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Alimentary system > 1. Oesophagus and stomach > Flashcards

1. Oesophagus and stomach Flashcards

1
Q

Digestion

A

breaking down macromolecules to allow absorption

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2
Q

Absorption

A

moving nutrients and water across a membrane

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3
Q

State the basic plan of the gut wall from the lumen outwards.

A

Epithelium, lamina propria, submucosa, muscularis, serosa/adventitia
There are nerve plexuses in the submucosa and muscularis
Serosa is a mixture of connective tissue and epithelium
Adventitia is only connective tissue

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4
Q

What vertebral level does the oesophagus start at?

A

C5

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5
Q

How long is the average oesophagus?

A

25-30 cm

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6
Q

At what vertebral level does the oesophagus pierce the diaphragm?

A

T10

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7
Q

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

A

Non-keratinising stratified squamous
Good for protection: acts as a barrier (temp/ texture)
Lubrication: Mucous secreting glands

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8
Q

What is the function of the oesophagus?

A

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

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9
Q

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

A

Upper oesophageal sphincter: skeletal muscle

Lower oesophageal sphincter: smooth muscle

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10
Q

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

A

Tonically active meaning they are both closed.

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11
Q

What happens when food goes into the mouth?

A

A reflex is set up by the swallowing centre in the brain leading to peristalsis.

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12
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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13
Q

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

A

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

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14
Q

What 2 types of muscle are in the oesophagus?

A

Circular

Longitudinal

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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

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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17
Q

Which 2 muscles are the upper oesophageal sphincter composed of?

A

Constrictor pharyngeal medius (circular)

Constrictor pharynges inferior (longitudinal)

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18
Q

What 2 portions are the lower oesophageal sphincter composed of?

A 
Internal component (circular)
External component: formed by the right crus of the diaphragm (voluntary control)
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19
Q

Pressure difference in oesophagus and stomach

A

Oesophagus: negative pressure
Stomach: positive pressure.

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20
Q

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

A

Rugae

Increase surface area, allow stomach to expand

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21
Q

How is reflux prevented?

A

By the diaphragm acting as the lower oesophageal sphincter

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22
Q

Describe the transition in epithelium from the oesophagus to the stomach.

A

Oesophagus: non-keratinising stratified squamous epithelia
Stomach: simple columnar epithelium

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23
Q

Gastro-oesophageal junction

A

Where oesophagus meets stomach

24
Q

Function of the stomach

A

Break food down into smaller particles stored (via acid and pepsin)
Hold food and release at a controlled steady rate into duodenum
Kill parasites and certain bacteria

25
Q

Describe the surface of the stomach

A

Simple columnar epithelium

Invaginates into mucosa: Tubular glands

26
Q

What are the 5 regions of the stomach?

A 
Cardiac
Fundus
Body
Pylorus
Pyloric Antrum
27
Q

What is produced in each region of the stomach and why?

A

Cardiac and pyloric: Entering and exiting, lots of mucous produced
Body and fundus: Main digestion takes place, acid and pepsinogen required as well as mucous
Antrum: Towards bottom, endocrine element, gastrin hormone helps facilitate stomach function

28
Q

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

A

2 L

150 mM H+

29
Q

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

A

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

30
Q

What does gastrin stimulate?

A

Acid production

31
Q

Describe the pH at the epithelial surface and in the lumen of the stomach

A

Epithelial surface: 6-7

Lumen: 1-2

32
Q

What constitutes stomach contractions?

A

Peristalsis (20%)

Segmentation (80%)

33
Q

Describe peristalsis in the stomach

A

Propels chyme towards the colon
More powerful as moves from lower oesophageal sphincter to pyloric sphincter
Driven by ANS: centrally coordinated, gnal down vagus nerve to stomach to propel food from one end to another

34
Q

Describe segmentation in the stomach

A

Weaker and less coordinated
Mix ingested food with stomach secretions to form chyme
Fluid chyme towards Pyloric sphincter
Solid chyme pushed back to body os stomach
Stretching activates enteric NS

35
Q

What do Gastric Chief Cells produce?

