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LSS2: Alimentary system > Oesophagus & stomach > Flashcards

Oesophagus & stomach Flashcards

1
Q

what is the structure of the gut wall

A
  1. Mucosa:
    Epithelium: single cell lining facing the gut content (thsi changes depending where in the gut you are)
    Lamina propria: loose layer of connective tissue connecting the epithelium to the muscularis mucosae
    Thin layer of muscle
  2. Submucosa: lots of nerves, blood vessels. Nerves responsible for controlling the gut and blood transferring content. Connective tissue (containing nerve plexus)
  3. Muscularis: smooth muscle
    (containing nerve plexus) both longitudinal and circular
  4. Serosa/Adventitia: connective tissue +/- epithelium (hold the gut to the body wall)
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2
Q

where does the oesophagus originate

A

c5- as it enters the throat

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3
Q

How long is the average oesophagus?

A

25-30 cm

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4
Q

At what vertebral level does the oesophagus pierce the diaphragm?

A

T10

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5
Q

Describe the cell type in the upper oesophagus and the reason for having this cell type.

A

Non-keratinising stratified squamous - this is good for protection - acts as a barrier and prevents the loss of water through the epithelium.

Rubust, wear and tear lining. Abrasive food passing through so the upper surface allows abrasion without loss of function.
‘Wear & Tear’ lining
(extremes of temp. & texture)

Lubrication – Mucus secreting glands
(also saliva, lubricates)

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6
Q

what is the function of the oesophagus?

A

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

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7
Q

What are the two important sphincters in the oesophagus?

A

Upper oesophageal sphincter and the lower oesophageal sphincter.

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8
Q

Describe the difference in structure of the lower and upper oesophageal sphincters.

A

The upper oesophageal sphincter is made up of only skeletal muscle whereas the lower oesophageal sphincter consists of both skeletal and smooth muscle, but largely smooth muscle

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9
Q

What state are the sphincters in when there is no food in the mouth?

A

They are tonically active meaning that they are both closed.

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10
Q

What happens when food goes into the mouth?

A

When food goes into the mouth, a reflex is set up by the swallowing centre in the brain leading to peristalsis.
Therefore the 2 spinchters only open if you swallow something.

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11
Q

How does muscle type change as you pass down the oesophagus?

A

You go from skeletal to smooth muscle as you move down the oesophagus.

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12
Q

What two types of muscle are in the oesophagus?

A

Circular and longitudinal

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13
Q

explain the peristaltic wave?

A

It is a local effect.
The oesophagus responds to the food bolus.
Nervous stimulus responds to contract the muscle above the food bolus and relax below the food bolus.
Causing the food to move down towards the stomach.

This is independent to gravity.

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14
Q

describe what happens when the first peristaltic wave isn’t enough

A

If it is a big bolus food, the contraction isn’t strong enough to move the food down. Therefore, another peristaltic wave is initiated. There is still food left so there is another second peristaltic wave which moves it to the stomach

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15
Q

What is the difference between the primary and secondary peristaltic waves?

A

Secondary peristaltic wave is initiated after the primary if the food gets stuck.

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16
Q

what is the gastro-oesophageal junction and what changes from the oesophagus to the stomach ?

A

It is where the oesophagus meets the stomach.
There is a transition of the epithelium.
Oesophagus is made up of non-keratinising stratified squamous epithelia: wear and tear lining and the stomach epithelium is made up of simple columnar epithelium: which is useful for absorption.

The lower oesophageal sphincter: it is less defined than the upper oesophageal sphincter
this is due to the diaphragm and the fold of the stomach. when stomach is empty, the diaphragm affects that regions.

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17
Q

How does the innervation change as you pass down the oesophagus?

A

It goes from motor neurons to autonomic nervous system as you move down the oesophagus.

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18
Q

The lower oesophageal sphincter is not considered a true anatomical sphincter. What is it formed by?

A

Diaphragm (muscular part), greater curvature of the stomach folding inwards, difference in pressure between the thorax and abdomen

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19
Q

What are the gastric folds in the stomach lining called and what is the point in them?

A

Rugae - when the stomahc is empty, these fold allow the stomach to reduce in size and as the stomach fills, it can expand– it becomes smooth. Stretches.
They increase surface area

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20
Q

how is a pool of acid prevented from going up the oesophagus?

A

Prevented by the diaphragm acting as the lower oesophageal sphincter.

