Lecture 25: Secretion Flashcards
What are endocrine secretions produced by?
Epithelia
What are the components of exocrine secretions?
3
- Mucus
- Electrolyte solution
- Digestive enzymes
What are the roles of mucus?
3
- Protection
- Lubrication
- Aid in mechanical digestion
What are the roles of an electrolyte solution?
2
- Dilute food
- Provide optimal pH for enzymes
What are electrolyte solutions essential for?
Chemical digestion of food
What do digestive enzymes aid in alongside chemical digestion?
Absorption
What are digestive enzymes essential for?
Chemical digestion of food
How many salivary glands are there?
3 pairs
How much fluid do salivary glands produce a day?
1.5L
What is the basal rate of secretion for the salivary glands?
0.3 ml/min
What is the stimulated rate of secretion for the salivary glands?
1.5 ml/min
What is the composition of salivary secretion?
- Mucus
- Dilute solution of NaHCO3/NaCl
- Digestive enzymes
What is the role of mucus in salivary secretions?
Lubrication
What is the role of a dilute solution of NaHCO3/NaCl in salivary secretions?
- Dilute food
- Provide optimal pH for digestive enzymes
What digestive enzymes are present in salivary secretions?
2
- Lingual lipase
- Alpha-amylase
What proportion of total salivary secretion is produced by the sublingual glands?
5%
What proportion of total salivary secretion is produced by the submandibular glands?
70%
What proportion of total salivary secretion is produced by the parotid glands?
25%
Is salivary secretion essential?
No
What does salivary secretion aid in?
3
- Talking
- Chewing
- Swallowing
How does salivary secretion aid in hygiene?
2
- Irrigation
- Dry mouth (from reduced or absent saliva)
What do lingual lipase help to begin digestion of?
Fats
What do Alpha-amylase help to begin the digestion of?
Starch
What are conscious nervous stimulations for salivary secretion?
(2)
- Thought/smell/sight of food
- Presence of food in the mouth
How does the parasympathetic nervous system influence salivary secretions?
It stimulates secretion of copious quantities of fluid
How does the sympathetic nervous system influence salivary secretions?
It stimulates small volumes of viscous fluid to be produced
What volume of gastric secretion is produced in a day?
2-3L
What is the rate of gastric secretion between meals?
15-30 ml/h
When eating what happens to gastric secretions from Mucous/Parietal/Chief cells?
They are superimposed on the basal rate
What is the function of mucus as a gastric secretion?
2
- Protection from abrasion
- Protection from acid
What is the function of intrinsic factor as a gastric secretion?
The absorption of vitamin B12 in the small intestine
What is pepsinogen as a gastric secretion?
The inactive form of pepsin
What is pepsin?
A gastric proteolytic enzyme that starts the digestion of proteins
How is pepsinogen converted to its active form?
By acid
What are the functions of gastric acid as a gastric secretion?
(5)
- Dilute food
- Denature proteins
- Activate pepsinogen
- Create optimum pH for pepsin
- Protection
What do mucous cells contribute towards gastric secretion?
Mucus
What do parietal cells contribute towards gastric secretion?
2
- HCl
- Intrinsic factor
What do chief cells contribute towards gastric secretion?
Pepsinogen
Where is the source of acid by parietal cells from?
The dissociation of of H2CO3, after H2O and CO2 react, giving HCO3- and H+
Where is the H-K ATPase found?
In the apical membrane of parietal cells
What does the H-K ATPase in the parietal cell do?
Pumps hydrogen ions into the lumen of the stomach in exchange for K ions
How does the anion counter transporter in the serosal membrane of the parietal cell work?
It ejects bicarbonate ions into the interstitial fluid in exchange for Cl- ions into the cell
Once in the parietal cell what do Cl- ions do?
Diffuse across the cell and enter the lumen of the stomach via a channel in the apical membrane
Gastric secretion is co-ordinated with what?
Eating and the arrival of food
What are the 3 phases of gastric secretion?
