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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
what is the function of the rectum/anus?
defecation - stretching of rectum as it fill gives the urge to defecate
26
What controls the gut?
◦ Autonomic nervous system (Parasympathetic and sympathetic) ◦ Enteric nervous system ◦ Hormones and paracrine substances
27
What neurotransmitter is released from pre and postganglionic cells?
Pre: ACh from both parasympathetic and sympathetic. Post: ACh(parasympathetic), neuropeptides, noradrenaline
28
What part of the nervous system is the main contributor to the digestive system?
Parasympathetic (rest and digest) on button
29
Where do pre and post ganglionic fibres synapse?
◦ The preganglionic fibre synapse with an autonomic ganglia outside the CNS ◦ Postganglionic fibre synapse on peripheral effector organs
30
Where do the cell bodies of the autonomic nervous system reside?
CNS
31
Which are the main nerves from the parasympathetic nervous system that contribute to the gut?
Vagus nerve (cranial nerve X) and Pelvic splanchnic nerves
32
What is the origin of the pelvic splanchnic nerves?
S2, S3, S4
33
What do postganglionic fibres of the parasympathetic system release?
ACh, Peptides (Gastrin releasing peptide, vasoinhibitory peptide)
34
Where do preganglionic parasympathetic fibres synapse and what do they innervate?
Synapse in the walls of the viscera and innervate smooth muscle/endocrine and secretory cells
35
Where are the main innervation of the vagus and pelvic splanchnic nerves?
Vagus: oesophagus to transverse colon Pelvic: transverse colon to anal canal
36
Where do parasympathetic fibres of GI tract originate?
brain and sacral spine (craniosacral)
37
What nerve roots contribute to the sympathetic nervous system?
T1-L2
38
What is the root of the nerves from the sympathetic system that innervate the gut and what do they form?
T5-L2 (thoracolumbar) Pass through (paravertebral) sympathetic trunk without synapsing join with other preganglionic fibres to Form (abdominopelvic) presynaptic splanchnic nerves
39
What is the root of the different splanchnic nerves?
``` o Greater (T5-9) o Lesser (T10-11) o Least (T12) ```
40
What do the thoracic splanchnic nerves synapse with and where are they found?
Synapse with prevertebral ganglia found anterior to the vertebrae
41
Which ganglia do the thoracic splanchnic nerves synapse with?
◦ Coeliac, renal, superior mesenteric, inferior mesenteric and others Greater with coeliac ganglia, lesser with superior mesenteric, least with inferior mesenteric
42
What do the postganglionic sympathetic neurones innervate?
Mainly innervate blood vessels
43
What is the main action of sympathetic system in GI tract
constrict blood vessels to reduce blood flow and inhibit function - off button
44
Describe the length of pre and post ganglionic fibres in sympathetic and parasympathetic fibres
para: long pre and short post symp: short pre and long post
45
in para and symp which fibres extend to viscera?
◦ para: Long preganglionic fibres extend to viscera (postganglionic fibres essentially in visceral wall) ◦ symp: Postganglionic fibres extend from prevertebral ganglia to viscera
46
What are the 2 main plexuses of the enteric nervous system and where are they found?
◦ Submucosal (Meissner's) in submucosa | ◦ Myenteric (Auerbach's) between circular and longitudinal muscle
47
What are the general functions of the submucosal plexus?
◦ Secretions | ◦ Blood flow
48
What are the general functions of the myenteric plexus?
motility
49
What is the enteric nervous system?
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
What does the enteric nervous system communicate with?
◦ 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
Which cells in the mucosa of GI tract secrete hormones?
enteroendocrine cells | o Generally identified by letters- G,S,D
52
Which cells in the gut secrete histamine?
Enterochromafin cells (ECL cells)
53
Describe endocrine transport of hormones to gut
``` 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
Describe paracrine transport of hormones to gut
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
Describe neurocrine transport of hormones to gut
o Peptides released by neurones in the GI tract | o Released after action potential
56
What are the two broad categories of GI hormones?
Gastrin family | Secretin family
57
What two hormones are included in the gastrin family?
gastrin | cholecystokinin
58
What cells release gastrin? Location?
G cells in ANTRUM of stomach
59
What stimulates release of gastrin?
Breakdown of proteins in stomach (small peptides + aas) Vagus nerve Stretch receptors in stomach (when fills w food)
60
Role of gastrin
Increases gastric acid secretion (by parietal cells)
61
What cells release CCK? Location?
I cells in duodenum + jejunum
62
What stimulates CCK release?
Fat and protein (and their breakdown products) | Detection of acid
63
Role of cholecystokinin (CCK)?
Increases pancreatic/gallbladder secretions (pancreatic fluid + bile) - Gall bladder contracts and pancreas stimulated Relaxes sphincter of Oddi
64
What two hormones are part of the secretin family?
Secretin | Gastric inhibitory polypeptide (GIP)
65
Which cells release secretin? Location?
S cells in duodenum
66
What Stimulates release of secretin?
H+ and fatty acids (low pH)
67
Role of secretin
Increases HCO3 from pancreas/gallbladder | Decreases gastric acid secretion
68
Which cells secrete GIP? Located?
Cells in duodenum + jejunum
69
What stimulates release of GIP?
Stimulated by sugars/carbs, amino acids, fatty acids (all food groups)
70
Role of GIP (gastric inhibitory polypeptide)
Increases insulin secretion | Decrease gastric acid secretion
71
What cells release somatostatin? Location?
D cells in antrum of stomach
72
What stimulates release of somatostatin?
Low pH
73
Role of somatostatin
Switches off G cells (gastrin release)
74
Which of the gastric hormones are secreted by endocrine method?
gastrin, CCK and secretin
75
Which of the gastric hormones are secreted by paracrine method?
somatostatin
76
Which of the gastric hormones are secreted by neurocrine method?
gastric releasing peptide
77
What secretes GRP?
post ganglionic fibres of vagus nerve
78
What is the action of GRP?
stimulates g cells to release gastrin which stimulates parietal cells to release H+
79
WHat type of hormones are released by GI tract
peptide hormones
80
Wat stimulates enteroendocrine cells?
food | stretch
81
Where in the abdomen might a patient complain of pain if there was a problem with a foregut structure?
Epigastric area
82
Where in the abdomen might a patient complain of pain if there was a problem with a midgut structure?
Peri-umbilical area
83
Where in the abdomen might a patient complain of pain if there was a problem with a hind gut structure?
Suprapubic area
84
Why does the different parts of the gut relate pain to different areas?
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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