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MD2001 > GI system > Flashcards

GI system Flashcards

1
Q

What are the functions of the GI system ?

A
  1. Absorption of Dietary Nutrients
  2. Motility (moving and mixing food through coordination contraction and relaxation of the walls)
  3. Storage (until next stage of GI ready for it)
  4. Excretion
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2
Q

What are the main layers of the GI tract ?

A

Mucosa, submucosa, muscularis externa, serosa

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3
Q

What are the components of the mucosa (describe each) ?

A

Epithelium- single cell layer, shed and replaced every 3 days. Apical side faces GI lumen while basolateral side faces interstitium and vasculature. May have vili and crypts depending on where in GI tract.

Lamina propria- Loose CT made of elastin and collagen fibres. Contains sensory nerves, blood, lymph vessels and sensory glands

Muscularis mucosa- thin layer of smooth muscle, increases SA by creating ridges and folds. Also role in motility.

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4
Q

What is the characteristic component of the submucosa ?

A

Meissner plexus, made of blood vessels and nerve bundles

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5
Q

Which layer of the mucosa is the submucosa similar to ?

A

Lamina propria

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6
Q

What are the components of the muscularis externa ?

A

Circula muscle

Myenteric plexus (Auerbach plexus)

Longitudinal muscle

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7
Q

How do the different muscles present in the muscularis externa lead contract (as coordinated by ENS) ?

A

Circular muscle is pinched, so that the diameteter of the lumen decreases. Longitudinal muscle contractions shorten the legnth of the tubes.

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8
Q

What is the function of these contractions ?

A

Mixing and moving the contents between compartments

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9
Q

Which structure regulate flow from one compartment to the next ?

A

Sphincter

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10
Q

What are the components of the serosa ?

A

A layer of CT and a layer of squamous epithelial cells

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11
Q

Which of the 4 main layers of the GI tract is not present everywhere ? Give an example.

A

The serosa. Oesophagus.

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12
Q

Which 3 divisions of the Autonomic NS regulate GI function ?

A

PSNS, SNS and ENS

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13
Q

Where is innervation of the PSNS derived from ?

A 
Vagus nerve (in the medulla oblongata) 
Pelvic-splanchnic nerves (S2-S4)
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14
Q

What does the PSNS respond to ?

A

Stretch of tube, P, Temperature, Osmolarity, Food composition

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15
Q

What are primary neurotransmitters used by the PSNS ?

A

ACh, Gastric-releasing peptide, substance P

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16
Q

What functions of the GI tract does the PSNS aid ?

A

Motility and Absorption of nutrients (by stimulating secretions)

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17
Q

Where is innervation of the SNS derived from ?

A

The nerves originate in thoracic (T5-T12) and lumbar (L1-L3) regions, then synapse in 1 of 3 ganglia.

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18
Q

What are the 4 ganglia in which the nerves of the SNS synpase and which part of the GI tract are innervated by each ?

A

Celiac ganglion, superior mesenteric and inferior mesenteric (innervate lower GI tract)
Superior cervical ganglion (innervate upper GI tract) )

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19
Q

Which neurotransmitters are used ?

A

Adrenaline and neuropepsin

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20
Q

What is the overall function of the SNS ?

A

Decreasing GI secretions and motility

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21
Q

What is the relationship between the PSNS and SNS, and the ENS ?

A

The PSNS and SNS synpase with ENS components and modulate it

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22
Q

Can the ENS operate autonomously ? How or how not ?

A

Yes, visa intrinsic regulations and sensory reflexes

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23
Q

What are the two main organisations of the ENS ?

A

Myenteric plexus and submucosal plexus

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24
Q

What is the primary role of the myenteric plexus ?

A

Regulating intestinal smooth muscle (leads to contractions)

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25
Q

What are the primary roles of the submucosal plexus ?

A

Regulating intestinal secretions and local absorptive environment, and synapsing on blood vessels, circular and longitudinal muscle and muscularis mucosa

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26
Q

What is the structural configuration of the myenteric plexus ?

