digestive system lecture 7 Flashcards
What are the principles of secretion?
What is the salivary gland secretion?
requires energy and blood flow
-glands, saliva (ONLY hypotonic secretion in GIT;
ptyalin, a salivary amylase (active at neutral pH); mucin)
What is regulating salvation?
What is secreted in gastric section?
ANS (parasympathetic – ALL Neural, NO hormonal regulation)
-different glandular cells in different locations composition of Mixed Gastric Juice
a) HCl b) Pepsinogen c) Mucin
Where are surface epithelila cells present?
What are the 4 functions of HCl?
-everwhere in the GIT
Precipitates Soluble Proteins :allows the proteins to remain longer in the stomach
-Denatures Proteins more readily digested
-Activates Pepsin
-Provides Optimal pH for Pepsin activity
What does the gastric mucosal barrier (GMB) do?
Where is it found
-it is the main protective layer and it has a specialization of tight junctions and sruface which makes them permeable to H+ on apical side (only found in stomach)
What does H+ions interact with?
What does the muci-bicarb layer adsorb?
What does muci bicard layer secreted?
H+ can freely pass across mucous gel but interact with bicarbonae and are neutralized (pH of 7 after it passes layer)
-bicarbonate layers
-secretes mucous and bicarbonate
What does rapid cell turnover (re-epthelization) produce
-produces up to 1 million new epithelilal cells per day specifically in the stoamch +SI
What are the factors that contribute to ulcers for a normal HCl ouput but weak input?
What are the drugs/bacteria?
normal HCl but weak barrier caused by: Aspirin & NSAIDs (can weaken barrier)
Helicobacter pylori (bacteria that burrows itself in layers between the mucous of these cells and produces toxins which damage mucousal layer
What factors contribute to a normal barrier but excessive hcl output?
gastrin producing tumors can cause this
What is part of the nervous vs hormonal input?
-vagus and sympathetic
-hormonal=gastrin, histamine, somatostatin
What are the 3 phases of gastric secretion?
cephalic=psychic and gustatory
gastric (when food is in stomach)
intestinal (when food is in intestine)
what do the neurons smooth muscle of GIT synapse on?
-they synapse on the secreting cell
What does the ENS do in neural regulation of secretion?
How can it be activated
-sends excitatory input onto secretory cells
-ENS can be activated when we have stretch in the stomach or when we think of food to send efferents in preparation for food
What does cephalic phase lead to and what is it mediated by?
-it is vagally mediated and leads to vasodilation
What does the sympathetic input for secretion regulation do?
inhibits secretion and leads to vasoconstriciton
What does the local enteric reflex do?
WHat do the vago-vagal reflex do?
it causes distention
-can reinforce stimulus
What do secretagogues act on?
What are secretagogues
act on gastrin secreting g-cell which leads to gastrin release in stomach, leading to increase in HCl by parietal cell
-amino acids or partially digested proteins which act on gatrin-releasing cells G-cells
What does the cephalic phase do?
-it prepares enzymes to be ready for when the meal arrives
What occurs when there is an increase in secretagogues?
To the g cell, parietal cell?
What type of loop is this?
-increased secretagogue causes increase in g-cell (gastrin release) which causes an increase in paritela cell–>increase in HCl
-this actiavtes pepsinogen to pepsin (more protein break down)
-this is a positive feedback
What does a low pH cause in the gastrin regulation cycle?
What does the g-cell have to sense the ph?
What type of feedback is this?
-it causes a release of somatostain which inhibts the g-cell and the parietal cell
-it has receptors to detect the pH which reduces number of secretagogues
-negative feedback
What 3 things does the parietal cell have a receptor for?
what does an histamine inhibitor do vs proton pump for ulcers/
-gastrin, histamine and Ach
-histamine inhibitor blocks about 70% where proton pump blocks about 90-95% of hcl secretion
What does a blockade or stimulation of one of the parietal cell receptors do?
What happens to sensitivity when you block vs when you stimulate histamine?
-changes the properties of one or both of the other 2 receptors
-blocked histamine means Ach and gastrin are less sensitive
-stimulation of histamine increases Ach/gastrin sensitivity
What does the intestinal phase (duodenal excitatory component do)?
-it activates secretagogues to activate cells in the duodenum which releases gastirn to increase HCl
What are the factors that lead to inhibition of gastric secretion?
-distention
ph<3.5
high osmolarity
chemical compostion
fat»proteins»carbs
-they all produce negative feedback
What is inhibitory 1 for intestinal phase?
-it is the enterogastric reflex (factors controlling antral peristalsis)
WHat do motor and secretory activities in the stomach reflect a balance between?
Both MOTOR and SECRETORY activities of
the stomach (at any moment in time) reflect a balance between EXCITATORY and INHIBITORY influences on the MUSCULAR and GLANDULAR cells in the gastric wall
What does the cystic duct join?
joins the gallbladder
What are the pancreatic proteases?
when is proenzyme active?
proenzyme not active untile cleaved at level of SI when converted to an enzyme
-trypsinogen uses enterokinase to convert into trypsin in SI
What other products can trypsin be used to cleave?
What does trypsin inhibitor do, what secretes it?
chymotrypsinogen into chymotrypsin
-protease into elastase
procarboxypeptidase into carboxypeptidase
-pancrease secreates it and it inactivates trypsin
