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Alimentary > The Oesophagus and Stomach > Flashcards

The Oesophagus and Stomach Flashcards

1
Q

Describe the basic layering of the gut wall (4 basic layers then 6 basic layers)

A

Mucosa
Sub-mucosa
Muscularis
Serosa/Adentitia

Epithelium
Lamina propria
Muscular mucosae 
Submucosa
Smooth muscle (circular then longitudinal)
Serosa/adventitia
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2
Q

Where are the nerves mainly found in the gut wall

A

Submucosa - nerves that control gut function

Smooth muscle

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3
Q

Where are most of the blood vessels found in the gut wall

A

Submucosa

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4
Q

At what vertebral level does the oesophagus start and end

A

C5-T10

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5
Q

What does the oesophagus run close to

A

Trachea
Aorta
Recurrent laryngeal nerves
Pericardium

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6
Q

What are the functions of the oesophagus

A

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

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7
Q

Describe the oesophagus epithelium

A

Non-keratinising stratified squamous
No absorption occurs so it is not thin
Wear and tear lining that can deal with extremes of temp. and texture
Lubricated by mucous secreting glands and saliva

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8
Q

What does tonically active mean

A

Both of the sphincters of the oesophagus are closed at rest and the upper sphincter opens when swallowing is detected by the swallowing centre of the brain

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9
Q

Describe the composition of muscle in the different levels of the oesophagus

A

Upper - skeletal
Middle - skeletal and smooth
Lower - smooth

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10
Q

How is bolus moved through the muscle

A

Peristalsis by circular muscle means muscle immediately above the bolus contracts while the muscle below relaxes
independent of gravity

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11
Q

What occurs when the first peristaltic wave to move bolus in the oesophagus is unsuccessful

A

A signal is sent up to the brain which initiates a second peristaltic wave to move the bolus into the stomach

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12
Q

How is reflux prevented in the stomach

A

diaphragm

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13
Q

Describe the epithelium in the stomach

A

Stratified squamous in the oesophagus and simple columnar epithelium in the stomach
Transition occurs at the Z line

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14
Q

How can pregnancy cause acid reflux

A

The foetus pushes the stomach and oesophagus up

Causes pressure differences between the thorax and abdomen and acid is more likely to pass up

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15
Q

What is the purpose of the rugae of the stomach

A

Gastric folds that allows the stomach to expand

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16
Q

What is the function of the stomach

A

Breaks food into smaller particles (acid + pepsin)
Holds food and releases it at a steady controlled rate into the duodenum
Kills parasites and certain bacteria

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17
Q

Describe the secretions of the stomach

A

Cardia & Pyloric Region - Mucus only
Body & Fundus - Mucus, HCl, pepsinogen (major protease)
Antrum - Gastrin (hormone produced to facilitate function/stimulates acid production)

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18
Q

Describe the structure of the stomach

A 
Fundus
Body
Cardia
Gastric
Pyloric antrum 
Canal
Pyloric 
Pylorus
19
Q

Describe the mucous cells in the invaginations of the stomach

A

Lots of mucous cells
Bicarbonate rich mucous to protect the stomach lining
Also helps protect the lining from active lipase and proteases

20
Q

Describe acid production in the stomach

A

2L of acid a day
150mM of H+
pH 6-7 at the epithelium but 1-2 at the lumen

21
Q

What are the two types of movement in the stomach

A

Peristalsis (20%)

Segmentation / mixing (80%)

22
Q

Describe peristalsis in the stomach

A

ANS essential

  1. Waves begin gently near the lower oesophageal sphincter and continues to the pyloric sphincter
  2. At the distal end they become stronger and more forceful (mixes the chyme)
  3. through the pyloric sphincter the chyme moves through in a back and forth fashion, breaking up larger materials
23
Q

Describe segmentation in the stomach

A

Stretching activates the enteric NS
Relatively weak that mixes food with secretions to form chyme
More fluid part is pushed to the pyloric sphincter, solid part pushed to the body

24
Q

Describe the gastric chief cell (+ultrastructure)

A

Protein secreting epithelial cell
Secretes pepsinogen + lipase

Abundant RER
Golgi packaging and modifying for export
Masses of apical secretion granules

25
Q

Describe the parietal cells (+ultrastructure)

A

Secretes HCl (+intrinsic factor)

Many mitochondria
Cytoplasmic tubulovesicles (contains H+/K+ ATPase) which fuses with the membrane and microvilli that project into canaliculi
Internal canaliculi (extends to apical surface/lumen)
26
Q

