GIT Physiology (GIT) Flashcards
What are the two types of digestion?
Mechanical - peristaltic movements create chyme.
Chemical - enzymes (secreted, brush border, cytosolic)
What organ secretes the digestive enzymes responsible for breaking down carbs, proteins and fats?
The pancreas.
Give examples of enzyme types that break down carbs, proteins, lipids and nucleic acids.
Carbs - carbohydrases such as pancreatic amylase
Proteins - Proteases e.g. pancreatic protease
Lipids - Lipases e.g. pancreatic lipase or emulsification by bile salts
Nucleic acids - ribonuclease in pancreatic juice
What form of carbohydrates is absorbable?
Complex carbohydrates must be broken down into monosaccharides in order to be absorbed.
What are the three aspects of GIT motility?
- Interdigestive clearing (clears gut after eating)
- Squishing (rhytmic contraction to break up food)
- Peristalsis (propulsion of food)
What controls GIT motility?
The ANS, hormones and the basal electric rhythm
Describe the process of interdigestive clearing.
When the stomach is empty, the basal electric rhythm predominates.
There are two types of waves: slow waves and spikes. Slow waves don’t create APs, but spikes cause AP to be generated, creating migrating motor complex (MMC).
These contractions pass through the entire GIT, lasting about 2 hours for each wave.
When does interdigestive clearing stop and start?
Stop when feeding begins and starts up again automatically.
What initiates the grinding/squishing of the stomach, and what does it do?
Stretch receptors (when food enters) trigger rhythmic circular muscle contraction and relaxation.
Describe the nervous control over squishing/grinding of the stomach.
Initiation is local - from stretch receptors in stomach.
However, frequency of digestion can be increased (PNS) or decreased (SNS) by the autonomic nervous system.
What triggers peristalsis?
When food has been squished up enough, peristalsis begins (changes in stretch receptor activation).
It also involves circular muscle contraction/relaxation to move the food down.
Describe autonomic nervous system control over peristalsis.
Like the squishing, frequency of peristalsis can be increase (PNS) and decreased (SNS) by the autonomic nervous system.
Describe the speed of motility of the colon and why it is like this.
Motility in the colon is very slow to allow sodium to be absorbed (water absorption)
What pressures cause the ileocaecal valve to either open or shut.
Increased ileum pressure causes the ileocaecal valve to open, allowing stuff to enter the colon.
Increased colonic pressure keeps the valve closed to prevent backflow.
Describe neural control of sphincters.
Sphincters are controlled by acetycholine.
Usually, acetylcholine causes smooth muscle and gut tube contraction.
Instead, we use indirect mechanism: acetylcholine acts on interneurons, which release NO/VIP to relax the sphincter.
