Transport ALONG the GIT Flashcards
What occurs to accommodate more food in the stomach?
- ↓Cholinergic activity and VIP and NO release = Relaxation
What occurs once food is in the stomach?
What is Gastric Motility?
What is a disorder that can occur in gastric motility?
LOOK AT DIAGRAM!
- A pattern is set up to determine the rate of contractions in the stomach. The pacemaker cells in the fundus allow for contractions to begin there, moving inferiorly. Tonic contractions and Peristalsis cause food to move along to the antrum.
- Where gastric acid is moved to empty into the duodenum. The fundus relaxes to store more food while it’s acted on by the acid, enzymes, and muscle movements. Emptying is regulated to ensure suitable amounts of chyme enter the duodenum -prevent ulcerations as it can be too acidic.
- Gastric stasis - delayed gastric emptying, which can lead to weight loss and bloating.
Explain the Gastro-gastric reflex
LOOK AT DIAGRAM!
It balances the gastric reservoir and antral pump.
Distension of fundus stimulates the excitatory reflex = Antral Contractions. Contractions of antrum with food in it stimulates the inhibitory reflex = Fundus Relaxation.
This is a Negative feedback system where the antrum and duodenum are distended.
What does gastric emptying depend on?
What would happen if the chyme in the duodenum is very fatty, hypertonic and acidic?
- • The propulsive force generated by the tonic contraction of the fundus.
• The stomach’s ability to differentiate types of food taken in e.g. consistency. - The force and rate of gastric emptying will decrease to give the duodenum time to digest and neutralise it.
How are liquids, solids, fatty foods, and indigestible solids emptied from the stomach?
Liquids:
• Empty quickly
• Rate of emptying affected by its nutrient content
Solids:
• Slower emptying
• Rate of emptying depends on the size of the particles
• Most solids are retained in the fundus and time is taken to breakdown the larger particles
Fatty foods:
• Empty slowly
• They float on top of the liquid layer
Indigestible solids:
• Emptied much later via MMC activity
What is the rate of gastric motility determined by?
- Type of food eaten - Carbs > Protein > Fatty foods > Indigestible solids
- Osmotic pressure of duodenal contents - Hyper-osmolar chyme = ↓Gastric emptying
- Vagal innervation from over-distension = ↓Gastric motility e.g. duodenal distension decreases gastric motility to prevent too much chyme being pushed out
- Hormones e.g. Somatostatin, Secretin, CCK, inhibit gastric emptying
- Injury to intestinal wall and bacterial infections = ↓Gastric motility
What does the stomach having myogenic control mean?
Explain the myogenic control of the stomach
- Stomach can generate its own electrical activity
- Done through the presence of the Pacemaker cells/Interstitial cells of Cajal (ICC), which gives off slow waves, called the BER.
The Intrinsic Basic Electric Rhythm (BER) determines the frequency of waves of contractions. Stomach muscle cells produce depolarisation, causing ripples of contraction moving towards the antrum.
The fundus is under vagal excitatory control.
How is movement through the small intestine controlled?
What are the hormones used in the small intestine?
- Hormones and nervous factors initiate and maintain peristalsis and mixing.
- CCK and Gastrin - stimulate/inhibit/promote bowel contractions and motility
What are the types of motility that occurs in the intestines?
What occurs in Segmentation?
- Segmentation (churned in stationary segments), Peristalsis, Migrating Motor Complex (MMC), and mass movement
- It starts in the ICC and divides the chyme to bring it into contact with the intestinal walls. It also moves the chyme to the ileum.
Rate of contractions are higher in the duodenum and jejunum, than the ileum.
What occurs in Peristalsis?
LOOK AT PICTURE!
The inner CIRCULAR muscles contract while the outer LONGITUDINAL muscles relax. They then switch to allow movement of the bolus along.
What is the Migrating Motor Complex (MMC)?
What is its function?
- Highly organised motor activity and is a recurring sequence of events, occurring when the stomach/intestines are EMPTY. It’s a burst of strong, high frequency contractions along the length of the intestines.
- Moves indigestible residues out of the stomach, removes dead epithelial cells, prevents bacteria overgrowth, and prevents colic bacteria from entering small bowels.
What is the colon’s role?
Describe the motility of the colon
- Absorption of water/ions, bacterial fermentation, storage of waste and indigestible material, and excretion of waste.
- Segmental/Haustral contractions mix contents. Peristalsis is much slower as it moves contents towards the anus. Distention initiates the contractions.
Mass movement also occurs through powerful contractions from the mid-transverse colon to push the contents into the rectum - for excretion.
What can occur with disorders in motility, fluid secretion and reabsorption?
What causes diarrhoea and constipation?
- Diarrhoea, Constipation
- With diarrhoea, there’s more frequent discharge of liquid faeces. In constipation, there’s difficulty in the emptying/opening of the bowels due to the faeces being stiffer than normal.
