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Stomach anatomy and motility Flashcards

1
Q

Describe the path taken by the cervical oesophagus

A
  • upper aspect is on the midline

- Passes to left as approaches thoracic inlet

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2
Q

Describe the thoracic oesophagus

A
  • Begins at thoracic inlet
  • Covered by serosa
  • Passes through inlet on left
  • Moves back to previous position dorsal to trachea
  • Runs in mediastinum
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3
Q

Describe the abdominal oesophagus

A
  • following passage through oesophageal hiatus of diaphragm
  • very short
  • terminates at cardiac of stomach
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4
Q

List the related structures at the cervical portion of the oesophagus

A
  • Common carotid artery
  • Internal jugular vein
  • Tracheal duct
  • Cervical lymph nodes
  • Vagosympathetic trunk
  • Recurrent laryngeal nerve
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5
Q

What happens to the thickness of the wall of the oesphagus going from cranial to caudal?

A
  • The wall thickens
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6
Q

What are the layers of the oesophageal wall?

A
  • Connective tissue adventitia (outer layer)
  • Muscular layer
  • Mucuous membrane (stratified squamous epithelium, tight junctions)
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7
Q

Describe the muscular coats of the oesophagus

A
  • Striateed intially in all species
  • In cat, pig, horse becomes smooth distally
  • get circular and longitudinal muscle neaer to stomach
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8
Q

Describe the tunica mucosa of the oesophagus

A
  • Stratified squamous epi
  • cornified in herbivores
  • lamina propria without glands
  • Lamina muscularis incomplete, most extensive in caudal aspect
  • Submucosa well developed
  • loosely binds mucosa and muscularis layers
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9
Q

What is different in the tunica mucosa of the oesophagus in dogs, pigs, cats and horses?

A
  • Dogs: mucous glands over entire length
  • Pig: glands only cranially
  • Cat and horse: glands only at pharyngo-oesophageal junction
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10
Q

Describe the tunica muscularis of the oesophagus

A
  • Inner and outer layers
  • Continuous cranilly with pharyngeal muscles
  • Mid-region, muscle layers arranged in intercrossing spirals
  • Caudally the outer fibres more longitudinal, inner circular and thicker
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11
Q

What are the 3 phases of swallowing?

A
  • Oropharyngeal
  • Oesopharyngeal
  • Gastro-oesophageal
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12
Q

Outline the process of swallowing

A
  • food to base of tongue
  • Pharyngeal muscles contract to push food to laryngopharynx
  • after contraction of pharyngeal muscles, cricopharyngeal and thyropharyngeal muscles relax
  • Opens oesophagus - bolus can pass
  • After bolus passage, muscles contract once more (duration of relaxation determined by sensory input from pharyngeal filling)
  • High sphincter pressure prevents aspiration or reflux of oesophageal contents
  • Peristaltic wave continues along oesophagus carrying bolus to lower oesophageal sphincter
  • if bolus not carried to stomach, secondary wave from local stimulation and carries bolus along
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13
Q

What is the difference in control of pharyngeal and oesophageal phases of swallowing?

A
  • pharyngeal controlled by central pattern generator- no peripheral feedback
  • Oesophagus works by peripheral feedback
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14
Q

Explain why conditions can affect pharyngeal or oesophageal phases of swallowing independently?

A

2 distinct pattern generators for the 2 regions

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15
Q

What is the blood supply to the cervical region of the oesophagus?

A
  • Thyroid and subcalvian arteries

- Branches from left and right common carotids

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16
Q

What is the blood supply to the thoracic region of the oesophagus?

A

Broncho-oesophageal artery

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17
Q

What is the blood supply to the abdominal region of the oesophagus?

A

Left gastric and splenic arteries

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18
Q

What is the venous drainage of the cervical portion of the oesophagus?

A

External jugular veins

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19
Q

What is the venous drainage of the thoracic portion of the oesophagus?

A
  • Oesophageal vein
  • In dogs and cats, pair of oesophageal veins drain into azygous via bronchooesophageal veins
  • In horse, oesophageal vein drains directly into azygous vein
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20
Q

Describe the lymphatics of the oesophagus

A
  • Cranial aspect into cervical, middle and caudal deep cervical nodes
  • Thoracic lymph from oesophagus drains into cranial and caudal mediastinal lymph nodes
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21
Q

where does the sympathetic innervation of the oesophagus come from?

A

From cervico-thoracic ganglion

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22
Q

where does the parasympathetic innervation of the oesophagus come from?

A

Branches of the vagus nerve

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23
Q

Where are the ganglia supplying the oesophagus found?

