GI 5

Question 1

What effect does cutting the vagal nerve to the distal stomach have on antral peristalsis

Answer 1

It’ll decrease antral peristalsis, make it sluggish as opposed to a controlled contraction because while there is ENS circuits and control, the vagal vagal reflex also plays a big part and not have that input leads to a much weaker antral peristalsis

Question 2

What’s the enterogastric reflex

Answer 2

It’s the duodenal factors (either hormonal or neural) acting on the stomach to decrease gastric emptying/antral peristalsis

Question 3

What causes vomiting

Answer 3

An increase in intra-abdominal pressure that surpasses that of the sphincter, simple pressure gradient, pressure will push it up and out
The pressure is increased by the contraction of abdominal muscles as well lowering the diaphragm, this reduces the space (volume) which increases pressure
Basically GIT is not crazy involved, like its not reverse peristalsis, GIT is not causing it, its really about the pressure
Note that those contractions also minorly elevate the LES such that its not as in the abdominal cavity as it usually is, making it easier to overcome

Question 4

In vomiting, describe the state of the different parts of GIT

Answer 4

The proximal stomach and esophagus relax
The upper duodenum and distal stomach will be in systole, so contracted, this is important to make sure the pressure pushes it out the mouth and not into GIT

Question 5

What controls the vomiting reflex

Answer 5

Controlled by the vomiting centre in the midbrain, so brainstem

Question 6

What can trigger the vomiting reflex

Answer 6

Pharyngeal stimulation (gag reflex)
GIT or urogénital distension
Pain
Biochemical disequilibrium
Vestibular signals
Psychogenic factors

Question 7

What efférents does the vomiting center activate just as its being triggered

Answer 7

Widespread autonomic discharge: meaning it activates both para and sympathetic NS, so your heart is fast and slow, sweats yet chills, etc
Nausea
Retching
Emesis

Question 8

What is emesis

Answer 8

It’s the actual things that lead to vomiting, so the relaxation of the upper GIT (so proximal stomach up) and the spasm/closure of the pyloric sphincter/duodenum as well as the contraction of the lower abdominals for increasing the pressure

Question 9

CTZ

Answer 9

Chemoreceptor trigger zone, located in teh medulla but is outside the blood brain barrier, it responds to triggers circulating in the body such as toxins from food poisoning, maybe therapeutic drugs (like chemotherapy), etc
So the chemoreceptors pick it up and if its suspicious then it triggers the vomiting center

Question 10

What are the stages of vomiting

Answer 10

Nausea: a psychic experience in that we dont know what causes it, likely of psychological basis
Retching: abrupt and uncoordinated respiratory movements with the glottis closed, so its like those small gags that nothing comes out, the glottis closes protectively
Emesis: the actual vomiting, expulsion of contents via the GIT, deep breath, glottis closes, abdominals contract, pressure pushes it out, once the muscles relax and pressure return to normal, you’re done

Question 11

Regions of the SI

Answer 11

Duodenum, jejunum and ileum

Question 12

What are the functions of the upper SI

Answer 12

Neutralization of the chyme, its very acidic and could be harmful to digestive tract, stomach is protected but SI is not
Osmotic équilibration: chyme is rich in nutrients and poor in liquid since that usually flows out before, so its initially hypertonic when it enters duodenum, but it’ll be iso-tonic when it leaves duodenum
Digestion
Absorption

Question 13

Intestinal contractions

Answer 13

They’re governed by the electrical characteristic of the smooth muscle, like in stomach with BER
So the frequency is set by BER but you still need spikes in order to pass threshold and get contraction, and as always contraction strength is proportional to # of spikes

Question 14

BER of stomach vs BER of SI

Answer 14

Frequency in stomach is 3/min, in SI it decreases as it gets farther down the tract, in duodenum as often as 12x/min but towards the ileum as little as 8x/min
Both have ICC, interstitial cells of cajal

