Lecture 20: Secretions from Salivary Glands and Stomach Flashcards
What triggers the cephalic phase
Anticipation of food
Cephalic phase is activated due to activation of ___efferents
PNS
What does PNS activity during cephalic phase result in
Increased secretion of saliva, gastric acid, gastrin and pancreatic enzymes
The cephalic reflex serves to ___ the GI tract
Prepare
What are the 3 phases of salivary and gastric secretion
- Cephalic
- Gastric
- Intestinal phase
What stimulates the gastric phase of salivary and gastric secretions
Mechanical stimulation of oral cavity and stomach
What stimulates the intestinal phase of gastric secretion
Regulation of stomach emptying and digestion/absorption in small intestine
What stimulates release of HCl in the cephalic phase
Vagus—> parietal
Vagus—> gastrin—> parietal
What % of HCl secretion occurs in cephalic phase
20%
What triggers HCl secretion in gastric phase
- Vagus—> parietal
- Vagus—> gastrin—> parietal
- Local reflex—> gastrin—> parietal
- Gastrin—> parietal
- Gastrin—> ECL—> histamine—> parietal
What inhibits the release of HCl in the gastric phase
PH <2 in stomach will trigger release of somatostatin which will inhibit parietal cells and decrease gastric acid
What % of HCl is secreted in gastric phase
70%
What triggers HCl release in intestinal phase
- Intestinal G cells activated
What inhibits HCl release in intestinal phase
- Low pH in duodenum activates somatostatin to inhibit parietal cells and decrease gastric acid
- Block G cells—> decrease gastrin
What % of HCl is secreted in intestinal phase
10%
What 4 glands produce saliva
Parotid, mandibular, lingual, and baccalaureate
In cattle saliva is a major source of what
Water and bicarbonate to the rumen
What is saliva composed of
Water, proteins, electrolytes and urea (ruminants)
What are some functions of saliva
- Stimulate taste buds
- Food lubrication
- Keeps mouth clean
- Contains lysozymes, buffer and antitoxic proteins
Salivary glands are ___glands
Acinar
What is the secretory unit of salivary glands
Acini
Fluid is secreted into the lumen of the acini and is modified through what
Intercalated and striated ducts
All salivary glands are composed of multiple ___that drain into ___ before being secreted into ___cavity
Acini, collecting ducts, buccal cavity
What is the salivary enzyme responsible for breaking down starch
Ptyalin (alpha-amylase)
What is the ideal pH in dogs, cats and pigs for ptyalin/alpha-amylase
6-7
What is mucin
Lubricant that facilitates swallowing and protects buccal surfaces
What ions are reabsorbed and secreted in salivary glands
Reabsorbed: Na+ and Cl-
Secreted: K+ and HCO3-
What is a salivary mucocele
Painless swelling in the neck or oral cavity that is a collection of saliva as a result of a damaged salivary gland or duct
__osmotic secretion by acini cells and selected reabsorption by duct cells creates a ___saliva
Iso-osmotic, hypotonic
What is the tonicity of normal saliva
Hypotonic
Acinar cells release ___ and ___ via exocytosis and secrete ___, ___ and ___
Proteins and mucous
Chloride, bicarbonate, and potassium
Salivary duct cells reabsorb __ and ___
Na+ and Cl-
What can not pass through tight junctions in salivary glands and what is the result
Tight junctions are impermeable to water, therefore creating the hypotonic saliva
What determines salivary osmolarity
Flow rate
Saliva is hypotonic at __salivary flow rates
Low
Saliva is isotonic at __salivary flow rates. And why?
