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3 - GI > Functions of the Stomach > Flashcards

Functions of the Stomach Flashcards

1
Q

State the functions of the stomach

A
  • Receive/store food
  • Disrupt food
  • Continue digestion
  • Disinfect
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2
Q

What adaptabilities help the stomach store food

A
  • Receptive relaxation:
  • Vagally mediated relaxation of orad stomach
  • Allows food to enter stomach without raising intra-gastric pressure too much
  • Prevents reflux of stomach contents during swallow
  • Rugae allow distension
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3
Q

Describe the regions of the stomach

A
  • Cardia at the LOS opening
  • Fundus on the superior border of stomach
  • Body in the middle
  • Antrum near the pylorus
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4
Q

Describe the epithelium of the stomach

A
  • From lower oesophagus to stomach
    • Abrupt transition of stratified squamous to columnar epithelium
      • Columnar epithelium more suited to secretion
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5
Q

Explain the actions of smooth muscle in the stomach

A
  • Extra oblique layer of muscle in stomach in addition to circular and longitudinal muscle
    • Help contract and grind food
  • Contractions
    • Mix/grind food and move contents along
  • Upper stomach has sustained contractions
    • Creates basal tone
    • Thinner epithelium to allow more relaxation when lots of food content
  • Lower stomach has thicker and more muscular walls
    • Strong peristalsis mixes stomach contents
    • Coordinates movements - contractions every 20 seconds
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6
Q

Describe the components of gastric secretion and their cellular origins

A
  • HCl - parietal cell
  • Intrinsic factor - parietal cell
  • Mucus/HCO3 - gastric mucous cells
  • Pepsinogen - chief cell
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7
Q

Describe where acid is released in the stomach

A
  • H+ (acid) is released from parietal cells in the stomach
  • A proton (H+) pump is located within parietal cells to release H+
  • H+ requires lots of ATP
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8
Q

What is the alkaline tide

A
  • During digestion of food in the stomach, HCO3 produced

- HCO3 enters capillary and increases pH of blood leaving stomach

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9
Q

How is acid production increased

A
  • Gastrin binds to CCK receptor on parietal cells
  • Histamine binds to H2 receptors
  • ACh from vagus nerve bind to muscarinic receptors
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10
Q

How is gastrin secretion controlled

A
  • Produced by G cells located in antrum
  • G cells stimulated by:
    • Peptides/amino acids in stomach lumen
      • Protein breakdown products stimulate more acid release
    • Vagal stimulation - acetylcholine and gastrin-releasing peptide (GRP)
      • Start releasing acid when see/smell food to prepare stomach
  • Vagus nerve controls both G cells and parietal cells to allow a finely balance of acid concentration
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11
Q

How is acid production inhibited

A
  • Essentially an inhibition of G cells
  • When food leaves stomach, pH drops
    • Food acts as a buffer
  • Low pH activates D cells
    • D cells release somatostatin which inhibits G cells (and ECL cells)
  • Stomach distension reduces
    - Reduced vagal activity
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12
Q

Describe the function of the stomach defences

A
  • Body is made of proteins
    • Stomach protects itself from digestion by secreting mucus containing dissolved HCO3
  • Mucus/HCO3
    • Released by surface mucus cells and neck cells in gastric glands
    • Forms thick alkaline viscous layer that adheres to epithelium
    • Epithelial surface kept at higher pH
  • High turnover of epithelial cells
    • Helps keep epithelia intact
  • Prostaglandins
    • Maintain mucosal blood flow
      • Supplying epithelium with nutrients to help secrete mucus and HCO3
    • Non-steroidal drugs inhibit prostaglandins
      - Cause damage
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13
Q

Describe the symptoms of GORD

A
  • Heartburn, cough, sore throat, dysphagia (difficulty swallowing)
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14
Q

Describe the causes of GORD

A
  • Lower oesophageal sphincter problems
  • Delayed gastric emptying (raised intra-gastric pressure)
  • Hiatus hernia - herniate cardia through diaphragm into thorax
  • Obesity
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15
Q

Describe the consequences of GORD

A
  • Oesophagitis
  • Strictures
  • Barrett’s oesophagus
    • Metaplasia of squamous epithelium to columnar
    • Increased risk of developing adenocarcinoma
    • Adenocarcinoma not normally seen in oesophagus and normally squamous cell carcinoma
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16
Q

