Lecture 3 : swallowing & stomach histology

Question 1

What is peristalisis? What 2 types of muscles does it involve?

Answer 1

• wave like contractions in the GIT
• it involves inner circular muscle & outer longitudinal muscle

Question 2

As food moves down the GIT by peristalisis, what happens behind and infront of the food bolus?

Answer 2

• behind - contraction - squeezing action
• infront - relaxation

Question 3

Which type of muscle contracts first during peristalisis ?

Answer 3

the longitudinal muscle contracts first and then halfway through the contraction, the circular muscle begins to contract

Question 4

What are the 2 types of peristalisis in the oesophagus?

Answer 4

1.** Primary** peristalisis
2. secondary peristalisis

Question 5

What is **primary **oesophagal peristalsis?

Answer 5

primary peristalsis is initaited when the bolus in the mouth is swallowed and enters the oesophagus

Question 6

What happens to the upper ** sphincter muscle**during peristalsis I?

Answer 6

• upper oesophageal sphincter opens rapidly and shuts quickly to prevent reflux

Question 7

What is secondary peristalsis?

Answer 7

secondary peristalsis involves the stretching/ distension of the oesophagus

Question 8

What does the complex reflex that causes secondary peristalsis involve?

Answer 8

• if the bolus **gets stuck **or moves slower than the primary peristalsis wave (eg if pooly lubricated), stretch receptors in the oesophagal lining are **stimulated **and cause a local reflex response called secondary peristalsis
• this forces the food further down the tube until it reaches the stomach

Question 9

Does a vagotomy (cutting of vagal nerve) impact peristalsis?

Answer 9

• Primary peristalisis **cannot occur **after a vagotomy as there is extensive vagal innervation in the upper portion of the uesophagus - very reliant on ANS
• Secondary peristalsis CAN occur as it can be triggered by many stimuli in the oesophagus eg air

Question 10

Compare the type of muscle present in the **upper **oesophagus vs the mid/lower oesophagus.

Answer 10

• striated muscle (skeletal) in the upper
• smooth muscle in the mid/lower

Question 11

How is peristalsis in the oesophagus controlled?

Answer 11

• **striated muscle **- contraction controlled by sequential activation of motor neurons
• smooth muscle - contraction controlled by enteric plexus (independent of the ANS)

Question 12

What neurotransmitter causes contraction behind the bolus?

remember - vagus nerve innervation

Answer 12

Ach

Question 13

What neurotransmitter causes relaxation ahead of the bolus?

Answer 13

NA - noradrenaline

Question 14

What is deglutitive inhibition?

Answer 14

• this happens as a result of multiple rapid swallows - eg swalloing water
• the pharynx contracts multiple times and the upper sphincter muscle is open
• this causes the peristalsis waves to be delayed

Question 15

What is oesophaeal achlasia?

Answer 15

• caused by failure of smooth muscle fibers to relax - the lower sphincter muscles to remain closed
• impaired peristalsis
• looks like - dilated oesophagus & shows tapering (narrowing) at the bottom

Question 16

What is a cork screw oesophaguus?

Answer 16

• a disorder that involves uncoordinated spasms of the oesophagus
• impaired motility

Question 17

What are gastric glands of the stomach?

Answer 17

glands in the stomach that contain cells that are involved in secretion

Question 18

What are** gastric pits** of the stomach?

Answer 18

• gastric pits allow the secretions of the gland to be emptied
  these pits are located on the epitheial layer of the stomach

Question 19

What are the main 4 anatomical regions of the stomach? Which 2 parts are histologically** indistinguishable **?

Answer 19

1. • cardia
2. fundus
3. body
4. pylorus

• The fundus and the body are indistinguishable

Question 20

What are the main functions of the stomach?

Answer 20

• **storage **
• mixing - gastric motility
• digestion - physical (gastric motility) and chemical (gastric acid production)
• hormone production - by the enteroendocrine cells in the gastric gland EG gastrin

Question 21

What are the **functions of the regions **of the stomach?

Answer 21

• cardia - relaxation & protection of oeso against acid
• fundus & body - mixing - physical digestion with the 3 muscles, chemical digestion with HCL, digestive enzymes & gastric acid
  ***Pylorus **- muscular & protection of SI against acid

Question 22

What are the 5 cell types & their functions in the gastric gland ?

Answer 22

1.** surface mucous cell** - protection of the stomach itself from being self digested
2. mucous neck cell - less columnar (compared to epitheial cell), mucous secretion
3.** Parietal cell -** strong eosinophilic straining (pink stain), secretes HCL an intrinsic factor
4. chief cells -produces pepsinogen and gastric lipase
5. enteroendocrine cells -hormone producing cells - gastrin

Question 23

What is the function of gastric mucous?

Answer 23

• mechanical protection - from auto-digestion
• viscosity protection

Question 24

What endogenous substances stimulate the secretion of mucous?

Answer 24

prostaglandins (group of compounds with hormone like effects in body)

Question 25

what drugs can inhibit prostaglandins and therefore limit surface mucous production?

Answer 25

• NSAID - anti inflam drugs

Question 26

What is the function of gastric acid?

Answer 26

• it denatures proteins - the protein folds unravel in the highly acidic environment
• also has a protective role - bacteria growth is limited in such conditions

Question 27

What is the most abundant organelle in the parietal cell? Why?

Answer 27

mitochondria
why? - because the process of HCL production is highly energy dependent

Question 28

How is HCL made by the parietal cells?

7 steps

Answer 28

1. the transport system is driven by a** H+, K+-ATPase** that uses the energy made from ATP hydrolysis
2. the H,K+ ATPase pumps hydrogen out of the cell in exchange for K+ into the cell
3. chloride ions leave by 2 routes
4. route 1: they can leave by the canalicular membrane via a chloride channel on the parietal cell
5. route 2: there is also a K+/CL-symporter on membrane
6. carbonic anhydrase breaks down carbonic acid into H+ and HCO3-
7. Hco3- leaves through basolateral mem

Question 29

What is intrinsic factor?

Answer 29

the protein required for the uptake of vitamin B12

Question 30

What does vit B12 initially bind to in the stomach?

Answer 30

haptocorrin (R factor)

Question 31

After binding to Haptocorrin, what does B12 bind to & what event happens?

Answer 31

intrinsic factor
* it is then endocytosed by the terminary ileum and B12 is released

Question 32

what is the clinical condition pernicious anaemia?

Answer 32

• autoimmune disease - body attacks parietal cells
• stomach cannot create intrinsic factor that helps with the absorption of vit B12
• as vit b12 is required for the production of red blood cells, lvl decreases

Question 33

what 3 main enzymes do chief cells produce?

Answer 33

1. pepsinogen (proenzyme that gets activated into pepsin)
2. gastric lipase
3. rennin

Question 34

What are the 3 main types of enteroendocrine cells & describe what they secrete?

Answer 34

1.** G cells** - secretion of gastrin into the blood, they promote gastric acid secretion
2.** D cells** - secretion of somatostatin
3. EC cells -** enterochromaffin cells** (neuroendocrine cells) - secrete serotonin and play key role in GIT** motility**