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Physiology > Lecture 40: GI Organisation and Regulation > Flashcards

Lecture 40: GI Organisation and Regulation Flashcards

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1
Q

What is the GI tract?

A
  • Long epithelium lined tube that originates during embryonic folding
  • Functional sections are separated by sphincters
  • Connected to accessory exocrine glands
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2
Q

How does the GI tract carry out it’s functions?

A
  • Reduces size of food for absorption
  • Deliver material to site of absorption
  • Absorb material and excrete the rest
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3
Q

How does the GI tract act as a barrier?

A
  • To pathogens and disease
  • To digestive enzymes and acid
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4
Q

What are the functions of the GI tract?

A
  • Digests food to extract and absorb metabolites and replace fluid and electrolytes
  • Expels waste
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5
Q

What structures make up the tube of the GI tract?

A
  1. Mouth
  2. Pharynx
  3. Esophagus
  4. Stomach
  5. Small intestine
  6. Large intestine
  7. Anus
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6
Q

What are the 4 mechanisms of the GI tract?

A
  1. Absorption
  2. Motility
  3. Secretion
  4. Digestion
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7
Q

What are the accessory exocrine glands of the GI tract?

A
  1. Parotid salivary glands
  2. Sublingual salivary glands
  3. Submandibular glands
  4. Liver
  5. Gall bladder
  6. Pancreas
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8
Q

What are the sphincters of the GI tract?

A
  1. Upper oesophageal sphincter
  2. Lower oesophageal sphincter
  3. Pyloric sphincter
  4. Hepatopancreatic sphincter
  5. Ileocecal valve
  6. Internal and external anal sphincters
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9
Q

Name the 4 layers of the gut wall:

A
  1. Mucosal layer
  2. Submucosal layer
  3. Muscularis layer
  4. Serosal layer
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10
Q

What is the muscosal layer made up of?

A

Epithelium, lamina propria, muscularis mucosae

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11
Q

What is the submuscosal layer made up of?

A

Submusosal plexus, connective tissue blood vessels

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12
Q

What is the muscularis layer made up of?

A

Inner circular muscle, outer longitudinal muscle, myenteric plexus

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13
Q

What is the serosal layer made up of?

A

Outer sheath

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14
Q

What do tight junctions control?

A

Movement between cells

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15
Q

What is epithelia and what is the function?

A

Selective barrier of polarised cells to control movement in and out of the body

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16
Q

What do cell membranes control?

A

Movement through cells

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17
Q

How is epithelia in the small intestine specialised?

A

Has absorptive cells near the surface and secretory cells located in the crypts

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18
Q

How often does epithelium of the SI shed?

A

Epithelium replaced every 5 days

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19
Q

What are plicae circulares?

A

Folds containing a core of sub mucosa

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20
Q

How do the mucosa and submucosa work together?

A
  • Blood and lymphatic vessels in submucosa carry nutrients
  • Muscularis mucosa moves villus for absorption
  • Submucosal plexus for neural control of secretion, absorption and villi movement
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21
Q

What are villi?

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A

Folds containing a core of lamina propria

22
Q

What are microvilli?

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A

Finger like projections on the surface of epithelial cells

23
Q

Describe the macroscopic blood supply of the GI tract:

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A
  • ~25% cardiac output at rest
  • Postprandial hyperaemia (increased blood flow after eating)
  • Venous return via liver (hepatic portal vein) for toxin removal
24
Q

Describe the microscopic blood supply of the GI tract:

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A

Dense capillary beds penetrate:
* Mucosa of stomach - secretion
* Villi of SI - absorption
* Crypts of SI - secretion
* Mucosa of LI - secretion and absorption

