L28 - control of GI secretion Flashcards
what are the major body secretory systems
- salivary glands
- stomach
- pancreas
- bile system
- intestine
define endocrine
define exocrine
secretion into blood
secretion into GI lumen
name the 3 salivary glands
- parotid gland
- submandibular gland
- sublingual gland
describe composition of parotid gland secretion
serous (watery)
high amylase
describe composition of submandibular gland secretion
serous & mucous
high [lysozyme]
describe composition of sublingual gland secretion
mainly mucus
some serous
describe general composition of saliva
water mucins (glycoproteins) lysozymes amylase lipase cells calcium phosphate
what are mucins
glycoproteins
what cells secrete initial saliva and where
acinar cells in the acinus (bottom of gland)
what is the ionic composition of primary saliva
Na Cl K HCO3 amylase
where does modification of the ionic content of saliva occur
intercalated duct
what is reabsorbed from the primary saliva
Na
Cl
what is further secreted into/remains in the primary saliva
K
HCO3
what happens to saliva composition when flow rate is increased
less time to modify / reabsorb /secrete
what controls flow rate?
neuronal input
what controls saliva secretion
PNS and SNA - salivary centres in medulla
what stimulates saliva secretion
smell & sight of food
pressure & taste receptors in mouth
does PSNS or SNS have greater effect on salivary secretion
PSNS
what type of saliva is stimulated by
PSNS
SNS
serousy
mucousy
list the functions of saliva (5)
- lubrication (aids speech and swallowing)
- protection (cooling, antimicrobial)
- taste (dissolves food)
- maintenance of teeth (alkaline pH prevents decay)
- digestion (amylase, lipase)
list the gastric secretions
- HCL
- Pepsin
- lipase
- mucus & HCO3
- intrinsic factor
function of HCL (gastric secretion)
optimum pH for stomach enzymes
dissolves food
kills bacteria
what is pepsins optimum pH
what is its function
2-3
digestion of proteins
function of mucus and HCO3 gastric secretion
forms a layer around stomach wall protecting cells from degradation
function of intrinsic factor gastric secretion
aids vitamin b12 absorption
what factors control HCL secretion into stomach
increasing : will increase secretion
ACh (neuronal)
Gastrin (endocrine)
histamine (paracrine)
decreasing : will increase secretion
somatostatin (endocrine)
secretin (endocrine)
what is alkaline tide and its purpose
- Cl is extracted from blood (at stomach) so it can be secreted as HCL
- HCO3 replaces this lost Cl- in the blood
- this makes the blood here more alkaline
what cells secrete HCL
gastric parietal cells
what receptors are found on gastric parietal cells
Histamine
ACh
Gastrin
what are the phases of gastric secretion in order
- cephalic phase
- gastric phase
- intestinal phase
what is secreted by the pancreas
digestive enzymes
HCO3
water
what is function of HCO3 secreted by pancreas
neutralises chyme
list the digestive enzymes secreted by the pancreas and what they degrade
amylase - polysaccharides
lipase - fats
ribonuclease/deoxyribonuclease - nucleic acids
trypsin/chymotrypsin/carboxypeptidase - proteins
how are degradative enzymes stored in the pancreas
as inactive forms (zymogens)
what pancreatic cells secrete HCO3 and mucin and what stimulates them to do so
Centroacinar (epithelial) cells
secretin
what does secretin stimulate the secretion of from the pancreas
HCO3 and mucin
what effect does high rate of secretion (flow rate) have on pancreatic juice composition
will mainly contain Na and HCO3
what is secreted from the fundus of stomach
lipase
what is secreted from the antrum of stomach
mucus
pepsinogen
gastrin
what is secreted from body of stomach
mucus
pepsinogen
HCL
what is secreted from the chief cells of gastric glands
pepsinogen
lipase
what is secreted from enteroendocrine cells of gastric glands
gastrin
somatostatin
what is secreted from parietal cells of gastric glands
HCL
intrinsic factor
what effect does low rate of secretion (flow rate) have on pancreatic juice composition
will mainly contain Na and Cl
what stimulates pancreatic secretion
secretin
cholecystokinin (CCK)
PSNS
when is secretin released
in response to H+ in duodenum
when is CCK released
in response to fats and AA in duodenum
what stimulates PSNS to increase pancreatic secretion
stomach and duodenum distension
what inhibits pancreatic secretion
somatostatin
describe bile composition
bile salts lecithin HCO3- cholesterol bile pigments trace metals
what blood waste materials are found in bile
cholesterol
trace metal
bile pigments
what is the function of bile salts and lecithin
fat digestion
how is bile secretion regulated
- when food is in the SI the bile duct opens (under hormonal control via CCK)
- bile released into SI
what hormone regulates bile secretion
cholecystokinin (CCK)
how is the release of pancreatic bicarbonate into the duodenum stimulated
- H+ in duodenum stimulates secretin
2. secretin stimulates release of pancreatic bicarbonate
