Lecture 3 : swallowing & stomach histology Flashcards
What is peristalisis? What 2 types of muscles does it involve?
- wave like contractions in the GIT
- it involves inner circular muscle & outer longitudinal muscle
As food moves down the GIT by peristalisis, what happens behind and infront of the food bolus?
- behind - contraction - squeezing action
- infront - relaxation
Which type of muscle contracts first during peristalisis ?
the longitudinal muscle contracts first and then halfway through the contraction, the circular muscle begins to contract
What are the 2 types of peristalisis in the oesophagus?
1.** Primary** peristalisis
2. secondary peristalisis
What is **primary **oesophagal peristalsis?
primary peristalsis is initaited when the bolus in the mouth is swallowed and enters the oesophagus
What happens to the upper ** sphincter muscle**during peristalsis I?
- upper oesophageal sphincter opens rapidly and shuts quickly to prevent reflux
What is secondary peristalsis?
secondary peristalsis involves the stretching/ distension of the oesophagus
What does the complex reflex that causes secondary peristalsis involve?
- 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
Does a vagotomy (cutting of vagal nerve) impact peristalsis?
- 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
Compare the type of muscle present in the **upper **oesophagus vs the mid/lower oesophagus.
- striated muscle (skeletal) in the upper
- smooth muscle in the mid/lower
How is peristalsis in the oesophagus controlled?
- **striated muscle **- contraction controlled by sequential activation of motor neurons
- smooth muscle - contraction controlled by enteric plexus (independent of the ANS)
What neurotransmitter causes contraction behind the bolus?
remember - vagus nerve innervation
Ach
What neurotransmitter causes relaxation ahead of the bolus?
NA - noradrenaline
What is deglutitive inhibition?
- 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
What is oesophaeal achlasia?
- 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
What is a cork screw oesophaguus?
- a disorder that involves uncoordinated spasms of the oesophagus
- impaired motility
What are gastric glands of the stomach?
glands in the stomach that contain cells that are involved in secretion
What are** gastric pits** of the stomach?
- gastric pits allow the secretions of the gland to be emptied
these pits are located on the epitheial layer of the stomach
What are the main 4 anatomical regions of the stomach? Which 2 parts are histologically** indistinguishable **?
- cardia
- fundus
- body
- pylorus
- The fundus and the body are indistinguishable
What are the main functions of the stomach?
- **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
What are the **functions of the regions **of the stomach?
- 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
What are the 5 cell types & their functions in the gastric gland ?
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
What is the function of gastric mucous?
- mechanical protection - from auto-digestion
- viscosity protection
What endogenous substances stimulate the secretion of mucous?
prostaglandins (group of compounds with hormone like effects in body)
what drugs can inhibit prostaglandins and therefore limit surface mucous production?
- NSAID - anti inflam drugs
What is the function of gastric acid?
- it denatures proteins - the protein folds unravel in the highly acidic environment
- also has a protective role - bacteria growth is limited in such conditions
What is the most abundant organelle in the parietal cell? Why?
mitochondria
why? - because the process of HCL production is highly energy dependent
How is HCL made by the parietal cells?
7 steps
- the transport system is driven by a** H+, K+-ATPase** that uses the energy made from ATP hydrolysis
- the H,K+ ATPase pumps hydrogen out of the cell in exchange for K+ into the cell
- chloride ions leave by 2 routes
- route 1: they can leave by the canalicular membrane via a chloride channel on the parietal cell
- route 2: there is also a K+/CL-symporter on membrane
- carbonic anhydrase breaks down carbonic acid into H+ and HCO3-
- Hco3- leaves through basolateral mem
What is intrinsic factor?
the protein required for the uptake of vitamin B12
What does vit B12 initially bind to in the stomach?
haptocorrin (R factor)
After binding to Haptocorrin, what does B12 bind to & what event happens?
intrinsic factor
* it is then endocytosed by the terminary ileum and B12 is released
what is the clinical condition pernicious anaemia?
- 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
what 3 main enzymes do chief cells produce?
- pepsinogen (proenzyme that gets activated into pepsin)
- gastric lipase
- rennin
What are the 3 main types of enteroendocrine cells & describe what they secrete?
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**
