Lecture 27 - GI Secretion Flashcards
What does the endocrine secretion do in GI secretions?
(Hormones)
Regulation of motility and secretion
- gastrin stimulation of stomach motility and gastric acid secretion
- CCK and secretin inhibition: stomach motility, stimulation: pancreatic secretion
What does exocrine secretion do in GI secretions?
Prepare food for digestion by:
- diluting it to the osmolality of the plasma
- altering pH for optimal digestion
- digesting food
- protection/lubrication
What are the major components of GI secretion?
mucus, enzymes, electrolytes or serous solutions
Where is the exocrine or serous secretions in GI tract produced?
Produced by Epithelial cells lining GI tract and associated organs
What are the roles of saliva?
Oral hygiene
- xerostomia (dry mouth, lack of saliva)
Aids in:
- talking
- chewing and swallowing by moistening and dissolving food
Assists in rendering food isosmotic
Amylase - starch digestion
What are the three main pairs of salivary glands?
Parotid (serous)
Submandibular (mixed mucous/serous)
Sublingual (mucous)
What are the types of acinus cell in the salivary glands?
Serous acinar cells - zymogen granules
Mucous acinar cells
What are the types of duct cells in the salivary glands?
Intercalated ducts
Striated ducts
What do the duct cells do in salivary glands?
Drain into mouth
Reabsorption from primary fluid
- dilute solution
- limited further secretion
What do the acinus cells do in salivary glands?
Site of primary secretion
- isotonic NaCl solution
What is the volume of saliva produced per day?
1.5L
What is the basal rate of saliva production?
0.5 mL/min
What are the main components of saliva?
Mucus
Digestive enzymes
Serous secretion
What produces the mucus found in saliva?
Sublingual & submandibular & buccal glands
What produces the digestive enzymes found in saliva?
a-amylase - parotid gland
salivary glands of tongue - lingual lipase
What produces the serous secretion found in saliva?
Primarily parotid, lesser extent submandibular
What is the serous secretion in saliva?
Hypo-osmotic solution of NaCl with slightly elevated K+ and HCO3
- composition varies with rate of secretion
What osmolarity is saliva?
Saliva is always hypo-osmotic
- Osmolarity increases as rate of secretion increases
What is the conc of ions in saliva vs plasma?
[Na+] & [Cl-] < in plasma
[K+] higher than plasma
[HCO3-] higher than plasma
- Na+ in saliva goes up when flow rate increases, not to point as what it is in plasma
What is the constant and variable in saliva secretion rate?
Rate of secretion by acini variable
Rate of absorption by duct is constant
What happens when there are slow rates of saliva secretion?
Primary fluid in contact with duct epithelium for extended period of time
Greater absorption of NaCl
- when we don’t eat: fluid more time to be absorbed
What happens when there are high rates of saliva secretion?
Primary fluid passes through ducts rapidly
Limited absorption of NaCl
Saliva
A. is hypertonic during stimulation of secretion.
B. helps digesting starch.
C. contains enzymes such as pepsin.
D. contains less bicarbonate than plasma.
B. helps digesting starch.
A - Always hypotonic regardless of stimulation
C - contains amylase and lipase
D - Higher than plasma
Which salivary duct produces primary fluid?
Acini salivary duct
What salivary duct modifies fluid?
Striated and excretory ducts
What do the salivary striated and excretory ducts do?
Modification of fluid by reabsorption of Na+ and Cl- without water
- Limited amount of K+ and HCO3- secretion depending on species
- Mucus
Describe the primary fluid produced by salivary acini ducts
Isotonic NaCl
- amylase
- mucus
What is the difference in duct cell epithelium in salivary glands vs pancreas?
Pancreas - leaky epithelium in ducts
Saliva - tight epithelium in ducts
What can move paracellularly in salivary acinus cells?
Na+ and H2O
What channels are found in the basolateral membrane of salivary acini cells?
Na/K-ATPase
K channel
NKCCI
H2O channel
What channels are found in the apical membrane of salivary acini cells?
Cl- channel
H2O channel
What is the duct cell mechanism in saliva secretion?
Isotonic primary saliva
-> Na+ reabsorbed
-> K+ secreted
-> HCO3- secreted
=> hypotonic saliva
What channels are found in the apical membrane of salivary duct cells?
ENaC
K+ channel
CFTR (Cl- channel)
Cl-/HCO3- exchanger
What channels are found in the basolateral membrane of salivary duct cells?
Na+/HCO3- cotransporter
NHE
What type of epithelium is found in salivary duct cells?
Tight epithelia
What nervous pathway is the main system in salivary secretion regulation?
Parasympathetic
What is the parasympathetic regulation of salivary secretion?
Main system
Acetylcholine
Stimulate blood flow
High amount of serous saliva
What is the sympathetic regulation of salivary secretion?
Noradrenalin (α1,B2)
Inhibits blood flow
Low amount of mucous saliva
What is the regulation of salivary secretion?
mainly nervous – both branches ANS regulate secretion
What is saliva secreted in response to?
- thought of food
- approach of food
- food in the mouth
- parasympathetic nervous system
What are the two reflexes involved in saliva secretion?
Conditioned reflex
Unconditioned reflex
What is the conditioned reflex of saliva secretion?
Due to sight and smell of food
Learned response – Pavlov
What is the unconditioned reflex of saliva secretion?
Due to presence of food in mouth and response to taste receptors
Secretion of a hypotonic salivary solution
A. depends on sympathetic activation.
B. requires a basolateral chloride and bicarbonate channel in acini.
C. requires para-cellular re-absorption of Na+ in acini.
D. requires leaky acinar epithelium.
D. requires leaky acinar epithelium.
A - Parasympathetic
B - Channel found in duct cell apical membrane, transporter not channel
What is the only salivary cell that secretes enzymes?
Acinar cells
