Physiology and pharmacology of gastric secretion Flashcards
What is the stomach?
A J shaped bag that relaxes receptively to accomodate food from the oesophagus
What drives receptive relaxation?
Vagus nerve
What are rugae?
Folds in the body of the stomach that allows the stomach to flatten out
What are the 5 regions of the stomach?
Cardia Fundus Body Antrum Pylorus
What is chyme?
Food with gastric juice
What is gastric juice made up from?`
Electrolyte solution
Bicarbonate
HCl
Various enzymes
Why is there no empyting of the contents of the stomach into the duodenum during mixing?
Due to the pyloric sphincter
What is retropulsion?
Waves of peristalsis that occur in the antral region that shifts chyme against the closed pyloric shincter causing to be bounced back
What is the strength of the antral wave governed by?
Gastric factors
Duodenal factors
How does distension increase motility?
Stretch of smooth muscle
Simulation of intrinsic nerve plexuses
Increased vagus nerve activity and gastrin release
How does the consistency of chyme influence gastric empyting?
Emptying is facilitated by thick liquid chyme
How does stretch of smooth muscle increase motility?
Causes stimulation of mechanoreceptors which excite intrinsic nerve plexuses which caust it to contract. These mechanoreceptors also signal via sensory fibers of the vagus nerve to the brain to increase vagus nerve activity and increased gastrin release
How does the duodenum delay gastric empyting?
Neuronal response
Hormonal response
What is the neuronal response?
Enterogastric reflex which decreases antral activity by signals form intrinsic nerve plexuses and the ANS
What is the hormonal response?
Release of enterogastrones (secretin and CCK) from the duodenum inhibits stomach contraction. These 2 hormones together coordinate the activities of the stomach, duodenum and gallbladder
How does fat drive the neuronal and hormonal response?
Delays gastric emptying required for digestion and absorption in the small intestine. It does this by releasing CCK
How does acid drive the neuronal and hormonal resposne?
Time is required for the neutralisation of gastric acid by bicarbonate secreted from the pancreas - important for optimal function of pancreatic digestive enzymes
How does hypertonicity drive the neuronal and hormonal response?
Products of carbohydrate and protein digestion are osmotically active and draw water into the small intestine - dnager of reduces plasma volume and circulatory disturbances (dumping syndrome)
What are gastric glands?
Invaginations of the stomach wall which extend through the mucosas into the lamina propria. The gastric pit divides into 2 or more gastric glands
What glands are present in the antrum (pyloric gland area)?
D cells - synthesise and release somatostatin
G cells - secrete gastrin
What glands are present in the oxynitic mucosa of the fundus and body?
Chief cells = pro-enzyme pepsinogen
Parietal cells = secretion of HCl, intrinsic factor, gastroferrin
ECL cells - histamine
Where does the secretion of HCl occur?
In the oxyntic mucosa instead of the pyloric gland area
What is the function of HCl?
Activates pepsinogen to pepsin
Denatures proteins
Kills most (not all) micro-organisms ingested with food
What is the function of pepsinogen?
Inactive precursor of the peptidase, pepsin. Once pepsin is formed it can act back on pepsinogen and convert more pepsinogen to pepsin, this is called autocatalysis
What is the function of intrinsic factor and gastroferrin?
Binds to vitamin B12 and iron facilitating subsequent absorption
What is the function of histamine?
Stimulates HCl secretion
What is the function of mucus?
Protectve
What is the function of gastrin?
Simulates HCl secretion
What is the function of somatostatin?
Inhibits HCl secretion
