Case 1 - Yaffas Flashcards
what is the enteric nervous system a part of
the autonomic nervous system found in the GI tract
what is the ENS involved in
coordination of reflexes
what are the two main plexuses of the ENS
submucosal and myenteric plexus
where is the submucosal/Mesissner’s plexus dound and what does it control
lies in the submucosa and controls mainly gastrointestinal secretion and local blood flow
where is the myenteric plexus and what does it control
lies between the longitudinal and circular muscle layers and controls motility
what does the myenteric plexus secrete
secretes vasoactive intestinal polypeptide
what are the resulting inhibitory signals of this useful for
inhibiting some of the intestinal sphincter muscles that impede movement of food
what do the sensory neurones of the ENS report on
mechanical and chemical conditions
what do the motor neurones of the ENS control
through intestinal muscles, control peristalsis and churning of the intestinal contents
what does the presence of bolus of food in the mouth initiate
reflex inhibition of the muscles of mastication which allows the lower jaw to drop
what does this drop initiate
a stretch reflex of the jaw muscles that leads to rebound contraction
what does this rebound contraction lead to
causes raising of the jaw to cause closure of the teeth but it also compresses the bolus again against the lining of the mouth, which inhibits the jaw muscles once again, allowing the jaw to drop and rebound another time
what does this lead to
physical breakdown of the food whcih is important for the digestion of many carbohydrates
what is the rate of digestion absolutely dependent on
the total surface area exposed to the digestive secretions
what happens after the voluntary phase
the bolus of food enters the posterior mouth and pharynx
what happens in the pharynx
it stimulates the epithelial swallowing receptor areas all around the opening of the pharynx, especially on the tonsillar pillars
what is the soft palate muscle contraction
the soft palate is pulled upward to close the posterior nares, to prevent the reflux of the food into the nasal cavities (nasopharynx)
what happens to the palatopharyngeal folds
pulled medially to approximate each other. in this way, the folds form a sagittal split, thought which the food must pass into the posterior pharynx. this slit performs a selective action , allowing food to pass with ease
what happens to the vocal cords
the larynx vocal cords are closed, and the larynx is pulled upward and anteriorly by the neck muscles. these actions, cause the epiglottis to swing backward over the opening of the larynx.
what does the upward movement of the larynx also do
pulled up and enlarges the opening to the oesophagus. At the same time, the upper 3-4cm of the oesophageal musclular wall, called the UOS relaxes, thus allowing food to easily and freely move from the posterior pharynx into the upper oesophagus. Between swallows, this sphincter remains strongly contracted, thereby preventing air from going into the oesophagus during respiration. The upwards movement of the larynx also lifts the glottis out of the mains stream of food flow, so that the food mainly passes on each side of the epiglottis rather than over its surface; this still adds another protection against entry of food into the trachea.
what happens once the larynx is raised
the pharynxgoesophageal sphincter becomes relaxed, the entire muscular wall of the pharynx contracts, beginning in the superior part of the pharynx, then spreading downward over the middle and inferior pharyngeal areas, which propels the food by peristalsis into the oesophagus.
what are the four stages of swallowing
cephalic stage
oral stage
pharyngeal stage
oesophageal stage
what are the two involuntary stages of swallowing
the pharyngeal and oesophageal stages
what does the upper oesophageal sphincter consist of
the cricopharyngeus muscle, the adjacent inferior pharyngeal constrictor, and the proximal portion of the cervical oesophagus
what is the UES innervation by
the vagus nerve
what innervates the musculature acting on the UES to facilitate its opening during swallowing
5th, 7th and 12th cranial nerves
what happens to allow the UES to open
the cricopharyngeus muscle has to relax. this occurs due to cessation of vagal excitation
what is UES opening also aided by
simultaneous contraction of the suprahyoid and geniohyoid muscles that pull open the UES and upward and forward displacement of the larynx and pulling forward of the hyoid bone
where is the brainstem central programme generator and what does it do
controls swallowing and is mainly in the medulla and extends into the pons and houses a vast array of neurones and interneurones
what are the nuclei in the CPG
the dorsal vagal motor nucleus and the nucleus ambiguous alongside the CN nuclei of 5,7,9,10 and 12
what do chemical receptors do
acid stimulus response - feedback control
what do thermal receptors do
hot or cold stimulus response - non-painful sensation
what do mechanical receptors do
distention stimulus; burning/pain response
what is the most powerful inducer of a swallow
mechanical receptors
the vagal afferents send sensations back to the system via the
nadose ganglion
the spinal afferents send sensations back to the system via the
dorsal root ganglion
what is primary peristalsis
This is a continuation of the peristaltic wave that begins in the pharynx and spreads into the oesophagus during the pharyngeal stage of swallowing.
This is quicker in someone sitting up/standing up, due to the influence of gravity.
what is secondary peristalsis
If the primary peristaltic wave fails to move all the food into the stomach, secondary peristaltic waves result from distention of the oesophagus itself by the retained food.
These waves continue until all the food has emptied into the stomach.
what are the secondary peristaltic waves initiated partly by
intrinsic neural circuits in the myenteric nervous system and partly by reflexes that begin in the pharynx and are then transmitted upward through vagal afferent fibres to the medulla and back again to the oesophagus through glossopharyngeal and vagal efferent nerve fibres.
what is the pressure of the UES
100mmHg
what is the pressure in the LES
20mmHg
what is the pressure inside of the oesophagus
-5mmHg
what does this negative pressure help with
acts to help the bolus to be pulled through from the pharynx which is at atmospheric pressure (0mmHg) through the sphincter and into the oesophagus.
what is this pressure negative?
