Week 1: esophagus and stomach Flashcards
What is the slow wave? What cells are involved?
It is a periodic change in the membrane potential of enteric SMC. Interstitial cells of Cajal (ICC) are pacemaker cells. They are connected to SMCs via gap junctions and the membrane potential changes in a slow wave pattern. The periodicity changes depending on where in the bowel you are and can be modulated by enteric motor neurons.
What types of neurons are part of the ENS?
Sensory neurons: detect changes in the lumen Motor neurons Interneurons
How does the signal to contract get from the ENS to the enteric SMCs?
There are swellings/varicosities along the length of the nerve that communicate with ICCs and also SMCs directly (the nerve releases neurotransmitter ‘en passage’)
What is the significance of mechanical and electrical thresholds in enteric SMCs?
When the slow wave reaches the mechanical potential a single muscle contraction occurs. When the membrane potential is depolarized even further, reaching the electrical potential, there is a series rapid membrane potential spikes that produces a stronger contraction.
What are some excitatory and inhibitory neurotransmitters in the ENS?
Excitatory: ACh, 5-HT
Inhibitory: VIP, NO, Purines
What is the function of the myenteric and submucosal plexuses?
Myenteric: motility
Submucosal: secretions and blood flow to the mucosa
What is co-localization?
occurs in enteric neurons- they can produce more than one neurotransmitter
What are the 4 extrinsic modifiers of ENS activity?
1) ANS (both SNS and PNS)
2) CNS
3) Immune
4) Endocrine
What is the peristaltic reflex? How is motility maintained in the interdigestive period so bacteria don’t overgrow?
- Distention by a food bolus is sensed and causes a reflexive (i.e. does not include CNS) relaxtion of aboral muscle (VIP, NO) and contraction of oral muscle (Ach, substance P)
- Motilin is released by enteroendocrine every 90 minutes or so, which produces a wave of peristalsis.
What is primary peristalsis in the esophagus and how is it initiated? What is secondary peristalsis in the esophagus and how is it initiated?
Primary peristalsis is initiated by the concious act of swallowing food. The remainder of the wave is mediated by the vagus.
Secondary peristalsis is initiated by esophageal distension or acid in the esophagus
What are the major components of gastric juice?
Water
Organic compounds (pepsinogen, intrinsic factor, gastric lipase, mucus)
Ions
What are the two major gland types in the stomach, where are they located and how do they differ in function?
- Gastric (oxyntic) glands are located in the body (corpus) and contain parietal (acid, IF) and chief (pepsin, lipase) cells, ECL cells (histamine), D cells (somatostatin),
- Pyloric glands are located in the pylorus and have ECL, D and G cells (gastrin)
The acid in the stomach facilitates absorption of what nutrients?
Protein (denaturation)
Iron, calcium, B12 (colbalamin)
What protects the stomach ?
The mucus layer and the bicarbonate secreted by epithelial cells
What are G-cells and ECL cells what do they secrete?
G-cells secrete gastrin in response to GRP released from vagus nerve(?) or the presence of peptides
Enterochromaffin-like cells release…..
What are the 3 secretagogues for parietal and chief cells, where do they come from and what receptors do they bind?
- Gastrin comes from G cells in the antrum and binds to CCK-2 receptors
- Histamine comes from ECL cells (paracrine) binds to H2 receptors
- Ach comes from vagal efferents binds to M3 receptors
**both acid and pepsin secretion are turned on**
