Physiology Week 1 Flashcards
What are the three parts of the pharynx?
nasopharynx, oropharynx, and laryngopharynx
Describe how the nasopharynx blocks passage of food into the lungs
At the base of the nasopharynx there is a soft palate and penduluous uvula that block passage of food into the lungs
Describe how the oropharynx prevents large particles from entering the lung
The mucous layer of the oropharynx traps any large particles in the air that we breathe - instead of entering the lung, pass with the mucous into the stomach
What is the pharynx?
Wiki says: The pharynx (plural: pharynges) is the part of the throat that is behind the mouth and nasal cavity and above the esophagus and the larynx, or the tubes going down to the stomach and the lungs.
The laryngopharynx is a common pathway that allows both air as well as food to pass through the lungs and stomach. What happens when the air goes to the stomach? What about when food goes to the lungs?
air in stomach - burp
food in lungs - cough
Describe swallowing AKA deglutination
1) In buccal phase, the tongue presses against the hard palate, and the food bolus is forced into the oropharynx
2) In the pharyngeal-esophageal phase, the uvula and larynx rise to prevent food from entering the nasal cavity/trachea. The tongue blocks off the mouth.
- The upper esophageal sphincter relaxes and food enters the esophagus.
- during this phase, respiration is inhibited via reflex
3) The constrictor muscles of the pharynx contract, and food is forced down esophagus. The upper esophageal sphincter contracts after food enters.
4) Persistalsis moves food to the stomach.
5) The gastroesophageal sphincter surrounding the cardial oriface opens and food enters the stomach,
Which muscle is a major contributor to the upper esophageal sphincter high pressure zone?
cricopharyngeal muscle (skeletal)
Pharyngeal muscles contract to push food bolus into esophagus. What are the two muscular layers of the pharynx?
outer circular
inner longitudinal
Describe the three outer circle muscles of the pharynx and their function
Inferior, middle, superior constrictors
During swallowing, these muscles constrict to push food downwards.
Describe the three inner longitudinal muscles of the pharynx and their function
stylopharyngeus, salpingopharyngeus, palatopharyngeus
during swallowing, these shorten and widen the pharynx
True/False: All of the pharyngeal muscles are innervated by CNX.
False - all but the stylopharyngeus which is innervated by CNIX (glossopharyngeal)
True/False: The swallowing center is located in the medulla and each half controls the ipsilateral side
True
The major peripheral sensory inputs to the swallowing center are carried by which three nerves?
1) maxillary branch of TRIGEMINAL (V)
2) GLOSSOPHARYNGEAL (IX) on posterior 1/3 of tongue, tonsil, pharynx, middle ear
3) VAGUS (X) superior laryngeal branch
The motor output of the swallowing center is via the motor branches of which 5 nerves?
1) trigerminal (V)
2) facial (VII0
3) glyossopharyngeal (IX)
4) vagus (X)
5) hypoglossal (XII)
What is oropharyngeal dysphasia and what causes it (2 factors)?
Oropharyngeal dysphasia is the failure of the normal propulsion of the bolus from the mouth to the esophagus.
Caused by failure of the driving fore (propulsion) or an obstruction to flow
What occurs in oropharyngeal dysphasia when:
a) the muscles that move larynx are weakened
b) the muscles around the soft palate or the superior pharyngeal constrictors are weakened
a) aspiration [food enters larynx]
b) regurgitation into the nose
Describe four sources of failure of propulsion (driving force) that would lead to oropharyngeal dysphasia
brain, cranial nerve, myoneural junction, muscle
Describe two sources of obstructions that would lead to oropharyngeal dysphasia
mass effect, incomplete UES sphincter relaxation
Describe four diseases that cause muscle weakness leading to oropharyngeal dysplasia
CVA, poliomyelitis, myasthenia gravis, dermatomyositis
Describe two diseases that would lead to obstructions to flow
tumor or abscess
cricopharyngeal achalasia [failure of relaxation of muscle around UES]
Describe the cause and symptoms of dermatomyositis
dermatomyositis is a acquired muscle dz/inflamm myopathy.
Cause is UNK, thought to be viral
Sx: difficulty swallowing, muscle weakness, stiffness or soreness; purple or violet upper eyelids; purple-red skin rash, SOB
Describe the types of muscle found in the esophagus and the related diseases.
Cervical esophagus and top of thoracic includes the upper esophageal sphincter, skeletal muscle
dz: polymyositis, myasthenia gravis
Lower 2/3 includes thoracic and abdominal parts and contains the lower esophageal sphincter, smooth muscle
dz; scleroderma and achalasia
Describe primary peristalsis in the esophagus.
When do the sphincters open?
Primary peristalsis is triggered by swallowing.
The lower esophageal sphincter relaxes before the propagating contraction.
When a person swallows, tension receptors stimulation contraction in the pharynx which coincides with relaxation of UES and LES. They remain relaxed until the wave reaches them.
Describe the latency of esophageal contractions.
In normal persistalsis, there is an increasing latency period for each subsequent contraction.
The contractions are thought to be controlled by excitatory motor neurons, whereas the latency is thought to be controlled by activation of inhibitory motor neuron.
Describe what happens to esophageal contractions when an NO Blocker or an NO Blocker plus Atropine is added.
When an NO blocker is given, the latency gradient disappears, suggesting that inhibitory motor neurons release NO prior to contractile wave.
When NO blocker and atropine [antimuscarinic agent] given, this results in simultaneous and low-amplitude contractions suggesting that excitatory cholingeric motor neurons release Ach to activate muscarinic receptors and produce contraction.
