GI 6

Question 1

Where does the MMC do its thing

Answer 1

Migrating motor complex, does its thing in the distal stomach and small intestine, up to the distal ileum
Does it during the interdigestive period, no food, fasting
It’s an intense pattern of cyclic motor activity, recurring at regular intervals of 90 minutes

Question 2

Intervals of MMC

Answer 2

Migrating motor complex
90 minute cycles of activity during the interdigestive period
The 90 minute cycle has 3 phases of activity
In phase 1 theres no spike potentials and therefore no contractions, lasts 60 mins
In phase 2 there’s irregular spike potentials and contractions (because contractions can only happen with spikes), 20 mins
In phase 3 we get regular spike potentials and contractions, lasts 10 mins, regular as in on basically all the BER given opportunities

Question 3

What makes the MMC migrating

Answer 3

Migrating in that it has to make its was down the stomach and SI, all phases arent active at once its a staggered process, so one “band” starts its phase 1 and then the next band and it staggers down til the end like this, and the important part, the 10 mins of strong contractions, they will also occur in this staggered way

Question 4

Why do we have an MMC as opposed to just waiting from fresh food to come in to then further push stuff out

Answer 4

Housekeeping function: many glandular structures keep secreting stuff into the stomach and SI and it accumulates, even if theres no food, same with the dead cells, theres a lot of cell turnover in the GIT
It’s also required to empty out large nondigestible particles, like a kid that eats a coin or smtg
The MMC produces enough force to propel any nondigestible content through the tiny pyloric sphincter

Question 5

What initiates the MMC

Answer 5

Gut peptide named motilin, dont have to know name
Important to know its not initiated by CNS or ANS, theyre obviously involved but not initiators
ENS must be intact to activate the pattern-generated circuitry

Question 6

What allows propagation in MMC process

Answer 6

ENS with modulation from ANS and gut peptides controls the propagation

Question 7

What can stop the MMC process

Answer 7

The ingestion of a meal, since it only happens in interdigestive periods

Question 8

Definition of digestion

Answer 8

The chemical breakdown of food into its building blocks, so by this definition digestion only includes the exocrine secretions, not endocrine, even thought they do have an effect on and interact with the GIT

Question 9

Exocrine secretions for digestion

Answer 9

Secretion in general is an active, energy dependent and blood flow dependent process, results in the release of fluids containing ions and enzymes
3 main types of enzymes in exocrine secretion: amylases (carbs), proteases (proteins) and lipases (fats)

Question 10

What regulates secretion of digestive enzymes at the level of the mouth

Answer 10

Nervous system, ANS

Question 11

What regulates secretion of digestive enzymes at the level of the esophagus

Answer 11

Nervous system ANS

Question 12

What regulates secretion of digestive enzymes at the level of the stomach

Answer 12

Both the nervous system (ANS) and hormonal control (gut peptides), leaning more to nervous

Question 13

What regulates secretion of digestive enzymes at the level of the SI

Answer 13

Both nervous (ANS) and hormonal control (gut peptides), leaning more to the hormonal

Question 14

What regulates secretion of digestive enzymes at the level of the LI

Answer 14

Both nervous and hormonal control but majority is hormonal

Question 15

What secretions occur at the level of the mouth

Answer 15

Saliva produced by the salivary glands, the parotid, sublingual and submandibular glands, secrete mucin for protection and lubrication and the saliva contains amylase to begin carb digestion
Salivary amylase for carb digestion in the mouth
Lingual lipase for lipid digestion in stomach

Question 16

Why does lipase start lipid breakdown in the stomach if it meets bolus in the mouth

Answer 16

Lipase requires an acidic environment to be active, which it only gets when it reaches the stomach as the mouth is neutral

Question 17

Saliva specs

Answer 17

0.5-1.5 L per day, a bicarbonate rich solution that is hypotonic (only fluid in the tract)
PH of 6.5-7
Contains amylase (active) and lipase (inactive), also has lysozymes for breaking down bacterial cell walls

