Overview of the GI Motility Flashcards
What are the layers of the intestines?
Mucosa (most internal), Muscular layer of submucosa with the Meissner plexus, Submucosa, Circular muscle layer with myenteric plexus, then longitudinal muscle layer, finally the most external layer is the serosa
Describe the splanchnic circulation
Blood from the gut, spleen and pancreas flows to the liver via the portal vein then blood filtered by the liver sinuses before leaving via hepatic vein into vena cava. This allows for removal of bacteria from entering the blood.
Describe the microvasculature of the Villus
Small arteriole and venule that interconnect with a system of multiple looping capillaries. The blood flow is directed to areas of local activity.
Increase in blood flow of the vilus can be caused by what?
- Vasodilator release from GI mucosa,
- Vasodilator release from GI glands,
- Decreased oxygen concentration in gut wall due to increased metabolism,
- Subsequent adenosine release
What is different about the structural layers of the oesophagus and distal rectum?
They lack the serosa and mesentery
What are the functions of the GI tract motility?
1) Propel ingested food along the entire length of GI,
2) Mixing and grinding of contents,
3) Aid absorption of nutrients and water,
4) Clear the stomach and intestines of luminal contents
Name and describe the two main types of GI tract motility
1) Fed state, this is peristalsis and mixing movements.
2) Interdigestive stage, also known as the migrating motor complexes, it is responsible for clearing the stomach and intestines of luminal contents
Describe the intrinsic and extrinsic controls of GIT motility
Extrinsic - Neural (PSNS which are branches of the vagus, pelvic and splanchnic nerves and SNS which originate from celiac, superior and inferior mesenteric and hypogastric plexuses) and hormonal.
Intrinsic - Myogenic, neural (ENS) and chemical
Where is the myenteric plexus and what are it’s functions?
It lies between circular and longitudinal smooth muscle layers and innervated both muscle layers. It is mainly concerned with motor control.
Describe where the submucosal plexus lies and their function
It lies between the circular smooth muscle and the mucosa. It innervates glandular epithelium, endocrine glands and blood vessels
Describe the process of smooth muscle contraction
It is initiated by calcium from the ECF or from the SR
- Calcium binds to calmodulin and froms a complex
- Ca-calmodulin-MLCK leads to the phorphorylation of MLC (requires 1 ATP)
- MLC is part of the myosin head
Phosphorylated mysosin head bins to actin and a power stroke occurs automatically
- A second ATP is required to release myosin head from actin
Describe features of the GI tract smooth muscle syncytium
The muscle fibres are connected by gap junctions and focal adhesions. The actin and myosin filaments are aligned diagonally and anchored at dense bodies. Contractile arrays anchored to sarcolemma by dense plaques
The intrinsic electrical activity is inititated by what?
Interstitial Cells of Cajal (ICC) which create continual slow, intrinsic electrical activity
What are the two types of electrical activity?
Slow waves (basal electrical rhythm - pacesetter potentials) and spike potentials
Describe features of slow waves?
They are slow undulating changes in resting membrane potential but they themselves do not cause muscle contraction. Instead they excite spike potentials.
