Upper GI tract Flashcards
What does the circular muscle do and what does the longitudinal muscle do in the stomach?
CIRCULAR:
-SEGMENTATION (weaker contractions
)
- keeps the food in thestomach for some time so it can be properly broken down
- 80% of contractions
LONGITUDINAL:
-PERISTALSIS
20% of contractions
-propels CHYME towards the colon
-more powerful contractions as moves food from the Lower Oesophageal sphinter to the Pyloric sphincter
What are the 5 parts that make up the foregut?
- Oesophagus
- Stomach
- Liver
- Pancreasa
- Bilary system( liver, gall bladder and bile ducts work together to secrete bile)
What 2 things make up the midgut?
- Small intesine
- Part of the large intestine
What 2 things make-up the Hind gut?
- Colum
- Rectum
What are the 4 layers of the GI tract?
MUCOSA-mainly epithelium(secretary and absorpative)
SUBMUCOSA-connective tissue and capillaries
MUSCULARIS(2 layers of muscle):
-CIRCULAR MUSCLE LAYER(constricts the bowel=divides it into segments =food passes between segments and stays for a while in each segmwent allowing absorption happening)
-LONGITUDINAL OUTER MUSCLE LAYER -propagates food through the intestinal tract
SEROSA/ADVENTITIA-connective tissue and epithelium(protective layer/lining)
There are subtle differences as you go from the Oesophagus down towards the rectum
How many teeth do we have and what is the makeup?
32:
- 8 incisors
- 4 canines
- 8 premolars
- 12 molars
Which muscles in the oral cavity are part of the GI tract?
MASSETOR MUSCLES -largest Jaw muscle responsible for biting
-several muscles that control the position of the mandible
What does the tongue do as part of GI tract?
propogates food into the pharynx
What is the function of the Oesophagus?
Porpagates food from the Pharyunx to the stomach
What is the structure and function of the Epithelium lining the Oesophagus?
SQUAMOS CELLS(non-keratinising)
PROTECTIVE LINING- e.g, against hot temperatures
MUCUS SECRETUNG GLANDs-lubricate food as it goes down
MUSCLES-Upper and Lower Sphincter
What happens to the lining of the Oesophagus on prolonged exposure to Acid?
Squamos epithelium cells change to columnar epothelium cells as these can secrete mucus to protect against the acid
METAPLASIA -change in cell type
What is the eosophical hiatus?
opening in the diaphragm through which the esophagus and the vagus nerve pass.
How is acid reflux prevented by the gastro-eosophagel junction?
- diaphragm pinches at the bottom of the Eosophagus preventing acid from going up
- acute angle between the oesophagus and stomach
- mucosal fold(rugae) in this area that prevents acid going up
- Oesophagus is 2 cm in the abdomen(+ve pressure) and goes through the thorax(-ve pressure) the differential betweent he different pressure means the lower end of the oesophagus in the abdomen is kept in a collapsed state which prevents the acid from going up
- Eosophageal ligaments suspend the juction at a certian angle
What is a Hiatus Hernia?
The Eosophageal Hiatus becomes enlarged=some of the stomach migrates into the chest = Gastro-Oesophageal junction is kept open=Acid reflux
What are the stages of swallowing?
STAGE 0: ORAL PHASE
- chewing and saliva prepare Bolus
- Both Sphincters CONSTRICTED
STAGE 1: PHARYNGEAL PHASE
- Pharyngeal musculature guides Bolus towards the oesophagus
- Both Sphincters OPEN
STAGE 2: UPPER OESOPHAGEAL PHASE
- upper sphincter contracts
- Superior muscle rings contract
- inferior muscle rings dialates
- sequential contraction of longitudinal muscle
STAGE 3: LOWER OESOPHAGEAL PHASE
- Lower sphincter closes as food passes through
What are the parts of the stomach?
CARDIA and PYLORIC REGION-secretes mucus
BODY and FUNDUS-Mucus, HCL, Pepsinogen
ANTRUM-has gastrin(secrets gastric acid)
76
What are the functions of the stomach?
- Breaks food into smaller particles by secreting acid and enzymes
- Holds food and releases it at a slow and steady rate into the Duodenum
- Kills parasites and certain bacteria
What are the functions of the Circular and Longitudinal muscles in the stomach?
Circular:
-SEGMETATION
- holds food and churns it in different parts of the stomach so it can be broken down properly
- 80% of contractions
- weaker contractions
Longitudinal:
-PERISTALSIS
-propels chyme towards the colon
- pushes food from the lower eosophageal sphincter to the pyloric sphincter and therefore the muscle contractions are stronger
- 20% of contractions
What are the main cells that are present in the stomach?
- Chief cells
- Parietal cells
What are the function of chief cells?
- secretes PEPSINOGEN which is converted (by HCL) to pepsin(an enzyme) that can break down proteins
- rich in RER and Golgi
- rich in apical sectertion granuales that secrete the protein into the lumen
What do Parietal cells do?
- involved in creating HCL
- has the H+/K+ ATPase Pump (
- needs lots of mitochondria so theres enough ATP for the pump to function
- series of Tubulovesicles and Canaliculi That alllow the HCL to be secreted
Describe how HCL is made in the stomach?
- CO2 enters the parietal cell and mixes with water, this reaction is catalysed by CARBONIC ANHYDRASE to form H2CO3
- K+ comes into the cell from the capillaries and gets secreted into the gastic lumen, it is exchanged for Na+ which then leaves the cell and goes in to the capillaries
- The H2C03 dissociates into H+ and HCO3-, the HCO3- is exchanged for Cl- via an antiporter
- The pump then brings K+ into the parietal cell in exchange for H+ which it pumps out into the gastric lumen
- The Cl- naturall diffuses out of the parietal cell into the gastric lumen and combines with the Cl- to form HCL
What does gastrin do and where is it secreted from?
- secreted from G-CELLS in the antrum of the stomach
- hormone that stimulates parietal cells to secrete HCL
- stimulate hisamine release chromaffin cells(adrenal glands)
What are the 3 main Stimuli in the Gastric Phase for the secretion of HCL and Enzymes?
- Neurostimulation from the vagus nerve in response to thought, sight, smell and taste of food=HCL secretion
- Local hormone stimulus-Gastrin-secreted by PANCREAS entering the blood stream and then stimulating the Parietsal cells
Local relexes-stomach DISTENDS with food triggering local responses through the nerves in the stomach wall(myenteric plexus and Submucous plexus) causing more HCL and enzymes to be secreted
What happens tot he stomach if the vagus nerve is cut?
- Lose muscle movement of the stomach
- and secretion of HCL
What stimulates/inhibits the secretion of HCL in the Intestinal Phase?
- Food enters the intestine and this sends signals to the brain which then sends signal to the stomach via the VAGUS NERVE to produce HCL
- the small bowel will secrete ENTERGASTRONE hormones( Gastric Inhibitory Peptides, Cholecystokinin, Secretin) which play a role in the ENTEROGASTORONE REFLEX which either stimulates or inhibites HCL secretion
What does bacteria H.Pylori do?
The stomach has a thick layer of mucosa to protect it form HCL Bacteria H.Pylori breaks down this mucus lining
Allows the HCL to destroy stomach cells and give rise to PEPTIC ULSERS
How can you produce a drug to decrease HCL secretion?
Drugs to block GASTRIN, HISTAMINE OR ACh binding to there corresponding receptors on Parietal cells as all these hormone stimulate the sectetion of HCL
Why would Chyme fatty acid secretion decrease HCL secretion in the stomach?
Chyme is digested food and stuff so once it enters the Small Bowel the stomach wont need to do anymore so HCL secretion will decrease
