HUBS192 Lecture 25 - GI Secretion Flashcards
what are exocrine secretions?
secretions into the lumen of the GI tract
-secreted outside onto the body surface (therefore it is referred to as exo)
what are endocrine secretions?
secretions into the blood, into the body or secreted into the interstitial fluid
what are exocrine secretions produced by?
produced by epithelia that line the surface of the GI tract
what are the components and functions of these components of exocrine secretions?
1) mucous
- protection and lubrication
- aids mechanical digestion
2) electrolyte solution
- dilutes food & provides optimal pH
- essential for chemical digestion of food
3) digestive enzymes
- essential for chemical digestion of food
- aids absorption
what are the 2 functions of electrolyte solution?
1) dilutes food
2) provides optimal pH
- which is essential for chemical digestion of food
what are the 2 functions of digestive enzymes?
1) essential for chemical digestion of food
2) aids absorption
what are the 3 pairs of salivary glands?
1) parotid glands
2) submandibular glands
3) sublingual glands
which gland produces the largest proportion of salivary secretion?
the submandibular glands
how many litres do the salivary glands produce per day?
1.5 L of fluid per day
what is the basal secretion of salivary glands?
0.3 mL/min
what is the stimulated secretion of salivary glands?
1.5 mL/min
what is the composition of the salivary glands?
1) mucous
- lubrication
2) dilute solution of NAHCO3/NaCI
- dilution of food
- optimal pH for digestive enzymes
3) digestive enzymes
- lingual lipase
- alpha amylase
what are the functions of salivary secretion?
1) aids in
- talking
- chewing
- swallowing
- dissolves food
- lubricates
2) hygiene
- irrigation
3) digestion
- dissolves food to allow tasting
- lingual lipase (fats)
- alpha amylase (starch)
are salivary secretions essential?
no they are not essential but are preferred
what are the 2 regulators of salivary secretion?
1) nervous control
2) autonomic nervous system
how does the nervous control regulate salivary secretion?
by the thought, smell, sight of food and the presence of food in the mouth
what are the 2 nervous systems that control the salivary secretion from the autonomic nervous system?
1) parasympathetic nervous system
2) sympathetic nervous system
what is the function of the parasympathetic nervous system in terms of salivary secretion?
stimulates the secretion of copious quantities of fluid
what is the function of the sympathetic nervous system in terms of salivary secretion?
stimulates the secretion of small volumes of viscous fluid
what is the volume of gastric secretion per day?
2-3 L per day
what is the volume of gastric secretion between meals?
slow rate of 15-30 mL/hour
what are the cells of gastric secretion secretion between meals?
surface cells secrete mucous
what is the gastric secretion when eating?
superimposed on basal rate
what are the 3 cells involved in gastric secretion when eating?
1) mucous cells
2) parietal cells
3) chief cells
what do parietal cells secrete?
150 mLs/hour of HCI acid (pH=1) and intrinsic factor
what do chief cells secrete?
pepsinogen
what is the function of intrinsic factor?
the absorption of vitamin B12 in the small intestine
what is pepsinogen?
the inactive form of pepsin that is a gastric proteolytic enzyme
what is the largest component of gastric secretions?
gastric acid
what is the function of pepsinogen?
starts the digestion of proteins
what are the 5 functions of gastric acid?
1) dilutes food
2) denotes proteins
3) activates pepsinogen to pepsin
4) creates optimum pH for pepsin action
5) protection
what is the active form of pepsinogen and how is this converted?
converted to the active form of pepsin by acid
what is the source of HCI acid for gastric secretion?
the parietal cells
how is the source of H+ for HCI acid generated?
source of H+
- comes from the formation of H2CO3 by carbonic anhydrase (CO2 + H2O H2CO3)
- dissociation of H2CO3 HCO3- + H+
how is the secretion of H+ for HCI acid generated?
ATP drives the pumping of H+ across the apical membrane of parietal cells into the lumen of the stomach in exchange for K+ (potassium ions)
how is the source of CI- for HCI acid generated?
through an anion counter transporter on the serosal membrane of parietal cells by ejecting HCO3- into the interstitial fluid and importing CI- ions into the cell
how is the secretion of CI- for HCI acid generated?
CI- ions diffuse across the cells and enter the lumen via a CI- channel in the apical membrane
how is the regulation of gastric secretion co-ordinated by?
co-ordinated with eating and the arrival of food
what are the 3 phases of gastric secretion?
