general principles function of GIT

Question 1

gastrointestinal tract smooth muscle is excited by?

Answer 1

almost continual slow intrinsic electrical stimuli.

Question 2

two basic types of electrical waves:

Answer 2

slow waves and spikes.

Question 3

describe the contractions of the gastrointestinal tract

Answer 3

occur rhythmically.
the rhythm is determined mainly by the frequency of slow waves of smooth muscles membrane potential.

Question 4

slow wave

Answer 4

are not action potentials but undulations in the resting membrane potential of smooth muscle ( cyclic waves of depolarization and repolarization)

interstitial cells of Cajal- cat as electrical pacemakers for smooth muscle cells.

Question 5

interstitial cells of Cajal ion channels

Answer 5

periodically open and generate inward (peacemaker) currents that producing a slow wave activity- cyclic changes in membrane potential.

Question 6

slow waves do not stimulate muscle contraction by themselves except where?

Answer 6

in the stomach.

Question 7

slow waves also trigger generation of what?

Answer 7

spike potentials

Question 8

spike potentials

Answer 8

are action potentials that stimulate muscle contraction
they are prolonged than those of skeletal muscles.

slow waves propagate and spike occurs at the peak of slow waves.

Question 9

each muscle layer function as what ?

Answer 9

Syncytium.
that is when an action potential is elicited anywhere within the muscle mass, it generally travels in all directions in the muscle.

Question 10

the normal resting membrane potential of spike wave in the smooth muscle fibers of the gut

Answer 10

-50 and -60

Question 11

spike waves appears where ?

Answer 11

slow waves peak
MP is more positive than -40 millivolts

higher the slow wave potentials rise, the greater the frequency of the spike potentials.

Question 12

The frequency range of the spike wave

Answer 12

between 1 and 10 spikes per second
higher spike frequency in small intestine

Question 13

the factors that stimulate depolarization / depolarize GIT smooth muscle membrane potential.

Answer 13

stretching of the muscle.

stimulation of acetylcholine released from the endings of parasympathetic nerves.

stimulation of specific gastrointestinal hormones.

Question 14

Factors that hyperpolarize the membrane.

Answer 14

the effect of norepinephrine or epinephrine on the fiber membrane

stimulation of the sympathetic nerves that secrete mainly norepinephrine at their nerves endings.

Question 15

the gastrointestinal tract has an intrinsic nervous system called ?

Answer 15

enteric nervous system.

Question 16

the enteric nervous system lies where?

Answer 16

beginning of the oesophagus and ending of the anus.
and is controlled by movement and secretion.

Question 17

the enteric nervous system is composed of wo interconnected plexuses.

Answer 17

1. outer plexus lying between the longitudinal and circular muscle layers called the myenteric plexus ( Auerbach’s plexus).
2. Inner plexus called the submucosal plexus (Meissner plexus) and lies in the submucosa.

Question 18

myenteric plexus

Answer 18

controls the gastrointestinal movements

Question 19

submucosal plexus

Answer 19

control gastrointestinal secretions and blood flow.

Question 20

Both myenteric and submucosal plexuses are connected to the ?

Answer 20

parasympathetic and sympathetic fibers.

Question 21

The enteric nervous system can function ………….of these extrinsic nerves

Answer 21

independelty

Question 22

sensory nerve endings that originate in the gastrointestinal epithelium

Answer 22

send afferent fibers to the enteric system.

send impulses to the spinal cord and the brain stem

Question 23

what is created by the sensory nerves

Answer 23

short reflexes within the gut
long reflexes that relayed to the gut from brain stem and prevertebral ganglia

Question 24

GIT sensory system nerves can be stimulated by:

Answer 24

1. irritation of mucosa
2. excessive gut distention
   3.chemical substances in gut.

Question 25

stimulation of the myenteric plexus can result in?

