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PHSL233 > Lecture 24 - Organisation and Regulation > Flashcards

Lecture 24 - Organisation and Regulation Flashcards

1
Q

What is the overall function of the GI tract ?

A

The gastrointestinal tract takes in food, digests it to extract and absorb metabolites for the growth and energy needs of the body plus fluid and electrolytes to replace losses, and expel the remaining waste.

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2
Q

What is the gastrointestinal system? (overall)

A

A long epithelium lined tube
Functional sections separated by sphincters
Connected to accessory exocrine glands.

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3
Q

What makes up the long epithelium lined tube of the GI system?

A

Mouth
Pharynx
Oesophagus
Stomach
Large intestine
Small intestine (Duodenum, Jejunum and Ilium)
Anus

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4
Q

What are the sphincters of the GI system?

A

Upper oesophageal sphincter
Lower oesophageal sphincter
Pyloric sphincter
Sphincter of Oddi
Ileocecal valve
Anal sphincters

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5
Q

What are the accessory exocrine glands of GI system?

A

Salivary glands
(Sublingual Salivary glands, Submandibular salivary glands, Parotid salivary glands)
Liver
Gall bladder
Pancreas

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6
Q

What are the layers of the GI tract?

A

In the GI tract we have 4 layers: mucosal, submucosal, muscle, and serosal.
These layer differs between area of GI tract

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7
Q

What makes up the mucosal layer of the GI tract?

A

Epithelium, lamina propria, muscularis mucosae

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8
Q

What makes up the sub-mucosal layer of the GI tract?

A

submucosal plexus, connective tissue, blood vessels

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9
Q

What makes up the muscle layer of the GI tract?

A

muscle layers, myenteric plexus

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10
Q

What is the serosal layer of the GI tract?

A

Outer sheath

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11
Q

What must the gut do to carry out the overall function of the GI system?

A

To do this gut must
- reduce size of food to allow absorption
- deliver material to site of absorption
- absorb necessary material & excrete the rest
- act as a barrier to pathogens and disease

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12
Q

What are the four main functions of the gastrointestinal system?

A

Motility
Secretion
Digestion
Absorption

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13
Q

What is the purpose of motility in the GI system?

A

Moves food along the tract.

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14
Q

What is the purpose of secretion in the GI system?

A

Maintain an environment for digestive functions
(Water, Salt, and Enzymes)

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15
Q

What is the purpose of digestion in the GI system?

A

Mechanical and chemical processes that break down food

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16
Q

What is the purpose of absorption in the GI system?

A

Uptake (or reuptake) of nutrients, salts and water into the body

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17
Q

What are the general principles of regulation in the GI system?

A

Regulate the composition of the lumen
GI reflexes initiated by stretch and chemical composition
Stimuli act on mechano-, osmo- and chemoreceptors

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18
Q

What type of stretch does the GI respond to?

A

Distension of GI wall by volume of contents

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19
Q

What does the receptors of the GI system respond to?

A

Chemical composition of luminal contents:
osmolarity of chyme
pH of chyme
concentration of products of digestion in the chyme e.g., amino acids, fatty acids

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20
Q

What is the regulation by homeostasis in the GI system?

A

Controlled variable: Conditions in the GIT lumen
Receptors: Special senses, Chemo, Osmo, Mechano Receptors.
Signal pathways: Neural (CNS and ENS), Hormones.
Effectors: GIT smooth muscle (motility), epithelial cells (secretion and absorption)

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21
Q

What are the phases of Gastric (stomach) Regulation?

A

Cephalic phase - Preparative
Gastric phase - Digestive
Intestinal phase - Controlled release

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22
Q

What happens in the cephalic phase of gastric (stomach) regulation?

A

Prepare for food intake
Detect: Sense food - sight, smell, taste
Prepare: the GIT lumen (CNS via ENS)

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23
Q

What happens in the gastric phase of gastric (stomach) regulation?

A

Digestion of stomach contents
Detect: Distension, pH, Nutrients
Prepare: Send signals via ENS, CNS, hormones (e.g. Gastrin)

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24
Q

What happens in the intestinal phase of gastric (stomach) regulation?

A

Control release of contents to match capacity of slow intestine
Detect: Stretch, acid , osmolarity, nutrients
Prepare: ENS, CNS, hormones (e.g CCK and Secretin)

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25
Q

Why do we have phased gastric (stomach) regulation?

A

The GI tract has different functions at different phases of digestion. The regulation of the stomach changes to facilitate these different functions.

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26
Q

What is the neural regulation of the GI tract?

A

Rapid precise regulation (e.g. secretion of saliva) that involves:
Extrinsic reflexes involving CNS
Intrinsic (local) reflexes of enteric nervous system (ENS)

27
Q

What is the role of extrinsic reflexes involving CNS in GI tract neural regulation?

A

Regulation and co-ordination of GI function over long distances or where we want external input
Examples:
- Gastrointestinal reflex
- Complex behaviours such as swallowing

28
Q

What is the role of intrinsic (local) reflexes of enteric nervous system (ENS) in GI tract neural regulation?

A

Regulation over centimetres (local reflexes)
e.g. Gastroenteric reflex
Signals originate in CNS but act via ENS

29
Q

What are the neuron types and ENS structures in GI tract innervation?

A

Neuron types:
- Autonomic NS neurons
- Enteric NS neurons
ENS structures:
- Submucosal plexus
- Myenteric plexus

30
Q

What are the autonomic NS neurons of the GI tract?

A

Parasympathetic, Sympathetic
Both Motor & Sensory.
Provide a route for interaction between CNS and ENS.

