Case 1 Flashcards
What layers does the GI tract include?
- serosa or adventitia (visceral peritoneum)
- muscularis propria (externa): (lets peristalsis happen)
- longitudinal smooth muscle
- (Auerbach’s (myenteric) plexus)
- circular smooth muscle
- submucosa (meisnner’s (submucosal) plexus)
- mucosa:
- muscularis mucosa
- lamina propria
- epithelium
what is the enteric nervous system?
part of the autonomic nervous system that is found in the lining of the GI Tract, beginning at the oesophagus and extending down to the anus
what is the ENS involved in? what does it work dependently or independently with?
It is involved in the coordination of reflexes (although it receives innervation by the autonomic nervous system, it can work independently of the brain and the spinal cord).
what is the ENS composed of? where is this situated?
- A submucosal plexus/ Meissner’s plexus that lies in the submucosa
- A myenteric plexus lying between the longitudinal and circular muscle layers
what does the Meissner’s plexus control?
mainly gastrointestinal secretion and local blood flow
what does the myenteric plexus control?
motility
This also secretes vasoactive intestinal polypeptide. The resulting inhibitory signals are especially useful for inhibiting some of the intestinal sphincter muscles that impede movement of food.
what neurones does the ENS consist of and what do these do?
The enteric nervous system includes afferent neurons, interneurons and efferent neurons.
Sensory neurons report on mechanical and chemical conditions.
Through intestinal muscles, the motor neurones control peristalsis and churning of intestinal contents.
what are the two types of movements that occur in the GI tract?
- Propulsive movements
2. Mixing movements
peristalsis - what can stimulation at any point in the gut cause?
a contractile ring to appear in the circular muscle, and this ring then spreads along the gut tube.
what is the usual stimulus that causes a contractile ring to appear? (peristalsis) what does this stimulus cause?
distention of the gut
That is, if a large amount of food collects at any point in the gut, the stretching of the gut wall stimulates the enteric nervous system to contract the gut wall behind this point, and a contractile ring appears that initiates a peristaltic movement.
what else is a stimuli for peristalsis?
- Other stimuli that can initiate peristalsis include irritation of the epithelial lining in the gut.
- Also, strong parasympathetic nervous signals to the gut will elicit strong peristalsis.
what does peristalsis require?
an active myenteric plexus
describe the movement of peristalsis, what actually happens?
- The contractile ring causing the peristalsis normally begins on the orad side of the distended segment and moves toward the distended segment, pushing the intestinal contents in the anal direction for 5-10cm before dying out.
- At the same time, the gut sometimes relaxes several centimetres downstream toward the anus, which is called “receptive relaxation,” thus allowing the food to be propelled more easily toward the anus than toward the mouth.
what are the different stages of swallowing?
- Cephalic Stage
- Oral Stage (Voluntary stage)
- Pharyngeal stage – involuntary and constitutes passage of food through the pharynx into the oesophagus
- Oesophageal stage – involuntary phase that transports food from pharynx to the stomach
what is the cephalic stage?
This is the point where one is thinking about having a meal:
All of this is part of the process of which would induce the activity of swallowing
what is the oral stage?
- Chewing (mastication)
- Salivation – lubricate the bolus and begin the process of digestion
- Movement of bolus
The bolus is pushed against the hard palate.
The rugae on the hard palate help move the bolus posteriorly into the back of the mouth into the pharynx.
mastication
- what is this
- what does it do
- how does this happen
- what muscles are involved - what innervation
- what causes chewing
- what happens to the food
• Mastication/ Chewing – this is the process by which food is crushed and ground by teeth.
It is the first step of digestion.
• Mastication increases the surface area of foods to allow more efficient break down by enzymes.
• During the mastication process, the food is positioned by the cheek and the tongue between the teeth for grinding.
• There are 4 muscles of mastication: masseter, temporalis, lateral pterygoid, medial pterygoid.
These are innervated by the mandibular branch (V3) of Trigeminal Nerve.
• Stimulation of specific reticular areas in the brain stem taste centres will cause rhythmical chewing movements.
Also, stimulation of areas in the hypothalamus, amygdala, and even the cerebral cortex near the sensory areas for taste and smell can often cause chewing.
• These muscles move the jaws to bring the teeth into intermittent contact, repeatedly occluding and opening.
