Salivary and Gastric Secretions Flashcards
What is the difference between endocrine and exocrine glands?
- exocrine use ducts to secrete (salivary and gastric glands)
- endocrine are ductless (enteroendocrine cells)
What do the secretions in the GIT do?
- digest
- lubricate
- protect
What is a hypotonic solution?
- low concentration of solutes outside cells
- high concentration of water outisde the cell
- water therefore moves into cell and cell swells
What is a hypertonic solution?
- high concentration of solutes outside cells
- low concentration of H2O outside the cell
- water leaves the cell to dilute and shrivels up
What is saliva?
- high volume hypotonic solution
- pH 6-7
- 99% H2O
- some electrolytes and enzymes
What are the 3 main functions of saliva?
- lubrication
- protection – oral hygiene/antimicrobial agents
- initiate chemical digestion
What are the 3 main salivary glands?
1 - parotid glands
2 - submandibular glands
3 - sublingual glands
The parotid glands are exocrine glands that secrete saliva in the oral cavity. What % do they contribute to total saliva and how and where are they located?
- contribute around 25% of total saliva
- parotid means behind the ears
- located towards back of jaw under the ears
The submandibular glands are exocrine glands that secrete saliva in the oral cavity. What % do they contribute to total saliva and how and where are they located?
- contribute 70% of total saliva
- secrete serous and mucus
- located at bottom of the jaw
The sublingual glands are exocrine glands that secrete saliva in the oral cavity. What % do they contribute to total saliva and how and where are they located?
- secret around 5% of mucus
- located under the tongue
What are dispersed salivary glands?
- small glands in oral cavity
- located in lips, cheeks, tongue and mucosa of the mouth
What are the main electrolytes secreted in saliva and why are they important?
- K+, HCO3-, Na+, Cl-
- maintain oral pH
What antibody is commonly present in saliva?
- IgA
- main antibody secreted in bodily fluids
What are the 4 enzymes in saliva?
1 - alpha amylase
2 - lysozyme
3 - lingual lipase
4 - lactoferrin
What is the function of alpha amylase present in saliva?
- hydrolysis of a-1,4 glycosidic bonds in starch
- hydrolyises to disaccharide maltose, trisaccharide maltotriose and a-dextrin
- accounts for aproximaltye 75% of starch digestion
What is the function of lysozyme present in saliva?
- antimicrobial
- hydrolyses (breaks down) peptidoglycans in walls of bacteria
What is the function of lingual lipase that is secreted by the dispersed salivary glands of the tongue?
- hydrolysis of lipid triglycerides
- chelates iron to prevent microbial multiplication
What is the function of lactoferrin that is secreted in saliva?
- iron building protection
- antimicrobial properties
What is the function of mucin in the oral cavity?
- lubrication
What are the 2 main waste products that are collected in the oral cavity?
- urea
- uric acid
What does acinus mean?
- group of cells clustered together
- resemble a berry
What are myoepithelial cells?
- hybrid of smooth muscle and epithelial cells
- generally found in exocrine ducts and around acinar cells
- able to contract increasing secretion
What are the 2 stages of saliva production, which include exocrine secretion and funneling of secretions?
1 - acinar phase (secretion of exocrine secretions)
2 - duct phase (exocrine secretions move into oral cavity)
In the first phase of saliva production, called acinar phase, which electrolytes are high in concetration, and what follows these?
- Na+
- Cl-
- H2O always follows Na+
Following the first phase of saliva productin, called the acinar phase, the second phase begins as the salive begins to move down the ducts, called the duct phase. What happens to the saliva as it travels down the ducts?
- NaCl (Na+ and Cl-) is removed back into the blood
- HCO3- and K+ enter the lumen and into the saliva
Why does H2O not follow Na+ in the duct phase of saliva production?
- the ducts are relatively impermeable to water
What is the salivary flow rate?
- the change in saliva composition depending on stimulus
When does flow rate of saliva increase?
- preparing to eat
- when eating
When flow rate is high due to eating or preparing to eat, what are concentrations of:
- Na+ and Cl-
- K+ and HCO3-
- high Na+ and Cl-
- saliva resembles isotonic plasam, but remains hypotonic
- resembles what is produced by acinar cells in phase 1 of saliva production
When flow rate is low, what are concentrations of:
- Na+ and Cl-
- K+ and HCO3-
- low Na+ and Cl-
- high K+ and HCO3-
- saliva resembles what is produced during phase 2 of saliva production
Saliva production requires the Na-K-Cl cotransporter (NKCC) cotransporter. What is thr function of the NKCC?
- membrane transport protein
- transport Na+, K+ and Cl= ions across the cell membrane
- all ions move in the same direction
The parasympathetic nervous system innervates the secretion of saliva. 2 nerves are stimulates to facilitate saliva secretion, what are they?
