GI PHYSIOLOGY II - SECRETION Flashcards
TRUE/FALSE: the GI tract secretes and then reabsorbs around 8L of fluid per day?
true
what is secretion? what is absorption?
- secretion = movement of solutes and water from body to lumen
- absorption = movement of solutes and water from lumen to body
what is endocrine secretion? what is exocrine secretion?
- endocrine = ‘secretions’ move into the body and not secreted as much
- exocrine = secretions produced by epithelia and move into the lumen
what are the 3 components of exocrine secretion?
- mucous
- electrolyte solution
- digestive enzymes
what are the functions of the 3 components of exocrine secretion?
- mucous: protection, lubrication and aids mechanical digestion
- electrolyte solution: dilution, provides optimal pH and essential for chemical digestion
- digestive enzymes: chemical digestion and aids absorption
what are the volume of electrolyte solution approximately that is secreted per day?
- plasma: total 3L
- saliva: 1.5L
- stomach: 3L
- pancreas: 1.5L
- liver: 0.5L
- small intestine: 1.5L
–> 8L perday from 3L of plasma meaning that reabsorption is important
what are the approximate pH of each region of the GI?
- plasma: 7.4
- saliva: 7.6
- stomach: 1
- pancreas: 7.8
- liver: 7.5
- small intestine: 7.5
what are the 2 types of salivary secretion? what are their rate of secretion?
- basal (resting) secretion: 0.3mL/min
- stimulated secretion: 1.5mL/min
what are the composition of saliva?
- mucus
- dilute solution of NaHCO3/NaCl
- digestive enzymes
what are the function of NaHCO3/NaCl in saliva?
- dilution of food
- ensure optimal pH for digestive enzymes
what are the 2 salivary enzymes?
- lingual lipase
- alpha-amylas
what are the functions of salivary secretion?
- aids
- hygiene
- digestion
What do salivary secretions aid in (2)?
What are their roles in hygiene (2)?
What are their roles in digestion(3)
- Talking
- Chewing and swallowing
- Irrigation
- Xerostomia - dry mouth
- Dissolving food for taste
- Lingual lipase for fats
- alpha amylase for starch
what regulates the salivary secretion?
- nervous: visual, smell or taste stimuli
- autonomic nervous system: both parasympathetic and sympathetic
what stimulates the secretion of copious quantities of salivary fluid?
parasympathetic
what stimulates the secretion of small volumes of viscous salivary fluid?
sympathetic
where are salivary secretions released? what are the names of these? what proportion of the total volume are these?
- sublingual 5%
- submandibular 70%
- parotid 25%
what is the amount of gastric secretion per day?
2-3L
what is the rate of secretion between meals? mostly what from where?
- slow rate of 15-30mL/hour
- mostly mucous and bicarbonate
- from surface epithelium cells
in stomach, where secretes what during eating?
- surface epithelial cells secrete bicarbonate and mucous
- parietal cells secrete acids and intrinsic factor
- chief cells secrete pepsinogen
what is the rate of gastric acid secretion while eating?
150mL/hour
what is the function of gastric mucous?
provide protection against abrasion and acid
what is the function of gastric intrinsic factor?
stabilise vitamin B12 and facilitates its absorption in small intestine
what is the function of pepsinogen?
- inactive form of pepsin - a gastric proteolytic enzyme
- converted to active form pepsin by acid
- starts digestion of protein
what is the function of gastric acid?
- dilute food
- denature protein
- activates pepsinogen to pepsin
- creates optimum pH for pepsin action
- protection against foreign bacteria
what is the source of acid in stomach?
- carbonic anhydrase –> form H2CO3
- dissociation of H2CO3 to give H+ and HCO3-
how does H+ being secreted into stomach?
- H+ - K+ ATPase on apical membrane of parietal cells
- pump H+ into lumen in exchange with K+
- K+ return to lumen through membrane channel
what is the source of chloride in stomach
- anion counter transporter at serosal membrane of parietal cells ejects HCO3- into interstitial fluid
- inports Cl- ions into cells
how does chloride being secreted into stomach?
- Cl- diffuse across cell
- then enters lumen via Cl- channel in apical membrane
TRUE/FALSE: gastric secretion coordinated with eating and arrival of food
true
what are the 3 phases of gastric secretion? what percentage of secretion associated with meals is related to each phase?
