58 - GI Mouth and Esophagus Flashcards
What are the two types of secretions from the salivary glands?
- Serous secretions
- Mucinous secretions
Describe serous secretions from salivary glands
First is serous, which is watery and contains alpha amylase. Although insignificant in adults, it’s involved in carb digestion and is a marker of serous secretion.
Describe mucinous secretions
Second is mucinous secretion, which can be found throughout the GI tract
It’s a highly glycosylated protein that coats and protects things.
With respect to saliva – remember from cell bio that parotid is mostly serous, submandibular is a mix and sublingual is mostly mucinous (still technically a mix). Minor glands form mucous product
Describe the mechanism by which water and salt is secreted into the lumen of the salivary gland
Two cell types play a role here - acinar cells and ductal cells
Ach stimulates acinar cells at muscarinic receptors to push Chloride out into the lumen. This active process ultimately results in water and Na following passively through the duct
What happens to Na and Cl as they pass through the duct?
. As fluid progresses up the duct, Na and Cl are removed and “replaced “ by bicarb and K.
Bicarb keeps pH at around 8 during active secretion.
How does differential secretion affect the lumen of the salivary gland?
Na reabsorption is greater than K secretion. The net result of this differential of secretion is an increase in hypotonicity of the liquid as it rises – Chlorine and bicarb balance each other out because of the luminal side antiporter.
Na/K pump is used on the luminal side allows for the gradient to remain (– increase Na gradient outside means there is passive diffusion (via channel) back into the cell where it gets kicked into the interstitial space because of Na/K pump)
What are the components of saliva?
1 - Alpha amylase 2 - IgA, lysozyme and lactoferrin 3 - Lingual lipase 4 - Mucin 5 - Water 6 - Electrolytes
What is the role of alpha amylase?
Alpha amylase is involved in starch digestion – less significant in adults due to development of the pancreas, therefore this may play a more significant role prior to the development of a fully functional pancreas.
What is the role of IgA, lysozyme and lactoferrin
Antimicrobials to protect from bacterial and fungal growth. If you remember from pathology, the infections people with IgA deficiency were prone to
What is the role of ligual lipase
Fat digestion. The expression is variable – also probably insignificant in adults, similar to alpha amylase. Pancreatic lipases take care of this function for adults.
What is the role of mucin
mucin is key in lubrication and protection of the mucosa.
What is the role of water?
Water – functions in taste, swallowing and speech.
What is the role of electrolytes?
Electrolytes – Key one to remember is bicarb. It functions to neutralize stomach acid that comes back up the esophageal tube – covers and coats to neutralize returning acid.
What would happen if you were lacking amylase and lipase?
Losing alpha amylase and lipase would probably be inconsequential as the pancreas takes care of this function
What would happen if you were lacking mucin and electrolytes?
Loss of mucin and electrolytes becomes problematic, mucin helps in protection from acid and probably abrasion as well (to some degree)
What would happen if you were lacking bicarb?
Loss of bicarb means you have stomach acidity problems.
