L4 - Gastric Reservoir

The relaxation of the gastric reservoir is mainly regulated by ________

reflexes

3 types of gastric relaxation

receptive, adaptive and feedback-relaxation

All 3 types of gastric relaxation involve sending signals to where

The vagus centre of the brain

What triggers receptive gastric relaxation

Mechanical stimuli in the pharynx

How does receptive gastric relaxation work

Triggered by mechanical stimuli in the pharynx (e.g., swallowing).

Signals are sent to the vagus centre in the brain.

This initiates vagal-mediated inhibition, leading to the relaxation of the gastric reservoir in preparation for incoming food.

What triggers adaptive gastric relaxation

Triggered by gastric distension (stretching) due to food intake.

How does adaptive gastric relaxation work

Triggered by gastric distension (stretching) due to food intake.

Tension receptors in the stomach detect distension and send signals to the vagus centre.

The vagus nerve activates inhibitory vagal fibres, which release non-adrenergic, non-cholinergic (NANC) neurotransmitters like NO (nitric oxide) and VIP (vasoactive intestinal peptide).

This leads to the relaxation of the proximal stomach, allowing it to accommodate more food.

What triggers feedback gastric relaxation

Triggered by nutrients in the small intestine.

How does feedback gastric relaxation work

Triggered by nutrients in the small intestine.

Signals are sent back to the stomach via neural and hormonal pathways.

This feedback mechanism helps modulate gastric emptying by further relaxing the stomach to prevent rapid entry of food into the small intestine.

It causes enhanced relaxation of the gastric reservoir, inhibition of the antral pump, and reduced opening of the pyloric sphincter

How do tension in the wall of the stomach, internal pressure of the stomach & the distending volume relate to each other

Tension developed circumferentially in the wall (T) is proportional to the internal pressure (P) multiplied by the square root of the distending volume (√V).

If either V or P increase, T also increases

What do some pufferfish have that can cause poisoning

TTX (tetrodotoxin)

What is this setup used for

An Intragastric Balloon (Ct P) is placed inside the stomach, usually in the proximal region. It expands in response to pressure changes, mimicking food intake. Measures stomach compliance (the ability to stretch and accommodate).

A strain gauge measures pressure changes within the balloon.

The pressure selector ensures controlled inflation and deflation of the balloon.

The 2 balloons setup (1 before & 1 after the sphincter) may be used to simulate conditions like delayed gastric emptying. By inflating the balloons near the pylorus, it can artificially create pyloric obstruction, allowing researchers to study gastric motility disorders and accommodation responses

Can sham feeding have an effect on gastric accommodation

Yes

(sham feeding = chewing food but not swallowing)

What could each of these columns of increasing gastric accommodation reflex represent

Name of sphincter at entrance to stomach

Lower oesophageal sphincter

Name of sphincter at exit from stomach

Pyloric

True/False: Each wave cycle of the stomach results in only a small amount of material into the duodenum

True

How can gastric emptying affect insulin secretion

Faster emptying leads to faster glucose absorption, triggering higher insulin release to manage blood sugar levels

Why is gastric motility important in clinical settings

Plays a crucial role in glucose metabolism, diabetes management & drug absorption

is faster/slower gastric emptying beneficial for T2Ds

Faster gastric emptying is often seen in early Type 2 diabetes and contributes to postprandial hyperglycaemia.

Medications are used to slow gastric emptying to reduce glucose spikes.

3 anatomical regions of the stomach

2 functional regions of the stomach

Difference in contractions between the 2 different functional regions of the stomach

Tonic contractions: Sustained contractions that last for minutes to hours that maintain compartmentalization and regulate movement between sections.

Phasic contractions: Rhythmic, short-duration contractions that mix and propel contents through the GI tract

The transport of digesta from the gastric reservoir into the antral pump is caused by two mechanisms, what are they

tonic contractions and peristaltic waves in the region of the gastric corpus

Who’s formula is this & what does it tell us

Poiseuille’s equation

it helps explain how fluids (such as gastric contents, bile, pancreatic secretions, and blood in the GI vasculature) move through tubular structures like the esophagus, intestines, and blood vessels.

What does each value in Poiseuille’s equation mean

Replace blood with chyme

Blood flow → Flow rate of chyme through the pylorus

ΔP = Pressure gradient between the antrum and duodenum

r = Radius of the pyloric sphincter (to the 4th power effect!)

η = Viscosity of chyme

L (λ) = Length of the pyloric sphincter

The function of the gastric pump can be differentiated into three phases ………

A: phase of propulsion,

B: phase of emptying,

C: phase of retropulsion and grinding

How do each of the 3 phases of gastric pump work

In the propulsion phase the duodenum contracts to temporarily resist the incoming chyme from the stomach and to regulate how much is accepted.

How does the sieving function of the stomach work

Liquids and small particles leave the stomach more rapidly than large particles.

This discrimination is called “sieving function“

What materials are moved in each of the phases of the gastric pump

“sieving effect”

Grinding of solid particles is caused by what

forceful jet-like retropulsion through the small orifice of the terminal antral contraction

How do contractions of the proximal duodenum & gastric emptying coordinate

Antro-duodenal co-ordination: Contractions of the proximal duodenum cease during the phases of gastric emptying.