- cephalic: head controls secretion - 20%
- gastric: stomach controls secretion - 70%
- intestinal: intestine controls secretion - 10%
what does the cephalic phase basically do?
prepare for arrival of food
what stimulate the cephalic phase?
- higher centers (CNS): thoughts, smell, sight of food
- chewing, tasting
how does extrinsic parasympathetic nervous system respond to the stimuli during cephalic phase?
- via ENS
- stimulates parietal cells, chief cells and goblet cells
- stimulate secretion of hormone gastrin
what does hormone gastrin do?
release into blood then stimulates parietal cells and chief cells
what does the gastric phase basically do?
ensure sufficient secretion to handle ingested food
what stimulates the gastric phase?
- stretch of stomach wall
- products of digestion stomach lumen
- elevated pH
describe the nervous and hormonal regulation of gastric phase?
- ENS local nervous reflex
- external nervous reflex associated with parasympathetic nervous system
- both above stimulate: secretion from gastric glands, motility and gastrin secretion
what does intestinal phase basically do?
controls delivery to small intestine
what stimulate the intestinal phase?
arrival in duodenum of:
- acidic chyme
- lipids and carbs
describe nervous and hormonal regulation of intestinal phase
- hormones involved: GIP, CCK, secretin
- nerves: long reflex duodenum to brain to stomach
- both activities above inhibit secretion and motility
how much does pancreas secrete per day?
1-1.5L
what are the 2 components of pancreatic secretion?
- enzymes
- alkaline fluid
which structure secrete enzyme in pancreas?
acinar cell
what are the pancreatic digestive enzymes?
- lipolytic –> lipase/phospholipase
- amylytic –> pancreatic amylase
- proteolytic –> trypsin, chymotrypsin, carboxypeptidase
- nucleolytic - ribonuclease/deoxyribonuclease
what stimulate the secretion of digestive enzyme in acinar cells of pancreas?
hormone cholecystokinin (CCK)
what stimulates CCK secretion?
arrival of lipids and carbohydrates in duodenum
TRUE/FALSE: proteolytic enzymes secreted as inactive precursors and activated in the stomach?
FALSE
although proteolytic enzymes are secreted as inactive precursors, however they are activated in duodenum, not stomach
name the precursors and proteolytic enzymes?
- trypsin - trypsinogen
- chymotrypsin - chymotrypsinogen
- carboxypeptidase - procarboxypeptidase
what does activation of the proteolytic enzymes involved?
- enterokinase (enteropeptidase): structure bound to duodenal membrane and concerts trypsinogen into trypsin
- then trypsin converts other enzymes to active form
where is the alkaline fluid (HCO3 rich) produced?
duct cells in pancreas
what stimulate the secretion of alkaline fluid/HCO3 in pancreas?
hormone secretin
what stimulate the secretion of secretin?
arrival of acidic chyme in duodenum
what are the functions of alkaline fluid?
- neutralises acid chyme delivered from stomach
- creates optimum pH for pancreatic and intestinal enzyme
what is the amount of biliary secretion per day?
0.5L
what are the products and what are their functions of the biliary secretion?
- bile salts: fat digestion
- HCO3- rich fluid: neutralise acid
- bile pigments: waste product for excretion
- cholesterol: excretion
briefly describe the production of bile
constantly secreted by liver, stored and concentrated in gallbladder and delivered to duodenum through bile duct with arrival of food
what initiate the delivery of bile?
- CCK and secretin
what events associated with CCK secretion?
- respond to products of digestion in duodenum
- contraction of gallbladder
- relaxation of hepatopancreatic ampulla
what does secretin do to bile?
mild stimulation of bile by liver
what stimulates bile secretion?
bile itself (enterohepatic circulation)
what does it mean by saying enterohepatic circulation of bile?
because bile is hard to produce metabolically, 95% of them is reabsorbed in ileum and then transported back to liver for another circulation
what is the amount of secretion from small intestine per day and where is it secreted?
1.5L from crypts/glands
what are the small intestinal secretion? what are their function?
- mucous for lubrication
- isosmotic fluid (mixture of NaCl and NaHCO3) to helps neutralise acid and dilute food to aid digestion
- digestive enzymes
what is the large intestine secretin and what does it do?
mucous for lubrication
