Lecture 8 - esophagus Flashcards
What is the swallowing reflex coordinated by?
By the medulla oblongata
What does the medulla oblongata do in regards to the swallowing reflex?
It stimulates the correct sequence of contraction and releaxation in the participating skeletal muscle, sphincters and smooth muscle groups.
The coordinated sequence of contraction and relaxation is necessary in the upper esophageal sphincter, esophagus, and lower esophageal sphincter to ……. to the stomach
deliver food
What is the upper third and lower 2/3 of the esophagus made of?
upper 1/3 of esophagus including the pharynx and UES - striated muscle
lower 2/3 including the LES - smooth muscle
What happens to pressure while swallowing at the UES?
Drop in pressure due to relaxation
What happens to pressure after the drop in pressure at the UES?
Sudden rise in pressure because of contraction and then it goes back to normal while it is at rest (50mmhg)
What happens to pressure at the LES?
The pressure remains stable until there is a drop in pressure due to relaxation of the sphincter to allow for acid reflux.
How many mechanisms mediate peristalsis?
3 main mechanisms:
- ) Enteric nueral circuitry relevant to peristaltic reflex
- ) Central control of peristalsis in the smooth muscle portion of the esophagus
- ) Electrical stimulation of intrinsic nerves in circular smooth muscle strips.
What is the Enteric nueral circuitry relevant to peristaltic reflex?
Essentially what happens is two different cycles:
- ) Sense stretch stimuli
- ) sensory neuron
Either goes to ascending interneuron or descending interneuron
Ascending - motor neuron - secrete ACh to smooth muscle cells - cause smooth muscle cell to contract
Descending - motor neruon - secrete NO to smooth muscle - relaxes the smooth muscle
Overall - The cycle is repeated to get food down.
What is central control of peristalsis in the smooth muscle portion of the esophagus?
ACh causes contraction
NO causes relaxation
Neurons in the brain stem release these signals to the LES and EOS and the same time but they do not contract and relax at the same time. It is delayed in the LES.
What is electrical stimulation of intrinsic nerves in circular smooth muscle strips?
Smooth muscle are all stimulated at the same time but contraction time is faster at the top because of distance.
Why does the LES stay relaxed during swallowing and what are its implications?
It stays open to allow for gastric reflux.
Implication - it isn’t good to have it open for a long time because this may cause an accumulation of acid reflux which will make the mucosa of the LES like the mucosa of the stomach which is linked with esophageal cancer.
What happens if you have neuronal nitric oxide synthase deficiency?
Won’t be able to relax the LES.
Why are there wiggly lines at the physiologic recording of a spontaneous transient relaxation of the LES?
Because of breathing the pressure rises when we inhale. Naturally, the acid reflux would go up since pressure increased. But because there is a branch of the phrenic nerve that goes over the LES, everytime the diaphragm is stimulated, the LES is also contracting to prevent acid reflux.