SOMETIMES, this fails.
E.g. during pregnancy. Fetus pushes the stomach upwards. the abdomen gets pushed in the thorax so pressure difference changes and causes acid upwards.

Stomach pushes upwards——oesophagus moves upwards so acid move from stomach to the oesophagus.

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21
Q

what is the main function of the stomach?

A

Break food down into smaller particles stored (due to acid & pepsin); hold food and release at a controlled steady rate into duodenum; kill parasites & certain bacteria.

22
Q

what are the regions of the stomach and what does it do?

A

Cardiac and pyloric region: immediately leaving and entering the stomach.
Lots of mucus produced

Body and Fundus:
where lots of digestion takes place. Need lots of mucus, HCL and pepsinogen ( main protease that breaks down the food).
Produces the acid.

Antrum:
Towards the bottom of the stomach.
There is an endocrine part.
Produces gastrin.

23
Q

what does the columnar epithelium allow?

A

Columnar epithelium invaginates into glands which is present throughout the stomach

24
Q

What feature do the mucus secreting cells of the stomach have that protects them from the acidity of the stomach?

A

They secrete HCO3- that sits on top of these cells and neutralises the acid that comes into contact with its surface.

Blue colour Mucins= gel coating.
HCO3- trapped in mucus gel

therefore pH at epithelial surface: 6-7
Lumen= 1-2

25
Q

How much acid is produced by the stomach per day and what is the concentration of protons?

A

2 L

150 mM

26
Q

how much more is the stomach more acidic than the blood

A

3 mill x that in the blood

27
Q

what cells produce pepsinogen?

A

Purple colour cells, these produce pepsinogen.

28
Q

what is gastrin and other cells present

A

Gastrin: endocrine cell.
There are lots of gastrin, this stimulates acid production.

Mucus producing cells which is found on the neck of the epithelium, produces ONLY mucus.

29
Q

descirbe the activity ofd the stomach, large and small intestine

A

Peristalsis occurs when you want to move food from one end to another, down the pyloris, ready for the intestine.
Propels chyme towards the colon –
more powerful as moves from LOS
to pyloric sphincter
Regulated by the autonomic nervous system.
20% of stomach contractions
CENTRALLY DRIVEN

Segmentation , mixing everything together. Less coordinated.
In the stomach: Weaker. Fluid chyme towards
Pyloric sphincter, solid chyme
pushed back to body if it isnt digested properly
Stretching activates enteric nervous system.

LOCAL CONTRACTION

80% stomach contractions

30
Q

What do Gastric Chief Cells produce?

State some histological features of Gastric Chief Cells

A

Protein secreting epithelial cell.

Gastric Chief Cells produce pepsinogen
.
They have a lot of RER to generate the proteins
They have Golgi apparatus for packaging and modifying for export
They have a lot of vesicles at the apical membrane (blue)

31
Q

State three structural features of the resting parietal cell.

A

Parietal cells- acid secreting cell.
Numerous mitochondria - provide energy for the active transport of protons into the lumen of the stomach
Cytoplasmic Tubulovesicles - contain H+/K+ ATPase channels
Internal Canaliculi - fluid filled reservoirs present within the resting parietal cell. Extends to apical surface

32
Q

what happens to the parietal cell in the active state?

A

Parietal cell: secreting
Tubulovesicles fuse with membrane and microvilli project into canaliculi and these canaliculi combine and project into the lumen.
Huge surface area of the tubulovesicles.

33
Q

What is the role of parietal cells?

A

Parietal cells pump protons into the lumen of the stomach and make it more acidic

34
Q

Describe the mechanism by which active parietal cells increase the proton concentration in the stomach.

A

Carbon dioxide diffuses into the cell from the blood and reacts with water with the action of carbonic anhydrase to produce bicarbonate and a proton. A sodium-potassium exchanger bring one potassium in and one sodium out. The K+ follows the concentration gradient and diffuses into the canaliculi (fused with TV, so increase H+/K+ ATPase). HCO3- is exchanged for Cl- - the Cl- then moves down the concentration gradient into the canaliculi. Then, ATP is used to actively transport H+ into the canaliculi (as lots of H+ in the stomach lume) with K+ moving out. There is a massive ATP driven movement of protons into the stomach lumen.

35
Q

What is the effect of inhibiting carbonic anhydrase?

A

This reduces the acid producing ability of the parietal cells because it is no longer able to convert water and carbon dioxide into H2CO3 (so H+ and HCO3- isn’t generated)

36
Q

What two proteins do you need a lot of to increase the acidity of the stomach?

