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Semester 3 - Gastrointestinal > Brief intro to the GI tract > Flashcards

Brief intro to the GI tract Flashcards

1
Q

What structures form the alimentary canal?

A

Mouth, oesophagus, stomach, pancreas, duodenum, jejunum, ileum, cecum (of colon), large intestine, anus

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2
Q

What are the general functions of the mouth?

A

◦ Physical breakdown of food
◦ Initial digestive enzymes released
◦ Infection control

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3
Q

What enzymes are released in the mouth?

A

Amylase and lipase

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4
Q

What is the general functions of the oesophagus?

A

Rapid transport of bolus to stomach through thorax

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5
Q

What sphincters are present in the oesophagus and what are there functions?

A

Upper oesophgeal sphincter prevents air from entering GI. Lower oesophageal sphincter prevents reflux into oesophagus

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6
Q

What are the general functions of the stomach?

A 
◦ Storage facility
◦ To produce chyme
--> Physical breakdown
--> Chemical breakdown - proteases - acid helps unravel proteins for proteases to work on
◦ Infection control (HCL)
◦ Secrete intrinsic factor(Vit B12)
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7
Q

What is the importance of intrinsic factor and which cells is it secreted by?

A

Required for absorption of vitamin B12, secreted by parietal cells in the stomach

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8
Q

How many muscular layers does the stomach have and what are they?

A

Has 3 muscular layers instead of 2. Inner oblique, middle circular, outer longitudinal.

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9
Q

What is chyme?

A

A fluid that passes out from the stomach that consists of gastric secretions and partially digested food

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10
Q

What are the general functions of the duodenum?

A

Neuturalisation/osmotic stabilisation of chyme, digestion

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11
Q

What does the duodenum contain to help neutralise/osmotic stabilisation of chyme?

A

Hc03 rich scretions - from pancreas and liver

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12
Q

WHat are the different parts of the duodenum?

A

Superior duodenal flexure, descending part, horizontal part, ascending part.

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13
Q

Which part of the duodenum does the liver and pancreas connect to?

A

Second part (descending part) to deliver bile and pancreatic secretions into the gut tube

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14
Q

Why does water enter the duodenum?

A

Chyme is hypertonic as all the small molecules exert osmotic pressure which draws water in

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15
Q

What is present in the duodenum to help with digestion?

A

pancreatic secretions - enzymes

bile - emulsify fat

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16
Q

Where is the junction between foregut and midgut?

A

2nd part of duodenum where major pancreatic duct and common bile duct join the duodenum

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17
Q

What are the general functions of the jejunum/ileum?

A 
◦ Final digestion
◦ Nutrient absorption
◦ Water/electrolyte absorption
◦ Bile recirculation
◦ B12 absorption
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18
Q

Where does the majority of digestion and nutrient absorption occur?

A

jejunum

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19
Q

where does the majority of water absorption occur?

A

ileum

  • The colon absorbs the water that is hard to absorb.
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20
Q

where does bile recirculation occur?

A

ileum

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21
Q

where does B12 absorption occur?

A

terminal ileum

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22
Q

What feature of the jejunum help with nutrient absorption

A

rich in folds that increase surface area

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23
Q

What are the general functions of the large bowel?

A 
◦ Final water absorption
◦ Temporary storage
◦ Final electrolyte absorption
◦ Some bile salt absorption
◦ Production of some SCFAs
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24
Q

Describe how the surface of large bowel is different to mall bowel?

A

large bowel has bacteria which forms a microbiome and is important for normal function and for general health

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25
Q

what is the function of the rectum/anus?

A

defecation - stretching of rectum as it fill gives the urge to defecate

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26
Q

What controls the gut?

A

◦ Autonomic nervous system (Parasympathetic and
sympathetic)
◦ Enteric nervous system
◦ Hormones and paracrine substances

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27
Q

What neurotransmitter is released from pre and postganglionic cells?

