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MD3002 Physiology > Overview of GI Physiology > Flashcards

Overview of GI Physiology Flashcards

1
Q

What does the GI tract require in order to successfully function?

A
  • Movement of food
  • Secretion of digestive juices
  • Absorption of food/electrolytes/vitamins and digestive products
  • Circulation of blood through the GI organ to carry away the absorbed substances
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2
Q

Where in the alimentary tract is food passed through?

A

The oesophagus

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3
Q

Where is food temporarily stored in the alimentary tract?

A

The stomach

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4
Q

Where does digestion and absorption take place in the alimentary tract?

A

The small intestine

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5
Q

Name the layers of the GI tract

A
  • Mucosa
  • Submucosa
  • Muscularis externa
  • Serosa (oesophagus does not have this)
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6
Q

Name the layers of the mucosa

A
  • Epithelium
  • Lamina propria
  • Muscularis mucosa
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7
Q

How often is the epithelium shed away?

A

2-3 days

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8
Q

What is the lamina propria?

A
  • Loose connective tissue made up of elastin and collagen fibres
  • Contain sensory nerves, blood and lymph vessels, secretory glands
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9
Q

What is the muscularis mucosa?

A
  • Thin layer of smooth muscle

- Further increases surface area by creating ridges and folds

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10
Q

What is the submucosa?

A
  • Thicker layer with similar compisition to lamina propria

- Incorporates blood vessels and nerve bundles that form a submucosal plexus - integral part of enteric nervous system

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11
Q

What is the muscularis externa?

A
  • Circular muscle + myenteric plexis + longitudinal muscle
  • ENS co-ordinates contractions to mix and move contents between compartments
  • Sphincters regulate flow from compartment to next
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12
Q

What is the serosa?

A
  • Outermost layer of CT + layer of squamous epithelial cells
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13
Q

How long and wide are smooth muscle fibres?

A
  • 200-500um long
  • 2-10um in diameter
  • In bundles of up to 1000 parallel fibres
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14
Q

How do the smooth muscle fibres connect to each other?

A
  • Via gap junctions (they form a syncitium)

- Connective tissue partly seperates each bundle, but with many points where bundles fuse forming a branching network

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15
Q

What does a syncitium allow for?

A

When an AP is evoked anywhere it typically goes in all direction

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16
Q

What is GI smooth muscle generally excited by?

A

Slow, intrinsic electrical activity

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17
Q

What are the 2 basic types of electrical waves?

A
  • Slow waves; 2 spikes
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18
Q

What does the intensity of GI muscle smooth waves vary between?

A

5 - 15 mV

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19
Q

What does the frequency of the GI smooth muscle vaary between?

A

3 - 12 per min

20
Q

What are considered true APs?

A

Spike potentials

21
Q

When do spike potentials occur naturally?

A

> ~-40mV

22
Q

How long does each GI spike last for?

A
  • 10 - 20 ms

- 10-40 X as long in GI muscle as APs in large nerve fibres

23
Q

What is the main ion responsible for APs in GI SM?

A

Ca2+

24
Q

What can cause hyperpolarisaion?

A
  • Norepinephrine

- Sympathetics

25
Q

What can cuase depolarisation?

A
  • Stretch
  • Acetylcholine
  • Parasympathetics
26
Q

Where does the Enteric nervous system lie?

A

In the wall of the gut, in between the longitudinal and circular muscle layers

27
Q

What is the enteric plexus?

A
  • Mostly linear chain of interconnecting neurons extending the entire length of GI tract
  • Mainly controls muscle activity
28
Q

What are the effects of the myenteric plexus when stimulated?

A
  • Increased tonic contraction/”tone” of gut wall
  • Increased intensity of the rhythmical contractions
  • Slightly increased rate of the rhythm of contraction
  • Increased velocity of conduction of excitatory waves along the gut wall, causing more rapid movement of the gut peristaltic waves
29
Q

What are the effects of the submucosal plexus?

A
  • Mainly controls function within small segments of intestine
  • Affects secretory and blood flow type activity
30
Q

What is the role of Vasoactive Intestinal Peptide (VIP)?

A
  • Inhibits sphincter muscles at the ends of different segements
31
Q

What nerve are almost all of the parasympathetic neurons that affect the GI tract from?

A

Vagus nerve

32
Q

Where do almost all sympathetic fibres that affect the GI system originate from?

A

T5 - L2

33
Q

What can sensory nerves of the GI tract by stimulated by?

A
  • Irritation of gut mucosa
  • Excessive distention of the gut
  • The presence of specific chemical substances in the gut
34
Q

What are the 3 types of GI reflexes?

A
  • Reflexes integrated within the enteric nervous system
  • Reflexes from the GI tract to prevertebral sympathetic ganglia
  • Reflexes from the GI tract to the brain stem or spinal cord and then back to the GI tract
35
Q

What are reflexes integrated within the enteric nervous system?

A

Reflexes controlling secretion, peristalisis, mixing, local inhibitory actions

36
Q

What are reflexes from the GI tract to prevertebral sympathetic ganglia and then back to GI tract?

A

Reflexes that transmit signals to other areas of the GI tract - gastrocolic reflex (stomach - colon); enterogastric reflexes (stomach and colon inhibiting gastric motility); colonoileal reflexes (inhibition of ileal emptying)

37
Q

What are reflexes from the GI taract to the brain stem or spinal cord and then back to GI tract?

A
  • Reflexes from stomach and duodenum to brain stem and back to stomach to control gastric motor and secretory activity
  • Pain reflexes causing general inhibition of entire GI tract
  • Defecation reflexes from the colon and rectum that travel via the spinal cord back to produce powerful colonic, rectal and abdominal contractions
38
Q

What stimuates gastrin secretion?

A
  • Protein
  • Distention
  • Nerve
    (Acid inhibits release)
39
Q

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

A
  • Propulsive movements

- Mixing movements

40
Q

What is the hypothesised reson for how waves of peristalsis move towards the anus?

A

Due to “polarised” myenteric plexus

41
Q

How long do local intermittent constrictive contractions last?

A

5 - 30 s (every few cm in gut wall)

42
Q

What vein carries blood from the gut, spleen and pancreas to the liver?

A

The portal vein

43
Q

What does blood pass through in the liver?

A

Minute liver sinusoids

44
Q

What does blood being passed through the liver allow for?

A

Allows bacteria/particulate matter that might enter the blood from the GI tract to be removed, preventing direct transport of potentially harmful agents into the remainder of the body

45
Q

What is the blood supply to the intestines called?

A

The mesenteric web

46
Q

What are some of the arteries in the mesenteric web?

A
  • Middle colic
  • Right colic
  • Ileocolic
  • Superior mesenteric
  • Jejunal
  • Ileal
  • Inferior mesenteric
47
Q

What is an increase in GI blood flow likely caused by?

A
  • Vasodilators released from GI mucosa e.g CCK, VIP
  • From glands e.g bradykinin
  • Via decreased O2 concentration in gut wall due to increased metabolism
  • Via subsequent adenosine release

MD3002 Physiology (24 decks)

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