A

Between the internal and external muscle layers

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24
Q

Describe the physiological characteristics of teh GI tract smooth muscle

A
  • Unitary (syncitial)
  • Mass of many fibres, contract as single unit
  • Arranged in sheets or bundles
  • Cells in contact, joined by gap junctions = free movement of ions between each muscle cell
  • Nerves innervating smooth mm branch over many fibres
  • Nerves do not make direct contact, diffuse junctions = transmitter secreted into local environment of muscle
  • Contraction and relaxation due to transmission of ACh and noradrenaline
  • Stretch of lumen = contraction of muscles (peristalsis)
  • Local tissue factors and hormones also influence activity
  • Some areas have spontaneous activity
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25
Q

What are the main neurotransmitters of the GI smooth muscle?

A
  • Acetylcholine (PS)

- Noradrenaline (S)

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26
Q

What type of synaptic junction is found at neuromuscular junctions of the GI smooth muscle and why?

A
  • Diffuse
  • secretes NT into local environment
  • Stimulates contraction of lots of muscle cells at once
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27
Q

What are the 4 regions of the stomach?

A
  • Cardia
  • Fundus
  • Corpus
  • Pylorus/antrum
    (in that order)
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28
Q

In a dorsoventral radiograph, where would the gas and fluid be in the stomach?

A
  • Gas: fundus

- Fluid: body (corpus)/pylorus

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29
Q

In a ventrodorsal radiograph, where would gas and fluid be found in the stomach?

A
  • Gas: corpus (possibly pylorus)

- Fluid: fundus

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30
Q

In a left lateral radiograph, where would gas and fluid be found in the stomach?

A
  • Gas: pylorus (poss. corpus)

- Fluid: fundus

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31
Q

In a right lateral radiograph, where would gas and fluid be found in the stomach?

A
  • Gas: fundus

- Fluid: pylorus

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32
Q

What are the muscle layers of the stomach?

A
  • Outer longitudinal

- Inner circular

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33
Q

Where is circular muscle found in the stomach?

A
  • Corpus and pylorus
  • Does not encircle fundus
  • Forms pyloric and cardiac sphincters (with contribution from internal oblique layer)
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34
Q

Where is the internal oblique layer of muscle found in the stomach?

A
  • Fundus and body around greater curvature

- Longest bundles closest to lesser curvature and often reach angular incisura

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35
Q

What is the function of the internal oblique muscle layer of the stomach?

A

Facilitates greates expansion

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36
Q

Describe the outer muscle layer of the stomach?

A
  • Continuous with oesophagus
  • Passes over surface and forms 2 bands alnog each curvature
  • Oblique course to long axis - external oblique fibres
  • Priminent in horse and pig
  • In these species fans out over fundus, not parallel as in cat and dog
  • Pyloric canal has heavy longitudinal muscle coat
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37
Q

Describe the parasympathetic supply to the stomach

A
  • Vagal
  • Ganglia in wall
  • Inhibits fundus
  • Stimulates pylorus
38
Q

Describe the pH gradient of the stomach

A
  • Increased in acidity (decreases in pH) as move from top to bottom
  • All regions are acidic
39
Q

Describe the non-glandular region of the stomach/oesophageal mucosa

A
  • Oesophagus

- Cornified stratified squamous epithelium

40
Q

Briefly outline the glandular regions of the stomach

A
  • Proper gastric glands (mucous, chief, parietal)
  • Pyloric glands (seromucous)
  • Cardiac glands (seromucous)
41
Q

List the mucosal cells of the stomach and their secretions

A
  • Parietal: HCl, intrinsic factor
  • Chief cells: pepsinogen
  • Endocrine cells includes G cells and ECL cells
  • G cells: gastrin
  • ECL cells: histamine
42
Q

Describe monogastric stomach microbiologi

A
  • Barrier to infection
  • minimal microbiology
  • Acid = barrier to infection and colonisation of lower intestinal tract
  • Age may impact barrier function
  • Neonatal stomachs may be infected by overgrowth (not as acidic, less flora present)
  • Food type affects barrier function
  • Pharmacology affects barrier function
  • Infectious dose of pathogen depends on tolerance to acid
43
Q

Describe the formation and secretion of HCl

A
  • DO NOT PRODUCE HCl IN CYTOPLASM
  • H+ and Cl+ transported independently and join up outside of parietal cell
  • Hydrogen ions generated by carbonic anhydrase on carbon dioxide to carbonic acid, then to hydrogen and bicarbonate
  • Bicarbonate actively pumped into interstitial fluid then to blood
  • K+ and Cl- transported into gland lumen by facilitated diffusion
  • H+ actively pumped into gastric fluid, stimulates uptake of K+
  • H+ and Cl- in gland lumen
  • Changes osmolarity, outward diffusion of water, HCl produced
44
Q

What are the factors that regulate HCl secretion?