Answer 25

Increased tonic contraction or tone of the gut wall increased intensity of the rhythmic contractions increased rate of the rhythmic of contraction increased velocity of conduction of excitatory waves along the gut wall cause rapid movement of the gut peristaltic waves.

Question 26

myenteric plexus neurons also

Answer 26

send inhibitory signals e.g nerve endings secrete vasoactive intestinal polypeptide (VIP)

Question 27

inhibitory signals

Answer 27

s inhibit contraction of the intestinal sphincter muscles and impede movement of food along the gastrointestinal tract.

Question 28

Pyloric sphincter inhibition

Answer 28

allows emptying of the stomach into the duodenum

Question 29

➢Inhibition of the ileocecal valve muscle

Answer 29

allows emptying from the small intestine into the cecum

Question 30

submucosal plexus to control local :

Answer 30

intestinal secretion absorption contraction of the submucosal muscle. *Submucosal muscle control the degree of infolding of the gastrointestinal mucosa

Question 31

*Parasympathetic supply to the gastrointestinal Tract has 2 divisions.

Answer 31

*Cranial division ➢cranial parasympathetic nerve fibers are almost entirely in the vagus nerves *Sacral division ➢The sacral parasympathetic originate in the sacral segments of the spinal cord. ➢Sacral parasympathetic function - execute the defecation reflexes.

Question 32

which c stimulation generally increases activity of the entire enteric nervous system - which in turn enhances activity of gastrointestinal functions

Answer 32

parasympathetic stimulation

Question 33

Sympathetic nervous system stimulation exerts its effects in two ways:

Answer 33

secretion of norepinephrine inhibits intestinal tract smooth muscle and inhibits the entire enteric nervous system

Question 34

strong stimulation of sympathetic system can inhibit? what?

Answer 34

motor movements impending movements of food through the gastrointestinal tract.

Question 35

. Reflexes integrated with the enteric nervous system and gut wall.

Answer 35

control GIT secretion, peristalsis, mixing contractions, local inhibitory effects.

Question 36

reflexes between the GIT and the sympathetic ganglia.

Answer 36

i. Gastrocolic reflex - transmit signals from the stomach cause evacuation of the colon. ii. Enterogastric reflexes - signals transmitted from the colon and small intestine to inhibit stomach motility and stomach secretion. iii.Colonoileal reflex - inhibit emptying of ileal contents into the colon.

Question 37

Reflexes between the gastrointestinal tract and the spinal cord or brain stem.

Answer 37

Vagovagal reflex - signals from the stomach and duodenum to the brain stem and back to the stomach— via the vagus nerves—to control gastric motor and secretory activity. ii. Pain reflexes that cause general inhibition of the entire gastrointestinal tract. iii.Defecation reflexes - signals travel from the colon and rectum to the spinal cord and back again to produce the powerful colonic, rectal, and abdominal contractions required for defecation

Question 38

the effect of major GIT hormones on GIT motility

Answer 38

* Hormones control gastrointestinal secretion and motility. * Hormones act on target cells with specific receptors for the hormone and do not require nervous connections to control gastrointestinal function

Question 39

Hormonal control of Gastrointestinal motility.

Answer 39

Gastrin is secreted by G cell of the antrum of the stomach.

Question 40

The primary actions of Gastrin

Answer 40

stimulate gastric acid formation or secretion. stimulate growth of the gastric mucosa

Question 41

Gastrin is secreted in response to the following stimuli:

Answer 41

1. Ingestion of a meal. 2. Stomach distention. 3. Products of proteins

Question 42

hormone that is secreted in the mucosa of small intestine by I cells response to fat, fatty acids and monoglycerides in the intestinal contents

Answer 42

cholecystokinin

Question 43

cholecystokinin stimulate.......to contract and whta?

Answer 43

gallbladder to contract and release bile into the small intestine.

Question 44

function of bile

Answer 44

Bile emulsify fatty substances – fat digestion and absorption.

Question 45

why does emptying of food slow or takes longer?