- Cephalic phase
- Gastric phase
- Intestinal phase
What controls the cephalic phase of secretion?
The head
What % of secretion from a meal is associated with the cephalic phase?
20%
What does the parasympathetic nervous system act through during the cephalic phase of secretion?
The enteric nervous system
What does the parasympathetic nervous system cause via the enteric nervous system during the cephalic phase of secretion?
- Parietal/chief/goblet cells to secret
- Secretion of the hormone gastrin
What does gastrin stimulate?
2
- Parietal cells
- Chief cells
What % of secretion from a meal is associated with the gastric phase?
70%
What controls the gastric phase of secretion?
The stomach
What does the gastric phase of secretion ensure?
There is sufficient secretion to handle ingested food
What are stimuli in the stomach during the gastric phase of secretion?
(3)
- Stretch/distension of the stomach wall
- Products of digestion are present
- Elevated pH
What is the local nervous reflex that controls gastric secretion?
The enteric nervous system
What is the external nervous reflex that controls gastric secretion?
Parasympathetic nervous system
What does nervous/hormonal regulation stimulate during gastric secretion?
- More secretion
- Motility
What does gastrin do during the gastric phase of secretion?
Further stimulates secretion and motility
What % of secretion from a meal is associated with the intestinal phase?
10%
What regulates the intestinal phase of secretion?
The small intestine
The intestinal phase of secretion controls what?
Delivery of substance to the duodenum
What are stimuli for the intestinal phase of secretion?
2
- Distension of the duodenum
- Arrival of acid chyme/lipids/carbohydrates
What hormones regulate gastric secretion?
3
- GIP
- CCK
- Secretin
What nerve regulates the intestinal phase of secretion?
The enterogastric reflex
What does the enterogastric reflex and GIP,CCK, Secretin hormones do during the intestinal phase of gastric secretion?
Both inhibit secretion and motility
What kind of organ is the liver?
An endocrine and exocrine organ
What is the volume of pancreatic secretion a day?
1-1.5L
What are the 2 main components of pancreatic secretion?
- Enzymes
- Alkaline fluid
What cells in the pancreas produces enzymes?
Acinar cells
What are enzymes produced in the pancreas important for?
Chemical digestion
What produces alkaline fluid in the pancreas?
Duct cells
What is alkaline fluid produced in the pancreas important for?
(2)
- Neutralising acid
- Providing the optimum pH for enzymes
The pancreas is the most important source of what?
Digestive enzymes
What stimulates the secretion of digestive enzymes by acinar cells?
Cholecystokinin (CCK)
What is the function of pancreatic enzymes?
Luminal chemical digestion of food
Proteolytic enzymes are secreted as what in the duodenum?
Inactive precursors
What is the precursor to trypsin?
Trypsinogen
What is the precursor to chymotrypsin?
Chymotrypsinogen
What is the precursor to carboxypeptidase?
Procarboxypeptidase
In the small intestine what does activation of enzymes involve?
Enterokinase
What is enterokinse bound to?
The duodenal membrane
What does enterokinase do?
Converts trypsinogen to trypsin
What does trypsin do?
Converts other enzymes to their active form
What is secretion of alkaline fluid stimulated by?
Secretin
What is the secretion of secretin stimulated by?
Arrival of acid chyme in the duodenum
What does alkaline fluid do?
Neutralises acid chyme that is delivered from the stomach
What is produced in Billary secretions?
2
- Bile salts
- HCO3-
What is the role of bile salts?
Fat digestion
What is bile secreted constantly by?
The liver
Where is bile stored and concentrated?
In the gallbladder
When is bile delivered to the duodenum?
With the arrival of food
What % of bile is reabsorbed and where is it reabsorbed?
95% is reabsorbed in the ileum
What stimulates the release of bile?
CCK
What is bile transported back to the liver in?
Enterohepatic circulation
What does the small intestine secretion contain?
3
- Mucus
- Isosmotic fluid
- Digestive enzymes