1 - facial nerve (cranium nerve 7)
2 - glossopharyngeal nerve (cranial nerve 9)
The parasympathetic nervous system innervates the secretion of saliva. Which 2 salivary glands does the facial nerve (cranium nerve 7) innervate?
1 - sublingual gland
2 - submandibular gland
The parasympathetic nervous system innervates the secretion of saliva. Which salivary glands does the glossopharyngeal nerve (cranium nerve 9) innervate?
- parotid gland
The sympathetic system is able to innervate saliva secretion. However, this reduces saliva secretion, which is why you get a dry mouth when nervous or in fight or flight response by inhibiting all 3 salivary glands. Which nerve in the sympatheirtc chain innervates this action?
- superior cervical ganglion and sympathetic postganglionic nerves
What is Sjögren’s syndrome?
- an autoimmune disease
- exocrine glands are destroyed
- tears and saliva glands affected
- causes dry eyes and mouth
What is Xerostomia?
- lack of adequate saliva
- tooth decay and halitosis (bad breath) is common due to bacterial
- may impair speaking or swallowing solid food
What is Schirmer’s test?
- patients put filter paper at bottom of eyes for 5 minutes
- measure of tear duct function
- used to assess Sjögren’s syndrome
What are gastric pits?
- located in the stomach
- indentations in the stomach
- denote entrances to 3-5 tubular shaped gastric glands
What do the exocrine glands in gastric pits secrete?
- mucous neck cells = thin mucus
- parietal cells = HCl and intrinsic factor
- chief cells = pepsinogen, gastric lipase
What hormones do the endocrine glands in gastric pits secrete?
- G cells secrete gastrin
- D cell secrete somatostatin
- Enterochromaffin-like cells secrete histamine
What gastric enzymes do chief cells of the gastric pits secrete?
- pepsinogen pro-enzyme (creates pepsin for protein digestion)
- gastric lipase
- rennin [Chymosin] (protein digestion)
What do parietal cells of the gastric pits secrete?
- HCL = maintenance of stomach pH of 1-3
- intrinsic factor = B12 digestion and absorption
How do branched canaliculi facilitate HCL secretion?
- increase surface area with villi
- where H+ and Cl- are secreted to reduce pH
Why are H+/K+-ATPase pumps and carbonic anhydrase enzymes important in the stomach?
- H+/K+ ATPase exchanges H+ for K+ on parietal cells
- carbonic anhydrase combines H2O and CO2 into HCO3- and H+
- HCO3- enters the blood and H+ used with H+/K+ ATPase
- BOTH maintain constant flow of H+ and keep pH low in stomach
There are 3 ways in which gastric acid can be secreted into the stomach. One of these is via ACh from the vagus nerve. How does this work?
- ACh binds with M3 receptors
- M1 causes and increase in Ca2+ through Gaq pathway
There are 3 ways in which gastric acid can be secreted into the stomach. One of these is gastrin that was secreted from G cells into the circulation. How does this work?
- gastrin binds with Gaq receptors on parietal cells
- causes and increase in Ca2+ through Gaq pathway
There are 3 ways in which gastric acid can be secreted into the stomach. One of these is histamine, how does this work?
- histamine is released from enterochromaffin-like cells in gastric pits
- histamine binds to H2 receptor on parietal cells
- H2 receptors activate Gas pathway
Gastric secretion can also be inhibited. Somatostatin can be secreted by D cells to inhibit gastric secretion. It can do this via paracrine (signalling between neighbouring cells) and endocrine (somatostatin enters circulation inhibiting H2 receptors). How does somatostatin inhibit gastric secretion?
- somatostatin binds to Gai receptors inhibiting the Gas pathway
- specifically adenylyl cyclase
What is the mechanims of action of omeprazole?
- proton pump inhibitor
- inactivates H+/K+-ATPase so no H+
What is the mechanims of action of cimetidine?
- inhibits H2 receptors
What is the mechanims of action of atropine?
- inhibits M3 receptors and vagal stimulation of acid secretion
The cephalic phases of gastric acid secretion is the first phase, what happens in this phase?
- the getting started phase (seeing/smelling food)
- sensory stimulus increases vagal activity
- innervates parietal, chief and gastrin secretion
The gastric phases of gastric acid secretion is the second phase, what happens in this phase?
- starts when bolus enters the stomach
- local neural secretary reflexes are stimulated
- parietal, chief, mucus secretion, G cells [gastrin stimulates parietal cells directly and indirectly via ECL histamine release] are stimulated
The stomach has 2 mechanisms that ensure that the acidic pH of the stomach does not damage the stomach. What cells at the top of the gastric pits secrete mucous?
- mucous glands secrete viscous mucus layer
- mucus layer is a physical barrier
Surface epithelial cells in the stomach secrete something into the mucus layer to help maintain a pH around 7. What is secreted?
- HCO3-
What sits between the epithelial cells of the stomach to enure no acid can leak through?
- tight junctions