What is the primary stimulus that increases salivary secretion
ACh
Describe the basics of swallowing
Initiated voluntarily
Followed by reflex control
Respiration is inhibited, preventing food from entering trachea
Three phases of esophageal motor activity
1 - Oral phase
2 - Pharyngeal phase
3 - Esophageal phase
Describe the oral phase
This is a voluntary phase
- Tip of tongue separates
a bolus of food by pressing against hard palate - Bolus moves into the pharynx where the food stimulates touch receptors
- Swallowing reflex is initiated
Describe the pharyngeal phase
- soft palate is pulled to prevent
reflux into nasopharynx - larynx & vocal cords pulled
upward - epiglottis swings downward
- UES relaxes
- pharynx muscles contract
- peristaltic wave initiates
Important ***
Primary and secondary peristaltic wave
Describe the esophageal phase
- UES constricts
- peristaltic wave below UES (1º peristalsis)
- if insufficient to clear bolus, 2 º peristalsis begins at site of distension
What is a main point about the initiation of peristalsis and GI motility
DISTENTION is key in starting these processes
Describe GERD
Gastroesophageal reflux disease
- Reflux of the gastric contents into esophagus
- Can lead to inflammation of mucosal surface of esophagus (esophagitis)
- Can eventually cause ulcer, edema, pre-cancerous lesion, bleeding
GERD can cause a motility issue or result from a motility issue
Common causes of GERD
- Weakened LES
- Weak peristalsis
- Hiatal hernia
- Gastric ulcer
- Delayed gastric emptying caused by a narrow pyloric region
Barrett’s esophagus
- Characterized by the replacement of squamous epithelial cells with columnar epithelial cells
- Gives the epithelial surface a dark red appearance compared to light pink (normal)
- Associated with an increased risk for the development of esophageal cancer
Describe cystic fibrosis in relation to impaired salivary secretion
- Cystic fibrosis leads to impared salivary secretion
- CFTR (cystic fibrosis transmembrane conductance regulator) is a chloride ion channel that is regulated by cAMP and is dysfunctional in CF patients
- CFTR is important for water and bicarb secretion into the lumen of salivary glands and causes ducts to clog, resulting in damage repaired by fibrosis
Sjogren syndrome
Similar to CF in terms of salivation
- Loss of function of CFTR due to autoimmune response
- Result is having a dry mouth
Dysphagia
Difficulty swallowing
- Can result from mechanical/functional impairments
Describe mechanical reasons for dysphagia
- Mechanical: tumors, stricture, herniation
- Can be caused by reflux disease, alcohol and tobacco use, viral infections from HPV
Describe functional reasons for dysphagia
- Functional: disruption of striated muscle, neuronal disorder
- Can be caused by dermatomyositis, cerebrovascular accident, Parkinson’s disease, achalasia
Achalasia is a result of denervation of esophageal smooth muscle and impaired function of the LES
Hiatal herniation
Hiatal hernias are diaphragmatic hernias which are caused by protrusion of the stomach through the diaphragm and into the thorax
Sliding hernia
- Most hiatal hernias are sliding hiatal hernias.
- The stomach slides into the thoracic cavity through the esophageal hiatus.
- Causes: coughing, bending, tight clothing, ascites, obesity, and pregnancy.
- Symptoms: commonly observed as reflux of gastric contents into the esophagus
Paraesophageal hernia
- A less common herniation of the stomach
- The greater curvature of the stomach protrudes through an opening or tear in the diaphragm
- Often occurs in conjunction with reflux disease, ulcers, gallstones, pancreatitis, and inflammation of the gallbladder
- The result of this hernia may be reflux esophagitis, vascular disruptions, or both
What exacerbates symptoms of hiatal hernias?
Patients diagnosed with a hiatal hernia should avoid the flat supine position and exercises which increase intra-abdominal pressure, both will exacerbate symptoms of the hernia.
On to case #2…
Go read case #2
What is the pathogenic mechanism of her GI disorder?
LES relaxation, delayed gastric emptying, damage/scarring of tissue causing impaired relaxation, loss of secondary peristalsis, pressure/tone changes, excess NO production (this last one is unlikely).
How may her lifestyle impact her symptoms?
- Sleep after eating because gravity no longer helps in the digestive process
- Smoking impacts the UES (skeletal muscle is innervated by NICOTINIC Ach receptor – probably also impacting esophageal motor activity – maybe inhibiting UES relaxation during pharyngeal phase of esophageal motor activity).
- Benzodiazepines shown to induce smooth muscle relaxation (sphincter issue)
What are some complications of chronic esophageal reflux disease?
Barrett’s is closer observed: cancer, lesion, obstruction, and dysphagia, incompetent LES.
What therapeutic strategy would you use to address her condition?
Proton pump inhibitors
- Decreases stomach acid very effectively
- Example: Prilosec (omeprazole)