• As mastication continues, the food is made softer and warmer, and the process of salivation begins.
what is the chewing reflex?
- The presence of bolus of food in the mouth initiates reflex inhibition of the muscles of mastication, which allows the lower jaw to drop.
- The drop in turn initiates a stretch reflex of the jaw muscles that leads to rebound contraction.
- This causes raising of the jaw to cause closure of the teeth, but it also compresses the bolus again against the linings of the mouth, which inhibits the jaw muscles once again, allowing the jaw to drop and rebound another time.
- This leads to the physical break down of food, which is important for the digestion of many carbohydrates (fruits and raw vegetables because these have indigestible cellulose membranes, that must be broken before the food can be digested.
what happens when the bolus of food enters the posterior mouth and pharynx?
- Here, it stimulates the epithelial swallowing receptor areas all around the opening of the pharynx, especially on the tonsillar pillars.
- Impulses from these pass to the brain stem to initiate a series of automatic pharyngeal muscle contractions
what are the pharyngeal muscle contractions that take place?
1) The soft palate is pulled upward to close the posterior nares, to prevent the reflux of food into the nasal cavities (nasopharynx).
2) The palatopharyngeal folds on each side of the pharynx are pulled medially to approximate each other. In this way, the folds form a sagittal slit through which the food must pass into the posterior pharynx. This slit performs a selective action, allowing food that has been masticated sufficiently to pass with ease.
Because this stage lasts less than 1 second, any large object is usually impeded too much to pass into the oesophagus.
3) The vocal cords of the larynx are closed, and the larynx is pulled upward and anteriorly by the neck muscles. These actions, combined with the presence of ligaments that prevent upward movement of the epiglottis, cause the epiglottis to swing backward over the opening of the larynx.
All these effects acting together prevent passage of food into the nose and trachea. Most essential is the tight approximation of the vocal cords, but the epiglottis helps to prevent food from ever getting as far as the vocal cords.
4) The upward movement of the larynx also pulls up and enlarges the opening to the oesophagus. At the same time, the upper 3-4cm of the oesophageal muscular wall, called the upper oesophageal sphincter (also called the pharyngoesophageal sphincter) relaxes, thus allowing food to move easily and freely 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 upward movement of the larynx also lifts the glottis out of the main stream of food flow, so that the food mainly passes on each side of the epiglottis rather than over its surface; this adds still another protection against entry of food into the trachea.
5) Once the larynx is raised and the pharyngoesophageal 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.
in summary what happens in the pharyngeal stage? how long does the process last?
Trachea is closed.
Oesophagus is opened.
Fast peristaltic wave initiated by the nervous system of the pharynx forces the bolus of food into the upper oesophagus.
The entire process is less than 2 seconds.
what does the upper oesophageal sphincter consist of?
the cricopharyngeus muscle, the adjacent pharyngeal constrictor and the proximal portion of the cervical oesophagus
what is the innervation of the UES?
UES innervation is the vagus nerve, whereas the innervation to the musculature acting on the UES to facilitate its opening during swallowing comes from the fifth, seventh, and twelfth cranial nerves.
what is the UES like at rest? what causes this?
The UES remains closed at rest owing to both its inherent elastic properties and neurogenically mediated contraction of the cricopharyngeus muscle.
what does it take for the UES to open?
the cricopharyngeus muscle has to relax. This occurs due to cessation of vagal excitation.
• UES opening is also aided by simultaneous contraction of the suprahyoid and geniohyoid muscles that pull open the UES + upward and forward displacement of the larynx + pulling forward of the hyoid bone.
what is at the centre of the swallowing system?
Brainstem Central Programme Generator (CPG)
central pattern generator for peristalsis
where is the CPG? and where does it extend? what else is involved?
- This is mainly in the medulla and extends into the pons and houses a vast array of neurones and interneurons which link together to produce the activity of swallowing.
- The interneurons consist of excitatory and inhibitory ones.
- There are also nuclei which include the dorsal vagal motor nucleus and the nucleus ambiguus alongside the CN nuclei of CN 5, 7, 9, 10 and 12.
- All of these CN combine together with the interneurons to allow the sequence to take place.
how is the cortex involved in swallowing?
- The cortex communicates with the brainstem salivatory nuclei.
- These send signals via motor neurons to the muscles of swallowing.
how many muscles are required in the entire swallowing process?
