Flashcards in physiology + pharmacology Deck (25)
how does the stomach produce semi-liquid chyme?
by mixing food with gastric secretions
what are the 2 types of mechanical activities of the stomach?
- orad = fundus and proximal body, tonie ie maintained
- caudad = distal body and antrum - phasic ie intermittent
what happens in the orad region of the stomach?
- relaxation (vagus) occurs during a swallow, allowing storage of ingested material
- there is no slow wave activity
- tonic contractions are weak due to thin musculature
- contents are propelled intermittently to caudad ragion by low amplitude tonic contractions of 1 min duration
- minimal mixing of contents alls for carb partial digestion by salivary amylase
- gastrin decreases contractions and hence rate of stomach emptying
what happens in the caudad region?
- slow waves occur continuously but only those reaching threshole elicit contraction
- pharis peristaltic contractions are driven by suprethreshold slow waves progress from midstomach to gastroduodenal unction, propelling the contents towards pylorous through which a very small volume of chyme flows into the duodenum
- velocity of contraction increases towards the junctions, overtaking the movement of chyme that rebounds against constricted distal antrum back into the relaxed body of the stomach - retropulsion
what is retropulsion?
when gastric contents are mixed, reducing chyme to small particles that pass through the pyloris
what does the strength of antral wave determine?
- the escape of chyme through pyloric sphincter
- it is governed by gastric factors and duodenal factors
what are the gastric factors?
- rate of emptying proportional to volume of chyme in stomach
- distentiosn increases due to stretch of smooth muscle, stimulation of intrinsic nerve plexuses, increased vagus nerve activity and gastrin release
duodenum delays emptying as it must be ready to release chyme, how does it do this?
- neuronal respone = the enterogastric reflec decreased antral activity by signals from intrinsic nerve plexuses and the ANS
- hormonal response - release of enterogastrone eg CCK from duodenum inhibits stomach contraction
which stimuli within the duodenum drive the neuronal and hormone response?
- FAT - delay in gastric emptying required for digestion and absoption in Small intestine
- acid = time is required for neutralisation of gastric acid by bicarbonate secreted from the pancreas (important for optimal function of pancreatic digestive enzymes)
- hypertonicity = products of carbohydrate and protein digestion are osmotically active and draw water into the small intesting - danger of reduced plasma volume and circulatory distarbances eg dumping syndrome
what are the classifications of the stomach in relation to secretions of the mucosa?
- the oxyntic gland area (proximal stomach including the fundus and body)
- the pyloric gland area (distal stomach, desigated the antrum)
what is the gastric mucosa composed of?
- a surface lining the stomach
- pits, invaginations of the surface
- glands, at the base of the pits responsible for several secretions
what cells do the pyloric gland area(antrum) have?
- D cells somatostatin
- G cell gastrin
what cells do the oxyntic mucosa (fundus and body) area have?
- parietal cell, hydrocholic acid, intrinsic factor gastroferrin
- enterchromaffin like cell, histamine
- chief cell pepsinogen
what are the gastric secetions of th oxyntc mucosa?
- intrinsic factor and gastrroferrin
what is the function of HCL?
activates pepsinogen to pepsin
kills most (not all) micro-organisms ingested with food
what is the function of pepsinogen?
inactive precursor of the peptidase, pepsin. Note: pepsin once formed activates pepsinogen (autocatalytic
what is the function of intrinsic factor and gastroferrin?
bind vitamin B12 and Fe2+ respectively, facilitating subsequent absorption
what is the function of histmaine?
stimulates HCL secretion
what is the funciton of mucus?
protective, pyloric gland area
what is the function of gastrin?
stimulates HCL secretion
what is the function of somatostatin?
inhibits HCL stimulation
what is the function of mucus?
how are hydrogen pumped out of the cell?
actively by hydrogen ATPase
how does bicarbonate leave the cell?
by the Cl/HCO3- antiporter