Digestive system lecture 6 Flashcards
What are the 3 stages of vomiting?
What siganls it?
What are the SI functions?
-3 stages:
ANS discharge and Nausea
Retching
Emesis
-Vomiting Centre vs. CTZ
-signaled by afferents throughout the body
-Small Intestine Functions – mixing, slow propulsion
What are the colon functions?
What are the long reflexes?
Colon Functions – mixing, very slow propulsion, storage
Long Reflexes – Gastroileal, Ileocolic, Gastrocolic reflexes stimulated by entrance of new meal into the stomach to empty
small intestine and colon
What happens in absence of vomiting center?
What about in absence of CTZ (chemoreceptor target zone)
in absence of vomiting center you cant vomit even with CTZ
-without CTZ you cant vomit in response to circulating emetic agents but youd still have normal afferent inputs that cant trigger this process
What happens in phase 1,II, and III in the MMC (migrating myoelectric (motor) complex)?
How long is each phase/
-Phase I (60 min): no spike potentials, no contractions
-Phase II (20 min) irregular spike potentials and contractions
-Phase III (10 min): regular spike potentials and contractions
What happens when there is no meal in the stomach?
What happens when there is a meal?
-no meal, means there is strong MMC acitivty
-with a meal the pattern is interrupted
What is the propagation rate from stomach to distal ileum
-5cm/min
What is the MMC restricted to?
What initiates the MMC?
MMC - restricted to Distal Stomach and Small Intestine
-ENS (enteric nervous system) – periodic activation of
pattern-generating circuitry
How does MMC propgate?
When does it get interrupeted?
PROPAGATION:
-via * ENS with modulation via ANS and Gut Peptides
-INTERRUPTION: Intake of a new meal
What is the MMC function?
“Housekeeping”
Gastric emptying of large, nondigestible part
What is an example of the gastric emptying of MMC function?
-allows penny to force through spincter, alos fiber which cant be digested by stomach
What are the 3 functions of git/
- MOTILITY (muscular activity)–>Propulsion & Physical Breakdown
- SECRETION (glandular activity)–>Chemical Breakdown
- ABSORPTION Transfer to Circulation
What does exocrine and endocrine secretion do?
Where does each go during gland excretion?
exocrine=secreted by glandular cells into GIT lumen
-lumen is external environment since it is continuous with it
secreted into GIT external environment
-endocrine=into bloodstream (internal environment
What are the 4 processes of digestion?
-Sequence of interdependent steps
* Duplication of Enzyme Activity
* Medium requirements – pH, ions
* Enzymes are proteins (body wants to recycle them)
What is the defintion of digestion?
What does it result from?
Where are the secretions released?
-Chemical breakdown of food to progressively smaller molecules
-Results from the secretory activity of a large number of exocrine glands found within and in association with the GIT
-The secretions are released into the lumen of the digestive tract
WHat type of activity is secretion, what does it depend on?
What does secretion result in?
-Secretion is an active, energy dependent and blood flow dependent process,
-resulting in the release of a fluid containing ions and a variety of enzymes
What are the 3 types of enzymes and what they breakdown?
-amylases=breakdown starches
-proteases=breakdown of protein
-lipases=breakdown of fats
What are the 2 patterns of regulation?
Where are they most present?
- Nervous (ANS) (mainly at the mouth/stomach)
- Hormonal (gut peptides) (most important for distal part of GIT)
What are the 3 salivary gland, what do they secrete?
What protects and lubricates?
- Parotid (serous fluid)
- Submandibular (mucin+serous)
- Sublingual (mucin rich fluid)
mucin-mucous
What 2 secretions allow for chemical digestion?
Secretion of salivary amylase
* Begins carbohydrate digestion
-Tongue produces lingual lipase (for lipid digestion)
What is the volume of saliva per day?
What are the ions in it, what type of solution is it?
What is the pH?
-VOLUME: 0.5 – 1.5 liters/day
IONS: Na+, K+, Cl-HCO3-, HYPOTONIC
-6.5-7.0 (neutral solution)
What converts starch (polysaccharaides) to maltose (Disaccharides)
What only operates at neutral pH?
What are the other kinds of secretions?
Which ones are present in largest quantity?
amylase and ptylin
-ptylin
-mucin, lipase and lyzosyme (breaks down bacterial cell walls
-ptylin and mucous
How are glands regulated by the ANS?
-parasympathetic is blocked by atropine, but when Ach releasd it increases secretion causing vasodilation (increase blood flow)
-sympathetic leads to vasoconstriction
How does the eyes/nose regulate salivary secretion?
How do the sensory receptors in the mouth regulate it?
How is salivary gland activated
eyes/nose are higher centers which lead to salivary centers in medulla
-sensory receptor in mouth are afferent signals which also lead to salivary center
-from the salivary center there is efferent signal (via parasym.) that activate salivary gland
What are the 2 main phases of secretion?
What type of secretion activates the first phase?
cephalic phase-psychic (conditioned reflex, like thinking of food)
and gustatory (taste, food in mouth-
2.gastric/intestinal (occurs when food is warm/spicy)
How much Mixed gastric juice is produced per day?