26 pairs
what receptors are involved in the swallowing process? what do they do? what are the most powerful inducers of a swallow?
• Sensory receptors in the oropharynx, larynx and oesophagus detect changes and send signals back to the brainstem and the cortex via CN 5, 7, 9, 10 and 12.
Chemical receptors – stimulus (acid); response (feedback control)
Thermal receptors – stimulus (hot/cold); response (non-painful sensation)
Mechanical receptors – stimulus (distention); response (burning/pain) – MOST POWERFUL INDUCERS OF A SWALLOW.
• These help mediate the swallowing response.
is swallowing a reflex?
no it’s a patterned response
what afferents are involved in the swallowing response?
• Vagal and spinal afferents send different types of sensations back into the system via the:
Nadose ganglion of the vagus afferents
Dorsal root ganglion of the spinal afferents
• The vagus afferents then go via the thalamus and into the cortex via the medulla.
• For spinal afferents, the system involved is the anterolateral system (spinithalamic tract) for nociception and mechanoreception.
how are breathing and swallowing linked?
- During the process of swallowing, the epiglottis closes off the larynx to prevent aspiration.
- For this period swallowing period, respiration is stopped.
- The salivatory nuclei are situated close to, if not exactly in the same location, as those nuclei controlling breathing.
- They work together to carry out this intricate procedure during swallowing.
what types of peristaltic movements does the oesophagus exhibit?
- Primary peristalsis
2. Secondary peristalsis
what is primary peristalsis?
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? when is it used? what are they initiated by?
- 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.
- The secondary peristaltic waves are 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 type of muscle is the pharyngeal wall?
striated muscle
what type of muscle is the oesophagus?
upper 1/3 = striated muscle
lower 2/3 = smooth muscle
what are peristaltic waves in the pharyngeal wall and upper 1/3 of oesophagus controlled by?
skeletal nerve impulses from the glossopharyngeal and vagus nerves from the nucleus ambiguus.
what is the muscle of the lower 2/3 of oesophagus controlled by?
by the vagus nerves acting through connections with the oesophageal myenteric nervous system.
what are the two high pressure zones of the oesophagus?
The UES - pressure can reach up to 100mmHg
The LES - pressure is around about 20mmHg (can be higher in pathological conditions)
what is the pressure of the inside of the oesophagus? why is this important? what causes this pressure?
• The inside of the oesophagus had a negative pressure of about -5mmHg.
This 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.
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? what is important about this pressure?
• In the stomach, there is a slightly higher pressure of +5mmHg than the oesophagus
This doesn’t overcome the LES pressure so reflux is prevented.
• The reason why continuous reflux is prevented is because the pressure in the LES is higher than in the stomach.
what is receptive relaxation of the stomach during oesophageal peristalsis?
- When the oesophageal peristaltic wave approaches toward the stomach, a wave of relaxation, transmitted through myenteric inhibitory neurons, precedes the peristalsis.
- Furthermore, the entire stomach and, to a lesser extent, even the duodenum become relaxed as this wave reaches the lower end of the esophagus and thus are prepared ahead of time to receive the food propelled into the esophagus during the swallowing act.
what is the LES/gastroesophageal sphincter normally like/pressure?
It normally remains tonically constricted with an intraluminal pressure in the oesophagus of 30mmHg.
what happens to the LES when a peristaltic swallowing wave passes down the oesophagus?
there is “receptive relaxation” of the lower oesophageal sphincter ahead of the peristaltic wave, which allows easy propulsion of the swallowed food into the stomach.
what is achalasia?
dysfunction of the LSE
what are stomach secretions like? how is the oesophagus affected by these secretions or not?
- The stomach secretions are highly acidic and contain many proteolytic enzymes.
- The esophageal mucosa, except in the lower one eighth of the esophagus, is not capable of resisting for long the digestive action of gastric secretions.
- Fortunately, the tonic constriction of the lower esophageal sphincter helps to prevent significant reflux of stomach contents into the esophagus except under very abnormal conditions.
which neurotransmitters cause constriction and relaxation of the muscles involved with sphincters and muscles involved in peristalsis?
- Acetylcholine causes constriction of muscles that will close sphincters and also those muscles that aid peristalsis.
- Nitric oxide causes relaxation of these muscles.
what are the 4 protective mechanisms to prevent oesophageal injury from the reflux of gastric acid?