Explain the process of HCl secretion from parietal cells

A
  1. Carbon dioxide diffuses down its concentration gradient from the blood into the parietal cell
  2. Carbonic anhydrase combines CO2 with water to form carbonic acid (bicarbonate + proton).
  3. Bicarbonate is exchanged with a chloride ion in the interstitial space.
  4. Cl- to move down their concentration gradient into the stomach lumen via chloride channels.
  5. Na+/K+ exchanger in the basolateral membrane pumps potassium into the cell
  6. Potassium channels moves out into the stomach
  7. Potassium exchanged for protons.
  8. Secreted proton combines with chloride to form hydrochloric acid.
27
Q

What is the function of pepsinogen

A

Pepsinogen breaks down into pepsin in an acidic environment and breaks down protein into peptide fragments.

28
Q

What is gastrin

A

Hormone secreted into the blood which then stimulates acid secretion in the stomach, predominantly through histamine release from chromaffin cells (lamina propia).
Gastrin producing cells are found in the pyloric antrum. (parietal)

29
Q

What are the 3 phases of gastric secretion

A

Cephalic phase
gastric phase
Intestinal phase

30
Q

Describe the cephalic phase of gastric secretion

A

Thought, sight, smell and taste of food
Vagus nerve (ACh) stimulate secretion from mucous cells, chief cells, parietal cells and G-cells via the submucosal plexus.
Gastrin (from G-cells) and histamine (from ECL cells) also stimulate parietal cell secretion
Small secretion for a few minutes

31
Q

Describe the gastric phase of gastric secretion

A

Distension in the stomach triggers the brain via the vagus nerves
Vagus nerve (ACh) stimulate secretion from mucous cells, chief cells, parietal cells and G-cells via the submucosal plexus
Increase motility via the myenteric plexus
Gatsrin and histamine stimulate parietal cell secretion.

3-4 hours of gastric activityand mechanical digestion.

32
Q

Describe the intestinal phase of gastric secretion

A

Mostly an inhibitory phase
Stretch receptors input into the enteric nervous system - reduces stomach activation
Cholecystokinin (I-cells) and Secretin (S-cells) into the blood.
Decreases parietal cell secretion and inhibits gastric motility and emptying.
Gastric emptying slows down
May also be excitatory - high protein concentrations in the duodenum stimulates gastrin secretion

33
Q

Which hormones are released during the intestinal phase of gastric secretion

A

Inhibitory:
Gastric inhibitory peptide
Cholecystokinin
Secretin

34
Q

How does omeprazole work

A

Drug

Proton pump inhibitor that inhibits K+ and H+ exchange

35
Q

How does ranitidine work

A

Histamine receptor antagonist

36
Q

What are the common drug targets for the stomach

A

ACh
Gastrin
Histamine

37
Q

Alternative HCl secretion

A
  1. Carbon dioxide and water delivered to the cell by the blood
  2. Carbon anhydrase (enzyme that produces hydrogen ions)
  3. Hydrogen and bicarbonate generated by carbon anhydrase
  4. Potassium from the blood is exchanged for sodium in the cell
  5. Bicarbonate is exchanged for chloride
  6. ATP used to actively secrete hydrogen in
  7. HCl is generated and secreted in the stomach lumen
38
Q

What are the functions of the HCl secreted

A

Kill pathogens
Alter protein structure to help digestion
Activate protease zymogens

39
Q

Describe the G cells

A

Enteroendocrine cells found in pits
Releases gastrin into the bloodstream
Gastrin stimulates gastric secretion and motility. Stimulation of smooth muscles- stronger contractions of the stomach and the opening of the pyloric sphincter to move food into the duodenum.

Gastrin also binds to receptors on cells in the pancreas and gallbladder where it increases the secretion of pancreatic juice and bile.

40
Q

What stimulates gastrin release

A

Vagus nerve stimulation
peptides in the stomach
Stomach distension

41
Q

Describe the enterochromaffin-like cells

A

Neuroendocrine cell found deep in the gastric glands (usually near parietal cells)
Secrete histamine which stimulates the secretion of acid from the parietal cells.

42
Q

Describe the D-cells

A

Enteroendocrine cells that secrete somatostatin

Somatostatin inhibits ECL production of histamine and parietal cell activity, inhibiting HCl secretion

43
Q

Describe the gastric stem cells

A

Pluripotent cells capable of differentiating into all of the different cells of the stomach, under the influence of different factors.

Alimentary (16 decks)

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