GI tract Flashcards
What structures make up the gut wall?
Mucosa:epithelium lamina propria (loose connective tissue) muscularis mucosae
Submucosa: connective tissue (containing nerve plexus)
Muscularis: smooth muscle - nerve complex in it
Serosa/Adventita: connective tissue, may have epithelium
How are the 32 teeth subdivided?
8 incisors
4 canines
8 premolars
12 molars
What muscle is the largest jaw muscle?
Masseter muscle
- temporalis and massater both used for biting and chewing
What enzymes do salivary glands excrete?
Lingual lipase (fat digestion) Salivary amylase (carbohydrate digestion
What three salivary glands are there?
Parotid
Sublingual
Submandibular
What are the intrinsic muscles of the tongue for?
Extrinsic muscles
Intrinsic muscles fine motor control & moving food Extrinsic muscles gross movement of tongue (in, out, up & down) Assists mechanical digestion
How is the oesophegus divided?
method 1.
Cervical- cm
Thoracic -most
Abdominal -cm
method 2. * measurement started by incisors
Upper 1/3 is 24 cm away
Middle is 24-30 cm
Lower 30-40 from incisors
Where does the upper 1/3 of the oesophagus come to?
Carina of trachea
What is the function of the Oesophagus?
Conduit for food, drink & swallowed secretions from pharynx to stomach
What is the prupose of the oesophagus epithelium?
- Non-keratinising
- ‘Wear & Tear’ lining (extremes of temp. & texture)
- Lubrication – Mucus secreting glands (& saliva
How is the upper oesophageal sphincter and lower oesophageal sphincter split?
Upper sphincter is a ‘true’ sphincter,
there is a debate whether the bottom one is a sphincter
The ‘Z line’ splits them.
It is where the pale pink mucosa of sqaumous epithelium meets red mucosa of gastric epithelium
What type of muscle controls pristalsis in the Oesophagus?
Circular muscle
What is the purpose of the epithelial transition near the gastro-oesophageal junction?
…
Why are gastric folds present near the gasto-oesophagul junction?
Increase surface of epithelium for more digestion and absorption can occur.
What are the three stages of swallowing?
Stage 0: Oral phase
Chewing & saliva prepare bolus
Both oesophageal sphincters constricted
Stage 1: Pharyngeal phase
Pharyngeal musculature guides food bolus towards oesophagus
Both oesophageal sphincters open
Stage 2: Upper oesophageal phase
Upper sphincter closes
Superior circular muscle rings contract & inferior rings dilate
Sequential contractions of longitudinal muscle
Stage 3: Lower oesophageal phase
Lower sphincter closes as food passes through
How is acid reflux from gastro-oesophagul prevented?
Diaphragm
Anatomically it lies at an angle to the stomach
What are the functions of the stomach?
Breaks food into smaller particles (acid & pepsin)
Holds food, releasing it in controlled steady rate into duodenum
Kills parasites & certain bacteria
What is found in the Cardia and Pyloric region of the stomach?
Mucus only
What is found in the body and Fundas of the stomach?
Mucus, HCL, Pepsinogen
What is found in the antrum of the stomach?
Gastrin
What two types of stomach contractions are there?
Peristalsis - 20%
Propels chyme towards colon
more powerful as moves from LOS
to pyloric sphincter
ANS essential
Segmentation - 80% Weaker. Fluid chyme towards Pyloric sphincter Solid chyme pushed back to body Stretching activates enteric NS
What is a gastric chief cell?
Cell in the stomach:
- Protein-secreting epithelial cell
- Abundant RER
- Golgi packaging and modifying for export
- Masses of apical secretion granules
What protein does gastric chief cell secrete?
Pepsinogen
- turns into pepsin by hydrochloric acid activation
How is the Parietal cell in the stomach adapted to be secreting HCl?
Many mitochondria (requires lots of ATP) Cytoplasmic tubulovesicles (contain H+/K+ ATPase) Internal canaliculi (extend to apical surface)
How does the parietal cell secrete HCl?
Tubulovesicles fuse with membrane
Microvilli project into canaliculi
- Na+K+ Pump brings K+ and Na+ out
- This K+ joins H+/k+ ATPase
- H+ comes from carbonic anhydrase breakdown
- Makes Cl- come into cell , when Na+ comes back into cells is makes NaCl which gets secreted too into the lumen
- This is why stomach is high in HCl and Na+
How would inhibition of carbonic anhydrase influence acid secretion in the stomach?
Would not have any H+ ions
What triggers HCl release?
Histamine receptors on parietal cell surfaces
Histamine release
What is the hormone gastrin?
Secreted by G cells in antrium
Pyloric antrum
Local peptide hormones -gastrin
Stimulate histamine release from
chromaffin cells (lamina propia)
= HCl release
- from antrum region of stomach
What is the Cephalic phase?
Thought, smell and taste of food starts histamine and gastrin release to activate pariatel cell
- vagus nerve involvement
What is the gastric phase?
Food in stomach – stretch- & chemo-receptors
Secretion of acid from
- vagus nerve involvement
What is the intestinal phase?
Signal via vagus nerve inhibits secretion of HCl and pepsin
- Gastric inhibitory peptide
Cholecystokinin
Secretin
How might you produce a useful drug to decrease acid secretion?
Omeprazole Ranitidine \: - Block histamine receptor - Block gastrin receptor - Hydrogen Potassium Atpase inhibitors
Which of the following stimuli would be most likely to
decrease acid secretion in the stomach?
- Chyme fatty acid content
- Increased acetylcholine secretion
- Increased gastrin secretion
- Protein content of the meal
- Stomach distension
Chyme fatty acid content and protein content of meal