The reason why it is negative is because of the lungs and the pleura and there is the mediastinal pleura which pulls against the oesophagus creating this negative pressure.
what is the pressure in the stomach and what does this mean
+5mmHg
this doesnt overcome the LES pressure therefore reflux is prevented
why is continuous reflux prevented
because the pressure in the LES is higher than in the stomach.
what precedes peristalsis
when the oesophageal peristaltic wave approaches the stomach, a wave of relaxation, transmitted through myenteric inhibitory neurones takes place
where is the LES found
at the lower end of the oesophagus
what is dysfunction of the LES called
achalasia
what does acetylcholine cause
constriction of muscles that will close sphincters and also those muscles that aid peristalsis
what does nitric oxide do
causes relaxation of these muscles
what are the four protective mechanisms to prevent oesophageal injury from reflux of gastric acid
what are pits glands
These represent invaginations of the epithelium into the submucosa.
In the small intestine, these pits are called crypts of Lieberkuhn. These are deep and contain specialized secretory cells.
what are the tubular glands secretions and where are they found
These are found in the stomach and the upper duodenum.
These secrete substances such as acid and pepsinogen in the stomach.
what does parasympathetic innervation of the glands in the GI tract do
strongly increases the rate of alimentary glandular secretion
what is the dual effect of sympathetic innervation of the glands in the GI tract
increase the amount of secretion
constriction of blood vessels that supply the glands
organic substance secretion
The nutrient material needed for the formation of the secretion must first diffuse or be actively transported by the blood in the capillaries into the base of the glandular cell.
Mitochondria located inside the glandular cell near its base use oxidative energy to produce ATP.
Energy from ATP, along with the appropriate substrates provided by the nutrients, is then used to synthesise the organic secretory substances.
The synthesis occurs in the ER and golgi
complex of the glandular cell.
Ribosomes adherent to the ER are responsible
for the synthesis of the proteins that are
secreted.
The secretory materials are transported through the tubules of the ER to the golgi complex.
Golgi complex – materials are modified, added to, concentrated, and discharged into the cytoplasm in secretory vesicle, which are stored in the apical end of the glandular cells.
Nervous or hormonal signalling causes exocytosis of these vesicles. It happens in the following way:
The control signals increase the cell membrane
permeability to calcium ions, and calcium e.
nters the cell.
The calcium causes the vesicles to fuse with the apical cell membrane.
The apical cell membrane breaks open, thus emptying the vesicles via exocytosis.
process of water and electrolyte secretion
Nerve stimulation of the basal portion of the cell membrane causes an influx of chloride ions.
The resulting increase in electronegativity induced inside the cell by excess negatively charged chloride ions then causes an influx of positive ions (e.g. sodium ions).
Due to the influx of ions (both positive and negative) an osmotic gradient is created, therefore water enters the glandular cells.
This increases the cell volume and hydrostatic pressure inside the cell, causing the cell itself to swell.
The pressure in the cell then initiates minute openings of the secretory border of the cell, causing flushing of water, electrolytes and organic materials out of the secretory end of the glandular cell.
what does saliva serous secretion contain
ptyalin (alpha amylase) which is an enzyme for digesting starches
what does the saliva mucus secretion cause
mucin for lubricating and for surface protective purposes
what are the two factors in saliva that destroy bacteria
Thiocyanate ions
These enter bacteria and become bactericidal.
Proteolytic enzymes (lysosome)
Attack the bacteria.
Aid the thiocyanate ions in entering the
bacteria.
Digest food particles, thus helping further to
remove the bacterial metabolic support.
what are salivary glands controlled mainly by
parasympathetic nervous signals all the way form the superior and inferior salivatory nucleu in the brainstem
what is an increase in the secretion of watery saliva mediated by
CN 7 and 9 from the superior and inferior salivatory nuclei in the brainstem via muscarinic receptors
what pathway does parasympathetic nerve stimulation occur via
the IP3 intracellular pathway, whereby calcium released in this pathway activates the relevant channels and transport proteins to cause this increase in secretion
what is sympathetic stimulation mediated by
Mediated by β-adrenergic receptors and causes an increase in secretion of viscous saliva (via T1-T3 nerves of the superior cervical ganglion which travel along the surfaces of blood vessel walls to the salivary glands).
Sympathetic stimulation increases salivation a slight amount, much less so than parasympathetic stimulation
what is an anatomic cause of oropharyngeal dysphagia
Zenker’s diverticulum
decreased compliance of cricopharyngeus
what is the pathophysiology of Alchasia
Achalasia results from the degeneration of neurons in the oesophageal wall (ganglion cells) in the myenteric plexuses, and the ganglion cells that remain often are surrounded by lymphocytes and, less prominently, by eosinophils.
This inflammatory degeneration occurs of the inhibitory neurons. The inhibitory neurons usually release nitric oxide causing the sphincter to relax.
The cholinergic neurons that contribute to LES tone by causing smooth muscle contraction are relatively spared.
what is the mechanism of acalasia
Loss of inhibitory innervation in the LOS causes:
The basal sphincter pressure to rise.
Sphincter muscle incapable of normal relaxation.
Oesophageal body smooth muscle aperistalsis.