How can the duodenum contract three to four times during an antral wave

Because of different frequencies between antral and duodenal contractions, the duodenum can contract three to four times during an antral wave

Regulation of gastric emptying depends on what

Balance between gastric reservoir and antral pump

Pyloric activity is modulated by what reflexes

antral inhibitory and duodenal excitatory reflexes

What causes rapid gastric & duodenal emptying

Rapid emptying is caused by tonic contractions of the reservoir (1a), deep peristaltic waves along the gastric body (1b), deep constrictions of the antral waves (2), a wide opening of the pylorus (3), a duodenal receptive relaxation (4) and peristaltic duodenal contractions (5).

What causes delayed gastric & duodenal emptying

Delayed emptying due to feedback inhibition is caused by a prolonged relaxation of the reservoir (6a), shallow peristaltic waves along the gastric body ( 6b), shallow antral waves (7), a small pyloric opening (8), a lacking duodenal relaxation (9) and segmenting duodenal contractions (10).

How do liquids empty from the stomach

Liquids empty exponentially, meaning a large volume empties early, then slows over time.

Liquids empty exponentially because they do not require grinding and pass through the pylorus based on a pressure gradient between the stomach and duodenum.

Do solids empty from the stomach at the same rate as liquids

No, solids have a lag phase before emptying begins

What happens during the lag phase of solid emptying from the stomach

The antrum grinds food into small particles (~1-2 mm) before they can pass through the pylorus

How does gastric emptying of solids occur after the lag phase

Once the solid is sufficiently broken down, the viscous chyme empties in a linear fashion (a fixed amount per unit time

Difference in force of antral contractions with a non-caloric meal & a nutrient meal

A nutrient meal reduces the force of antral contractions.

(Prevents overloading the duodenum with too much nutrient-rich chyme at once)

How does pyloric opening change after a nutrient meal compared to a non-caloric meal

A nutrient meal reduces pyloric opening

How does peristalsis in the duodenal bulb change after a nutrient meal compared to a non-caloric meal

A nutrient meal reduces peristaltic waves in the duodenal bulb.

How does segmental activity in the middle duodenum change after a nutrient meal compared to a non-caloric meal

A nutrient meal enhances segmenting activity in the middle duodenum.

What does this image represent

gastric emptying scintigraphy images at different time points (0 to 240 minutes), tracking the movement of a radiolabeled meal through the stomach.

What does this graph depict

The graph shows the percentage of gastric retention over time, demonstrating the rate of gastric emptying.

What condition is commonly diagnosed by scintigraphy images and tracking gastric retention

Gastroparesis, a condition where the stomach empties slower than normal without an obstruction.

What is the clinical significance of having more than 10% gastric retention at 240 minutes?

It suggests delayed gastric emptying, which is a diagnostic criterion for gastroparesis.

what is a ¹³CO₂ breath test used for

A non-invasive diagnostic test used to assess various metabolic and gastrointestinal conditions. It works by measuring the amount of ¹³C-labeled carbon dioxide in a person’s breath after they ingest a substrate (a substance labeled with the stable carbon-13 isotope). The breakdown and absorption of this substrate release ¹³CO₂, which is then exhaled and measured.

Used to detect Helicobacter pylori, a bacterium associated with ulcers and gastritis. The patient ingests ¹³C-urea, and if H. pylori is present, it breaks down the urea, releasing ¹³CO₂ in the breath.

Assesses how quickly the stomach empties by tracking the breakdown of ¹³C-labeled octanoic acid or ¹³C-labeled spirulina.

Interpret this graph

This graph represents the results of a ¹³C-CO₂ breath test over time, measuring the ¹³C atom fraction (×10³) in exhaled breath after a labeled meal.

The Y axis represents the concentration of ¹³C-labeled CO₂ in the breath, indicating how much of the ingested ¹³C-labeled substrate has been metabolized and exhaled.

1. Different Test Conditions (HF, LFE, LFW)

   • HF (High-Fat, black circles)

     • Shows a slower rise but maintains a higher peak for a longer duration.

   • LFE (Low-Fat, Energy-Matched, gray circles)

     • Peaks faster than HF but declines slightly quicker.

   • LFW (Low-Fat, Weight-Matched, open circles)

     • Has the fastest rise to peak and also declines the quickest.

Before the meal (baseline), all three groups have similar low ¹³C levels.

After eating the labeled meal, the ¹³C fraction rapidly increases, reaching a peak around 60-90 minutes post-meal.

The different meal compositions affect the rate of metabolism and CO₂ excretion, with low-fat meals (LFE, LFW) being metabolized faster than high-fat meals (HF).

HF has a delayed response but sustains higher levels longer, suggesting slower digestion and metabolism of the labeled substrate.

Name all the sphincters of the GI tract

What prevents duodeno-gastric reflux

pyloric sphincter

Effect of duodenal stimuli like oleic acid on antral contractions, duodenal contractions, pyloric tone & pyloric contractions

inhibit antral contractions

evoke duodenal contractions

increase pyloric tone

elicit frequent pyloric contractions

Gastric motility is mostly

Peristaltic waves

glucose disposal rate (how quickly glucose is cleared from the blood) is influenced by two main factors - what are they

65% is due to insulin muscle mass

35% is due to gastric emptying

Why do we regulate gastric emptying

to prevent infection, for absorption & digestion