High because there is not enough time to reabsorb Na+, Cl- and HCO3-
The pH ___ when salivary secretion rate increases
Increases
What salivary gland consists of just serous cells that provide proteins to saliva
Parotid gland
What salivary glands consist of a mixture of serous and mucous cells
Sublingual and submandibular
Ptyalin (alpha-amylase) hydrolyzes starch to what
Maltose
What enzyme is frequently present in young animals on a milk diet but less in mature animals
Lingual lipase
What does lingual lipase do
Hydrolysis of triglycerides into diacylglyceride and free fatty acids
In ruminants and other herbivores saliva contains ___ and ___
Lysozymes and antitoxic proteins
What is the purpose of lysozymes in ruminants and other herbivore saliva
Antibacterial effect- breaks beta 1-4 glycosidic bond between N-acetylmuramic acid and N-acetylglucosamine in peptidogylcan which is the major bacterial cell wall polymer
The loss of peptidoglycan via salivary lysozymes results in ___ in a ___environment
Rapid cell lysis in a hypo-osmotic environment
What are tannins
Plants defense mechanism as they provide a bitter taste
What are some negative effects of tannins
- Decrease food intake
- Reduce ruminal protein digestion
- Inhibit digestive enzymes
- Overall negative effect on nutrient absorption in SI
How do ruminants and other herbivores combat tannins that are present in their natural diet
Parotid gland produces proline-rich proteins which bind and neutralize tannins
Do deers or cattle have larger parotid glands and why
Deer as their diet consists of more tannins
How does saliva buffer rumen fluid
Bicarbonate
Why does the saliva need to buffer ruminal fluid
Microbial activity in the rumen is producing VFA therefore bicarbonate production will control pH
What are the 4 major components of gastric juce
- HCl
- Pepsinogen
- Mucus
- Intrinsic factor
What is the purpose of HCl
Decrease pH of stomach, activate pepsinogen, aids in protein digestion, kills bacteria
What is the purpose of pepsinogen and what is the active form
Pepsin is active form that digests proteins
What is the purpose of mucus secretion
Protect the gastric mucosa from acidic actions of HCl
What is the purpose of intrinsic factor
Necessary for absorption of Vitamin B12 in lieum
What activates pepsinogen
HCl
What species have a glandular stomach
Dogs and cats
What species have a non-glandular and glandular stomach
Horses
Which portion of the stomach contains chief cells, parietal cells, and enteroendocrine cells
Glandular
What do chief cells do
Pepsinogen—> pepsin
What do parietal cells do
Secrete HCl
What do surface mucous cells do
Protect against acid and mechanical damage
What do mucous neck cells do
Serve as stem/progenitor cells
What do D cells, G cells and ECL cells do
Produce hormones that regulate gastric secretion and motility
How do parietal cells form HCl
ATP dependent protein pump excretes H+ and Cl- enters lumen down electrical gradient
Cl- is exchanged for ___ on basolateral membrane producing an alkaline tide
Bicarbonate
What catalyzes bicarbonate from OH- and CO2
Carbonahydrase
When does an alkaline tide occur
After meal
During alkaline tide the ___ blood is more alkaline than ___ blood
Venous, arterial
What 3 receptors stimulate HCl production
M3, CCK, and H2
How does nervous system control HCl secretion
PNS and CNS activates parietal cells via M3 receptors
How does the endocrine system control HCl secretion
- Gastrin is secreted from G cells and binds to CCK-B receptors
- Gastrin stimulates histamine release which binds to H2 receptors
What receptor does gastrin bind to do secrete HCl
CCK-B
What cell secretes histamine that then binds to __receptors
ECL cells, H2 receptors
Gastrin is released in response to what 3 things
- Small peptides and AA in stomach
- Distention of stomach
- Vagal stimulation
What two intracellular mechanisms mediate activation of H/K ATPase
- PNS (ACh) and gastrin released onto M3 and CCK-B receptors stimulate IP3/DAG which increase CA2+
- Histamine binds H2 receptors and increase cAMP
___ and ___ stimulate the proton pump
Ca2+ and cAMP
What are the 3 pathways and 2 intracellular mechanisms to secrete/increase HCl
3 pathways:
1. Gastrin binds CCK-B
2. ACh binds M3
3. Histamine binds H2
2 intracellular mechanisms:
1. Gastrin and ACh increase Ca2+
2. histamine increases cAMP
Ca2+ and cAMP stimulate proton pump, provides H+ for HCl
___ and ___ down regulate HCl production
Somatostatin and prostaglandins
How does somatostatin down regulate HCl
Inhibits cAMP
How do prostaglandins down regulate HCl
Inhibit G cells which secretes gastrin and ECL cell which secretes histamine
What 3 components make up the gastric mucosal barrier
- Compact epithelial cell lining
- Gastric mucus covering
- Bicarbonate
What are some causes of gastric ulcers
- Defect in mucosal barrier
- Hyper secretion of HCl
- Helicobacter pylori
What are some therapeutic approaches to treating gastric ulcers (broad approaches)
- Reduce acid production (vagotomy or pharmacologically via proton pump inhibitors)
- Stimulate re-epithelialzation
- Antibiotics for Helicobacter
What specific treatments can be done to control ACh secretion to decrease HCl secretion
- Vagotomy
- Atropine
What specific treatment can be done to reduce histamine secretion to control HCl secretion
Cimetidine
What specific treatment can be done to reduce activity of proton pump to reduce HCl secretion
Omeprazole
Pepsinogen is produced and secreted by ___
Chief cells
Pepsinogen is stored in what
Zymogen granules
Why is pepsin released as proenezyme
To prevent auto digestion
What is the function of pepsin
Cleave proteins to peptides
How is pepsinogen stimulated
- PNS (vagus)
- Gastrin
- Secretin from duodenum