Question 18

Amylase

Answer 18

Produced in salivary gland, mainly parotid, breaks down carbs at a neutral pH
Specifically from starch to maltose (disaccharide)

Question 19

Gland regulation by the parasympathetic NS

Answer 19

ANS wants more secretion, activates parasympathetic channels, acts on secretory cell by releasing ACh onto muscarinic receptors which increases secretion and also vasodilation
Makes sense since if you want cells to do more work you need to get them more nutrients

Question 20

Gland regulation by the sympathetic NS

Answer 20

ANS activates the sympathetic branch, net result is vasoconstriction and a decrease in secretion

Question 21

Regulation of salivary secretion

Answer 21

Sensory receptors get activated, afferent pathway to the salivary centre in medulla, efferent response by parasympathetic pathway leads to salivation
Note that the sensory receptors can be activated by anything in the mouth and even by other things like sight or smell
Anything from sight or nose or other goes to higher centre first and then to salivary centre, this is the cephalic phase

Question 22

Cephalic phase

Answer 22

When a stimulus other than sensory in the mouth triggers salivation, has to go through the higher areas of the brain before getting to the salivary centre of the medulla, thats the cephalic phase

Question 23

Stomach secretions

Answer 23

1.5-2L per day, isotonic acidic mixed gastric juice, pH 1-2
Main characters: HCl, pepsinogen, intrinsic factor and mucin
Surface epithelium secretes a mucous alkaline fluid, mainly into tubular glands, like invaginations into the stomach

Question 24

Cardia and pylorus secretions

Answer 24

In stomach, have tubular glands lines with surface epithelial cells the secrete an alkaline, mucin-rich fluid

Question 25

Fundus and body secretions

Answer 25

Also have tubular glands but they secrete acid, enzymes and intrinsic factor

Question 26

Parietal cell

Answer 26

In stomach, responsible for producing intrinsic factor and HCl to make stomach acidic, what it itself produces has a pH of 0.8, when mixed with the rest reaches 1-2 Cell with some invagination on tubular/apical side used to maximize surface area and HCl secretion, also very mitochondria rich due to high energy demand Note invaginations are called canaliculi

Question 27

Chief cell

Answer 27

Also in stomach, makes pepsinogen, which is required for protein breakdown

Question 28

Mucous neck cells

Answer 28

In stomach, cells that are specialized to produce mucous

Question 29

Why do parietal cells have so many mitochondria

Answer 29

Lots of mitochondria because high energy demand because the H ion concentration that these cells are putting out is really high but that of the blood isnt, so it takes a lot of energy to have to pump them in against their gradient constantly, energetically expensive Note: for every H pumped into parietal cells a HCO3- is pumped out, done according to carbonic anhydrase buffer, co2 and water goes in, catalyzed, H stays and HCO3- goes

Question 30

How do H ions get from the parietal cells to the stomach lumen

Answer 30

Once the H ions are produced in the cell using carbonic anhydrase and nutrients from blood, the H/K ATPase pump pushes it out Note: H is pumped out against its gradient, K is brought in also against its gradient, and on the basolateral side of the cell theres an Na/K pump keeping intracellular K high, bringing in 2 K for every 3 Na it pushes out to blood

Question 31

Postprandial alkaline tide

Answer 31

Basically the effect of having basic urine post meal because you’ve pumped so much H into stomach for digestion that your bicarbonate levels are also higher

Question 32

What does HCl do in the stomach

Answer 32

It precipitates soluble proteins, makes them fall out of solution so they can stay longer in the stomach for processing Denatures proteins, making them easier to digest Activates pepsin and provides an optimal pH for it to act in, activates it by converting pepsinogen from chief cells to pepsin

Question 33

Intrinsic factor

Answer 33

Produced by parietal cells, required for the absorption of vitamin B12, basically it needs to be there otherwise B12 never makes it to the small intestine (distal ileum) to be absorbed and we end up with pernicious anemia It’s a glycoprotein and essential for life, RBCs will be too big, not normal