upper GI tract Flashcards
what is digestion
the process of breaking down macromolecules to allow absorption
what is absorption
the process of moving nutrients and water across a membrane
what are the 18 components of the GI system
parotid gland sub mandibular gland sub lingual gland oesophagus liver gall bladder stomach pancreas duodenum jejenum transverse colon ileum descending colon ascending colon appendix sigmoid colon rectum anus
what is mucosa
epithelium
lamina propria (loose connective tissue)
muscularis mucosae
what is submucosa
connective tissue (containing nerve plexus) has blood vessels
what is muscularis
smooth muscle containing nerve plexus
what is serosa/adventitia
connective tissue +/- epithelium
how many teeth are there in total
32
what are the different kinds of teeth
incisors
canines
premolars
molars
how many incisors are there
8
how many canines are there
4
how many premolars are there
8
how many molars are there
12
what is the masseter muscle
largest jaw muscle
responsible for biting
what is temporalis muscle
moves jaw up and down
what do several muscles control the position of
the mandible
what do the salivary glands contain
lingual lipase (fat digestion) salivary amylase (carbohydrate digestion)
food mixed with saliva (aq secretion and digestive enzymes)
what do intrinsic muscles of the tongue do
fine motor control and moving food
what do extrinsic muscles of the tongue do
gross movement of tongue (in, out, up and down)
assists with mechanical digestion
how far does the trachea run
C5 - T10
where does the oesophagus start
cricoid thyroid cartilage
how are parts of the oesophagus measured
by how far they are from front teeth
some of the oesophagus is in the abdomen
what is the oesophagus divided into
3rds
upper
middle
lower
what is the function of the oesophagus
conduit for food, drink and swallowed secretions from pharynx to stomach
peristalsis
what is the structure and function of epithelium
non keratinising
wear and tear, lining (can deal with extremes of temp and texture)
lubrication - mucous secreting glands (and saliva)
what is the function and structure of muscle
tonically active
swallowing centre
what separates the upper and lower oesophageal sphincter
the z line
what muscle is the upper third made of
skeletal muscle
what muscle is the middle third
skeletal and smooth muscle
what muscle is found in the lower third of the oesophagus
smooth muscle
how many stages of swallowing are there
4
stage 0, 1, 2, and 3
what happens in stage 0 - oral phase
- chewing and saliva prepare bolus (upper and lower sphincter closed)
- both oesophageal sphincters are closed
what happens in stage 1 - pharyngeal phase
pharyngeal musculature guides food bolus towards oesophagus
both oesophageal sphincters open
what happens in stage 2 - upper oesophageal phase
upper sphincter closes
superior circular muscle rings contract
inferior rings dilate
sequential contractions of longitudinal muscle
what happens in stage 3 - lower oesophageal phase
lower sphincter closes as food passes through
what is reflux prevented by
the diaphragm
describe the epithelial transition
lining changes (stomach lined with simple columnar and oesophagus - stratified squamous)
what are gastric folds called
rugae
allows element of expansion and aids with digestion
what are the functions of the stomach
- breaks food into smaller particles (acid and pepsin)
- holds food, releasing it in a controlled steady rate into the duodenum
- kill parasites and certain bacteria
what is found in cardia and pyloric region
mucus
what is found in the body and fundus
mucus
HCL and pepsinogen
what do G cells in the antrum produce and what does it invaginate into
gastrin
invaginates into mucosa - tubular glands
how much acid is produced daily
2L/day
what is the conc of acid produced by the stomach
150 mM H+
3 mill x that of in the blood
what does mucin do and what does it have trapped inside
provides a gel coating (lubricating)
HCO3- is trapped in mucus gel
what is the pH at epithelial surfaces
6-7
what is the pH at the lumen
1-2
what is peristalsis
20% stomach contractions propels chyme towards colon more powerful as moves from LOS to pyloric sphincter ANS essential autonomic function
what is segmentation
80% stomach contractions weaker - fluid chyme towards pyloric sphincter - solid chyme pushed back to body - stretching activates enteric NS - activated by stretch receptors located locally in stomach
what do gastric chief cells do
protein secreting epithelial cell secrete pepsinogen abundant RER golgi packaging and modifying for export masses of apical secretion granules
what do parietal cells contain in their resting state
many mitochondria (requires lots of ATP) internal canaliculi (secretory surface - intracellular in resting state) cytoplasmic tubulovesicles (contains H+/K+ ATPase)
what do parietal cells contain in their secreting phase
microvilli project into canaliculi
tubulovesicles fuse with membrane
make HCl
how do parietal cells make HCl
1) carbon dioxide diffuses into cell
2) combines with carbonic anhydrase
3) mixes with water > hydrogen and bicarb ions
4) sodium potassium pump on basolateral membrane
5) K enters > through channel in apical membrane >canaliculi
6) sodium leaves
7) bicarbonate leaves cell by transporter
8) chloride comes in and goes through own transported in apical membrane and can
enter canaliculi
9) ATP process - H+ ion produced goes out across the pump and K+ comes back in
exchange
10) H+ and Cl- forms = hydrochloric acid
what is pepsinogen
secreted in inactive form
acid breaks it down into pepsin - active
secreted by gastric chief cells
where is gastrin produced
pyloric antrum
what does gastrin do
reaches parietal cell via systemic circulation
stimulated by distension, small peptides and amino acids, stimulation of vagus nerves
acts on receptors on parietal cells
stimulates histamine release from chromaffin cells (lamina propria)
what are the phases of gastric secretion
cephalic phase
gastric phase
intestinal phase
what happens in cephalic phase
thought, sight, smell and tastes of food (conditioned)
vagus nerve activated
gastrin released and acts on parietal cells and histamine
acetylcholine is involved
what happens in the gastric phase
food in stomach - stretch and chemoreceptors
HCl and pepsinogen
chemoreceptors activate secretion of acid (release of gastrin > release of acid)
what happens in the intestinal phase
excitatory intestinal phase - protein concentration in duodenum stimulates gastrin secretion
local peptides released in duodenum - gastric inhibitory peptide, cholecystokinin, secretin
enterogastrones - enterogastric reflex
what are some useful drugs to decrease acid secretion
omeprazole
ranitidine - H2 receptor = blocked
chyme fatty acid content
