Phys Review - Choudhury - KK Flashcards
What is role do water and mucus play in saliva?
- Facilitate speech
- Dissolve particles
- Allow for tasting of food
- Provide lubrication for swallowing
- Assist in forming food into bolus
What is the function of salivary α-amylase?
Carbohydrate digestion (cleaves α-1,4 glycosidic bonds)
What is the function of salivary lingual lipase?
Initiates fat digestion
What is the function of salivary ribonuclease?
Hydrolysis of RNA
What are the antibacterial components of saliva?
- Lysozyme (esp. against Bacillus and Strep)
- Lactoperoxidase (esp against bacteria in milk and mucosal lining)
- IgA glycoprotein (against viruses and bacteria)
- Lactoferrin (chelates iron, thus inhibiting microbial growth)
What is the role of bicarbonate in saliva?
- Neutralizes acid produced by bacteria, thus inhibiting tooth decay
- Neutralizes gastric acid refluxed from stomach into esophagus
Why is saliva hypotonic?
Allows for the ability to taste carbs and fats
-can’t taste protein (i.e. tofu)
What is the initial site of saliva synthesis?
Acinus of salivary gland
What cells modify the ionic profile of saliva?
Ductal cells
What is secreted into the acinus?
H2O, K+, Na+, Cl-, HCO3-, zymogens of salivary enzymes
Describe the movement of salivary components in the ducts
- Ductal cells are impermeable to water
- Na+ and Cl- reabsorbed
- K+ and HCO3- secreted
What happens to the concentration of saliva at high flow rates?
Less time for ductal cells to modify constituents, so concentrations more closely resemble plasma
(higher Na+ and Cl-, lower K+ than at baseline)
What happens to the concentration of saliva at low flow rates?
More time for ductal cells to modify constituents, so less resemblance to plasma
(Low Na+ and Cl-, high K+)
What are the ionic transporters found on the luminal surface of ductal cells?
Na+/H+ exchanger
Cl-/HCO3- exchanger
K+/H+ exchanger
What part of the nervous system controls most of salivary production/concentration?
ANS, specifically parasympathetic division
-more profound stimulation/inhibition from parasympathetic as opposed to sympathetic
What factors stimulate salivary production?
Conditioned responses (smell, sight, taste, sound)
Chewing
Spicy/sour foods
Smoking
What factors inhibit production of saliva?
Sleep
Fear
Anti-cholinergics, anti-nicotinics, anti-depressants
Dehydration
Fatigue
What factors modulate production of saliva?
Blood secretion
Myoepithelial cell contraction
Hormonal secretion
Describe xerostomia
Dry mouth due to absent saliva production
Caused by: drugs, radiation tx, autoimmune disease
Leads to: buccal infections, dental caries
Describe Sjögren’s syndrome
Autoimmune disease involving salivary and lacrimal glands
Glandular atrophy leads to xerostomia and dry eyes
Results in difficulty chewing, swallowing, and speaking
Describe drooling in the instance of abnormal saliva production
Excessive salivation due to increased nervous stimulation
Tx: anticholinergics, removal of sublingual salivary glands
What are conditions in which unusual local reflexes and or increased neurological stimulation lead to excessive salivation?
Parkinson’s
Tumors of mouth or esophagus
Describe cystic fibrosis as it relates to saliva production
Pts lack CFTR or chloride channel
Results in elevated Na+, Ca++, and protein in saliva
Describe Addison’s disease as it relates to saliva production
Decreased Na+ reabsorption leads to increased Na+ in saliva
Describe primary aldosteronism and Cushing’s as they relate to saliva production
Increased Na+ reabsorption leads to decreased levels of NaCl and increased K+ levels in saliva
Describe digoxin therapy’s effect on salivary production
Increased Ca++ and K+ in saliva
Describe GERD
Disease characterized by stomach fluid refluxing into esophagus, causing “heartburn”
Results from weak LES or decreased salivary bicarb
Can lead to irritation or ulceration of esophageal lining
Describe Barrett’s esophagus
Pre-cancerous change in terminal esophagus
Due to chronic acid exposure
Squamous epithelium replaced by columnar epithelium
Considered a complication of GERD
Can evolve into esophageal cancer
What is dysphagia?
Difficulty swallowing, commonly seen in elderly pts
Caused by various abnormalities
Increased risk for aspiration, choking, malnutrition
What are some structural causes of dysphagia?
Tongue can’t propel food bolus into esophagus
Diverticula in pharyngeal or esophageal wall
What are some functional causes of dysphagia?