Question 15

Proximal vs distal BER rhythms in SI

Answer 15

Frequency is greater, helps that the smooth muscle there is more excitable (less Ach has the same ability to initiate contraction), the thickness of the smooth muscle is also thicker, also leading to stronger contractility
So both frequency and amplitude are higher in the proximal SI

Question 16

Segmentation in the SI (how)

Answer 16

There’s the myogenic response to distension, so stretching of the duodenum triggers the circular muscle)
The ENS coordinates and organized a contraction
ANS and hormones can also modulate it (para will increase it, sym will decrease)

Question 17

What’s the purpose of segmentation in SI

Answer 17

Mixing of contents ofc but also slow propulsion, slow because we want to maximize nutrient absorption

Question 18

If we have contraction all throughout SI, how do we ensure it goes aborally and not back up

Answer 18

We have more frequent and stronger contractions in the proximal GI and the opposite for distal GI so the net result is a stronger and more frequent force in the aboral direction, even if theres one step backwards theres still 3 forward
This actually helps with the whole slow thing it has going on

Question 19

Peristalsis in SI

Answer 19

Does not happen often, and if it does its infrequent, weak, and over a short distance, maybe a few centimeters
Likely in pathological condition like diarrhea

Question 20

What do we need for intestinal peristalsis, on the rare occasion it does happen

Answer 20

It’s mediated by a series of local reflexes, so ENS must be intact, it involves both the longitudinal and circular muscles of the tract and it can be modulated by the ANS as well as hormones

Question 21

What’s the law of the intestine

Answer 21

Concept of radial stretch, that when you eat the lumen expands in all directions, this distension triggers sensory receptors that act locally but also through ENS such that, up ahead, where the bolus is going, the longitudinal muscle contracts and the circular muscle relaxes. It also triggers a response behind the bolus, where the circular muscle contracts and the longitudinal muscle relaxes, so the opposite
Contraction of longitudinal muscle shortens the tube, and relaxing the circular muscle decreases resistance
This ensures that the pressure behind the bolus is stronger than the front such that we get aboral flow

Question 22

Ileum colon junction

Answer 22

Ileocecal valve/sphincter, end of SI and start of LI
Separates the ileum and the cecum (associated with appendix), the first part of the LI

Question 23

Anatomy of the LI

Answer 23

ileum finishes off the SI, ileocecal valve, cecum, ascending colon, transverse colon, descending colon, sigmoid colon, rectum
Note that the appendix is associated with the cecum

Question 24

SI vs LI absorption

Answer 24

SI mainly absorbs all the nutrients so LI is left with water and ions, minerals and stuff

Question 25

Main functions of the colon

Answer 25

Absorption of water and ions Propulsion of bolus down the tract, very slowly, like 50-60 hours Storage, since its holding this stuff for a few days

Question 26

How does eating a new meal affect whats already in process in LI

Answer 26

We get stretch at the stomach, this induces the gastroileal reflex, just like it sounds, in response to stomach receiving food it speeds up and stimulates motor activity in SI/ileum to get food down to the LI faster Were stimulating the ileum so more ileum activity gives the ileocolic reflex, basically ileum action increase sigmoid colon action so it empties more into rectum, minor reflex Also starting in response to the stomach receiving a meal is the gastrocolic reflex, leads to increased activity in the sigmoid colon, promoting the moving of stuff to the rectum, enough stretch from rectum content can lead to defecation, but not always

Question 27

Interdigestive period

Answer 27

Period during which we are not eating, do not have a meal incoming, but we still need to digest without that external push We’re still going to have motility of GIT if theres nothing in tract, it’ll move out digestive juices, dead cells, etc During this period we get intense pattern of myoelectric activity

Question 28

Motor activity during the interdigestive period

Answer 28

Recurs at regular intervals, moves sequentially over distal stomach and SI up to the distal ileum Rate is like 2-10cm /min