A

Dense parallel neuronal configuration

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27
Q

What are enteric glial cells ?

A

Structures which support ENS neurones

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28
Q

What is the path from innervation to secretion when mechanoreceptors or chemoreceptors are stimulated ?

A

Mechanoreceptors or chemoreceptors stimulated in musosa—-> signal transmitted back to neurons in submucosal plexus —-> other neurons in submucosal or myenteric plexuses stimulated —–> they regulate endocrine or secretory cells

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29
Q

What neurotransmitters are used in the ENS ?

A 
Enkaphalins
Vasoactive intestinal peptide
Substance P
ACh
Nitric Oxide
Serotonin
30
Q

ACh:

1) Which NS ?
2) Which structures ?
3) What function ?

A

1) PSNS and ENS
2) Smooth muscles, glands
3) contracts wall muscles, relaxes sphincters, increases salivary gastric and pancreatic secretions

31
Q

VIP

1) Which NS ?
2) Which structures ?
3) What function ?

A

1) PSNS and ENS
2) Smooth muscles, glands
3) relaxes sphincter, increase pancreatic and intestinal secretions

32
Q

Noradrenaline

1) Which NS ?
2) Which structures ?
3) What function ?

A

1) SNS
2) Smooth muscles, glands
3) Relaxes muscle wall, contracts sphincters, decrease salivary secretions

33
Q

Neuropeptide Y

1) Which NS ?
2) Which structures ?
3) What function ?

A

1) SNS and ENS
2) Smooth muscles, glands
3) Relaxes muscle wall, decrease intestinal secretions

34
Q

Gastric-releasing Peptide

1) Which NS ?
2) Which structures ?
3) What function ?

A

1) PSNS and ENS
2) Glands
3) Increase gastric secretions

35
Q

Substance P

1) Which NS ?
2) Which structures ?
3) What function ?

A

1) PSNS and ENS
2) Smooth muscles, glands
3) Contracts muscle wall, increase salivary secretions

36
Q

Enkaphalins

1) Which NS ?
2) Which structures ?
3) What function ?

A

1) ENS
2) Smooth muscles, glands
3) Constricts sphincter, decrease intestinal secretions

37
Q

Which non-neuronal signalling molecules exist ?

A

Hormones and Paracrine

38
Q

CCK (cholecystokinin)

1) Releasing cell ?
2) Structures it affects ?
3) Function ?

A

1) I cells
2) Panreas, gall bladder, stomach
3) Increase enzyme secretion, contracts gallbladder, increase gastric emptying

39
Q

Gastrin

1) Releasing cell ?
2) Structures it affects ?
3) Function ?

A

1) G cells
2) Stomach
3) Increase gastric acid secretion

40
Q

Motilin

1) Releasing cell ?
2) Structures it affects ?
3) Function ?

A

1) M cells
2) GI smooth cells
3) Increase contractions and migrating motor complexes

41
Q

Secreting

1) Releasing cell ?
2) Structures it affects ?
3) Function ?

A

1) S cells
2) Pancreas, stomach
3) Releases HCO3- and pepsin

42
Q

Glucose-dependant-insulinotropic peptide

1) Releasing cell ?
2) Structures it affects ?
3) Function ?

A

1) K cells
2) Pancreas, stomach
3) Releases insulin, inhibits acid secretion

43
Q

Give me 3 examples of paracrine secretions.

A

Histamine, Prostaglandins, Somastatin

44
Q

Give me 6 examples of hormones.

A

CCK, Gastrin, Motilin, secretin, GDIP.

45
Q

Histamine

1) Releasing cell ?
2) Structures it affects ?
3) Function ?

A

1) Mast Cells
2) Stomach
3) Increase gastric acid secretions

46
Q

Prostaglandins

1) Releasing cell ?
2) Structures it affects ?
3) Function ?

A

1) Cells lining the GI tract
2) Mucosa
3) Increase blood flow and mucus and HCO3- secetion

47
Q

Somastatin

1) Releasing cell ?
2) Structures it affects ?
3) Function ?