31
Q

What are the enteric NS neurons of the GI tract?

A

Sensory (mechano / chemo)
Interneurons
Efferent neurons (motor and secretory),
Interstitial cells of Cajal (GI Pacemakers)

32
Q

What is the role of the submucosal plexus in the GI tract?

A

Controls the mucosa (secretion, absorption, movement of villi)

33
Q

What is the role of the myenteric plexus in the GI tract?

A

Controls the muscularis (motility)

34
Q

What does Extrinsic (external) regulation by the CNS mostly act via in the GI tract?

A

Mostly acts via the peripheral autonomic pathways innervating the ENS.
Does not directly innervate gastrointestinal intestinal epithelial or muscle

35
Q

What does extrinsic (external) regulation by the CNS mostly in the GI tract do?

A

Modulates the activity of the enteric nervous system
Parasympathetic nervous system
Sympathetic nervous system
Respond to both internal and external stimuli

36
Q

What is the effect of the parasympathetic nervous system in the GI system?

A

Usually stimulates activity
- Acetylcholine, detected by muscarinic receptors

37
Q

What is the effect of the sympathetic nervous system in the GI system?

A

Usually inhibitory
- Noradrenaline, detected by α adrenergic receptors

38
Q

What is the internal stimuli for regulation by CNS in the GI system?

A

luminal composition and volume

39
Q

What is the external stimuli for regulation by CNS in the GI system?

A

Mood, thought, smell, sight

40
Q

What do both sympathetic and parasympathetic interact with in the GI system?

A

Afferent fibers of sensory ENS neurons
- Detect information regarding state of gut and relay it (via autonomic NS) to the CNS
Efferent fibers of the ENS
- Signal a response in smooth muscle cells or epithelial cells
Exception: Upper structures involved in swallowing are directly controlled (don’t have ENS neurons).

41
Q

Where are terminals of ENS sensory neurons located in gut?

A

In all layers

42
Q

What do the ENS sensory neurons in gut sense and where does it relay information?

A
  • Nature of luminal contents – pH, osmolality, nutrient content (via interactions with enteroendocrine cells),
  • Stretch/contraction
  • Painful stimuli
    Relay it to CNS via the Autonomic pathways
43
Q

What do the sympathetic pathways do in response to external stimuli via ANS?

A

Reflexes that generally inhibit GI function.
Noradrenaline, detected by α adrenergic receptors.

44
Q

What do the parasympathetic pathways do in response to external stimuli via ANS?

A

Reflexes that generally stimulate GI function
Acetylcholine, detected by muscarinic cholinergic receptors.

45
Q

What is the CNS response pathway to internal stimuli in the GI tract (GI lumen contents)?

A

Long Reflex Path – Gut to brain and back again!

46
Q

What is the enteric nervous system grouped into?

A

Submucosal plexus
* Secretory activity of epithelial and glands
Myenteric plexus
* Smooth muscle

47
Q

What is the ENS?

A

The ENS is self contained system that can perform short local reflexes (over cm’s) independent from the CNS

48
Q

Where are the ENS receptors in the GI system?

A

In the GI tract wall

49
Q

What do the GI tract wall ENS receptors respond to?

A

Respond to various stimuli
- Stretch, pH, osmolarity, products of digestion

50
Q

What do the GI tract wall ENS receptors modulate?

A

Through local reflexes modulate
- Smooth muscle, secretory cells

51
Q

What are the stimulatory ENS neurotransmitters in the GI tract?

A

Acetylcholine and tachykinins (Substance P, neurokinin A – you don’t need to know the details)

52
Q

What is the inhibitory ENS neurotransmitters in the GI tract?

A

Mainly nitrous oxide – (also VIP, ATP)

53
Q

What does adrenaline do in the GI tract?

A

Adrenaline from the sympathetic nervous system will send inhibitory signal to ENS neurons – ENS neurons inhibit by different neurotransmitters.

54
Q

Where is the myenteric plexus in the GIT?

A

Between longitudinal and circular muscle layers

55
Q

Where is the submucosal plexus in the GIT?

A

Between mucosa and circular muscle layers

56
Q

What is the hormone response time in GI tract?

A

Hormones have a slow but sustained action due to long time for meal digestion (few hours)

57
Q

Where are GI hormones secreted?

A

GI hormones are secreted by enteroendocrine cells throughout the intestinal tract

58
Q

What are the Enteroendocrine cells?

A

Located in epithelial layer
Exposed to luminal contents
- Respond to changes in luminal contents
- Granules containing hormones in the basolateral pole.
Regulated by both extrinsic (hormones) and intrinsic stimuli (inside gut).

59
Q

What type of hormone are GI hormones?

A

Peptide hormones - water soluble with extracellular receptors

60
Q

What are GI hormone features? (5)

A

Peptide hormones
Participate in feed back regulation of some aspect of luminal contents
Often regulate more than one cell type in more than one organ
Potentiation is common
Often have a trophic effect

61
Q

What is the function of the GI immune system?

A

Barrier function
Active immune response
Modulator of GI tract (and systemic) physiology
Tolerance

62
Q

What does the GI immune system respond to?

A

Food antigens, pathogens
NOT commensal/mutualistic bacteria
- Important to target some but not others

63
Q

What happens once GI immune system activated?

A

Releases inflammatory and other mediators that modulate GI function
- Histamine, prostaglandins, leukotrienes, cytokines

64
Q

What does the GI immune system consist of?

A

Mesenteric lymph nodes, Peyers patches & range of immune cells
- (Intraepithelial lymphocytes, B & T cells, mast cells, macrophages, eosinophils)

PHSL233 (32 decks)

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