Oesophagus and stomach Flashcards
Oesophagus; Gastrooesophageal sphincter; Stomach; Gastric gland; Gastric acid secretion
Where does the oesophagus start and end?
C5 to T10
What two important structures ensure food and air get to the correct destination?
Epiglottis
Upper oesophageal sphincter
@ rest spincter tonically active and epiglottis is upright
During swallowing sphincter relaxes and epiglottis covers trachea
How long is the oesophagus?
approx 25cm
What kind of epithelium is found in the oesophagus and what is its purpose?
stratified squamous Lubricate bolus by mucous secreting glands & saliva Non-keratinising Protect from: -temperatures -acidity -textures
What kind of muscle is found in the oesophagus?
Skeletal at start, mix of skeletal and smooth in middle, smooth at end
What are the 4 main components of the oral cavity and their purposes?
Teeth - biting and ripping food
Muscles - movement of the jaw
Salivary glands - produce saliva containing enzymes
Tongue - form bolus, eating and taste (intrinsic and extrinsic muscles)
What are the stages of swallowing?
0-Oral - chewing and saliva prepare bolus for swallowing, both sphincters constricted
1-Pharyngeal - pharyngeal musculature guides bolus towards oesophagus, both sphincters open
2-Upper oesophageal - upper sphincter closes, superior circular muscle rings contract as inferior ones constrict, sequential contractions of longitudinal muscle help guide food down gullet
3-Lower oesophageal - as food passes through lower sphincter, it closes & peristalsis pushes food into stomach
What does the upper oesophageal sphincter consist of?
Constrictor pharangeus medius (circular)
Constrictor pharangeus inferior (longitudinal)
What are the 3 phases of gastric acid secretion?
Cephalic
Gastric
Intestinal
What are the afferents and efferents of the cephalic phase?
Afferents: -sight -smell -taste -thought Efferents: -Vagus nerve stimulates secretion via submucosal plexus -parietal secretion stimulated by G and ECL cells Effects: -small secretion for a few minutes
What are the afferents and efferents of the gastric phase?
Afferents: -reduced pH -stomach distension -chemoreception of nutrients Efferents: -Vagus nerve stimulates submucosal plexus and myenteric plexus -Gastrin and histamine from G cells and ECL cells stimulates parietal cell secretion Effect: -mechanical digestion for 3-4 hours
What are the afferents and efferents of the intestinal phase?
Afferents: -Duodenal stretch -Reduced pH -Duodenal distension Efferents: -Cholecystokinin from I cells -Secretion from S cells -Inhibited gastric motility and emptying -Decreased parietal secretion -Stretch receptors input to the enteric nervous system to decrease activation of stomach Effects: -Gastric emptying slows -Gives time for downstream organs to deal with contents
What is the role of the gastro-oesophageal sphincter?
Ensures one way traffic
Z line border separates stomach acid from vulnerable oesophagus
How does the diaphragm aid the gastro-oesophageal sphincter?
prevents reflux
What are the two components of the gastro-oesophageal sphincter?
Internal - oesophageal wall
External - diaphragm
What are the 3 key functions of the stomach?
Digestion of nutrients
Storage reservoir for food
Immunological protection
What is the stomach lined with?
Columnar epithelia
Invaginations into gastric pits that contain specialist exocrine and endocrine cells
What are the 5 sections of the stomach?
Cardia Fundus Body Pyloric antrum Pyloric canal
Which sections of the stomach secrete mucous?
Pyloric canal
Cardia
Body
Fundus
Which sections of the stomach secrete HCl, mucous and pepsinogen?
Body
Fundus
Which section of the stomach secretes gastrin?
Pyloric antrum
What is the purpose of rugae?
Folds allow a large increase in sfa and volume
Allows distension
What are the cell types found in the gastric gland and where?
in increasing depth order: Surface mucous cell Mucous neck cell Parietal cell Enterochromaffin-like cells (ECL cells) Chief cell (body and fundus) D cells G cell Gastric stem cells
What is the purpose of surface mucous cell and mucous neck cells?
Secrete bicarbonate rich mucous to:
- protect stomach lining
- keep pH near lining around 7
- protect against active lipase & proteases
What is the purpose of parietal cells?
Secrete acid to:
-kill ingested pathogens
-activate protease zymogens
-alter protein structure to aid digestion
Secrete intrinsic factor - a glycoprotein to aid absorption of B12
How do features of the parietal cell aid secretion?
Lots of canaliculi that extend to apical surface
When secreting, cytoplasmic tubulovesicles fuse with membrane and microvilli project into canaliculi to create a large sfa for acid secretion
Rich in mitochondria to provide energy for membrane transport
What is the purpose of enterochromaffin-like cells?
Neuroendocrine cells
Secrete histamine to stimulate acid secretion from parietal cells
What is the purpose of chief cells?
Produces a protease zymogen - pepsinogen
Produces gastric lipase to remove fatty acids from triglycerides
How is HCl secreted?
1) CO2 diffuses down concentration gradient into parietal cell
2) CO2 + H2O → H+ + HCO3- by carbonic anhydrase
3) HCO3- exchanged with Cl- in interstitial space
4) Cl- diffuses down concentration gradient into stomach lumen via Cl- channels
5) Na+/K+ exchanger in basolateral membrane and Cl- channels in apical membrane enable K+ to be pumped into cell in exchange for H+
6) K+ re-enters cell via K+ channels
7) Secreted H+ combines with Cl- = HCl
What are features of a chief cell?
Abundant golgi and RER
Masses of apical secretion granules
What is the purpose of D cells?
Enteroendocrine cells that sercrete somatostatin
Inhibitory effect on GI function:
-Somatostatin inhibits ECL production of histamine and parietal cell activity ∴ inhibit HCl secretion
What is the purpose of G cells?
Release gastrin into bloodstream in response:
- Vagus nerve stimulation
- Presence of peptides in stomach
- Stomach distension
What does gastrin do?
Travels in blood to receptor cells in stomach:
-Stimulates gastric secretion and motility - stronger contractions and opening of pyloric sphincter
Also binds to receptors in pancreas and gall bladder:
-increase secretion of pancreatic juice and bile
What is the purpose of gastric stem cells?
Pluripotent
Differentiate into all the stomach cell types under influence of different factors