Anti-reflux barrier:
- involves LES and diaphragm
- limits frequency of reflux
Oesophageal clearance:
- involves gravity and peristalsis
- limit duration of acid contact
Acid neutralisation:
- involves saliva (HCO3) and HCO3 (secreted and blood)
- limit duration of acid contact
Tissue resistance:
- cell junctions + membranes, Na/H exchange, epithelial restitution, blood flow
- protect epithelium during acid contact
throughout the alimentary tract, the secretory glands have two functions?
- Secretion of Digestive enzymes
2. Secretion of Mucus - provides lubrication and protection to alimentary tract
what are digestive secretions dependent on?
- The digestive secretions are dependent on the presence of food in the alimentary tract.
- In parts of the GI tract, the digestive enzymes secreted are specific to certain foods.
what are the different types of glands? whre are each found? what do each produce?
• Goblet Cells/ Mucous Cells
These are single-cell mucous glands.
These function mainly in response to local irritation of the epithelium.
They secrete mucous directly onto the epithelial surface to act as a lubrication that also protects the surfaces from excoriation and digestion.
• Pits
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.
• Tubular Glands
These are found in the stomach and the upper duodenum.
These secrete substances such as acid and pepsinogen in the stomach.
• Salivary Glands/ Liver/ Pancreas
These provide secretions for digestion or emulsion of food.
what is the effect of contact of food with the epithelium in the GI tract?
- The presence of food in a particular segment of the GI tract causes the glands to secrete large quantities of juices.
- Direct contact of food with the glandular cells causes this local secretion in the GI tract.
• This local epithelial stimulation also activates the enteric nervous system of the gut wall:
The types of stimuli that do this are:
Tactile stimulation/ Chemical irritation/ Distention of the gut wall
• The resulting nervous reflexes stimulate both the mucous cells on the gut epithelial surface and the deep glands in the gut wall increase their secretion.
what does stimulation of parasympathetic nerves innervating the glands in the GI tract cause? where is this particularly true?
strongly increases the rate of alimentary glandular secretion.
• This is particularly true in the upper GI tract (innervated by the glossopharyngeal and vagus parasympathetic nerves), e.g. Salivary glands and oesophageal glands.
what do some glands in the distal large intestine increase secretions in response to?
• Some glands in the distal large intestine (innervated by the pelvic parasympathetic nervous system) secrete secretion as a response to the mechanical presence of food.
what does the remainder of the GI tract secrete secretion as a result of?
due to local neural and hormonal stimuli in those particular segments of the tract.
what is the effect of stimulation of sympathetic nerves innervating the glands in the GI tract?
• Stimulation of sympathetic nerves innervating the glands in the GI tract has a dual effect:
- Increase in the amount of secretion.
- Constriction of the blood vessels that supply the glands.
- Sympathetic stimulation alone usually slightly increases secretion.
- But, if parasympathetic or hormonal stimulation is already causing abundant secretion by the glands, superimposed sympathetic stimulation usually reduces the secretion, sometimes significantly so, mainly because of vasoconstrictive reduction of the blood supply.
hormonal regulation of secretion of glands
- what does it regulate
- where particularly important
- where liberated and response in to what
- what happens to the hormones
- what secretion particularly important for
- The hormones in the help regulate the volume and character of the secretions.
- They are particularly important in the stomach and the intestine.
- They are liberated from the GI mucosa in response to the presence of food in the lumen of the gut.
- The hormones are then absorbed into the blood and carried to the glands, where they stimulate secretion.
- This type of stimulation is particularly valuable to increase the output of gastric juice and pancreatic juice when food enters the stomach or duodenum.
what are the two things that secretory glands secrete mainly?
- Organic substances (enzymes etc).
2. Water and electrolytes.
describe the process of organic substance secretion
- how are the substances formed inside and cell and how is it released
- 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 enters 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.
describe the 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 is mucus? what composed of?
• Mucus is a thick secretion composed mainly of:
Water
Electrolytes
Mixture of several glycoproteins (which themselves are composed of large polysaccharides bound with much smaller quantities of protein)
what are the functions of mucus?
Lubrication of the GI tract
Protection of the GI tract
desribe and explain what mucus does - its properties
- Mucus adheres tightly to the food or other particles and spreads as a thin film over the surfaces.