A

1) D cells
2) Stomach and pancreas
3) Inhibits peptide hormones an gastric acid secretions

48
Q

What is one significant difference between prostaglandins and somastatin, and histamine ?

A

The release and actions of the first two more widespread

49
Q

What are the 3 digestive phases (describe what happens in each: when does it start and which kind of response is elicited) ?

A

Cephalic (thought of food or conditions suggestive of previous food intake. Primarily neural and causes ACh and VIP releases stimulating secretions by salivary glands stomach, pancreas, intestine)

Gastric (begins when food enters stomach. Distention elicits neural, hormonal, paracrine responses)

Intestinal (when stomach contents reach duodenum. Response is primarily hormonal, but also neural and paracrine)

50
Q

What is the main function of the mouth ?

A

Mechanical and chemical breakdown of food

51
Q

List the salivary glands. How much saliva do they produce per day ?

A

Sublingual, submandibular, parotid gland. Produce 1-1.5 L saliva per day

52
Q

What is the relation of saliva and plasma in terms of tonicity ?

A

Saliva is hypotonic to plasma

53
Q

What is the composition of saliva determined by ?

A

By ductal modification of primary secretion.

54
Q

Is action of the oesophagus voluntary or involuntary ?

A

Initiated: largely voluntary

Once it is initiated: involuntary

55
Q

Which reflex activities take place as food goes down from mouth to oesophagus ?

A

Soft palate closes access to nasopharynx, larynx and hyoid bone move upwards and epiglottis closes, upper oesophageal sphincter relaxes

56
Q

What is the Parasympathetic process taking place in the oesophagus ?

A
  • Afferent feedback to swallowing centre
  • Efferent responses through other nuclei (muscle contracted proximal to distal, and coordinates swallowing reflex with other functions like breathing)
57
Q

What is peristalsis?

A

Series of coordinated muscle contractions (above food) and relaxations (below food) commencing after oesophageal sphincter and taking 6-10 seconds

58
Q

What are the functions of the stomach ?

A

Accepting and storing food
Mixing food with secretions
Digesting food
Delivering food to small intestine through pyloric sphincter

59
Q

Where are the stomach secretions derived from ?

A

Gastric invagination = pits

60
Q

Which regional differences exist in the pits ?

A

Near sphincter, pits have more mucus cells to secrete mucus to protect that areas from the very acidic environment.

61
Q

What are examples of cells found in the pit ?

A

G cells (gastrin), D cells (somastatin), chief cells (pepsinogen), parietal cell (HCl and intrinsic factor)

62
Q

How is the food mixed in the stomach ?

A

Thanks to waves of contraction produced by pacemaker cells in the stomach

63
Q

How long is the duodenum ?

64
Q

How long is the jejunum ?

A

Next 2.3 m

65
Q

How long is ileum ?

66
Q

What are the main functions of the small intestine and how does the structure of the small intestine facilitate this ?

A

Absorption of macronutrients, vitamins and minerals. Thanks to large SA created by vili and microvili. Also, mixing visa segmentation and propulsion via peristalsis. (thanks to migrating motor complexes).

67
Q

What are the sections of the large intestine ?

A

Caecum, ascending transverse and descending colon, rectum, and anus

68
Q

What is the main function of the large intestine ?

A

Water and ion absorption (no significant nutrient absorption), and motility of content (mixing and moving them forward for defecation)

69
Q

What part of the NS controls salivary secretions and what are the two steps involved in modifying salivary secretions ?

A

The SNS and PSNS.
1- Cl- and Na+ and wanter transported into the duct lumen
2- Ductal cells modify this fluid by reabsorbing Na+ and Cl-, and secreting K+ and HCO3-

70
Q

How is motility regulated in the large intestine ?

A

Through segmentation, peristalsis and reflexes controlling sphincter contraction and relaxation (ileocecal sphincter regulating how much enters chyme entering AND internal and external anal sphincters regulate fece

MD2001 (35 decks)

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