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MD2001 > Gastrointestinal System > Flashcards

Gastrointestinal System Flashcards

1
Q

What is the primary function of the GI?

A

Absorption of dietary nutrients, a process maximised by secretions added along the “tube” that convert large molecules to smaller ones - digestion

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2
Q

What are other functions of the GI system?

A

+ Storage

+ Excretion

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3
Q

What is the mucosa?

A

A single cell layer forming a continuous inner lining of GI tract

Mucosa = epithelium + lamina propria + muscularis mucosa

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4
Q

How often is the mucosal epithelia shed and replaced?

A

Every 2-3 days

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5
Q

Where does the apical side of the mucosal epithelium layer face?

A

GI lumen

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6
Q

Where does the basolateral side of the mucosal epithelium layer face?

A

Interstitium & vasculature

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7
Q

What are features of the mucosa in regards to the muscularis mucosa?

A

+ Thin layer of smooth muscle

+ Further increases surface arrea by creating ridges and folds

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8
Q

What are the features of the mucosa in regards to villi and crypts?

A

+ Extent of villi and crypts vary with GI section function e.g absorption vs motility

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9
Q

What are the features of the mucosa in regards to the lamina propria

A

+ Loose CT made up of elastin & collagen fibres

+ Contain sensory nerves, blood & lymph vessels, and secretory glands

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10
Q

What are the 4 different GI layers?

A
  1. Mucosa
  2. Submucosa
  3. Muscularis externa (ME)
  4. Serosa
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11
Q

What are features of the submucosa layer of the GI?

A

+ Thick layer with similar compostition to lamina propria

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

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12
Q

What are features of the muscularis externa (ME) layer of the GI?

A

ME = circular muscle + myenteric plexus + longitudinal muscle (Auerbach plexus)

+ Muscle layers named based on circulation

+ ENS co-ordinated contractions to mix and move contents between compartments

+ Sphincters regulate flow from one compartmetn to the next

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13
Q

What is the ENS?

A

Enteric nervous system: a subdivision of the autonomic nervous system (ANS) that directly controls the gastrointestinal system

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14
Q

What are features of the Serosa layer of the GI

A

+ Outermost layer of CT and layer of squamous epithelial cells

+ Some GI tract sections do not have a serosal layer (e.g oesophagus) but connect directly with adventitia (i.e CT that blends into abdominal or pelvic wall)

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15
Q

Gi function is regulated by which 3 divisions of the autonomic nervous system (ANS)?

A

+ Parasympathetic (PSNS)
+ Sympathetic (SNS)
+ Enteric (ENS)

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16
Q

Where is innervation derived from in the PSNS?

A

+ Vagus (medulla oblongata)

+ Pelvic-splanchnic nerces (S2-S4)

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17
Q

What do the sensory and motor components of the PSNS respond to?

A

+ Stretch
+ Pressure
+ Temperature
+ Osmolarity

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18
Q

In the PSNS, what primary NTs are used?

A

+ Acetylcholine (ACh)
+ Gastric releasing peptide
+ Substance P

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19
Q

What is the role of the PSNS in the GI system?

A

PSNS stimulates:

  • GI secretions
  • motility facilitating digestion
  • absorption of nutrients
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20
Q

Where do the nerves of the SNS originate?

A

+ T5-T12

+ L1-L3

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21
Q

Where do the nerves of the SNS synapse?

A 
In 1 of 3 ganglia:
- celiac
- superior mesenteric
- inferior mesenteric 
(for lower GI system)
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22
Q

What are features of the SNS?

A

+ Upper GI tract innervates by nerves that synapse in superior cervical ganglion

+ Generally decreases GI secretions and motility

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23
Q

What are features of the ENS?

A

+ PSNS & SNS usually synapse with ENS components and modulate the ENS

+ But ENS can operate autonomously via intrinsic regulation & sensory reflexes

+ ENS nerves are organised into myenteric & submucosal plexuses

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24
Q

What are features/functions of the myenteric plexus?

