Week 2- 1/3 - Stomach complete** Flashcards
State the 4 layers of the stomach wall
mucosa
submucosa
muscularis
serosa
Stomach: What is the function of the Mucosa?
to produce secretions and absorb the products of digestion
Stomach: What structures lie in the Mucosa layer? 4
blood vessels
nerves
lymph vessels
muscularis mucosae
Stomach: What type of tissue is the submucosa?
connective tissue
Stomach: What structures lie within the submucosa? 2
blood vessels and nerves
Stomach: Describe the structure of the Muscularis 2
a layer of circular muscle and a layer of longitudinal muscle
Stomach: What structures lie within the Muscularis?
the myenteric plexus
Stomach: Describe the structure of the serosa
- What does it consist of?
it is a thin layer of connective tissue
peritoneum
Oesophagus: What is the oesophagus?
a continuation of the laryngopharynx connecting the pharynx to the stomach
Oesophagus: Where does it lie in relation to the Trachea?
- Where does it travel? 2
dorsal
it travels through the mediastinum it passes through the oesophageal hiatus of the diaphragm
Oesophagus: How do the oesophageal muscles differ to those elsewhere in the GI tract?
they are striated
Oesophagus: What happens during the Oral Phase during swallowing? 2
food is mixed with saliva to form a bolus
the tongue moves the bolus to the back of the mouth
Oesophagus: State the names of the 3 stages of swallowing
oral phase
pharyngeal stage
oesophageal phase
Oesophagus: What happens during the first part of the Oesophageal Phase of swallowing? (up until breathing resumes) 5
the upper sphincter of the oesophagus opens
food passes into the oesophagus
the entrance to the trachea is reopened
the upper oesophageal sphincter closes
breathing resumes.
Oesophagus: What happens during the second part of the Oesophageal Phase of swallowing? 2
the swallowing centre in the medulla initiates a wave of contractions in the circular muscle layer
the peristaltic wave travels along the oesophagus to the lower oesophageal sphincter, carrying the bolus ahead of it
Oesophagus: What happens during the Pharyngeal Stage of swallowing? 2
the vocal folds close
the epiglottis covers the entrance to the trachea
Stomach: Which artery supplies the stomach?
- What about venous drainage?
the coeliac artery
the hepatic portal vein
Stomach: What name is given to the ridges in the stomach?
- What is their purpose?
rugae
they allow the stomach to stretch and increase in capacity as food enters
Stomach: What 2 regions make up the stomach?
the glandular region and the non-glandular region
Stomach: In most species, which part of the stomach is non-glandular?
- Where can this part be found?
- What is it lined with instead?
the oesophageal portion
it is the portion of the stomach that is closest to the oesophageal opening
stratified squamous epithelium
Stomach: In the horse, what is the name given to the folded margin dividing the glandular and non-glandular portions of the stomach?
- Why do horses often get stomach ulcers?
the margo plicatus
because the non-glandular region is not well adapted for handling acidic secretions
Stomach: State the names of the 4 regions of the glandular stomach
cardia
fundus
corpus
pylous
Stomach: State the other name given to the oesophageal sphincter.
- What name is given to the sphincter closest to the pylous?
cardiac sphincter
pyloric sphincter
Stomach: What is the function of the Fundus?
- What about the corpus and pylorus?
storing food
mixing food
Stomach: Describe the path of ducts of glands in the glandular stomach.
- Where is most gastric juice formed?
ducts of glands open into the stomach lumen through the glandular neck
in the corpus and pylorus
Stomach: Which nerve fibres innervate the stomach? 3
sympathetic fibres
parasympathetic fibres
intrinsic fibres of the enteric nervous system
Stomach: Describe the 2 possible reflexes of the Enteric nervous system and what they involve.
the long reflex arcs involve the CNS
the short reflex arcs are contained within the wall of the gastrointestinal system
Stomach: What is the function of the Enteric nervous system? 4
- Can it function independently from the CNS?
it controls motility
endocrine and exocrine secretions microcirculation of the gastrointestinal tract
regulates immune and inflammatory processes
yes
Stomach: The parasympathetic and sympathetic impulses interact with the enteric nervous system. Where is parasymp and symp imput from CNS exerted?
