) GI motility or secretion

Excitatory

Increasing

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Vagovagal reflexes

have both afferent and efferent limbs
ACh and Substance P released from postganglionic neurons excites contraction
release of VIP and NO inhibit contraction

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Sympathetic innervation:

Post ganglionic adrenergic fibers arise from ___

Prevertebral and paravertebral ganglia

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Activation of sympathetic nerves is most often (inhibitory/excitatory), (decreasing/increasing) GI motility or secretion

Inhibitory

Decreasing

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Most sympathetic fibers synapse on cells of the ___ plexuses where the ___ released inhibits _____ release by activating ____ receptors.

Intramural (submucosal and myenteric)
norepinephrine
parasympathetic acetylcholine
alpha 2 presynaptic

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Factors which influence the _____ (inhibitory) and the ____ (stimulating) act through the intramural plexuses

Muscularis externa

Muscularis mucosae

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Sympathetic fibers innervate ____ in the gut directly causing ____
What type of receptor?

Blood vessels
Vasoconstriction
Alpha 1

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True or false: GI smooth muscle is multi unit

False: single unit

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BER

Basal electrical rhythm (rate of slow waves)

stomach=3/min
duodenum=12/min
slows from duodenum to ileum
colon does not have BER
BER is set by pacemaker cells

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True or false: The frequency and amplitude of slow waves can be modified

False. Frequency cannot, amplitude can

sympathetic decreases
parasympathetic increases

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More action potentials =

Greater force of contraction

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Initial rising phase of the AP is due primarily to Ca entry into the cell through ___ channels. Depolarization occurs coincident with ___

L-type Ca

⬆️Gk+

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Initial APs occur where on the slow wave?

Near the peak on the rising phase

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True or false: the intestine can contract in the absence of APs

False. The stomach can

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Two functional types of movements of the GI tract

Mixing-local constrictive contractions (segmentation) and peristaltic contractions
Propulsive-peristalsis moves contents down through the GI tract. Distension is the stimulus for peristalsis

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Peristaltic reflex or “law of the gut”

Muscles toward the mouth contract first, then moves downward.
-simultaneous relaxation of the smooth muscle in front of the distension that is mediated through ENS

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Migrating Motor Complex

Strong wave of contractile activity that spreads down through the GI tract between meals

once every two hours during fasted period (interdigestive period)
function is to sweep clean the lumen between meals

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Control of contractile activities of the GI system involves 4 things:

CNS
ENS
Electrical coupling between cells
Humoral factors

*motile activity of the gut is the NET result of the integration of these 4 influences

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Circular layer of muscularis externa tends to make sections ___ while the longitudinal layer tends to make sections ___

Longer and thinner | Shorter and wider

Known transmitters which excite smooth muscle contraction:

ACh | Substance P

Known transmitters which relax GI smooth muscle

NO | VIP

Transmitter released by enteric interneurons

Serotonin (5-HT)

___ increases Force of stomach contractions and ____ is responsible for the MMC

Gastrin | Motilin

___ is secreted in the small intestine. It tends to decrease gastric motility and increases gall bladder contractility

Cholecystokinin (CCK)

___ decreases motility of most of the GI tract

Secretin

____ mildly decreases gastric motility

Gastric inhibitory peptide (GIP)

3 phases of swallowing

1. Oral/voluntary 2. Pharyngeal 3. Esophageal

In which phase of swallowing: The soft palate move upward, superior constrictor muscles and palatopharyngeal fold move toward one another thus preventing reflux of rod into the nasopharynx

Pharyngeal

In which phase of swallowing: | Tactile receptors initiate swallowing reflex at pharynx level

Oral or Voluntary phase

In which phase of swallowing does: | Primary and secondary peristalsis

Esophageal phase

In which phase of swallowing do: Vocal cords pull together Larynx moves against the epiglottis (prevent food from entering trachea) Respiration is reflexively inhibited

Pharyngeal phase

In which phase of swallowing does: UES relax UES constricts

Pharyngeal | Esophageal

In which phase of swallowing is: | Modulated and coordinated by a medullary "swallowing center"

Pharyngeal | Continues to esophageal

The muscle layer of the upper third of the esophagus is ___. The lower third is ___. The central region is ____. Innervation of the 3 regions?

Skeletal/striated Smooth Mixed Vagus

Pressure at UES

Resting : 40mmHg Upon swallowing the pressure rapidly drops then rapidly increases immediately after the bolus passes to prevent entry of air

Pressure at LES In a normal person the pressure at the LES is always higher than ___ except ___

Resting: 30mmHg Gastric pressure except during swallowing

What type of nerve stimulation causes contraction of LES?

Both parasympathetic and sympathetic (Parasympathetic inhibitory fibers also exist) *The ENS alone can maintain construction when extrinsic nerves are cut

The LES is tonically contracted by ___

Extrinsic and intrinsic nerves, hormones; and neuromodulators

LES relaxation is primarily mediated by ___

Vagovagal reflex that causes relaxation of the circular muscle layer

A condition where the LES does not relax fully during swallowing.