A

Carbonic Anhydrase and H+/K+ ATPase

37
Q

How does pepsinogen turn into pepsin?

A

The acid makes the pepsinogen unfold and this causes autocatalysis (pepsinogen metabolises itself) of pepsinogen to produce pepsin.

Chief cell produces pepsinogen, so the pepsin precursor is secreted into the stomach lumen, parietal cell drives lots of acid, acid produces pepsin, which acts on large proteins to break them down toi peptides.

38
Q

What are the two stimuli for gastrin production?

A
  • Acid production itself
  • Local peptide hormones that are being produced by pepsin
  • if there is food in the stomach, gastrin will be produced
39
Q

where do you find the gastrin and what does gastrin do?

A

In the pyloric antrum region.

Yellow cells which produces gastrin.
It is secreted into the blood and come from the blood into the stomach to stimulate acid secretion.
It does this by histamine release from chromaffin cells (lamina propia).
The parietal cells have stimulating receptors and histamine is one that stimulates the production of acid.

40
Q

What is the effect of gastrin?

A

Gastrin is produced in the pyloric antrum and passes into the bloodstream before returning to the lumen of the stomach where it causes an increase in acid secretion by the stomach epithelium.

41
Q

How can gastrin indirectly increase acid secretion?

A

Gastrin stimulates the release of histamine from chromaffin cells (in the lamina propria) - this stimulates acid secretion

42
Q

What are the three phases of gastric secretion?

A

Cephalic, Gastric, Intestinal

43
Q

Describe the cephalic phase of gastric secretion.

A

This is before the food even enters your mouth.
Stomach prepares the arrival of the food.

The vagus nerve from the medulla stimulates the enteric nervous system to increase the production of acid and pepsin. vagus nerve produces acetylcholine ( parasympathetic nerve) and this stimulates histamine production and so does gastrin.
You also get an increase in gastrin production (which causes further increase in acid production).

Acetylcholine is driving the production of acid in the cephalic response.

44
Q

Describe the gastric phase of gastric secretion.

A

You have central and local RESPONSE on the gastric secretion and local is much more powerful
LOCAL:
Lining of the gut.
There are lots of nerves in the stomach lining, and these nerves have local effect, response to local stimuli.
Stomach there is a chemical change and physical. This is detected by this nervous network which then DIRECTLY activate the muscles and activate glands to start churning the food, releasing more pepsin to facilitate more digestion.

CENTRAL:
Once the food is in the stomach, stretch and chemoreceptors send messages to the brain. The brain then activates the vagus nerve and increases pepsin and acid production. Once the process has been started, the enteric nervous system will take over and cause churning of the stomach.

45
Q

Describe the intestinal phase of gastric secretion.

A

Food has left the stomach and entered the intestine, so you have well mixed chyme.

Chyme enters the small intestine and if the pH is < 2 or the chyme has a high lipid content, this acts as a stimulus that goes up to the brain and inhibits acid and pepsin production.

46
Q

What are the three hormones produced in the enterogastric reflex? What is the name given to this group of hormones?

A

Cells within the small intestine produce hormones which ALL have an inhibitory effect on the stomach.

Gastric Inhibitory Peptide, Cholecystokinin and Secretin
These are enterogastromes
They decrease the production of acid and pepsin
The enterogastric reflex is a reflex that is controlled by hormones.
These travel in the blood.

47
Q

Describe the excitatory process when chyme has a high protein content.

A

This is dependant on the protein concentration in duodenum. It stimulates gastrin secretion.

If the chyme entering the small intestine has a high protein content it will stimulate the release of gastrin so that more acid is produced hence more pepsinogen is converted to pepsin so the proteins will be better digested.

This happens as high protein content means that the stomach hasn’t effectively broke down the protein.

48
Q

State two drugs that decrease acid secretion and their targets.

A

Omeprazole - proton pump inhibitor

Ranitidine - histamine receptor antagonist

49
Q

Which of the following structures within the

parietal cell contains the most H+/K+ ATPase?

A 
Canaliculi
Carbonic anhydrase 
Golgi body 
Mitochondria 
Tubulovesicles -->
50
Q

Which of the following stimuli would be most likely to

decrease acid secretion in the stomach?

A 
Chyme fatty acid content -->
Increased acetylcholine secretion 
Increased gastrin secretion 
Protein content of the meal 
Stomach distension

LSS2: Alimentary system (24 decks)

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