- It has sufficient body that it coats the wall of the gut and prevents actual contact of most food particles with the mucosa.
- Mucus has a low resistance for slippage, so the particles can slide along the epithelium with great ease, thus preventing excoriative or chemical damage to the epithelium.
- Mucus causes faecal particles to adhere to one another to form the faeces that are expelled during a bowel movement.
- Mucus is strongly resistant to digestion by the GI enzymes.
- The glycoproteins of mucus have amphoteric properties (able to react both as an acid and an alkali). This allows them to buffer small amounts of either acids or alkalis; also, mucus often contains moderate quantities of bicarbonate ions, which specifically neutralize acids.
where is saliva secreted from? and what type of secretion does each secrete?
Parotid glands – serous secretion only (mainly serous acinar cells)
Submandibular glands – serous and mucus secretion
Sublingual glands – serous and mucus secretion (mainly mucus acinar cells)
Buccal glands – mucus secretion only
what is the amount of daily secretion of saliva?
800-1500ml (average = 1000ml).
saliva contains two major types of protein secretions - what are these? what do they contain?
- Serous secretion
Contains ptyalin (α-amylase), which is an enzyme for digesting starches. - Mucus secretion
Contains mucin for lubricating and for surface protective purposes.
what is the pH of saliva? why?
between 6.0-7.0 (a favourable range for the digestive action of ptyalin).
what ions does saliva contain?
- Saliva contains large amounts of potassium and bicarbonate ions.
- Saliva also contains small amounts of sodium and chloride ions. There is a higher concentration of these ions in the plasma as opposed to the saliva
what do salivary glands contain?
acini and salivary ducts.
salivary secretion is a two stage process - what is the first stage?
- Acini – “primary secretion”
This contains ptyalin and/or mucin in a solution of ions in concentrations similar to that of the extracellular fluid.
The ions secreted by the acini into the salivary duct are sodium ions (Na+), chloride ions (Cl-) and small amounts of bicarbonate ions (HCO3-).
Sodium ions enter the lumen via tight junctions too.
Water is also added to the salivary duct as a result of osmosis.
This leads to an isotonic, plasma-like primary secretion.
what is the second stage of salivary secretion?
Sodium ions are actively reabsorbed from all the salivary duct lumen and small amounts of potassium ions are actively secreted into the lumen in exchange for the sodium.
The sodium ion concentration of the saliva becomes greatly reduced, whereas potassium ion concentration becomes increased.
There is excess reabsorption of sodium ions over potassium ions.
This creates electrical negativity (around -70mV) in the salivary ducts.
As a result, chloride ions are passively reabsorbed from the lumen (to make the lumen more positive).
Chloride ion concentration in the salivary fluids is greatly reduced, matching the ductal decrease in sodium ion concentration.
Small amounts of bicarbonate ions are secreted by the ductal epithelium into the lumen of the duct. This is caused by the passive exchange of bicarbonate for chloride ions.
summarise the salivary duct stage of secretion
There is reabsorption of sodium ions and chloride ions (NaCl) from the duct.
There is some secretion of potassium ions and bicarbonate ions into the duct.
The cell membranes of the epithelial lining of the duct have low water permeability (less aquaporins) and so hardly any water enters the duct via osmosis. This leads to the final saliva being hypotonic.
What transporters are present in acinar cells? what do each do?
Na+, K+-ATPase (P-type pump):
- maintains concentration gradients for Na+ and K+
- small direct contribution to membrane potential
Na+, K+, 2Cl- cotransporter:
- electrically neutral
- uses inward gradient for Na+ to drive Cl- up its gradient - secondary active transport
K+ channels:
- recycles K+ and maintains membrane potential
Ca2+ activated Cl- channel:
- allows Cl- efflux down its electrochemical gradient
Aquaporin 5 wager channel:
- allows H2O efflux driven by a small osmotic gradient
what is the concentration of ions in resting salivation compared to that of plasma? |
- Sodium chloride concentration of the saliva (15 mEq/L) is about 1/7 to 1/10 of their concentration in the plasma.
- The concentration of potassium ions (30 mEq/L) is 7 times as great as the plasma.
- The concentration of bicarbonate ions (50-70 mEq/L) is about 2-3 times as great as the plasma.
what happens to different concentrations of ions during maximal salivation? why?
