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Gastrointestinal System > Lecture 4.1: The Stomach > Flashcards

Lecture 4.1: The Stomach Flashcards

1
Q

Stomach Functions (4)

A

Storage
Haematopoietic
Protection
Digestion

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2
Q

Stomach Functions: Storage

A

Ingestion»digestion – holds it for a few hours
Mixing – production of chyme

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3
Q

Stomach Functions: Haematopoietic

A

Production of intrinsic factor needed for vitamin B12 absorption

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4
Q

Stomach Functions: Protection

A

Mucus rich lining (self care) bacteriolytic

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5
Q

Stomach Functions: Digestion

A

Secretion of protease (pepsin) aided by HCl

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6
Q

Structure of the Stomach (5)

A
  • Lower Oesophageal Sphinchter
  • Cardia (surrounds opening of oesophagus into the
    stomach)
  • Fundus (region above the cardiac orifice)
  • Body (Corpus)
  • Pylorus (consists of pyloric antrum and pyloric canal
    which terminates at pyloric orifice)
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7
Q

Generalised structure of the wall of the GI tract (out to in)

A
  • Serosa, continuous with parietal peritoneum which
    lines the abdominal cavity
  • Muscularis externa = smooth muscle: outer layer is
    longitudinal, inner layer is circular (in stomach there is
    a 3rd oblique layer)
  • Submucosa – loose connective tissue
  • Muscularis Mucosa (2 thin layers of smooth muscle)
  • Lamina propria
  • Layer of epithelial cells (with basement membrane)
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8
Q

Stomach mucosa is simple columnar epithelia which
produces….?

A

A protective alkaline secretion

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9
Q

Where do gastric glands empty their secretions?

A

Gastric pits which are dotted within the epithelia in the millions

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10
Q

What do Mucous Neck Cells do?

A

Secrete Mucous

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11
Q

Where are Chief Cells (Peptic Cells) found? What do they do?

A

Basal Region
Secrete Pepsinogens

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12
Q

What do Parietal Cells (Oxyntic Cells) secrete?

A

HCl and intrinsic factor

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13
Q

What do G-Cells (Enteroendocrine Cells) secrete?

A

Gastrin

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14
Q

What cells secrete Grehlin?

A

Gr Cells

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15
Q

What cells secrete Somatostatin?

A

D Cells

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16
Q

What types of glands and cells are mostly found in the cardia of the stomach? (1)

A

Mucous Secreting Glands

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17
Q

What types of glands and cells are mostly found in the fundus and body of the stomach? (4)

A
  • Mucus Secreting Neck Cells
  • Acid Secreting Cells (Parietal or Oxyntic)
  • Chief Cells secreting Pepsinogen
  • Other local hormone producing cells
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18
Q

What types of glands and cells are mostly found in the pyloric region of the stomach?

A
  • Mucus Secreting Cells
  • G Cells (releases Gastrin)
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19
Q

Why is it important for pH of stomach acid to be low (1-3)? (4)

A
  • Helps breakdown connective tissue and muscle
  • Activates pepsinogens
  • Can combine with calcium and iron to facilitate their
    absorption
  • Defence mechanism – killing pathogens
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20
Q

What stimulates production of HCl by parietal cells?

A

Arrival of food

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21
Q

Structure of Parietal Cells

A
  • Cytoplasm of these cells has an elaborate series of
    branches
  • These fuse to form deep canaliculi
  • Increased surface area available for release of HCl
22
Q

What proteolytic enzymes are released from chief (peptic) cells?

A

Pepsin

23
Q

Pepsin is released as inactive precursors known as?

A

Pepsinogen

24
Q

What are pepsinogens contained in?

A

Membrane bound zymogen granules

25
Q

What is Intrinsic Factor?

A
  • Glycoprotein that binds to VitB12 (cobalamin) in the
    upper small intestine
  • Protecting it from digestion
  • Intrinsic factor/Vit B12 complex absorbed in the ileum
26
Q

What is the use of Vit B12?

A

Needed for erythropoiesis

27
Q

What happens if there is a lack of Vit.B12?