- What do plexuses in the gastrointestinal tract wall contain and what is each elements function? 3
on nerve cells in the gastrointestinal wall
sensory cells which react to changes in lumen content and wall stretch
interneurones which propagate impulses along the tract wall
motor neurones which connect to smooth muscle or epithelial cells
Stomach: State the name of a group of specialised gastrointestinal cells.
- What is their structure?
- What is their function?
- Are they found everywhere?
interstitial cells of cajal
they are modified smooth muscle cells
they functions as a pacemaker for gut contractions
no they are found in different frequencies in different parts of the gi tract
State the names of 3 clinical diseases associated with ENS dysfunction
ileus
spasmodic colic
vagal indigestion
Imaging: How would megaoesophagus appear on a radiograph?
the oesophagus would be uniformly dilated
Imaging: Why might you want to take a radiograph of the oesophagus? 4
difficulty swallowing
regurgitation
potential foreign body
persistent bad breath
Imaging: How would you position the animal for a lateral radiograph of the oesophagus?
such that the head is on the left hand side of the screen
Imaging: Why is it difficult to image the oesophagus when awake?
- But why dont we want to perform it under general anaesthetic?
the oesophagus is normally empty and flaccid
because it can induce generalised distension of the oesophagus
Megaoesophagus: What is the main clinical sign?
- Which species is it most common in?
regurgitation
dogs
Imaging: Describe how we can see the oesophagus in action on an awake radiograph? 2
the patient is fed a barium sulphate paste
the images are taken after swallowing
Imaging: Other than awake radiography, how else could we see the oesphagus in action?
- How does this work?
fluoroscopy
this is a type of advanced real time radiography where the animal sits or stands in a box and eats contrast media while a continuous xray beam is targeted
Where is the spleen attached to the stomach? 2
the spleen follows the greater curvature of the stomach
the gastrosplenic ligament of the greater omentum attaches the head of the spleen to the stomach
Ventrodorsal imaging of the stomach: Where would you expect gas to collect on a VD view of the stomach?
in the corpus and pyloris region
Dorsoventral imaging of the stomach: Where would you expect gas to collect in the stomach on this view?
in the cardia and fundus regions
Left Lateral Radiograph of stomach: where would you expect gas to collect?
in the pylous region
Right lateral radiograph of stomach: where woudl you expect gas to collect?
in the cardia and fundus region
Name the acute stomach pathology that is an emergency.
- What does the stomach look like on a radiograph?
gastric dilation and volvulus
a smurf head
GDV: When is this condition most likely to occur?
- Explain the mechanism of this condition 4
following exercise after eating
the combination of eating and exercising causes the stomach to fill with gas and dilate
the gas travels up and causes the stomach to flip
this twists the cardia and pylorus regions so nothing can enter or leave the stomach
since no liquid or air can leave the stomach it continues to dilate and can rupture
GDV: What other organs can be affected by a GDV and why? 2
the spleen can be affected because the head of the spleen is attached to the greater curvature of the stomach so the spleen can rotate as the stomach rotates resulting in congestion and splenomegaly
the diaphragm can become compressed by the stomach
which reduces thoracic space resulting in decreased tidal volume and shortness of breath
GDV: What other non-organ structures can be affected?
the vena cava and portal vein can become compresse by the stomach leading to reduced venous return to the heart
Define Zymogen.
- Give an example of one
an inactive precursor of an enzyme which requires a biochemical change for it to become an active enzyme. pepsinogen
Which enzyme digests proteins in the stomach?
- What is the precurser for this enzyme?
pepsin
pepsinogen
state the 4 functions of the stomach
temporary storage of food
mechanical degradation of food
biochemical degradation of food using gastric juices
destroy foreign bateria with acidic conditions
State the 5 types of cell found lining the stomahc or in the gastric pits of the glandular stomach
mucin producing cells
chief cells
parietal cells
endocrine cells
enterochromomaffin like cells
What conditions are required for Pepsin to work optimally?