- During maximal salivation, the salivary ionic concentrations change considerably because the rate of formation of primary secretion by the acini can increase as much as 20x.
- This acinar secretion then flows through the ducts so rapidly that the ductal reabsorption of NaCl is considerably reduced.
- Therefore, when copious quantities of saliva are being secreted, the sodium chloride concentration in the saliva rises only to 1/2 or 2/3 that of plasma (normally 1/7 to 1/10), and the potassium concentration rises to only 4 times (normally 7 times) that of plasma.
describe the function of saliva for oral hygiene - what exactly in saliva does this?
• During sleep, little secretion occurs.
• This secretion maintains healthy oral tissues.
• The flow of saliva itself helps wash away pathogenic bacteria, as well as food particles that provide their metabolic support.
• Saliva contains several factors 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.
how are salivary glands controlled? what stimulates this?
• Salivary glands are controlled mainly by parasympathetic nervous signals all the way from the superior and inferior salivatory nuclei in the brainstem.
• The salivatory nuclei are excited by tactile stimuli from the tongue and other areas of the mouth and pharynx.
• Salivation can also be stimulated or inhibited by nervous signals arriving in the salivatory nuclei from higher centres of the CNS.
E.g. smelling liked foods increases salivation. This is caused by the appetite area of the brain.
what happens to saliva when there is parasympathetic stimulation? what nerves? what nuclei? what receptors?
An increase in the secretion of watery saliva (water and electrolyte secretion) is mediated by CN 7 & 9 from the superior and inferior salivatory nuclei in the brain stem via muscarinic receptors.
what causes the changes that parasympathetic innervation brings about?
Parasympathetic nerve stimulation occurs via the IP3 intracellular pathway, whereby calcium released in this pathway activates the relevant channels and transport proteins to cause this increase in secretion. (has an effect on chloride ion channel in apical membrane and potassium ion channel in basolateral membrane)
what happens to saliva when there is sympathetic stimulation? what nerves? what ganglion? what receptors?
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).
does sympathetic stimulation increase salivation?
a slight amount, much less so than parasympathetic stimulation.
what does salivation also occur in response to? what does saliva do once swallowed?
- Salivation also occurs in response to reflexes originating in the stomach and upper small intestines - particularly when irritating foods are swallowed.
- The saliva, when swallowed, helps to remove the irritating factor in the gastrointestinal tract by diluting or neutralizing the irritant substances.
does blood supply to the glands affect saliva production? why? what causes changes in blood supply?
• Blood supply to the glands affects saliva production. This is because secretion always requires adequate nutrients from the blood.
• The parasympathetic nerve signals that induce copious salivation also moderately dilate the blood vessels.
• In addition, salivation itself directly dilates the blood vessels, thus providing increased salivatory gland nutrition as needed by the secreting cells.
Part of this additional vasodilator effect is caused by kallikrein secreted by the activated salivary cells, which in turn acts as an enzyme to split one of the blood proteins, to form bradykinin, a strong vasodilator.
what are oesophageal secretions like in character? and what do they do?
entirely mucous in character and principally provide lubrication for swallowing.
what glands is the oesophagus lined with at different parts? why different in different parts? ?
• The main body of the oesophagus is lined with many simple mucous glands.
• At the gastric end and to a lesser extent in the initial portion of the oesophagus, there are also many compound mucous glands.
Upper oesophagus compound mucous glands - The mucus secreted by these prevents mucosal excoriation by newly entering food.
Oesophagogastric junction compound mucous glands - protect the oesophageal wall from digestion by acidic gastric juices that often reflux from the stomach back into the lower oesophagus.
Despite this protection, a peptic ulcer at times can still occur at the gastric end of the oesophagus.
what is dysphagia? what can it affect if severe?
the symptom of difficulty of swallowing.
- Dysphagia refers to problems with the transit of food or liquid from the mouth to the laryngopharynx or through the oesophagus.
- Severe dysphagia can compromise nutrition, cause aspiration, and reduce quality of life.
epidemiology of dysphagia - age
16-22% over 50 years old
55% over 70 years old
what are the complications of dysphagia?
Aspiration, penetration Pneumonia Nutritional compromise Increased length to hospital stay (people suffering from dysphagia as a symptom post-stroke are likely to stay in hospital for twice as long as those patients who do not have dysphagia post-stroke) Poorer outcomes Reduced quality of life NHS costs
what are the signs and symptoms of dysphagia?
