GIT - Lecture 6 Flashcards
How is the GI motility organized in the interdigestive period?
into an intense pattern of cyclic myoelectric (motor) activity
How often does the intense pattern of cyclic myoelectric activity recur in the GIT in the absence of a meal?
every 90 minutes
Where does the cyclic motor activity of the GIT move during the interdigestive period?
over the distal stomach and small intestine
What is the rate of GI motility during the interdigestive period?
moves over portions of the GIT at 2-10 cm/minute
How many phases are in the migrating myoelectric complex?
3
What happens to spike potentials and contractions during phase I of the MMC?
no spike potentials, no contractions
What happens to spike potentials and contractions during phase II of the MMC?
irregular spike potentials and contractions
What happens to spike potentials and contractions during phase III of the MMC?
regular spike potentials and contractions
Why is it called the “migrating” myoelectric complex
because it moves down the length of the GIT
How long does phase I of the MMC last?
60 min
How long does phase II of the MMC last?
20 min
How long does phase III of the MMC last?
10 min
When is the MMC interrupted?
when we consume a meal
Why is the MMC important?
because it allows us to move food in the interdigestional period that haven’t moved at other times
What is the function of the MMC?
gastric emptying of large, nondigestible particles even in the absence of a meal
Which nervous system does the MMC need in order to be initiated?
the enteric nervous system
Which nervous system does the MMC need in order to be propagated?
the enteric nervous system
What helps the ENS propagate MMC?
ANS and gut peptides
What is the function of the exocrine secretions?
chemical breakdown of food
What are the 2 kinds of gland secretion?
endocrine and exocrine
Are gland secretions that move into GIT external environment considered exocrine or endocrine?
exocrine
Are gland secretions that move into the blood stream and internal environment considered exocrine or endocrine?
endocrine
What is important to consider about the enzymes involved in digestion?
their medium requirements: pH, ions
Digestion results from the secretory activity of a large number of ___ glands found within and in association with the GIT.
exocrine
Where are exocrine secretions released in the digestive tract?
the lumen
What kind of process is secretion?
active, energy and blood flow dependent
What does secretion result in the release of?
fluids containing ions and enzymes
What are the 3 types of digestive enzymes?
- amylases
- proteases
- lipases
What is the pattern of nervous system regulation of secretion?
decreases from proximal -> distal
What is the pattern of hormonal regulation of secretion?
increases from proximal -> distal
Which nervous system regulates secretion?
ANS
Which hormones regulate secretion?
gut peptides
What are the 3 salivary glands?
- parotid
- submandibular
- sublingual
Which secretion of the mouth protects and lubricates?
mucin
What does mucin lubricate?
the bolus
Which 2 secretions in the mouth allow for chemical digestion?
- salivary amylase
- lingual lipase
What does salivary amylase begin?
carbohydrate digestion
What does lingual lipase begin?
lipid digestion
What fluid does the parotid gland release?
serous fluid
What fluid does the sublingual gland release?
mucin-rich fluid
What fluid does the submandibular gland release?
mixed fluid (serous + mucin-rich)
Which is the only secretion in the GIT that is hypotonic?
saliva
What is the volume of saliva produced every day?
0.5-1.5 liters/day
What are the 4 ions present in saliva?
Na+, K+, Cl-, HCO3-
What is the pH of saliva? Why?
6.5-7.0 because of the bicarbonate secreted into it
What can starch (polysaccharide) be broken down into by saliva? With which enzyme?
maltose by the enzyme ptylin
Where does lipase break down fats?
at the level of the stomach
What do lysozymes break down?
bacterial cell walls
What do lysozymes protect us from?
bacteria in food
Which branch of the ANS increases secretion?
parasympathetic system
How can you block secretion?
by giving atropine
What happens when ACh is released onto a secretory cell?
it will depolarize and the depolarization will lead to secretion (exocytosis)
What also increases when secretion increases?
vasodilation
What would happen to secretion if the sympathetic system were activated?
it would decrease
Does the sympathetic system cause vasoconstriction or vasodilation?
vasoconstrction
What activates afferents that feed into the salivary centres in the medulla?
sensory receptors in the mouth
What do the salivary centres in the medulla send out to the salivary glands?
efferents via parasympathetic supply
What activates higher centres in the cortex and then in turn activates salivary centres in medulla?
smelling food or seeing food
What is the first phase of secretion?
cephalic
What is the cephalic phase made of?
- psychic
- gustatory
What are the 3 phases of secretion?
- cephalic
- gastric
- intestinal
How much mixed gastric juice is produced per day?
1.5-2 L/day
What are the ions found in mixed gastric juice?
Na+, K+, Cl-, H+
Which ion is the most important in mixed gastric juice?
H+
What is the pH of mixed gastric juice?
1-2
What kind of fluid is mixed gastric juice?
isotonic
What gives the stomach its low pH?
the HCl found within it
What are the 4 main components of mixed gastric juice?
- HCl
- pepsinogen
- intrinsic factor
- mucin
Which enzymes break down proteins into smaller proteins? (4)
- pepsin
- trypsin
- chymotrypsin
- elastase
Which enzymes break down smaller peptides into individual amino acids? (2)
- aminopeptidase
- carboxypeptidase
What do surface epithelial cells throughout the GIT secrete? (2)
mucous and alkaline fluid
How do we increase the surface area of secretion in the stomach?
by tubular glands
What kind of fluid do the cardiac and pyloric tubular glands secrete?
alkaline, mucin-rich fluid
What kind of fluid do the fundus and body tubular glands secrete? (3)
acid, enzymes and intrinsic factor
What are the 3 important cells found in the fundus and body of the stomach?
parietal cells, chief cells, mucus neck cells
What do parietal cells release into the lumen of the tubular gland?
HCl
What do chief cells release?
pepsinogen
What do mucus neck cells produce?
mucus and alkaline fluids
What do surface epithelial cells release?
HCO3 and mucus
What do the canaliculi of the parietal cells do?
increase their apical surface area for the secretion of HCl
What do parietal cells have a lot of? Why?
mitochondria, because producing HCl requires a lot of energy
What is the mEq of H+ and Cl- of the HCl produced by the parietal cells?
150 mEq H+ and 150 mEq Cl-
For every HCl molecule moving into the lumen, 1 molecule of ___ is going to move into the capillary.
HCO3- (bicarbonate)
As we acidify the lumen, we create an ___ of the blood.
alkalization
Cl- entering the cell is ___ transported across the canalicular membrane.
actively
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 an excess of in the cell?
OH-
What happens to pH when there is an excess of OH- in the cell?
it increases
When there is an increase in the intracellular pH, what happens to CO2?
it diffuses in from the plasma and combines with water to produce H2CO3
When does CO2 combine with water in the presence of?
carbonic anhydrase
What does H2CO3 react with to produce H20 and HCO3?
excess OH-
What happens to the alkalinity in the venous blood during HCl secretion?
it increases