Answer 45

CCK slows the emptying of food from the stomach to allow adequate time for digestion of the fats in the upper intestinal tract.

Question 46

cholecystokinin inhibits what?

Answer 46

appetite e by stimulating sensory nerve in the duodenum and send signal via the vagus nerve to inhibit feeding centers in the brain

Question 47

the first gastrointestinal hormone to be discovered.

Answer 47

Secretin secreted by S cells in the mucosa of the duodenum Secretion of secretin occur in response to acidic gastric juice emptying into the duodenum from the pylorus of the stomach.

Question 48

secretin stimulate what?

Answer 48

pancreatic secretion of bicarbonate to neutralize the acid in the small intestine. and secretin has a mild effect on GIT tract motility.

Question 49

What is secreted by K cells

Answer 49

the gastric inhibitory peptide is a glucose-dependent insulinotropic peptide. secreted in the mucosa of upper small intestine.

Question 50

is secreted mainly in response to fatty acids and amino acids (response less to carbohydrate).

Answer 50

Gastric inhibitory peptide GIP slows emptying of gastric contents into the duodenum when the upper small intestine is already overloaded with food. also GIP stimulate insulin secretion.

Question 51

Motilin

Answer 51

is secreted by the stomach and upper duodenum by Mo cells during fasting.

Question 52

the function of motilin

Answer 52

to increase gastrointestinal motility.

Question 53

Motilin is released periodically and stimulates waves of gastrointestinal motility called ?

Answer 53

interdigestive myoelectric complexes occurs in the stomach and small intestine every 90 min during fasting.

Question 54

ingestion of food inhibits GITs....

Answer 54

motility

Question 55

Two types of movements occur in the gastrointestinal tract:

Answer 55

propulsive -Move food forward along the tract and rate of propulsion allow digestion and absorption. mixing-Keep the intestinal contents until thoroughly mixed

Question 56

Propulsive movements — Peristalsis

Answer 56

Peristalsis mechanism: A contractile ring is formed by the circular muscle around the gut and then moves forward

Question 57

peristalsis stimulation:

Answer 57

➢ Large amount of food collects in the gut cause distention (stretching) of the gut wall stimulates the enteric nervous system to contract the gut wall. ➢ Chemical or physical irritation of the epithelial lining in the gut. ➢ Parasympathetic nervous signals to the gut triggers a strong peristalsis.

Question 58

congenital absence of the myenteric plexus result in what ?

Answer 58

in weak or absence of peristalsis in affect portion of the GIT tract.

Question 59

congenital absence of the myenteric plexus result in what ?

Answer 59

in weak or absence of peristalsis in affect portion of the GIT tract.

Question 60

paralyze the cholinergic nerve endings of the myenteric plexus results in weak or blocked peristalsis in the entire gut is due to ?

Answer 60

Atropine

Question 61

The "Law of the Gut”

Answer 61

- peristaltic waves move toward the anus with downstream receptive relaxation. Law of the Gut” - peristaltic waves move toward the anus with downstream receptive relaxation * Peristalsis can “theoretically” occur in either direction from a stimulated point. * Peristalsis toward the mouth is inhibited while continuing toward the anus. * Gut wall distention initiates peristalsis on the orad side and moves toward the anal direction. * The gut smooth muscles relax downstream toward the anus - receptive relaxation allow food to be propelled more easily toward the anus than toward the mouth

Question 62

Segmentation Contractions—Mixing Movements

Answer 62

Mixing movements differ in different segments of the alimentary tract. * Peristaltic contractions cause most of the mixing when intestinal content is blocked by a sphincter. * Local intermittent segmentation contractions lasting between 5 to 30 seconds occur in the gut wall

Question 63

Blood passes through liver sinusoids is (lined by

Answer 63

reticuloendothelial cells leaves vai hepatic veins to IVC

Question 64

Sympathetic stimulate

Answer 64

vasoconstriction of the arterioles and decreased blood flow