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PHYSIOLOGY III > LECTURE I (GI Function) > Flashcards

LECTURE I (GI Function) Flashcards

1
Q

What are the four layers of the Gastrointestinal wall? (from outer to inner)

A
  • Serosa (outer connective tissue)
  • Muscularis Externa (Outer Longitudinal smooth muscle layer + Inner Circular smooth muscle layer)
  • Submucosa
  • Mucosa
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2
Q

What are the layers that make up the Mucosa?

A
  • Mucous membrane (inner epithelial layer serving as a protective surface)
  • Lamina propria
  • Muscularis mucosa

[some areas are modified for secretion and absorption]

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3
Q

What is the importance of the Submucosa layer?

A
  • Contains larger blood an lymph vessels (supplies inward mucosal layer + outward which muscle layer)
  • SUBMUCOSAL PLEXUS (nerve network) lies within it
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4
Q

What is the importance of the Serosa?

A
  • Outer connective tissue
  • Secretes SEROUS FLUID that lubricates an prevents friction between the digestive organs and surrounding viscera
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5
Q

Gastrointestinal Smooth Muscle Functions as a _________________

A

Syncytium

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6
Q

What is the difference between the longitudinal muscle layer and the circular muscle layer?

A

Longitudinal muscle layer = bundles extend longitudinally down the intestinal tract + shortens the tube

Circular muscle layer = extends around the gut + decrease diameter

[each bundle of smooth muscle fibres is partly separated from the next by loose connective tissue]

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7
Q

What are slow waves?

A

Slow undulating changes in resting membrane potential

[undulating = having a smoothly rising and falling form or outline]

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8
Q

What are the properties of Slow waves?

A
  • Do not themselves cause muscle contraction (except stomach)
  • Excite appearance of INTERMITTENT SPIKE POTENTIALS -> spike potentials excite the muscle contraction
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9
Q

What are intermittent spike potentials stimulated by?

A
  • Stretch
  • Acetylcholine
  • Parasympathetics
  • Specific GI hormones
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10
Q

What is depolarisation stimulated by?

A
  • Norepinephrine/Epinephrine
  • Sympathetics -> cause hyperpolarisation (e.g K+ exiting cell)
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11
Q

What are the properties of Spike potentials?

A
  • True action potentials
  • Threshold is -40 mv
  • The higher the slow wave potential rises, the greater the FREQUENCY of the spike potentials
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12
Q

Entry of __________ _____ causes smooth muscle contraction

A

Calcium Ions

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13
Q

What are the Plexus’ that make up the Enteric Nervous System?

A
  • MYENTERIC PLEXUS/AUERBACH’S PLEXUS [outer plexus between the longitudinal and circular muscle layers -> controls mainly gastrointestinal movements]
  • SUBMUCOSAL PLEXUS/MEISSNER’S PLEXUS [inner plexus within the submucosa -> controls mainly gastrointestinal secretion + local blood flow]
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14
Q

What’s the difference between sympathetic and parasympathetic nerve fibers?

A

Sympathetic = mainly post-ganglionic

Parasympathetic = pre-ganglionic

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15
Q

What does the Myenteric plexus consist mainly of?

A

A linear chain of many interconnecting neurons that extends the entire length of the gastrointestinal tract

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16
Q

What does a stimulated Myenteric plexus cause?

A
  • Increased TONIC CONTRACTION/TONE of the gut wall
  • Increased INTENSITY of the rhythmical contractions
  • Slightly increased RATE of the rhythm of contractions
  • Increased VELOCITY of conduction of excitatory waves -> more rapid movement of the gut PERISTALTIC WAVES
17
Q

Sensory signals originate from the GI epithelium and are integrated in the Submucosal plexus to help control what?

A
  • Local intestinal secretion
  • Local absorption
  • Local contraction of the submucosal muscle
18
Q

______________ stimulation inhibits Gastrointestinal Tract activity

A

Sympathetic

19
Q

What are sensory nerves stimulated by?

