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Year 1 - BRS > 11.1 - Upper GI tract > Flashcards

11.1 - Upper GI tract Flashcards

1
Q

What is the main function of the GI tract?

A
  • GI system AKA alimentary system / digestive system
  • digestion - process of breaking down macromolecules to allow absorption
  • absorption - process of moving nutrients and water across a membrane - in GI tract this is into blood circulation or lymphatics
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2
Q

What are the components of the GI system? (Know to label)

A
  • salivary glands - parotid, sublingual, submandibular - developed as outpouchings of epithelial lining of mouth
  • food down oesophagus –> stomach –> duodenum (D1,2,3,4) –> jejunum –> ileum –> colon at ileocaecal valve
  • caecum –> appendix
  • ascending, transverse, descending, sigmoid colon
  • rectum, anus
  • blood with nutrients absorbed from food –> liver
  • gall bladder
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3
Q

What are the three sections of the GI tract?

A
  • upper - oesophagus and foregut - stomach, pancreas, gall bladder
  • mid - midgut - small intestine and part of transverse colon (large intestine)
  • lower - hind gut - entire colon, rectum, anus
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4
Q

What are the four layers of the gut wall and what are they made of?

A
  • mucosa - epithelium, lamina propria (loose connective tissue), muscularis mucosae
  • submucosa - connective tissue (containing nerve plexus, usually contains nerves and blood vessels)
  • muscularis - smooth muscle (containing nerve plexus)
  • serosa/adventitia - connective tissue with/without epithelium
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5
Q

What is the muscularis/muscle layer divided into?

A
  • circular (inner layer)
  • longitudinal (outer layer)
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6
Q

How many teeth do we have and what types?

A
  • 32 teeth in total
  • 8 incisors
  • 4 canines
  • 8 premolars
  • 12 molars
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7
Q

What muscles are involved with controlling chewing? (Muscles of mastication)

A
  • masseter - largest jaw muscle, responsible for biting
  • temporalis
  • medial and lateral pterygoid muscles (behind masseter)
  • innervated by trigeminal nerve
  • several muscles control position of mandible
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8
Q

What salivary glands do we have and what enzymes are in saliva?

A
  • parotid gland - serous saliva
  • sublingual gland - mucous type
  • submandibular gland - 70% of saliva composition, mixed type
  • food mixed with saliva (aqueous secretion and digestive enzymes) - lingual lipase (fat digestion) and salivary amylase (carbohydrate digestion)
  • main function is lubrication, initiates digestion
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9
Q

What two groups of muscles are involved with tongue and what are their functions?

A
  • intrinsic muscles - fine motor control and moving food
  • extrinsic muscles - gross movement of tongue (in, out, up, down) and assist mechanical digestion
  • majority of tongue innervated by CN XII (hypoglossal)
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10
Q

Where might you see some constrictions in the oesophagus?

A
  • level of cricoid cartilage at top
  • level of the left main bronchus and aorta
  • level of the diaphragm
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11
Q

At what vertebral level does the oesophagus start and end?

A
  • starts C5
  • ends T10 (where it passes through diaphragm)
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12
Q

What is the function of the oesophagus?

A

Conduit for food, drink and swallowed secretions from pharynx to stomach

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13
Q

Describe the epithelium structure and function of the oesophagus.

A
  • non-keratinising
  • ‘wear and tear’ lining to protect from extreme temperatures, textures and acid reflux
  • lubrication of food bolus - mucus secreting glands and saliva
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14
Q

Describe the oesophageal sphincters.

A
  • tonally active
  • swallowing centre
  • upper and lower oesophageal sphincters (upper is true, lower is controversial as to whether it is a sphincter or not)
  • lower has Z line where pale pink mucosa of squamous epithelium meets red mucosa of gastric epithelium
  • Barrett’s oesophagus extends Z line upwards as loads of pink squamous epithelium undergo metaplasia to become gastric epithelium
  • prevent acid reflux
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15
Q

Describe the muscle structure and function of the oesophagus.

A
  • peristalsis
  • circular muscle - segmental role - allows food to remain in certain parts of oesophagus for some time
  • longitudinal muscle - propagates food movement down oesophagus
  • upper third - skeletal striated muscle type
  • middle third - skeletal/smooth muscle
  • lower third - smooth muscle type
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16
Q

Describe the gastro-oesophageal junction and explain how acid reflux is prevented.

A
  • acid reflux prevented by diaphragm pinching lower oesophagus
  • this junction lies at an acute angle to the stomach by ligaments which helps prevent reflux
  • we are seeing more adenocarcinomas in metaplastic epithelium at junction - theory is prolonged acid exposure and damage can change cells to columnar cells - persistent metaplasia = unstable cells = dysplasia = cancer
  • gastric folds called rugae allow more digestion and absorption to occur
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17
Q

What are the two ways of dividing the oesophagus up?

A
  1. divide into parts of the body cavity it runs through - cervical, thoracic and abdominal oesophagus (thoracic main one, cervical only few cm neck, abdominal only few cm abdomen)
  2. during endoscopy intubation - upper 1/3 24cm from incisors, middle 1/3 24-32cm, lower 1/3 32-40cm
18
Q

What are the four stages of swallowing?

A
  • stage 0 - oral phase
  • stage 1 - pharyngeal phase
  • stage 2 - upper oesophageal phase
  • stage 3 - lower oesophageal phase
19
Q

Describe stage 0 - the oral phase.