Describe the intrinsic and extrinsic sphincters located in the lower esophagus.
intrinsic - smooth muscle LES
extrinsic - crural diaphragm (skel muscle)
anatomically superimposed on each other and anchored by the phrenoesophageal ligament
Describe neural control of esophageal peristalsis in the proximal portion (upper 1/3) of the esophagus
skeletal muscle
Innervated by somatic lower motor neurons whose cell bodies are located in the brain stem’s nucleus ambiguous (NA)
vagus nerves from the NA release Ach where they activate nicotinic receptors to produce relaxation followed by contraction
Describe neural control of esophageal peristalsis in the more distal portion (lower 2/3) of the esophagus
smooth muscle
innervated by vagal pregang fibers whose cells bodies are found in the dorsal motor nucleus (DMN)
- synapse with neurons whose cells body are located in the MYENTERIC PLEXUS
vagus nerves from the DMN release Ach that activates nicotinic receptors
Describe the action of atropine/NO synthase inhibitors in the proximal esophagus vs the distal esophagus
In the proximal esophagus, increases the latency of contraction
In the distal esophagus, decreases the latency of contraction
Overall increases the speed of contraction
Briefly describe the difference between primary and secondary peristalsis
primary - initiated by swallowing, medulla
secondary - initiated by esophageal distension, local enteric reflexes
[THIS IS VERY SIMPLE VERSION]
Describe the contractions secondary peristalsis
Triggered by distention in smooth muscle portion of the esophagus
Contraction nearer to the mouth is followed by a descending pressure wave that coordinates LES opening.
Describe the enteric nervous system’s role in secondary peristalsis
Upon distension, intrinsic sensory neurons in the myenteric plexus activate both ascending excitatory nerve pathways and descending inhibitory nerve pathways within the myenteric plexus.
Ascending interneurons activate excitatory motor neurons that release Ach to smooth muscle leading to contraction above the bolus.
Descending interneurons activate inhibitory motor neurons that release NO and VIP to cause relaxation of smooth muscle below the bolus
Describe the evidence that shows LES relaxation is strictly neurogenic. [2 drugs]
Tetrodotoxin (TTX) blocks LES relaxation - TTX acts strictly on neurally-mediated responses but has no effect on smooth muscle.
Hexamethonium also blocks LES relaxation. This is a nicotinic receptor antagonist.
Overall, vagal stimulation is what relaxes LES.
What is the major inhibitory neurotransmitter in LES relaxation?
nitric oxide
What occurs to peristalsis when NO is blocked?
latency prior to esophageal contraction shortens
basal LES pressure inc
LES relaxation abolished
Describe three symptoms of esophageal/LES dysfunction
1) gastroesophageal reflux symptoms
2) dysphagia [failure of propulsive force, obstruction to flow, in coordination of contraction and relaxation]
3) esophageal pain (non-cardiac)
Describe GERD, its causes, and risk factors
LES does not close all the way allowing reflux of food, liquid, and stomach acid which causes symptoms and may damage the esophagus.
Risk factors - EtOH, hiatal hernia, obesity, pregnancy, scleroderma, smoking
Certain medications can bring it on or make it worse, examps are TCAs, anticholinergics, beta blockers, bronchodilators
Describe a hiatal hernia including its symptoms
A hiatal hernia occurs when part of your stomach pushes upward through your diaphragm
Many have no symptoms, but some have GERD
Describe Barrett’s esophagus
Change in the normal lining of the esophagus to a lining similar to the lining of the stomach
Basically, squamous –> columnar mucosa
GERD damages squamous lining and then through metaplasia, squamous cells are replaced by columnar cells.
Goblet cells are needed to dx
Why is Barrett’s esophagus a cause for concern?
Can lead to esophageal cancer, which only has a 5% recovery rate
What causes erythema seen in Barrett’s esophagus?
hyperemia (inc in blood flow) of capillaries under and in the mucosa
Esophageal causes are the second most common causes of chest pain after cardiac. Describe the three basic steps in diagnosing non-cardiac chest pain.
1) rule out cardiac cause
2) trial of proton pump inhibitors
3) if no improvement, send for pH monitoring vs manometry vs upper endoscopy
Describe the autoimmune component of myasthenia gravis and how this disease is treated
The immune system destroys neuromuscular junctions [motor end plates, and therefore the Ach receptors located there]
Leads to failure of pharyngeal propulsion
Therapy involves stopping this immune rxn and prolonging Ach activity [immunosuppressants and Achesterase inhibitors]
fun fact- myasthenia commonly involves bulbar innervated muscles
Describe esophageal achalasia
Rare disease where the LES fails to relax. Leads to difficulty swallowing food.
Characterized by incomplete LES relaxation, inc LES tone, and lack of peristalsis of the esophagus.
Describe nutcracker esophagus
disorder of the movement of the esophagus
super strong contractions that are very painful
Describe parasympathetic innervation of the GI tract
cranial and sacral regions of spinal cord innervate via vagal and pelvic nerves
vagus innervates most of tract and gut via nicotinic and muscarinic receptors
True/False: The biggest parasympathetic innervation to GI tract is from muscarinic receptors
FALSE - nicotinic
Describe sympathetic innervation of the GI tract
innervates through thoracic and lumbar regions of spinal cord via celiac, superior, mesenteric and inferior mesenteric ganglia
Describe the preganglionics of the GI tract
cholinergic forming nicotinic synapses post ganglionic noradrenergic nerves
Describe ENS innervation to the GI tract
innervates through neurons that lie within the wall of the GI tract and is as an independent integrative system
innervate all regions of GI tract
Describe the effector control mechanisms regulated by the enteric nervous system (4)
1) contraction of muscle coats
2) secretion
3) absorption across the mucosal lining
4) blood flow inside the walls of the GI tract
True/False: The gut has the highest concentration of serotonin in the body
True