A
  • ACh from cholinergic neurones
  • Gastrin
  • Histamine
45
Q

What happens to the pH of blood and urine of monogastrics after a meal and why?

A
  • Both rise
  • Bicarbonate secreted into blood in H+ generation
  • Known as alkaline rise
46
Q

Describe the mechanism of pepsin formation

A
  • Pepsinogen synthesised and stored in chief cells
  • Is zymogen for pepsin (inactive)
  • HCl creates environment where pepsinogen unfolds, cleaves self (autocatalysis)
  • pepsin cleaves off 44 AAs from pepsinogen to produce more pepsin (positive feedback, pepsin = more pepsin)
  • Hydrolyse peptide linkages within protein molecules
  • Preferentially acts on linkages involving aromatic acids e.g. phenylalanine and tyrosine
  • Breakdown to short peptides rather than individual amino acids
47
Q

Describe the mechanism of pepsin secretion

A
  • pepsinogen release only active in acid environments (pH 2.0)
48
Q

What are the 3 phases of gastric secretion (in order)?

A
  • Cephalic
  • Gastric
  • Intestinal
49
Q

Describe the cephalic phase of gastric secretion

A

0 CNS derived

  • See, smell, taste (think) food - prepares stomach for food
  • Neural output via PS fibres running in vagus
  • Output synapses in submucosal plexus
  • Postganglionic PS fibres innervate mucous cells, chief cells, parietal cells, G-cells
  • Short phase, overlaps with gastric phase
50
Q

Describe the gastric phase of gastric secretion

A
  • Begins when food arrives in stomach
  • Distension
  • Increase pH of gastric contents
  • Presence of undigested materials (esp proteins)
  • triggers gastric juice secretion
  • lasts several hours, gastrin stimulates contractions (mixing waves)
  • Maintains high er pH at mucosal surface and therefore ongoing aacid secretion until thoroughly mixed
51
Q

Describe the neural component of the gastric secretion phase

A
  • Stretch and chemoreceptors in mucosa trigger local (submucosal and myenteric plexuses) and vagal reflex arcs
  • Postganglionic release of ACh at parietal cells
52
Q

Describe the hormonal response component of the gastric secretion phase

A
  • Neural stimulation and presence of peptides in chyme - stimulates secretion of gastrin
  • Gastrin in circulation, stimulates parietal and chief cells via blood steam
  • Accelerates secretion rates
53
Q

Describe the intestinal phase of gastric secretion

A
  • Chyme enters small intestine
  • Several hours of mixing
  • Waves of contractions sweep down stomach
  • Arrival of partly digested proteins to duodenum => secretion of gastrin from duodenal wall G-cells, increased acid and enzyme production
  • Higher acid release in response to protein meal
  • Quickly dampened by CCK and gastric inhibitory peptide
54
Q

Describe the neural response in the intestinal phase of gastric secretion

A
  • Chyme leaving stomach releives some of distention - less stimulation
  • Food entering duodenum stretches walls => enterogastric reflex
  • Less gastric contractions
55
Q

Describe the hormonal response in the intestinal phase of gastric secretion

A
  • Arrival of lipids and carbohydrates in duodenum => release of CCK and gastric inhibitory peptide
  • Reduces gastric secretions and contractions (slow motility)
  • Drop in pH below 4.5 stimulates release of secretin by enteroendocrine cells of duodenum
  • Inhibits parietal and chief cells
  • Stimulates buffer release fromo pancreas
  • Pancreas take in bicarbonate
56
Q

What are some of the negative feedback elements in gastric secretion?

A
  • Duodenal signals

- Stomach pH falling towards 2.0 inhibits gastrin release

57
Q

Describe how gastrin affects HCl production

A
  • Digestive tract hormone
  • Released in response to peptides directly stimulating G-cells
  • Also from vagal stimulation
  • Acts on ECL cells to produce histamine, and direct to parietal cells
  • Both actions increase HCl production
  • Inhibited if pH drops below pH 2.0
58
Q

Describe how histamine affects HCl production

A
  • Stimulates HCl production and secretion
  • Stimulated by gastrin action on ECL cells
  • Activates adenylate cyclase to use cAMP messenger to stimulate ion pump (K+ into parietal cell, H+ out into lumen of gland)
59
Q

What are the 2 neural controls of HCl production and secretion

A
  • From CNS and short reflex in wall of stomach

- Both trigger gastrin secretion

60
Q

Describe the control by the CNS in HCl production

A
  • Long reflex arcs via vagal nerves
  • Cephalic phase of digestion
  • Sight, smell, taste of food
61
Q

Describe the control by the short reflexes in teh wall of the stomach in HCl production

A
  • Walls stretch

- Peptide stimulation of sensory nerve endings

62
Q

Define “zymogen”

A
  • Enzyme precursor
  • AKA proenzyme
  • Is a protein precursor that is converted into an enzyme when activated by another enzyme e.g. pepsinogen for pepsin
63
Q

Define “endopeptidase”

A

An enzyme which breaks peptide bonds other than the terminal ones in a peptide chain (trypsin, chymotrypsin)

64
Q

Define “exopeptidase”

A

An enzyme which breaks the terminal bond in a peptide chain (carboxypeptidase)

65
Q

Give some of the pancreatic proteases and state whether they are endo or exopeptidases

A
  • Trypsin
  • Chymotrypsin
  • Elastase
  • All endopeptidases (different specificities)
  • Carboxypeptidase (exo)
66
Q

What is the action of trypsin?