A

Pepsinogen

36
Q

State 3 histological features of Gastric Chief Cells.

A

Abundant RER
Golgi apparatus for modification and packaging of proteins into granules
Masses of apical secretion granules

37
Q

State 3 structural features of the resting parietal cell.

A

Many mitochondria: provide energy for the active transport of H+ into the lumen of the stomach
Cytoplasmic Tubulovesicles: long cytoplasmic tubular vesicles, string like, contain H+/K+ ATPase channels
Internal Canaliculi: fluid filled reservoirs (extend to apical surface)

38
Q

What is the role of parietal cells?

A

Acid secretion

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

39
Q

How do parietal cells change when they are in the active state?

A

Tubular vesicles fuse with membrane and project into canaliculi
Canaliculi combine and open outwards into lumen of stomach
= huge SA in terms of tubular vesicles (containing H+/K+ ATPase) and a large interconnected reservoir leading out into the lumen of the stomach

40
Q

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

A

CO2 diffuses into the cell from the blood and reacts with H2O with the action of carbonic anhydrase to produce HCO3- and a H+.
A Na+-K+ exchanger takes 1 K+ in and 1 Na+ out.
K+ follows the concentration gradient and diffuses into the canaliculi.
HCO3- is exchanged for Cl- : the Cl- then moves down the concentration gradient into the canaliculi.
ATP is used to actively transport H+ out into the canaliculi with K+ moving into the cell
Massive ATP driven movement of H+ into the stomach lumen.

41
Q

How would inhibition of carbonic anhydrase influence acid secretion in the stomach?

A

Reduces the acid producing ability of the parietal cells because it is no longer able to convert H2O and CO2 into H2CO3 (so H+ and HCO3- isn’t generated)

42
Q

What 2 proteins do you need a lot of to increase the acidity of the stomach?

A

Carbonic Anhydrase and H+/K+ ATPase

43
Q

How does pepsinogen turn into pepsin?

A

Acid activates pepsinogen to produce pepsin.

44
Q

What does pepsin do?

A

Breaks proteins into smaller peptides

45
Q

Where are Gastrin producing cells predominantly found?

A

Pyloric antrum

46
Q

What is the action of gastrin?

A

Stimulates histamine release from chromaffin cells (lamina propia)
Histamine binds to parietal cells, stimulating acid production

47
Q

Secretion 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.

48
Q

What are the 3 phases of gastric secretion?

A

Cephalic
Gastric
Intestinal

49
Q

Describe the cephalic phase of gastric secretion.

A

Before the food enters your mouth.
Thought, sight, smell and taste of food (conditioned)
Vagus nerve from the medulla stimulates the enteric nervous system to increase the production of acid and pepsin.
ACh stimulates histamine production (causes further increase in acid production).

50
Q

Describe the gastric phase of gastric secretion.

A

Once the food is in the stomach, stretch and chemoreceptors send messages to the brain.
Brain 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.

51
Q

Describe the intestinal phase of gastric secretion.

A

Chyme enters the small intestine

52
Q

What happens if the pH is <2 or there is a high lipid content of the chyme entering the small intestine?

A

Stimulus goes up to the brain

Causes inhibitory effect on stomach, switches off acid and pepsin production.

53
Q

What are the 3 hormones produced in the enterogastric reflex? What is the name given to this group of hormones?

A

Gastric Inhibitory Peptide, Cholecystokinin and Secretin
= enterogastromes
Decrease the production of acid and pepsin
Controlled the enterogastric reflex

54
Q

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

A

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

55
Q

State 2 drugs that decrease acid secretion and their targets.

A

Omeprazole: proton pump inhibitor, prevents H+/K+ exchange
Ranitidine: histamine receptor antagonist

Alimentary system (15 decks)

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