A

+ A dense parallel neuronal configuration

+ Primary role of regulating intestinal smooth muscle

+ Participates in tonic & rhythmic contractions

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25
Q

What are features/functions of the submucosal plexus?

A

+ Primarily regulates intestinal secretions & local absorptive environment

+ Can also synapse on blood vessels, circular & longitudinal muscle, muscularis mucosa

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26
Q

What are ENS neurones supported by?

A

Enteric glial cells - resemble brain astrocytes

27
Q

What are the plexuses of the ENS?

A

+ Myenteric

+ Submucosal

28
Q

How are reflex actions in the ENS regulated?

A

+ Neural circuits involving mechanoreceptor/chemoreceptor stimulation in the mucosa regulate many GI reflex actions

+ Signal transmitted back to neurons in submucosal plexus, which stimulate other neurons in submucosal or myenteric plexus that regulate endocrine or secretory cells

29
Q

What are some NTs of the ENS?

A

+ Enkaphalins: constrict circular muscle around sphincters

+ VIP, substance P, ACh, nitric oxide, serotonin (5-hydroxytryptamine (5-HT))

30
Q

What hormones are involved in the GI system?

A 
\+ Cholecystokinin (CCK)
\+ Glucose-dependent insulinotropic peptide
\+ Gastrin
\+ Motilin
\+ Secretin
31
Q

What are the 1) releasing cells, 2) associated structures and 3) functions of CCK?

A
  1. I cells
  2. Pancreas, gallbladder, stomach
  3. Increases enzyme secretion; contracts gallbladder; increases gastric emptying
32
Q

What are the 1) releasing cells, 2) associated structures and 3) functions of glucose-dependent insulinotropic peptide?

A
  1. K cells
  2. Pancreas, stomach
  3. Releases insulin; inhibits acid secretion (H+)
33
Q

What are the 1) releasing cells, 2) associated structures and 3) functions of gastrin?

A
  1. G cells
  2. Stomach
  3. Increases gastric acid secretion (H+)
34
Q

What are the 1) releasing cells, 2) associated structures and 3) functions of motilin?

A
  1. M cells
  2. Gastrointestinal smooth muscle
  3. Increases contractions and migrating motor complexes
35
Q

What are the 1) releasing cells, 2) associated structures and 3) functions of secretin?

A
  1. S cells
  2. Pancreas, stomach
  3. Releases HCO3-, water and pepsin, decrease gastric acid H+
36
Q

What are features of paracrines involved in the GI system?

A

+ Released and act locally

+ Prostaglandins & somatostatin are more widespread in their release and actions than histamine

37
Q

What paracrines are involved in the GI system?

A

+ Histamine
+ Prostaglandins
+ Somatostatin

38
Q

What are the 1) releasing cells, 2) associated structures and 3) functions of histamine?

A
  1. Enterochromaffin-like cells, mast cells
  2. Stomach
  3. Increases gastric acid secretion (H+)
39
Q

What are the 1) releasing cells, 2) associated structures and 3) functions of prostaglandins?

A
  1. Cells lining GI tract
  2. Mucosa
  3. Increases blood flow and mucus and HCO3- secretion, decreasing gastric acid (H+) secretion and maintaining GI barrier properties
40
Q

What are the 1) releasing cells, 2) associated structures and 3) functions of somatostatin?

A
  1. D cells
  2. Stomach and pancreas
  3. Inhibits peptide hormones and gastric acid secretion (H+)
41
Q

Which GI NTs & NMs contract the wall muscle?

A

+ ACh
+ Substance P
+ Enkephalins

42
Q

Which GI NTs & NMs relax the wall muscle?

A

+ Norepinephrine
+ Neuropeptide Y
+ Vasoactive intestinal peptide

43
Q

What are the 3 digestive phases?

A

+ Cephalic
+ Gastric
+ Intestinal

44
Q

What is involved in the cephalic phase of digestion?

