Gastro VI Flashcards
When is the MMC active?
During the interdigestive period, meaning the period between meals.
Describe what happens in phase 1 of MMC.
Nothing happens. It’s just normal BER with no spike potentials or contractions.
Describe what happens in phase 2 of MMC.
There are irregular spike potentials on the BER, which will lead to irregular contractions.
Describe what happens in phase 3 of MMC.
There are regular spike potentials on all BER peaks, so there is maximal contraction of musculature during this time.
What is the purpose of the MMC?
This is the activity of the GIT that is important for moving contents out. This is a housekeeping function. It is during this period that larger, nondigestible items (such as coins) will be removed that can’t pass through the pyloric sphincter on their own (such as fruit pit).
How does the MMC vary in terms of timing across the distal stomach and SI?
Like BER, it is staggered over time as you move down.
How does the MMC pattern compare in the interdigestive period vs when a meal has been ingested?
Before the meal comes, there will be regular cycling. The MMC pattern will be interrupted when there’s a meal in the stomach. When the meal has passed later, the MMC will begin again.
Where does MMC take place?
Distal stomach and small intestine
What initiates MMC?
We are not sure, but we think it might be gut peptides.
How does the MMC propagate between cells?
It propagates via the ENS with modulation via ANS and gut peptides
How is the MMC interrupted?
By the intake of a new meal
What is the difference between exocrine and endocrine secretion in the GIT?
Exocrine: goes into GIT, which is considered the external environment
Endocrine: goes into the bloostream, which is considered the internal environment.
Secretion requires what inputs (generally) to function:
It requires energy and blood flow.
What are the 3 main secretory enzymes present in the GIT? State their name and function.
Amylases: breakdown of starches
Proteases: breakdown of proteins
Lipases: breakdown of lipids
What is the main factor regulating secretion as you descend through the GIT?
The amount of neuronal vs hormonal secretion depends on the location in the GIT. Most nervous (ANS) activation occurs at the early part of the GIT. Hormonal effects are more important at the distal parts of the GIT.
In the mouth, what are the major salivary glands?
- Patotid
- Submandibular
- Sublingual
What is the main function of saliva in the mouth?
Secretion of salivary amylases, which beings the process of chemical breakdown of starches
What enzyme is secreted by the tongue?
Lingual lipase
Describe the composition of the secretions of the:
a) Parotid gland
b) Sublingual gland
c) Submandibular gland
a) Serous fluid (not much mucous)
b) Mucin-rich fluid
c) Mixed fluid
How much saliva do we produce per day?
0.5-1.5 L/day
What are the major ions present in saliva? What is the overall osmolarity of saliva?
Ions: Na+, K+, Cl-. HCO3-
Hypotonic
What is the typical pH of saliva?
Neutral: 6.5-7
What is the main amylase produced in the mouth? What is its function? Under what circumstances can it function?
The main amylase (thing to break down carbohydrates) is Ptyalin. Breaks them down from polysaccharides into disaccharides. It will only function at neutral pH, so it can’t function in places like the stomach.
How do parasympathetic and sympathetic inputs affect gland regulation?
Parasympathetic: leads to increase secretion and increased blood flow (since it is an energy-dependent process). Also causes vasodilation.
Sympathetic: is usually inhibitory and contributes to vasoconstriction.
Draw and describe the mechanism(s) determining the regulation of salivary secretion.
Stimulation can come from 2 places:
- Smells, sights, etc. sent to higher centers, which communicate with salivary center in medulla
- Stimulation of taste glands, sending afferents to salivary centers
The salivary center then sends efferents via the parasympathetic supply to the salivary glands
What are the phases of secretion?
- Cephalic: includes psychic and gustatory
- Gastric
- Intestinal
What is the typical pH of mixed gastric juice?
1-2
What is the major ionic composition of mixed gastric juice? What is its osmolarity?
Isotonic, mainly contains H+ as dominant ion
What are the 4 main components present in mixed gatric juice?
Pepsinogen, intrinsic factor, mucin, HCl
What type of cells/glands in the GIT are responsible for secretions?
Surface epithalial cells, tubular glands
What types of cells secrete alkaline, mucin-rich fluid?
Cardiac and pyloric tubular glands
What types of cells secrete acid, enzymes, and intrinsic factor?
Fundus and body tubular glands
The parietal cell secretes […]
HCl
Describe the structure of a parietal cell.
It is filled with mitochondria and has intracellular canaliculi through which secretions leave.
Chief cells release […]
pepsinogen
Describe the structure of chief cells.
Contain lots of mitochondria
Mucin cells produce […]
mucin
Describe the steps involved in the secretion of HCl by a parietal cell.
- Cl- enters the cell via active transport across the canalicular membrane.
- H+ gets pumped into the cannaliculi via H+/K+ ATPase and via passive dissociation of intracellular water.
- H+ secretion leads to an excess of OH- in the cell, increasing pH in the cell. This causes CO2 to diffuse in from the plasma and combine with water in the presence of carbonic anhydrate. This forms H2CO3.
- The H2CO3 will reaction with excess OH- to yield H2O and HCO3-.
- HCO3- diffuses into circulation, causing increased alkalinity in the venous blood
What is the postprandial alkaline tide?
It is caused by the addition of HCO3- into the capillary blood by carbonic anhydrase in parietal cells. It results in increased alkalinity in the venous blood.
Name 3 enzymes present in saliva. What is their function?
Mucin, lipase, lysozyme (breaks down bacterial cell walls)