Reduced appetite/ refusing to eat?
Weight loss?
Food modification?
Food residue after eating?
Drooling/ dry mouth/ coughing/ throat clearing?
Change in voice/ changes in respiratory status (breathless)/ changes in temperature?
what are the two types of dysphagia based on cause?
- Dysphagia caused by an oversized bolus or a narrow lumen is called structural dysphagia.
- Dysphagia due to abnormalities of peristalsis or impaired sphincter relaxation after swallowing is called propulsive dysphagia.
what are the two types of dysphagia based on position?
• Dysphagia is classified into two types:
1) Oropharyngeal Dysphagia
2) Oesophageal Dysphagia
what is oropharyngeal dysphagia? what does it result in?
difficulty emptying material from the oropharynx into the oesophagus.
• It results in poor bolus formation and control so that food has prolonged retention within the oral cavity and may seep out of the mouth.
Drooling and difficulty in initiating swallowing are other characteristic signs.
• Poor bolus control also may lead to premature spillage of food into the laryngopharynx with resultant aspiration into the trachea or regurgitation into the nasal cavity.
- Abnormal bolus transfer to the oesophagus
- Difficulty initiating a swallow
- Only one manifestation of the primary disease (e.g. stroke)
what are causes of oropharyngeal dysphagia?
Anatomic e.g. Zenker’s diverticulum: decreased compliance of cricopharyngeus
Neurologic e.g. stroke: weak pharyngeal contraction, incoordination of UES and pharyngeal contraction
Muscular e.g. myasthenia gravis: weak pharyngeal contraction
what are 1/3 of oropharyngeal dysphagia cases a result of? how does positioning and size of lesion affect the resulting dysphagia?
• 1/3 of oropharyngeal dysphagia cases are as a result of unilateral hemispheric strokes.
The lesion size is more important than the location, because there are many areas in the brain that control swallowing and so a larger lesion is like to damage more of these areas.
Anterior lesions and lesions in subcortical white matter may experience high risk of aspiration.
Dysphagia tends to be less severe after hemispheric stroke and remains prominent in the rehabilitation brainstem stroke.
what is oesophageal dysphagia? what does it result from?
- Oesophageal dysphagia is difficulty passing food down the oesophagus.
- It results from either a motility disorder or a mechanical obstruction.
- Abnormal bolus transport through the oesophagus
- Food stops after initiation of swallow
- Oesophagus is location of the primary disease (e.g. achalasia – LES fails to open during swallowing, which leads to a backup of food within your oesophagus)
what are the different treatments for dysphagia? depending on type and does dysphagia improve after stroke?
• Treatment of dysphagia depends on both the locus and the specific etiology.
• Oropharyngeal dysphagia most commonly results from functional deficits caused by neurologic disorders.
Treatment focuses on utilizing postures or maneuvers devised to reduce pharyngeal residue and enhance airway protection learned under the direction of a trained swallow therapist.
• Aspiration risk may be reduced by altering the consistency of ingested food and liquid.
• Dysphagia resulting from a stroke (in 50% of people) usually, but not always, spontaneously improves within the first few weeks after the event. More severe and persistent cases may require gastrostomy and enteral feeding. Feeding by a nasogastric tube or a percutaneous endoscopic gastrostomy (PEG) tube may be considered for nutritional support; however, these maneuvers do not provide protection against aspiration of salivary secretions or refluxed gastric contents.
• The majority of causes of esophageal dysphagia can be treated by esophageal dilation.
• A common symptom is a gurgly/wet voice that worsens after drinking water.
• Soft Diet - The soft diet for dysphagia eliminates all foods that may be difficult to chew.
• The goal of dysphagia therapy – safe, adequate, independent, satisfying, nutritional and hydrational needs.
what are interventions for dysphagia?
- Postural modifications
- Manoeuvres
- Head postures
- Biofeedback
- Sensory stimulation – pharyngeal electrical stimulation
- Combinations
- Dietary modifications – viscosity matters
what is the management of dysphagia?
- Swallow assessment within 4 hours or arrival in hospital.
- Nil By Mouth (NBM) if unable to swallow.
- Intravenous infusion (IVI)
- SALT (Speech and language therapy) assessment.
- Feeding by alternative route.
- Nutritional assessment for ALL including weight.