A
  • Irritation of the gut mucosa
  • Excessive distention of the gut
  • Presence of specific chemical substances in the gut
20
Q

What are the different Gastrointestinal Reflexes?

A
  • Reflexes integrated entirely within the gut wall enteric nervous system
  • Reflexes from the GUT to the PRE-VERTEBRAL SYMPATHETIC GANGLIA and then back to the GI TRACT
  • Reflexes from the GUT to the SPINAL CORD or BRAIN STEM and then back to the GASTROINTESTINAL TRACT
21
Q

What are the different hormones used for Gastrointestinal Motility control?

A
  • Gastrin
  • Cholecystokinin (CCK)
  • Secretin
  • Motilin
22
Q

What is Gastrin?

A
  • Secreted by the G cells of the antrumof of the stomach
  • Stimulate gastric acid secretion
  • Stimulate growth of gastric mucosa
23
Q

What is Cholecystokinin (CKK)?

A
  • Secreted by I cells in the DUODENUM and JEJENUM mucosa
  • Contracts gallbladder
  • Inhibits stomach contraction
24
Q

What is Secretin?

A
  • Secreted by S cells in the DUODENUM mucosa
  • promotes pancreatic bicarbonate secretion
25
Q

What is Motilin?

A
  • Secreted by the STOMACH and UPPER DUODENUM
  • Increases GI motility
26
Q

What are the different types of movements in the GI tract?

A
  • PROPULSIVE MOVEMENTS = cause food to move along tract at an appropriate rate to accommodate digestion and absorption
  • PERISTALTIC WAVES move toward the anus with DOWNSTREAM RECEPTIVE RELAXATION
  • MIXING MOVEMENTS = keep intestinal contents thoroughly mixed at all times
27
Q

What is the usual stimulus for intestinal peristalsis?

A

Distention of the gut

28
Q

What is blood flow in each area of the gastrointestinal tract dependent on?

A

The level of local activity

29
Q

What are the possible causes of the increased blood flow during Gastrointestinal activity?

A
  • Several vasodilator substances are released from the mucosa of the intestinal tract during the digestive process (CCK, vasoactive intestinal peptide, gastrin, secretin)
  • GI glands release the kinins KALLIDIN & BRADYKININ
  • Decreased O2 concentration
30
Q

What does stimulation of the parasympathetic nerves going to the stomach and lower colon cause?

A

Increased local blood flow

31
Q

What does stimulation of sympathetic nerves cause?

A

Intense vasoconstriction of the arterioles with greatly decreased blood flow

32
Q

What is important about sympathetic vasoconstriction in the gut?

A

It allows shutoff of gastrointestinal and other splanchnic blood flow for short periods during heavy exercise and in circulatory shock

[circulatory shock = when the body’s vital tissues are in danger of cellular death for lack of blood flow]

33
Q

What is the difference between Sympathetics/Parasympathetics and Slow waves?

A

Slow waves = Cause spike potentials

Sympathetics/Parasympathetics = Change rate of spike potentials

34
Q

What does the mucous membranes contain?

A
  • Exocrine glands (for secretion of digestive juices)
  • Endocrine glands (for secretion of blood borne GI hormones)
  • Epithelial cells (for absorbing nutrients)
35
Q

What does the Lamina propria contain?

A

Gut-associated lymphoid tissue (GALT)

[for defence against disease causing intestinal bacteria]

36
Q

________ is continuous with the mesentery to suspend the organs from thinner wall of the body

A

Serosa

37
Q

What happens to the small absorbable units that results with digestion?

A

Along with water, vitamins and electrolytes they are all transferred from the lumen to the blood stream to lymph

38
Q

What are the effects of Norepinephrine?

A
  • Slight inhibition of intestinal tract smooth muscles
  • Major extent inhibition on the neurons of entire enteric nervous system

PHYSIOLOGY III (7 decks)

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