A

Breaks peptide bonds involving AAs arginine and lysine

67
Q

What is the action of chymotrypsin?

A

Targets peptide bonds involving tyrosine and phenylalanine

68
Q

What is the action of carboxypeptidase?

A
  • Exopeptidase
  • Removes last amino acid of polypeptide chain
  • Not specific to identities of AAs in volved
  • Generates free AAs
69
Q

Describe the conversion of trypsinogen to trypsin

A
  • Chyme enters duodenum

- Enteropeptidase from SI triggers conversion of trypsinogen (released from pancrease) to trypsin

70
Q

What are the basic functions of the stomach?

A
  • Storage of food
  • Mechanical degradation of food
  • Secretion of gastric juices
71
Q

Breifly describe the rotation of the stomach in volvulus in the dog

A
  • Stomach twists around longitudinal axis of digestive tract
  • Rotation commonly clockwise (viewing animal from behind)
  • Can rotate up to 360degrees this way, 90degrees anticlockwise
72
Q

What are teh effects of distension and volvulus on blood supply to the stomach?

A
  • Prevents blood supply to and from stomach
  • Blood flow to heart reduced
  • Blood flow to stomach lining cut off
  • Blood flow to liver and spleen cut off
73
Q

List the organs in contact with the stomach

A
  • Diaphragm (left crus bound to fundus of stomach)
  • Liver (lesser curvature)
  • Spleen (greater curvature)
  • Duodenum at pylorus
74
Q

Briefly describe the histological appearance of the non-glandular regions of stomachs of pigs and herbivores

A
  • Stratified squamous epithelium
  • May see division between glandular and non-glandular = margo plicatus
  • Mucosa (made up of epithelium, lamina propria, mscularis mucosa)
  • Submucosa
  • Muscular layers
  • Serosa
75
Q

Briefly describe the histological appearance of the glandular cardiac region of the stomach

A
  • Single layer columar epithelium

- Forms gastric pits (mucus production)

76
Q

Briefly describe the histological appearance of the glandular fundic region of the stomach

A
  • Parietal cells present (look like fried eggs, pink, dark yolky nucleus)
  • Surrounded by darker smaller cells = chief cells
  • May also be MALT present
  • Mucosa, submucosa, musclaris, serosa
77
Q

Briefly describe the histological appearance of the glandular pyloric region of the stomach

A
  • Single columnar epithelium
  • Very long gastric pits
  • Similar to cardia
  • Mucosa, submucosa, muscularis, serosa
78
Q

Where is gatrin synthesised?

A

G cells in stomach and duodenum

79
Q

When is gastrin secreted?

A
  • IN response to peptides directly stimulating G-cells
  • Also by vala secretion
  • Stops when pH<2
80
Q

What is the activity of gastrin?

A
  • Stimulates parietal cells in stomach to secrete HCl

- Stimulates Chief cells to secrete pepsinogen

81
Q

Where is somatostatin stored and secreted?

A
  • Stored in pancreas

- Secreted by gastric glands in stomach

82
Q

Under what conditions is somatostatin secreted?

A
  • Low pH in stomach
83
Q

What is the action of somatostatin?

A
  • Inhibits release of gastrin and HCl from stomach
  • Inhibits secretin and cholecystokinin release from duodenum
  • Inhibits release of glucagon and insulin from pancreas
84
Q

Where is histamine secreted from?

A

ECL cells in stomach

85
Q

When is histamine secreted in the stomach?

A

In response to stimulation of ECL cells by gastrin

86
Q

What is the function of histamine in the stomach?

A

Regulates HCl secretion

87
Q

Where is grehlin secreted from?

A

Stomach and pancreas

88
Q

Under what conditions is grehlin secreted?

A
  • When stomach empty, grehlin secreted

- When stomach strethc, secretion stops

89
Q

What is the action of grehlin?

A
  • Increases food intake by stimulating hunger at the level of the hypothalamus
90
Q

What is the action of acetylcholine in the stomach?

A
  • Helps regulate HCl secretion

- Causes Chief cells to secrete pepsiinogen

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