Upper GI tract (36) Flashcards
What is digestion?
the process of breaking down macromolecules to allow absorption
Which structures make up the foregut?
- oesophagus
- stomach
- liver
- pancreas
- biliary system
What are the layers of the gut wall?
- mucosa: epithelium, lamina propria, muscularis mucosae
- submucosa: connective tissue containing nerve plexus
- muscularis: smooth muscle containing nerve plexus
- serosa/adventitia: connective tissue
What is the function of the oesophagus?
- conduit for food, drink and swallowed secretions from pharynx to stomach
- traverses 3 different body cavities: neck, thorax and abdomen
What is the structure of the epithelium in the oesophagus?
- squamous, non-keratinising
- mucus secreting glands–> lubrication of food
- ‘wear and tear’ lining for extremes of temp.
What is the is the structure of the muscle in the oesophagus?
- inner circular muscle
- longitudinal muscle
What is the gastro-oesophageal junction?
- passes through diaphragmatic hiatus- diaphragm prevents reflux
- where pale pink mucosa (squamous) of oesophagus meets red mucosa of stomach (columnar)- EPITHELIAL TRANSITION
- gastric folds- rugae
Why are gastric folds present?
inc. absorptive SA
What are the 4 phases of swallowing?
- stage 0: oral phase- food broken down by teeth, saliva, tongue
- stage 1: pharyngeal phase- food goes from oral cavity to pharynx
- stage 2: upper oesophageal phase- upper sphincter opens + closes, sequential contractions of longitudinal muscle
- stage 3: lower oesophageal phase- lower sphincter opens and closes
What is absorption?
the process of moving nutrients and water across a membrane
What are the functions of the stomach?
- secrete acid and pepsin to break food into smaller particles
- hold food, releasing it in a controlled rate into duodenum
- kill parasites and certain bacteria
What is the structure of the stomach?
- cardia- just below oesophagus
- fundus- bulbous bit
- body- most of stomach
- antrum
- pylorus- outlet
- pyloric sphincter
What is the function of the circular muscle in the stomach?
- segmentation
- keeps food in stomach so can get broken down
- weaker contraction than peristalsis
- fluid chyme towards pyloric sphincter, solid chyme pushed back to body
What is a gastric chief cell?
- protein- secreting epithelial cell, so rich in RER and Golgi
- secretion granules at apex- release protein into lumen
- secretes PEPSINOGEN (proenzyme)
What is a parietal cell?
- helps to create HCl (which is important to pepsinogen–>pepsin)
- contain tubulovesicles, which house the H+/K+ ATPase pumps
- many mitochondria bc requires lots of ATP
- internal canaliculi- deep infoldings that inc. SA
How does the parietal cell work?
- CO2 comes from capillaries, mixes with water, using enzyme CARBONIC ANHYDRASE–> HCO3- and H+ produced
- K+ comes into cell from capillaries and gets secreted into gastric lumen
- K+ gets exchanged w/ H+ using the pump, and comes into the cell
- H+ goes into lumen and combines w/ Cl- to give HCl
What is the role of HCl?
converts pepsinogen to pepsin
What is gastrin?
- hormone secreted by G cells in antrum of stomach
- stimulates parietal cell to produce HCl
What are the phases of gastric secretion?
- cephalic phase
- gastric phase
- intestinal phase
What structures make up the mid gut?
- small intestine
- part of large intestine
What structures make up the hind gut?
- colon
- rectum
How many teeth do we have and what types?
32 in total
- 8 incisors
- 4 canines
- 8 premolars
- 12 molars
What muscle is responsible for biting/largest jaw muscle?
masseter muscle
What digestive enzymes are produced by the salivary glands?
- lingual lipase–> breaks down lipids
- salivary amylase–> breaks down carbohydrates
What is the purpose of peristalsis?
to propel chyme towards the colon by moving it to pyloric sphincter
What nerve supplies the stomach?
vagus
How is stomach secretory activity stimulated in the cephalic phase?
sight/thought/taste/smell of food–> cerebral cortex–> hypothalamus and medulla oblongata–> vagus nerve (PNS)–> stomach
(N.B. here, gastric juice secreted before food even enters stomach)
ALSO hormonal stimulation- gastrin stimulates parietal cells
How is stomach secretory activity stimulated in the gastric phase?
stomach distension (stretch) activates stretch receptor bc food occupying stomach--> stimulates vagus nerve- 'vasovagal reflex' or submucosal plexus (local)--> stomach AND food chemicals/rising pH activate chemoreceptors--> G cells secrete gastrin into blood--> travels to parietal cells in stomach
How is stomach secretory activity stimulated in the intestinal phase?
enterogastric reflex
enterohormones send signal to brain–> vagus nerves
How might you produce a useful drug to decrease acid secretion?
- block histamine- H2 receptor blockers
- somatostatin- suppresses G cell receptors
- block H+/K+ pump