- How are these conditions achieved?
ph 1-3
the secretion of HCL into the stomach lumen
What is the function of Mucin producing cells?
to secrete mucus
What is the function of Chief cells?
to produce store and secrete pepsinogen
What is the function of Parietal cells?
to release hydrogen and chloride ions out of the cell and into the stomach lumen
What are the 2 types of Endocrine cells found in the stomach?
- What does each one do?
g and d cells
g cells secrete gastrin into the blood
d cells secrete somatostatin
What is the function of Enterochromaffin like cells? (ECL)
to release histamine
How come Pepsin doesnt digest Chief cells? 2
chief cells make and store pepsin in an inactive form called pepsinogen
pepsinogen is released into the stomach lumen and converted to pepsin outside of the chief cells
How come HCL doesnt dissolve the cells lining the stomach wall and the Parietal cells? 3
the parietal cells make hydrogen ions and chloride ions separately and release them into the lumen where they combine to form hcl
mucin producing cells produce mucus containing hydrogen bicarbonate to protect the lining of the stomach
a negative feedback loop prevents constant release of gastric juices
State the 3 Phases of Gastric secretion
cephalic phase
gastric phase
intestinal phase
Describe the events occuring in the Cephalic phase of Digestion 5
taste, smell, chewing and thoughts of food stimulate the medulla oblongata
the medulla oblongata sends impulses to the enteric plexus of the stomach via the vagus nerve
this stimulates postgangionic neurones in the enteric plexus
this stimulates cheif cells to produce pepsinogen, parietal cells to produce hydrogen and chloride ions, G cells to produce gastrin
the gastrin produced by G cells enters circulation and stimulates further secretion of hydrogen and chloride ions and pepsinogen.
Describe the events occuring in the Gastric Phase of digestion 6
food arrives in the stomach causing it to distend
this distension actives a parasympathetic reflex via chemo and stretch receptors
impulses are sent to the medulla oblongate via the vagus nerve. the medulla oblongata responds by sending impulses to the stomach via the vagus nerve
this stimulates the stomach to increase secretions and increase stomach muscle contractions
the stomach distension also activates local reflexes to increase secretions.
Describe the events occuring in the Intestinal Phase of Digestion 6
the stomach empties, chyme enters the duodenum and distension reduces
if the ph of the chyme is less than 2 then further secretions are inhibited by several different mechanisms
nerve impulses are sent to the medulla oblongata via the vagus nerve
this inhibits motor impulses in the stomach
a local enteric gastric reflex is triggered which inhibits gastric secretion
secretin, gastric inhibitory polypeptide and cholocystokin are produced in response to carbohydrates and lipids in the duodenum to inhibit gastric secretions.
The intestinal Phase aims to decrease gastric secretions and slow gastric contractions. Which negative feedback loops help decrease gastric secretions? 5
reduction in stomach distension reduces local stimulation and secretions
if the stomach ph falls below 2 then gastrin release is inhibited. if the duodenum ph falls below 4.5 then secretin is released which inhibits chief cells and parietal cells producing secretions
if the duodenum ph falls below 4.5 this stimulates the entero-gastic reflex which reduces secretions
lipids and carbohydrates in the duodenum secrete cck and gip which reduce secretions.
The intestinal Phase aims to decrease gastric secretions and slow gastric contractions. How does it achieve a slow in contractions?
if the duodenum ph falls below 4.5 then the enterogastric reflex is stimulated which reduces stomach contractions
Describe the actions of Gastrin 3.
- When does gastrin secretion stop?
gastrin is released due to peptides in the stomach and vagal stimulation
it is released into the blood by G cells
it stimulates ECL cells to produce histamine which stimulates local chief and parietal cells to produce secretions
when the ph of the sotmach falls below 2
What effect does Vagus stimulation have on the stomach? 2
it acts on the proximal stomach, suppressing muscle contractions which allows it to relax and dilate
it acts on the distal stomach resulting in intense peristalsis
What effect does Vagal Acetylcholine from Parasympathetic impulses have? 3
it stimulates chief cells to secrete pepsinogen
it stimulates parietal cells to secrete hydrogen and chloride ions
it stimulates g cells to secrete gastrin