A

Pre: ACh from both parasympathetic and sympathetic.
Post: ACh(parasympathetic), neuropeptides, noradrenaline

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28
Q

What part of the nervous system is the main contributor to the digestive system?

A

Parasympathetic (rest and digest) on button

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29
Q

Where do pre and post ganglionic fibres synapse?

A

◦ The preganglionic fibre synapse with an autonomic ganglia outside the CNS
◦ Postganglionic fibre synapse on peripheral effector organs

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30
Q

Where do the cell bodies of the autonomic nervous system reside?

A

CNS

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31
Q

Which are the main nerves from the parasympathetic nervous system that contribute to the gut?

A

Vagus nerve (cranial nerve X) and Pelvic splanchnic nerves

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32
Q

What is the origin of the pelvic splanchnic nerves?

A

S2, S3, S4

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33
Q

What do postganglionic fibres of the parasympathetic system release?

A

ACh, Peptides (Gastrin releasing peptide, vasoinhibitory peptide)

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34
Q

Where do preganglionic parasympathetic fibres synapse and what do they innervate?

A

Synapse in the walls of the viscera and innervate smooth muscle/endocrine and secretory cells

35
Q

Where are the main innervation of the vagus and pelvic splanchnic nerves?

A

Vagus: oesophagus to transverse colon
Pelvic: transverse colon to anal canal

36
Q

Where do parasympathetic fibres of GI tract originate?

A

brain and sacral spine (craniosacral)

37
Q

What nerve roots contribute to the sympathetic nervous system?

38
Q

What is the root of the nerves from the sympathetic system that innervate the gut and what do they form?

A

T5-L2 (thoracolumbar)
Pass through (paravertebral) sympathetic trunk without synapsing
join with other preganglionic fibres to Form (abdominopelvic) presynaptic splanchnic nerves

39
Q

What is the root of the different splanchnic nerves?

A 
o Greater (T5-9)
o Lesser (T10-11)
o Least (T12)
40
Q

What do the thoracic splanchnic nerves synapse with and where are they found?

A

Synapse with prevertebral ganglia found anterior to the vertebrae

41
Q

Which ganglia do the thoracic splanchnic nerves synapse with?

A

◦ Coeliac, renal, superior mesenteric, inferior mesenteric and others

Greater with coeliac ganglia, lesser with superior mesenteric, least with inferior mesenteric

42
Q

What do the postganglionic sympathetic neurones innervate?

A

Mainly innervate blood vessels

43
Q

What is the main action of sympathetic system in GI tract

A

constrict blood vessels to reduce blood flow and inhibit function - off button

44
Q

Describe the length of pre and post ganglionic fibres in sympathetic and parasympathetic fibres

A

para: long pre and short post
symp: short pre and long post

45
Q

in para and symp which fibres extend to viscera?

A

◦ para: Long preganglionic fibres extend to viscera (postganglionic fibres essentially in visceral wall)
◦ symp: Postganglionic fibres extend from prevertebral ganglia to viscera

46
Q

What are the 2 main plexuses of the enteric nervous system and where are they found?

A

◦ Submucosal (Meissner’s) in submucosa

◦ Myenteric (Auerbach’s) between circular and longitudinal muscle

47
Q

What are the general functions of the submucosal plexus?

A

◦ Secretions

◦ Blood flow

48
Q

What are the general functions of the myenteric plexus?

49
Q

What is the enteric nervous system?

A

One of the divisions of the nervous system
◦ Can operate completely independently (second brain)
◦ But has extensive connection with the ANS
◦ Exists from oesophagus to anus

50
Q

What does the enteric nervous system communicate with?

A

◦ Parasympathetic (vagus and pelvic nerves) - preganglionic fibres extend to myenteric and submucosal plexuses
◦ Sympathetic (prevertebral ganglia) -postganglionic fibres extend to myenteric and submucosal plexuses

51
Q

Which cells in the mucosa of GI tract secrete hormones?