What type of fluid is it, what type of ions compose it?
What is the pH?
1.5 – 2 liters/day
Isotonic Fluid: Na+, K+, Cl- , H
pH 1 – 2
What does H+ ion produce in mixed gastric juice
what are the 4 things in mixed gastric juice
-H+ most importat since it produces acidic pH of stomach
-HCl
-pepsinogen
-intrinsic factor
-mucin
What are the enzymes involved in protein digestion?
-initally pepsin, trypsin, chymotrypsin an elastase
then aminopeptidase and carboxypeptidase break them down into individual amino acid
What do surface epithelial cells secrete?
What do cardiac and pyloric tubular glands secrete?
Surface epithelial cells throughout the GIT secrete a mucous, alkaline fluid
-CARDIAC and PYLORIC tubular glands secrete an alkaline, mucin-rich fluid
What does the body and fundus tubular glands secrete?
What do tubular glands do?
-FUNDUS and BODY tubular glands
secrete acid, enzymes and Intrinsic Factor
-tubular glands increase SA of inner GIT for secretion
What do the parietal cell, chief cell and the mucous neck cells secrete in the fundus and corpus?
-parietal (oxyntic) cell)=Hcl
-chief cell=pepsinogen
-mucous neck cell=mucin
Where is HCl secreted?
Why is it filled with mitochondria?
-HCl is produced and secreted into canaliculis which contrains channels that connect with lumen
-filled with mitochondria so that it has enough energy to produce HCl
What is the basal side of the tubular gland in contact with?
What is the ratio of bicarbonate to H+ ion, where is each secreted to/from?
What does bicarbonate do?
-contact with blood
-for every H+ ion pumped out of lumen, 1 bicarbonat ion is pumped back into blood ot diffused back into blood (1;1)
-bicarbonate in blood alkanizes it at the level of the stomach
What does carbonic anhydrase do?
Where is the H+/K+ ATPase, what does it do, what do you need for the function?
Where can ATPase H+/K+ be found?
-takes CO2 in blood and produces H+ and HCO3-
-H+/K+ ATPase is at the apical part of the cell and moves H+ ions into lumen, need ATP for function
-only in this part of body which makes it a good target for ulcer medication
Where is the Na+/K+ ATPase?
What does it do?
-basolateral portion of cell and it is important for maintaing ionic gradient
How much secretion do we get from the postprandial (urinary) alkaline tide?
-we get 2L of secretion bc when moving HCl we are also putting water into lumen of stomach
What is parietal cell secretion?
What is the pH?
What is secretion dependent on?
-pure HCl fluid
-constant composition of pH-0.8
secretion is independent of stimulus type or magnitude
What is pH of mixed gastric juice?
What is it modified by?
What does it pH depend on?
-pH=1-2
modified by non parital alkaline gastric secretions
-depends on number of parieal cells that are active (which lowers pH)
What are the 4 functions of HCl?
-precipitaes soluble proteins (allwos the proteins to remain longer in the stomach)
-denatures proteins (more readily digested)
-activates pepsin
-provides optimal pH for pepsin activity (need low pH for pepsin)
What is pepsinogen?
When is it active?
-secreted by chief cells and it is a zymogen which means it is not active at when it is secreted from these cells
-only active when in contact with HCl in the stomach
What can pepsin do when formed?
What can pepsin do, at what pH?
- it can do autocatalysis, can cleave off pepsinogen into pepsin on its own (HCl pH<6)
-convert protein into polypeptides pH2-3
What is special about intrinsic factor, what is it?
What is it required for?
What does it protect?
-only secretion of the stomach essential to life
-it is a glycoprotein which is secreted by parietal cells
-required for absorption of vitamin B12 in the distal small intestine (ileum)
-protects vitamin b12 as it moves through GIT
What happens when there is intrinsic factor defiency?
Why does it form?
What does it lead to
-pernicous anemia bc RBC are not able to form properly due to lack of vit B12, which is neccessary for producing DNA
leads to macrocytic RBC
What happens when vit B12 is coupled with intrinsic factor?
What happens without ileum?
-it is absorbed at the level of the distal ileum
-cant absorb vit B12 without ileum
What are the locations of mucin secretion?
-all surface epithelial cells
-cardiac and pyloric tubular glands
-mucous neck cells (fundus and corpus)
What happens when CL- enters the cell?
After this what is H+ available for?
-Cl- entering the cell is actively transported across the canalicular membrane
-H+ available from the dissociation of intracellular water, is also actively pumped into the canaliculi in exchange for K+
What does the secretion of H+ leave in the cell?
What does result in and cause/produce?
-excess OH-
-resulting in an increase in intracellular pH.
-This causes more CO2 to diffuse in from the plasma (together with cellular
metabolic CO2 ) combines with water in the presence of Carbonic Anhydrase to produce H2CO3
what does H2CO3 react with in the scheme for HCl secretion, what does it restore, and give rise to?
how does water move into canaliculi
H2CO3 reacts with the excess OH- to yield H2O and HCO3-
-the latter diffuses into the circulation, restoring the intracellular status quo, and
giving rise to an increased alkalinity in the venous blood
-it moves into canaliculi passively