25
What are the different neuron types in the enteric NS?
* Afferent sensory * Mechanoreceptors * Chemoreceptors * Interneurons * Efferent (motor and secretory)
26
What are the structures of the ENS?
* Submucosal plexus - controls mucosa (secretion, absorption, movement of villi) * Myenteric plexus - controls muscularis (motility)
27
What are the homeostatic variables of the GI tract?
* Controlled variables: conditions in lumen * Receptors: chemo, mechano, osmo * Signals: neural and hormonal * Effectors: GI tract smooth muscle and epithelial cells
28
What is phased regulation of the GI tract?
* GI tract has different functions at different phases of digestion * Regulation of the stomach changes to facilitate these functions
29
What is the cephalic phase?
Preparative - Detect: food - sight, smell, taste - Prepare: GIT lumen - CNS via ENS
30
What is the gastric phase?
Digestive - Detect: distension, pH, nutrients - Prepare: send signals via ENS, CNS, hormones e.g. gastrin
31
What is the intestinal phase?
Controlled release - Detect: stretch, acid, osmolarity, nutrients - Prepare: ENS, CNS, hormones e.g. CCK and secretion
32
What do the extrinsic reflexes of the GIT involve?
CNS * Regulation and coordination of GI function over long distances e.g. complex behaviours such as swallowing
33
What do the intrinsic (local) reflexes involve?
ENS * Regulation over centimetres e.g. relaxation of the internal anal sphincter in response to rectal distention
34
What do ENS regulation provide?
Rapid precise regulation of smooth muscle and secretory and absorptive epithelial cells
35
Describe the response of the ENS to a change in GIT lumen content:
1. Chemo, osmo, mechanoreceptors 2. ENS 3. GIT smooth muscle: motility - myenteric plexus; controls motility - submucosal plexus; controls secretion and absorption 4. GIT epithelium: absorption/secretion
36
Where are the receptors of the ENS located and what do they respond to?
* GI tract epithelium and wall * Respond to stretch, pH, osmolarity, products of digestion
37
What are the stimulatory neurotransmitters of the ENS?
Acetylcholine and tachykinins
38
What are the inhibitory neurotransmitters of the ENS?
NO, VIP, ATP
39
What are the 2 sensory pathways of the extrinsic regulation of the GIT?
1. External receptors 2. Long reflex loop
40
What are the external receptors of the extrinsic regulation of the GIT?
* Somatic and special senses detect conditions that might impact the GIT * CNS sends messages to ENS via the autonomic NS
41
What is the long reflex loop of the extrinsic regulation of the GIT?
* Receptors send messages to brain via ENS and afferent autonomic pathways * Brain sends coordinating messages back to ENS via efferent autonomic neurons
42
Describe the sympathetic regulation of the GIT:
* Usually inhibitory * Noradrenaline, detected by α-adrenergic receptors * Short pre-ganglionic and long post-ganglionic
43
Describe the parasympathetic regulation of the GIT:
* Usually stimulates activity * Acetycholine, detected by muscarinic receptors * Long pre-ganglionic and short post-ganglionic
44
How fast acting are hormones and how are they regulated?
* Slow but sustained action * Regulated by intrinsic and extrinsic stimuli
45
Where are GI hormones secreted and where are their effectors?
* Secreted by enteroendocrine cells throughout the intestinal tract * Multiple effector sites - coordinate phases of digestion
46
How are enteroendocrine cells positioned and what do they respond to ?
* Exposed to the lumen of the GIT * Respond to changes in the luminal contents by releasing (exocytosis) granules containing hormones - Can also be neural receptors
46
Name the 4 functions does the immune system has in the GIT:
1. Modulator of GIT 2. Barrier 3. Active immune response 4. Tolerance
47
How is the immune system a modulator of the GIT?
1. Interacts with intestinal bacteria 2. Releases inflammatory and other mediators e.g. Histamine, prostaglandins, leukotrines, cytokines
48
Describe the immune system tolerance in the GIT:
* Learning to recognise self * Inducing tolerogenic responses to innocuous food, commensals and self-antigens
48
What components of the immune system make up the GIT?
* Epithelial barrier * Mesenteric lymph nodes * Peyers patches * Immune cells Note: be able to label diagram on onenote
48
What does the active immune response respond to in the GIT?
Food antigens, pathogens, commensal/mutualistic bacteria

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