A

Pernicious Anaemia
It is an autoimmune condition that affects your stomach

28
Q

How does an ulcer form?

A

Breaching of the mucosal barrier –> Gastritis –> Persistent Erosion –> Ulcer

29
Q

Control of Gastric Secretions (3 phases)

A
  • Cephalic
  • Gastric (major)
  • Intestinal (minor)
30
Q

(Cephalic Phase) Anticipation of food – sight, smell – accounts for …% acid secretion

A

~40%

31
Q

Cephalic control is mediated by what nerves?

A

Vagus Nerves

32
Q

How does vagal activity increase acid secretion?

A
  • Postganglionic neurons in myenteric plexus release
    ACh – stimulate parietal cells
  • Vagal stimulation promotes gastrin release from G
    cells (via gastrin releasing peptide from enteric
    neurons) – in turn promotes acid release
  • ACh and gastrin stimulate release of histamine from
    mast cells and enterochromaffin like cells
  • Histamine can trigger acid release
33
Q

What hormones can prevent acid release?

A
  • Histamine H2 antagonists (cimetidine)
34
Q

How long does the Gastric Phase of acid release last?

A

2-3 hours

35
Q

Gastric Phase accounts for …% of acid secretion

A

~50%

36
Q

What is Gastric Phase of acid secretion triggered by?

A
  • Triggered by food in stomach
  • Distension and the presence of amino acids and.
    peptides (EtOH and caffeine also very potent)
  • Distention promotes local myenteric reflexes and
    longer vasovagal reflexes which result in ACh release
    and therefore increased secretions
  • ACh also promotes the release of gastrin – stimulus for
    acid secretion
37
Q

Intestinal Phase accounts for …% of acid secretion

A

~10%

38
Q

As the duodenum expands with chyme a low pH, fat and hypertonic chyme results in…? (4)

A
  • Somatostatin release (from D cells) inhibit parietal cells
    and this acid secretion
  • Acid promotes secretin release which in turn inhibits G
    cells
  • Fatty acids cause the release of GIP, CCK which both
    inhibit acid secretion
  • Secretin, GIP, CCK – collectively called enterogastrones
39
Q

When empty, what is the volume of the stomach?

A

~50ml

40
Q

When full, what is the volume of the stomach?

A

~4000ml

41
Q

In the absence of eating, gastric contractility occurs episodically about every…mins?

A

90

42
Q

Bursts of contraction (of the stomach) are called…?

A

Migrating Motor Complexes (MMCs)

43
Q

What hormone is gastric motility stimulated by?

A
  • Motilin
  • Small polypetide (22aa) from enterochromaffin cells
  • Acts via GPCR on enteric neurons to promote smooth
    muscle contraction
  • Erythromycin binds to motilin receptors
44
Q

Gastric Motility when we are eating: Mixing (4)

A
  • Waves of contraction originate in the corpus and
    move towards the antrum
  • Pushing stomach contents ahead of them to the
    pylorius
  • Pyloric sphincter closes in advance of the wave –
    which stops just short of the sphincter
  • The antrum now contracts and contents move back to
    wards the corpus –retropulsion
  • This is sometimes called the gastric mill
45
Q

How many hours to reduce contents to a appropriate size to pass through the pyloric sphincter to the duodenum?

A

3hrs

46
Q

What is a significant predictor of the rate of gastric
emptying?

A

The composition of chyme

47
Q

What in the duodenum increases contraction of pyloric sphincter?

A

Fatty Acids

48
Q

What receptors detect hyperosmolar chyme and delay
emptying of the stomach?

A

Duodenal osmoreceptors

49
Q

Presence of what in the duodenum delays gastric emptying?

A

Appearance of acid in the duodenum delays gastric emptying

50
Q

Why was ranitidine (used for acid reflux) stopped being prescribed?

A

Ongoing investigations uncovered levels of N-Nitrosodimethylamine (NDMA), a probable human carcinogen, increase over time

51
Q

What is the Triangle of Death in Medicine?

A

A medical term describing the fatal combination of hypothermia, acidosis and coagulopathy

Gastrointestinal System (22 decks)

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