A

enteroendocrine cells

o Generally identified by letters- G,S,D

52
Q

Which cells in the gut secrete histamine?

A

Enterochromafin cells (ECL cells)

53
Q

Describe endocrine transport of hormones to gut

A 
Peptides released from endocrine cells
o Into portal circulation
o Pass through liver
o Enter systemic circulation - through portosystemic anastomoses
o End up pretty close to where they were
54
Q

Describe paracrine transport of hormones to gut

A

o Relating to or denoting a hormone which has effect only in the vicinity of the gland secreting it.
o Peptides released by endocrine cells
o Act in local environment
o Diffuse short distances

55
Q

Describe neurocrine transport of hormones to gut

A

o Peptides released by neurones in the GI tract

o Released after action potential

56
Q

What are the two broad categories of GI hormones?

A

Gastrin family

Secretin family

57
Q

What two hormones are included in the gastrin family?

A

gastrin

cholecystokinin

58
Q

What cells release gastrin? Location?

A

G cells in ANTRUM of stomach

59
Q

What stimulates release of gastrin?

A

Breakdown of proteins in stomach (small peptides + aas)
Vagus nerve
Stretch receptors in stomach (when fills w food)

60
Q

Role of gastrin

A

Increases gastric acid secretion (by parietal cells)

61
Q

What cells release CCK? Location?

A

I cells in duodenum + jejunum

62
Q

What stimulates CCK release?

A

Fat and protein (and their breakdown products)

Detection of acid

63
Q

Role of cholecystokinin (CCK)?

A

Gall bladder contracts and pancreas stimulated

Relaxes sphincter of Oddi

64
Q

What two hormones are part of the secretin family?

A

Secretin

Gastric inhibitory polypeptide (GIP)

65
Q

Which cells release secretin? Location?

A

S cells in duodenum

66
Q

What Stimulates release of secretin?

A

H+ and fatty acids (low pH)

67
Q

Role of secretin

A

Increases HCO3 from pancreas/gallbladder

Decreases gastric acid secretion

68
Q

Which cells secrete GIP? Located?

A

Cells in duodenum + jejunum

69
Q

What stimulates release of GIP?

A

Stimulated by sugars/carbs, amino acids, fatty acids (all food groups)

70
Q

Role of GIP (gastric inhibitory polypeptide)

A

Increases insulin secretion

Decrease gastric acid secretion

71
Q

What cells release somatostatin? Location?

A

D cells in antrum of stomach

72
Q

What stimulates release of somatostatin?

73
Q

Role of somatostatin

A

Switches off G cells (gastrin release)

74
Q

Which of the gastric hormones are secreted by endocrine method?

A

gastrin, CCK and secretin

75
Q

Which of the gastric hormones are secreted by paracrine method?

A

somatostatin

76
Q

Which of the gastric hormones are secreted by neurocrine method?

A

gastric releasing peptide

77
Q

What secretes GRP?

A

post ganglionic fibres of vagus nerve

78
Q

What is the action of GRP?

A

stimulates g cells to release gastrin which stimulates parietal cells to release H+

79
Q

WHat type of hormones are released by GI tract

A

peptide hormones

80
Q

Wat stimulates enteroendocrine cells?

A

food

stretch

81
Q

Where in the abdomen might a patient complain of pain if there was a problem with a foregut structure?

A

Epigastric area

82
Q

Where in the abdomen might a patient complain of pain if there was a problem with a midgut structure?

A

Peri-umbilical area

83
Q

Where in the abdomen might a patient complain of pain if there was a problem with a hind gut structure?

A

Suprapubic area

84
Q

Why does the different parts of the gut relate pain to different areas?

A

Visceral afferent nerves follow the sympathetic supply to that section of the gut back to the spinal cord. Eg jejumum follows the lesser splanchnic nerve back to T10-11 spinal level

Semester 3 - Gastrointestinal (17 decks)

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