Digestion 6 Flashcards
What happens to GI mobility during interdigestive periods?
It goes into an intense pattern of cyclic myoelectric activity (migrating motor complex (MMC))
At what intervals do Migrating motor complex occur?
at regular intervals of about 90 min
How does MCC move in the GIT?
moves sequentially over the distal stomach and small intestine at about 2-10 cm/min
In the 90-minute interval, what happens in MMC? (phases)
Phase 1: BER, no spikes, no contractions (60 mins)
Phase 2: Irregular spikes and contractions (20 mins)
Phase 3: Regular spikes and contractions (10 mins)
Were does MMC occur?
In the distal stomach and small intestines
When is MMC interupted?
When there is a meal intake
What initiates MMC and what ensures it’s propagation and modulation?
I: NOT CNS, NOT ANS, the ENS has periodic activation of a pattern-generating circuitry
P: The ENS
M: ANS and gut peptides
What is the function of the MMC?
Housekeeping, moving things that didn’t during normal propulsion —> Gastric emptying of large, non-digestible particles
How can MMC allow gastric emptying of large non-digestable particles in the distal stomach?
The pyloric sphincter will not be closing completely (no retropulsive flow), allowing bigger elements to be forced out
Where do exocrine secretions go?
To the external environment e.g. GIT lumen
Where do endocrine secretions go?
To the internal environment e.g. Blood stream
Digestion is ….
It results from ….
Chemical breakdown of food to progressively smaller molecules
The secretory activity of many exocrine glands
Secretion depends on what 2 things to be an effective process?
Energy
Blood flow
What are the 3 types of enzymes?
Amylases
Proteases
Lipases
What are the patterns of regulation of secretion?
The nervous system (ANS) has decreasing input from the mouth to the large intestine
Hormones (Gut peptides) have increasing input from the stomach to the large intestines
What are the three salivary gland of the mouth?
Parotid
Sublingual
Submandibular
In the mouth, which secretions allow protection and lubrification?
Mucin
In the mouth, which secretions allow chemical digestion? And digestion of what?
Salivary Amylase (begin carbohydrate)
Lingual lipase (lipid)
Is the lingual lipase active as soon as it is secreted in the mouth?
No, It gets activated in a acid environment
Which glands of the mouth secrete which secretions?
Parotid: serous
lingual: mucin
Mandibular: mixed
What amount of saliva is produced per day?
0.5 - 1.5 liters/day
What ions are in saliva? what type of solution does this give?
Na
K
Cl
HCO3
Saliva is hypotonic
What is the salive pH?
6.5 - 7 because of the HCO3 concentrations
What is digested in the saliva? By what?
Polysaccharides like starch are transformed into disaccharides like maltose
This is done by the ptyalin amylase which operates at a pH of 7
What are 4 secretions found in saliva?
Ptulin (amylase)
Mucin
Lipase
Lysosome
What are the ANS regulation of the salivary glands?
P: release ACh onto ENS to increase secretion and vasodilatation (can be blocked by atropine)
S: inhibit secretions and increase vasocontriction
Explain the pathway of secretion regulation.
Afferent from sensory receptors in the mouth or from the eyes/ nose reach the salivary centers
Efferents fibres vis parasympathetic supply reach the glands
What are the phases of secretion?
Psychic - conditioned reflex
Gustatory
GAstric
Intestinal
How mush gastric juice is produced in a day?
1.5-2 L
What ions are in gastric juices? what type of solution does this give?
NA
K
Cl
H +++++
Isotonic solution
What is the pH of gastric juices?
1-2
Which secretions are in the gastric juices (main function)? (4)
HCl
Pepsinogen (breakdown proteins)
Intrinsic factor (digest, absorb B12)
Mucin (move and protect)
Which type of cells are responsible for the secretion of different fluids in the stomach? How is their structure important?
The surface Epithelial cell: Tubular glands
They help in increasing surface area to allow more secretion at once
How are the tubular glands different throughout the stomach?
Cardiac and Pyloric tubular glands secrete an ALKALINE and MUCIN RICH fluid
Fundus and body tubular glands secrete acid, enzymes and intrinsic factors
What are the different kinds of cells in the fundus and body tubular glands?
Parietal cells
Chief cells
Mucus neck cells
What do each cell of the fundus tubular glands secrete?
Parietal: HCl
Chief: Pepsinogen
Mucus: Mucin
Describe the important structures of the parietal cells?
canaliculi – > increase surface area
Mitochondria –> need a lot for energy needed in the carrying of HCl against its concentration gradient
How do the material for HCl enter the parietal cells?
Cl is actively transported across the canalicular membrane
H is available from the dissociation of intracellular water and is actively pumped into the canaliculi in exchange for K
Why is the intracellular pH of parietal cells high?
The secretion of H leaves an excess of OH
If the cell has a higher intracellular pH, what molecules enter the cells and what does it do?
CO2 diffuses from the plasma and combines with water IN THE PRESENCE OF CARBONIC ANHYDRASE to produce H2CO3
What does H2CO3 do once it’s synthesized?
It reacts with the excess OH to make H2O and HCO3
What does HCO3 do once it’s synthesized?
It diffuses into the circulation, restores the intracellular pH and increases the venous blood blood alkalinity
How can the amount of HCO3 be measured clinically? What can it mean?
The level of alkalinisation in the blood or urine reflects the HCO3 in the venous blood and so how much acid is produced by the cell on the other side
How does water enter the parietal cell?
Passively
What happens to the HCl once it’s synthesized?
It goes against it’s gradient and requires a lot of energy
What are the characteristics of the parietal cell secretions?
Pure HCl fluid:
Constant composition with a 0.8 pH
The secretion is independent of type / magnitude of stimulus (all or nothing and all the same)
What are the characteristics of the mixed gastric juices secretions?
The pH is between 1 and 2
It involves non-parietal alkaline gastric secretions and the pH is dependent on the number of active parietal cells (more active = lower pH)