A
  • chewing and saliva prepare bolus
  • both oesophageal sphincters constricted
20
Q

Describe stage 1 - the pharyngeal phase.

A
  • pharyngeal musculature guides food bolus towards oesophagus
  • both oesophageal sphincters open
21
Q

Describe stage 2 - upper oesophageal phase.

A
  • upper sphincter closes
  • superior circular muscle rings contract and inferior rings dilate
  • sequential contractions of longitudinal muscle
22
Q

Describe stage 3 - lower oesophageal phase.

A
  • lower sphincter closes as food passes through
23
Q

What is the anatomy of the stomach?

A
  • stomach starts at gastro-oesophageal junction
  • cardia - region just below oesophagus, in stomach
  • fundus - protrudes above G-O junction
  • body
  • distal part - pyloric antrum
  • pylorus - sphincter empties gastric contents into small bowel
24
Q

What are the functions of the stomach?

A
  • breaks food into smaller particles through acid and pepsin
  • holds food and releases it in a controlled steady rate into duodenum
  • kills parasites and some bacteria through release of acid and enzymes
25
Q

What are the sections of the stomach and what do they secrete?

A
  • cardia and pyloric region - mucus only
  • body and fundus - secrete mucus, HCl, pepsinogen
  • antrum - secretes gastrin
26
Q

What is the pH of the stomach?

A
  • pH at lumen is 1-2
  • stomach produces 2L of acid a day, with 150mM H+
  • compared to pH 6-7 at epithelial surface
27
Q

How is the epithelium of the stomach protected?

A
  • mucus layer
  • mucins - gel coating - HCO3- trapped in mucus gel
28
Q

What is peristalsis?

A
  • 20% of stomach contractions
  • propels chyme towards colon
  • more powerful as moves from LOS to pyloric sphincter
  • ANS essential
29
Q

What is segmentation?

A
  • 80% of stomach contractions
  • weaker
  • fluid chyme towards pyloric sphincter
  • solid chyme pushed back to body
  • stretching activates enteric NS
30
Q

What do gastric chief cells do?

A
  • protein-secreting epithelial cell
  • secretes pepsinogen (facilitates initial protein digestion)
  • abundant RER
  • Golgi packaging and modifying for export
  • masses of apical secretion granules
31
Q

What are parietal cells? (Resting)

A
  • secretes HCl and intrinsic factor
  • many mitochondria (requires lots of ATP)
  • internal canaliculi (extend to apical secretory surface)
  • cytoplasmic tubulovesicles (contain H+/K+ ATPase which pumps HCl into stomach lumen)
32
Q

What are parietal cells (secreting) like?

A
  • microvilli project into canaliculi
  • tubulovesicles fuse with membrane
33
Q

How is HCl produced and secreted by parietal cells?

A
  1. Na+/K+ pump brings K+ into cell and Na+ out –> K+ moves into canaliculi
  2. H2CO3 formed from H2O + CO2 from interstitial fluid is broken down by carbonic anhydrase into H+ and HCO3- –> H+ moves into canaliculi (catalysed by H+K+ATPase - H+ into lumen, K+ back into parietal cell)
  3. HCO3- out = Cl- into cell then into canaliculi
  4. you are left with H+ and Cl- in canaliculi which combine –> HCl
  • end results: release H+ and Cl- into gastric lumen
  • increase alkaline in bloodstream from stomach
34
Q

What triggers the production and secretion of HCl?

A

Histamine acting on histamine receptors on parietal cells

35
Q

What does gastrin do?

A
  • made by pyloric antrum by G cells
  • reaches parietal cell via systemic circulation
  • stimulated by distension, small peptides and amino acids, stimulation of vagus nerve
  • acts on receptors on parietal cells
  • gastrin is a local peptide hormone
  • stimulates histamine release from chromaffin cells (lamina propria)
36
Q

What are the three phases of gastric secretion?

A
  • cephalic phase
  • gastric phase
  • intestinal phase
37
Q

What happens in cephalic phase?

A
  • thought, sight, smell and taste of food stimulates vagus nerve which stimulates parietal cell through ACh
  • starts formation of HCl
  • ACh can also stimulate HCl secretion along with gastrin and histamine (which interacts with H2 receptors)
38
Q

What happens in the gastric phase?

A
  • food reaches stomach by activation of stretch and chemoreceptors
  • this sends signals via vagus nerve to brain which sends signal back through vagus nerve to activate HCl secretion
  • HCl inhibits further gastrin release
39
Q

What happens in intestinal phase?

A
  • chyme reaches duodenum
  • signal comes via vagus nerve which inhibits gastric HCl and pepsin secretion through inhibitory hormones like gastric inhibitory peptide, cholecystokinin, secretin
  • also excitatory: excitatory intestinal phase - protein concentration in duodenum stimulates gastrin secretion
  • enterogastrones - enterogastric reflex
40
Q

How might you produce a useful drug to decrease acid secretion?

A
  • receptor blockers which block histamine receptor - cimetidine and ranitidine block acid secretion
  • omeprazole
  • K+/H+ ATPase pump inhibitors prevent HCl formation
41
Q

Which of the following stimuli would most likely decrease acid secretion in stomach?
1. chyme fatty acid content
2. increased ACh secretion
3. increased gastrin secretion
4. protein content of the meal
5. stomach distension

A

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Year 1 - BRS (73 decks)

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