1) cephalic phase
2) gastric phase
3) intestinal phase
what controls the cephalic phase of gastric secretion?
head controls secretion
what controls the gastric phase of gastric secretion?
stomach controls secretion
what controls the intestinal phase of gastric secretion?
intestine controls secretion
what is the purpose of cephalic phase?
prepares for the arrival of food
how is the parasympathetic nervous system via the enteric nervous system stimulated by?
stimulation of higher centres by the thought, smell, sight of food, chewing and taste
what does the parasympathetic nervous system via the enteric nervous system stimulate?
- stimulates parietal cells, chief cells and goblet cells
- stimulates the secretion of the hormone gastrin that are released into the blood and stimulates parietal cells and chief cells
what is the purpose of the gastric phase?
ensures sufficient secretion to handle ingested food
what does the stimuli in the stomach detect?
1) stretch/distention of the stomach wall
2) products of digestion stomach lumen
3) elevated pH
what are the 2 nervous and hormonal regulation reflexes?
1) local nervous reflex
2) external nervous reflex
what nervous system does the local nervous reflex innervate?
the enteric nervous system
what nervous system does the external nervous reflex innervate?
the parasympathetic nervous system
what do the local nervous reflex and the external nervous reflex stimulate?
- secretion
- motility
- gastrin secretion (further simulation of secretion and motility)
what 3 hormones inhibit gastric secretion and motility?
1) GIP
2) CCK
3) Secretin
what is the purpose of the intestinal phase?
controls the delivery to the small intestine
what does the stimuli in the small intestine detect?
- distention of the duodenum
- arrival in the duodenum of acid chyme, lipids ad carbohydrates
what are the 2 nervous and hormonal regulation components that inhibit secretion and motility?
1) hormones
2) nerves
what is the nerve that inhibits gastric secretion and motility?
enterogastric relex nerve
how much fluid volume does the pancreas secrete per day?
1-1.5 L/per day
what are the 2 components of pancreatic secretion?
1) enzymes which secrete acing cells for chemical digestion
2) alkaline fluid produced in duct cells that neutralise acid to make an optimum pH for the digestive enzymes
what are the lipolytic enzymes?
lipase and phospholipase
what are the amylytic enzymes?
pancreatic amylase
what are proteolytic enzymes?
trypsin, chymotrypsin and carboxypeptidase
what are nucleolytic enzymes?
ribonuclease and deoxyribonuclease
what are the pancreatic enzymes secreted by?
secreted by acinar cells
what do pancreatic enzymes stimulate the secretion of?
secretion of digestive enzymes by acinar cells stimulated by the cholecystokinin hormone (CCK)
what stimulates cholecystokinin secretion?
arrival of lipids and carbohydrates into the duodenum
what is the function of digestive enzymes?
luminal chemical digestion of food
what are proteolytic enzymes secrete as and what are they activated by?
secreted as inactive precursors and activated in the duodenum
what is the inactivate precursor of trypsin?
trypsinogen
what is the inactive precursor of chymotrypsin?
chymotrypsinogen
what is the inactive precursor of carboxypeptidase?
procarboxypeptidase
what does activation in the small intestine involve?
enterokinase (or enteropetidase) bound to the duodenal membrane that converts trypsinogen trypsin
what is the function of trypsin?
trypsin converts other enzymes the active form
where is the secretion of alkaline (HCO3 rich) fluid produced by?
produced by duct cells in the pancreas
what is the secretion of alkaline (HCO3 rich) fluid?
stimulated by hormone secretion
-secretion of secretin by the arrival of acidic chyme in the duodenum
what is the function of alkaline (HCO3 rich) fluid?
-neutralises acid chyme delivered to the stomach creating the optimum pH (6.7-9.0) for pancreatic and intestinal digestive enzymes
how much bile fluid is secreted by the liver per day?
0.5 L/per day
what are the products associated with digestion of bile secretion?
- bile salts
- HCO3- rich fluid from ducts
what are the excretory products of bile secretion?
- bile pigments (waste products)
- cholesterol
what is the function of bile salts?
fat digestion
what is the function of HCO3- rich fluid?
-neutralises acid
what is the function of bile pigments?
excretion of the liver
what stimulates bile secretion?
bile stimulates its own secretion by enterohepatic circulation
where is bile stored and concentrated?
in the gallbladder
where is bile delivered to with the arrival of food?
delivered to the duodenum
what does the hormone cholecystokinin (CCK) do in relation to the initial delivery of bile that is under hormonal control?
- produced in response to products of digestion in the duodenum
- contracts the gallbladder
- relaxes the hepatopancreatic ampulla
what is the hormone secretin mildly stimulated by?
mild stimulation of bile by the liver
what percentage of enterohepatic circulation is reabsorbed into the ileum?
95%
what does GIP stand for?
gastro inhibitory peptide