Neurological defects
Defects in muscle layers
What disease states can cause dysphagia?
Neurologic disorders
Stroke
Parkinson’s
Myasthenia gravis
Xerostomia
Describe achalasia
Special form of dysphagia
Characterized by: increased LES pressure with failure of LES to relax, along with absence of peristalsis within esophagus
Caused by: Nerve degeneration (esp. enteric NS), lack of NO/VIP, Chagas disease (Trypanosoma cruzi)
How does achalasia appear on barium esophagram?
Esophageal dilation with “bird’s beak” appearance of LES
Discuss the incompetent LES
Most common cause of reflux
Caused by various factors, i.e. drugs, hormones, neuro-humoral agents
Describe diffuse esophageal spasms
Irregular, uncoordinated, sometimes powerful contractions of the esophagus
Can cause dysphagia, regurgitation, and chest pain
Cause is unknown
May result from disruption of nerve activity
Describe a hiatal hernia
Herniation of part of the stomach into the thorax through a tear or area of weakness in the diaphragm
Results in sx similar to GERD
What do mucus neck cells secrete?
Mucus
Bicarbonate
What do parietal cells secrete?
HCl
Intrinsic factor
What do chief cells secrete?
Pepsinogen
Renin
What do enterochromaffin-like (ECL) cells secrete?
Histamine
What do G cells secrete?
Gastrin
What do D cells secrete?
Somatostatin
Where are the oxyntic glands located? What types of cells are contained within these glands?
Located in fundus and body/corpus of stomach
Contain parietal, chief, and mucus cells
Where are the pyloric glands located? What types of cells do they contain?
Located in antrum and pyloric regions of stomach
Contain mostly G cells and mucus cells
What stimulus is required for gastric mucus secretion?
None, mucus secretion is tonic
Increased secretion with irritation of mucosa
What stimulus is required for bicarbonate secretion from gastric mucosa?
None, secreted with mucus
What stimulate parietal cells to release HCl/IF?
ACh, gastrin, histamine
What stimulates ECL cells to secrete histamine?
ACh, gastrin
What stimulates chief cells to secrete pepsinogen and/or gastric lipase?
ACh, acid, secretin
What stimulates D cells to secrete somatostatin?
Acid in the stomach
What stimulates G cells to secrete gastrin?
ACh, peptides/amino acids in stomach
What receptors are present on parietal cells? 5
CCKB
M3
H2
Somatostatin
Prostaglandin
What agonists act on parietal cells? Where do they bind? What does binding result in?
ACh - binds to M3 receptors
Gastrin - binds to CCKB receptors
Histamine - binds to H2 receptors
All increase acid secretion
NOTE: these can directly bind receptors on parietal cells. ACh can also act indirectly, binding to ECL cells and stimulating histamine release
What antagonists act on parietal cells? Where do they bind? What does binding result in?
Somatostatin - binds to SST receptors
Prostaglandins - bind to PG receptors
Binding results in inhibition of histamine pathway stimulation
Describe the alkaline tide
- Production of HCl in parietal cells results in increased HCO3- as a byproduct
- This HCO3- is secreted into bloodstream, thus raising pH
What are the three phases of gastric acid secretion?
Cephalic
Gastric
Intestinal
Describe the cephalic phase of gastric acid secretion
30% of total acid secretion
Governed by conditioned reflexes, leading to increased vagal stimulation (↑ parasympathetic outflow)
Describe the gastric phase of gastric acid secretion
- 50-60% of total acid secretion
- Distension of gastric mucosa by food activates local vagal and ENS reflexes
- stims release of acid and pepsinogen
- Presence of peptides/amino acids stimulates gastrin release
Describe the intestinal phase of gastric acid secretion
- Peptides in duodenum stim gastrin release in stomach
- Chyme from stomach inhibits brainstem reflexes, decreasing vagal tone
- Hormones released to inhibit acid secretion
What three duodenal hormones inhibit gastric acid secretion?
Secretin
GIP
CCK
What protects the stomach lining from the effects of acidic gastric juice?
Gastric mucosal cells
- Secrete HCO3--rich mucus that neutralizes acid
- Membranes are impermeable to HCl
- Connected by tight junctions so HCl can’t pass between
What are some causes of peptic ulcer formation? (6)
H. pylori
Zollinger-Ellison syndrome
NSAIDs
EtOH
Bile acids
Stress
Describe the steps of ulcer formation
- Acid and pepsin break though mucosal barrier
- Acid stims histamine release
- Histamine stims parietal cells to release acid
- Acid diffuses through broken barrier
- Cycle continues