Achalasia *associated w/ degeneration of nerve ganglion cells within the myenteric nerve plexus, often as a result of an autoimmune attack

LES incompetence causes ___

Gastric reflux

A hiatal hernia occurs when ___

Part of the stomach moves upward into the thoracic cavity.

Achalasia (and Hirschsprung's disease) are due to __

Absence of ENS ganglion cells at the LES (and internal anal sphincter) which prevents relaxation and thus passage of material through the sphincter

This part of the stomach is more muscular and controls the rate of chyme efflux

Antrum

This sphincter separates the stomach and small intestine

Pyloric

Reflex of relaxation of the orad portion of the stomach is mediated by ____. What are the transmitters?

Vagal efferents | VIP and NO

Amount of food that can be stored in the stomach without a substantial increase in intragastric pressure

1 L

As pressure builds in the antrum, some chyme is forced into the ___ while most is forced ___

Into the duodenum | Back in the body of the stomach by retropulsion

Gastric emptying is regulated by ___ mechanisms

Neural and hormonal

Receptors in the small intestine can sense and respond to :

Acidity Far content Osmotic pressure

__ is released in response to food in the stomach and increases stomach motility and thereby promotes gastric emptying

Gastrin

Acid, fats, and hyoertonicity all tend to ___ gastric motility and ___ stomach emptying

Decrease | Reduce

Peptides in the duodenum ___ gastric emptying

Decrease | *to enhance digestion in the stomach

GI irritation causes paracrine release of ___ from ____ which stimulates vagal afferents to the vomiting center

Serotonin (5-HT) | Enterochromaffin

A chemoreceptor ___ lies in the floor of the 4th ventricle. When stimulated directly by certain drugs (____) it causes vomiting. This is mediated by ____

"Emetic trigger zone" Morphine, digitalis Dopamine and serotonin receptors

Vomiting due to psychic stimuli (odors, disquieting events, etc) probably only involves what?

The vomiting center

That small intestine is the longest segment of the GI tract and it typically takes chyme between ___ to ___ hours to traverse it

2 to 4

Most frequent type of movement in the small intestine

Mixing/chopping

___ by chyme elicits localized contraction of the circular muscle layer at spaced intervals

Stretch/distension

BER of: Duodenum? Ileum?

D: 12/min I: 9/min *frequency decreases along length

The tissue of the small intestine is made more "excitable" by the distension of the stomach and the beginning of the entry of chyme into the duodenum

Gastroenteric reflex

Muscles contract just behind the bolus of chyme while the muscle in front of the bolus relaxes

Law of the Gut | Myenteric Reflex

Overdistension of one segment of the intestine will cause reflex relaxation in the rest of the intestine

Intestinointestinal reflex

The stomach and terminal part of the ileum interact reflexively. Increased activity in the stomach will increase motility of the ileum and accelerate the movement of chyme through the ileocecal sphincter

Gastroileal reflex

Gastric distension increases activity in the colon

Gastrocolic reflex

MMC occurs in the ___ state about every ___ hours. It starts in the ___ and goes to the ___. It is inhibited by ___

Fasted 2 Stomach, ileocecal sphincter Motilin

Four phases of the MMC

1. Quiescence; slow waves; little or no mechanical activity 2. Irregular APs, contractions gradually increase in frequency and intensity 3. Intense electrical and mechanical activity lasting 3-6 minutes 4. Rapid decline in electrical and mechanical activity

The ileocecal valve and sphincter are normally ___ to prevent ___

Closed | Efflux of colonic contents back into the small intestine

Distension of the cecum causes ileocecal sphincter to ___

contract

Distension of the terminal ileum causes ileocecal sphincter to ___

relax

Gastrin and the gastroileal reflex ___ the ileocecal valve

Relax

Haustrations of the colon

Similar to small intestine segmentation

Taenia coli are present in the __

Colon (large intestine) | -3 strips of longitudinal smooth muscle

The ___ and ___ reflexes increase mass movement activity (propulsive peristaltic waves that move contents analward/caudad)

Gastrocolic | Duodenocolic

BER in the colon

No BER | -humans have irregular, intermittent slow waves in the colon

Mass movement from the sigmoid colon fills the rectum while reflexively relaxing the internal anal sphincter and contracting the external anal sphincter

Rectosphincteric reflex

The EAS is normally ___ at rest, and is a ___ muscle under ___ control via the ____ n.

Relaxed Striated Voluntary Pudendal

Other reflexes that act to reduce motility

1. Peritoneointestinal (peritoneum irritatikn) 2. Renointestinal (kidney irritation) 3. Vesicointestinal (bladder irritation) 4. Somatointestinal (irritation of skin over stomach)

Gas in the GI tract has 3 sources:

1. Swallowed air (stomach; belching) 2. Bacteria (primarily large intestine; 90% reabsorbed, 10% flatulence) 3. Diffusion from blood

Noise made by movement of gas and chyme through the intestines due to peristalsis

Borborygmi