A

+ Triggered by thought of food, conditions suggestive of previous food intake

+ Primarily neural & causes ACh & VIP release
- stimulates secretion by salivary glands, stomach, pancreas, intestines

45
Q

What is involved in the gastric phase of digestion?

A

+ Begins when food and oral secretions enter stomach

+ Coincides with distension

+ Elicits neural, hormonal, paracrin GI response

46
Q

What is involved in the intestinal phase of digestion?

A

+ Begins when stomach contents reach duodenum

+ Initiates primarily hormonal, but also paracrine & neural responses

47
Q

What is secretion?

A

The act of transporting molecules or fluid from the body to the GI lumen

48
Q

What is the role of the upper GI tract?

A

+ Minimal role in nutrient absorption

+ Transports and prepares food to be absorbed
- i.e breaking into smaller pieces, hydrating it to improve environment for enzymatic actions

49
Q

What is the role of the mouth and associated structures?

A

Mouth: mechanical + chemical breakdown
- mastication = chewing

Teeth: cut, tear & pierce, crush and grind
- jaw muscles provide force and movement

Tongue: repositions food, tastes

50
Q

What are features of the salivary glands and their secretions?

A

+ Saliva:

  • watery fluid lubricates mouth - begins food digestion
  • protective

+ 1-1.5 L saliva/day mainly by sblingual, submandibular and parotid glands

+ Hypotonic to plasma
- composition determined by ductal modification of primary secretion

51
Q

What is peristalsis?

A

+ Series of co-ordinated muscle contractions/relacxtions (waves)

+ Commences after upper oesopheageal sphincter

+ Journey takes ~6-10s

52
Q

What is the function of the stomach?

A

+ Accept & stores food
+ Mix food with secretions
+ Digest food
+ Deliver food to small intestine

53
Q

What do pacemaker cells do in the stomach?

A

Initiate an action potential that drives waves of contraction thorugh the stomach, mixing and grinding its contents

54
Q

What are the 3 sections of the stomach?

A
  1. Fundus
  2. Body
  3. Antrum
55
Q

What are the 3 primary motility functions of the stomach?

A
  1. Accommodation via receptive relaxation
  2. Mixing via slow wave-initiated contractions and retropulsion
  3. Gastric emptying
56
Q

What is included in gastric secretions?

A 
\+ Ions
\+ Water
\+ Mucus from mucous neck cells
\+ Pepsinogen from chief cells
\+ Intrinsic factor and H+ from parietal cells
57
Q

Regulation of H+ secretion occurs at the level of the H+-K+ ATPase. What increases secretion of H+?

A

+ ACh from nerves
+ Gastrin from G cells
+ Histamine from enterochromaffin-like cells

58
Q

Regulation of H+ secretion occurs at the level of the H+-K+ ATPase. What decreases secretion of H+?

A

+ Somatostatin from D cells

+ Prostaglandins

59
Q

The small intestine id the longest section of GI tract: what does this comprise of?

A

+ Duodenum ~0.3m
+ Jejunum ~2.3m
+ Ileum ~3.4m

60
Q

What occurs in the small intestine?

A

+ It is where most macronutrient, vitamin, and mineral absorption occurs:
- facilitated by huge surface area increase created by villi (10-fold) and microvilli (20-fold)

+ Mixing via segmentation; propulsion via peristalsis

61
Q

What are the components of the large intestine?

A
  1. Cecum
  2. Ascending, transverse, descending, sigmoid colon
  3. Rectum
  4. Anus
62
Q

What occurs in the large intestine?

A

+ Significant water and ion absorption

+ Motility of contents: segemtation via mixing, propulsion via peristalsis and mass movement

63
Q

What is the role of the ileocecal sphincter?

A

To regulate the amount of chyme entering the large intestine

64
Q

What is the tole of the internal and external anal sphincters?

A

To regulate the faeces exiting the GI system

MD2001 (52 decks)

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