Describe the treatment of GORD

A
  • Lifestyle modifications - decrease weight, not sleeping flat, eating earlier before sleep
  • Pharmacological
    • Antacids - layer over epithelium to prevent acid secretion
    • H2 antagonists - prevent histamine activating parietal cell
    • Proton pump inhibitors - decrease acid production
  • Surgery (rare)
17
Q

Describe causes of acute gastritis

A
  • Heavy use of NSAIDS - decrease prostaglandins -> decrease blood flow -> inflammation
  • Lots of alcohol
  • Chemotherapy
  • Bile reflux
18
Q

Describe the symptoms of acute gastritis

A
  • Asymptomatic
  • Or pain, nausea, vomiting
  • Occasionally bleeds - can be fatal
19
Q

Describe the causes of chronic gastritis

A
  • Bacterial - H-pylori infection
  • Autoimmune - antibodies to gastric parietal cells
    • Parietal cells cannot produce intrinsic factor
    • If infected, cannot absorb B12 and can lead to pernicious anaemia
    • Symptoms - symptoms of anaemia
      • Glossitis - big red tongue
      • Anorexia
      • Neurological symptoms
20
Q

Define peptic ulcer disease

A
  • Defects in gastric/duodenal mucosa

- Must extend through muscularis mucosa

21
Q

Give causes of peptic ulcer disease

A
  • Stomach acid
  • H-pylori
  • NSAIDS
  • Zollinger-Ellison disease
  • Smoking - only contributes to relapse of ulcer disease
  • Stress
22
Q

What are symptoms of peptic ulcer disease

A
  • Epigastric pain (foregut) - sometimes back pain
    • Burning/gnawing
    • Follows meal times
      • Acid in contact with ulcer during digestion - very serious pain 1 hour after eating
    • Often at night
  • Bloating
  • Vomiting
  • Bleeding/anaemia - if blood vessels affected
    • Ulcer on the lesser curve of the stomach can erode into the left gastric artery
    • Duodenal ulcer can erode into the gastro-duodenal artery
  • Perforation - undigested food enters peritoneal space
    • Air can irritate the phrenic nerves to the diaphragm, leading to referred pain to C3-C5
  • Obstruction
  • Early satiety
  • Weight loss
23
Q

Describe Zollinger-Ellison disease

A
  • Gastrin secreting tumour - stimulate parietal cells and therefore produce more acid
  • Leads to ulceration of stomach and small intestine
24
Q

How are investigations for upper GI pathology carried out

A
  • Upper GI endoscopy - biopsies (benign, malignant, H-pylori)
  • Urease breath test - detect H-pylori
  • Erect chest x-ray - perforation - gas in peritoneal cavity
  • Blood test - anaemia
25
Q

Describe the treatment for gastric pathology

A
  • Eradicate H-pylori
  • Stop NSAIDS
  • Endoscopy for bleeding ulcers
  • Proton pump inhibitors
  • Antacids
26
Q

Describe the spread and shape of H. pylori

A
  • Fecal to oral

- Helix shaped/gram negative/microaerophilic

27
Q

Describe some virulence factors of H. pylori

A
  • Produces urease
    • Converts urea to ammonium (basic in solution)
      • Increases local pH to survive acidic environment
  • Has flagellum
    • Good motility
    • Lives in mucus layer/adheres to gastric epithelia
28
Q

Describe how H. pylori causes problems

A
  • Releases cytotoxins (proteases) - direct epithelial injury
  • Expresses enzymes
    • Urease - ammonia toxic to epithelia
  • Possibly degrades mucus layer
  • Promotes inflammatory response - self injury
29
Q

Describe how different parts of the stomach specialise in different roles

A
  • Cardia predominantly mucus secretion
  • Fundus/body mainly mucus, HCl and pepsinogen secretion
  • Antrum mainly gastrin and somatostatin
30
Q

Describe how different parts of the stomach which are infected by H. pylori can have different consequences

A
  • If in antrum (home of G cells) - duodenal ulceration
  • If in antrum and body - asymptomatic
    • Area that produces acid inflamed so decreased acid production
  • If predominantly in body - can lead to cancer
31
Q

Outline the ways in which gastric acid secretion may be reduced by drugs

A
  • Pharmacological intervention
    • H2 blockers
    • Proton pump inhibitors
  • Medication can be given to coat the stomach to prevent acidic damage (antacids)

3 - GI (14 decks)

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