lecture 25 Flashcards
define secretion and absorption
secretion is the movement of solutes and water from the body into the lumen.
absorption is the movement of solutes and fluid into the body
what are the three components of exocrine secretion in the GI tract
mucous, protection and lubrication of tissues and aids in mechanical digestion
digestive enzymes: these do chemical digestion and help absorption
electrolyte solute: dilutes food, provides optimal pH for enzymes, also aids chemical digestion
about how much do we secrete a day, why don’t we die 2
we secrete about 8 litres a day, but we reabsorb most. whats lost in urine is replaced with drinking water
how much is secreted from the salivary glands in each state and what are the components
about 1.5L, basal is 0.3ml/min 1.5ml/min when stimmed
made of digestive enzymes like amylase, has bicarbonate solution to provide optimal pH for enzymes, has mucous for taste, lubrication and protection
functions of salivary secretions
aids in chewing, talking and swallowing as lubrication.
helps in hygiene as it irritates bacteria out of mouth when swallowed
also luminal digestion using lingual lipase and alpha amylase
what are the 2 regulation methods of salivary secretion, describe
CNS regulation. producing saliva when we receive external signal of food, or when food is in mouth
PNS causes secretion of more saliva
SNS causes secretion of a viscous fluid in small volumes to augment the PNS response
how much secretion is in stomach and whats the basal secretion like
2-3L per day. in a fasting basal state we have slow secretion, mostly just gastric pit cells secreting mucous and bicarbonate
whats secretion like in the stomach when eating
this is above and beyond the basal level
surface epithelial cells secrete mucous and bicarb. parietal cells secrete the HCl and intrinsic factor to help B12 absorption
chief cells do pepsinogen
what activates pepsinogen
the HCl in the stomach
what is our source of H+
in the parietal cells carbonic anhydrase does:
CO2 + H2O –> H2CO3
H2CO3 then dissociates into
H+ and HCO3-
outline the four steps of HCl secretion in the parietal cells
1 carbonic anhydrase makes HCO3- and H+
2 secretion of H+ using H+/K+ ATPase
3 source of chloride
4 secretion of chloride
in secretion of HCl outline steps 3 and 4
3: source of chloride. uses anion counter transporter, serosal membrane of cell ejects HCO3- and imports Cl-
4: secretion of chloride. Cl- diffuses across cell, Cl- enters lumen via channel of the apical membrane
what are the three phases of gastric secretion
cephalic secretion- CNS controlled
gastric secretion- stomach control
intestinal secretion - intestine control
describe the cephalic phase
this is 20% of gastric secretions, this involves preparation for food arrival. the CNS will start secretions with stimuli of thought, smell, sight of food. chewing and taste will also stimm. in prep for food the extrinsic PNS will act via the enteric nervous system. this stimulates parietal, chief and goblet cells.
this PNS stimulation will also stimulate secretion of gastrin into the blood, which stimulates the parietal and chief cells.
what is function of the gastric phase and how much secretion does it do?
70% of the secretions associated with a meal, this phase ensures there is enough secretions in the stomach to handle the ingested food.
stimuli for the gastric phase of stomach secretions
stretch and distension of the stomach wall due to presence of food. having products of digestion in the lumen and, elevated PH of the stomach
what are the regulations of the gastric phase what do they do?
enteric nervous system in a local reflex, long reflex with the PNS. both stimulate secretion of gastric glands, motility and gastrin secretion- which further stimulates secretion and motility
how much and what it do- intestinal phase
its about 10% of gastric secretions, this phase serves to control the delivery of chyme into the small intestine
stimuli for the intestinal phase of secretions in stomach
distenstion of the duodenum, also the arrival of acidic chyme and lipids and carbs in the small intestine
what are the hormones release in the intestinal phase secreted in response to
secretin is released in response to decreased PH
CCK and GIP are released in response to lipid and carb presence in SI lumen
what are the regulators of intestinal phase of gastric secretions
CCK, secretin and GIP. enterogastric reflex as well- duodenum to stomach to brain.
both regulate motility and gastric secretions
how much and what does the pancrease secrete
1-1.5L per day secreting alkaline solution (duct cells make bicarb to neutralise acid and give good PH for enzymes), we also have enzyme secretion from acinar cells
whats the secretory stimulation for pancreatic enzymes
secretion of digestive enzymes is stimulated by CCK. which itself is stimulated by carbs and lipids into duodenum
hwo do we activate the proteolytic enzymes
the activation occurs in the small intestine using membrane bound enterokinase. this enterokinase converts trypsinogen to trypsin. trypsin then converts the other enzymes to active form, those enzymes being chymotripsin and carboxypeptidase
what is secretion of alkaline fluid from pancreas caused by
secretin is secreted in small intestine by low PH, secretin then stimulates duct cells of pancreas to stimulate bicarbonnate secretion
how much bile secretion do we have per day
about 0.5L per day, consisting of Bile salts
HCO3
- rich fluid – ducts
Excretory products
Bile pigments – waste products
Cholesterol
describe regulation of biliary secretions
its under hormonal control by CCK hormone. CCK is released in response to fat in the duodenum, CCK causes gall bladder to contract and relaxation of hepatopancreatic ampulla. thus releasing bile. bile also causes own secretion in hepatopancreatic circulation
describe hepatopancreatic circulation
Bile metabolically expensive to produce so 95% reabsorbed in ileum. it is Transported back to liver in enterohepatic circulation it is
Reabsorbed and secreted
Stimulation of bile secretion
discuss intestinal secretions
1.5L per day. mucus for lubrication, digestive enzymes and sosmotic fluid to help neutralise. this is SI
LI just secreted mucus for lubrication
