Lecture 25: SECRETION Flashcards
How many pairs of salivary glands are there?
3
How much fluid do the salivary glands produce?
1.5L per day
What amount of saliva do each of the salivary glands secrete?
Sublingual (5%), submandibular (70%) and parotid (25%)
What is basal saliva secretion?
0.3 ml/min
What is stimulated saliva secretion?
1.5 ml/min
What is the composition of saliva?
Mucus, a dilute solution of NaHCO3 and NaCl, digestive enzymes
What is the purpose of mucus in saliva?
Lubrication
What is the purpose of a dilute solution of NaHCO3 and NaCl in saliva?
To dilute food and provide an optimal pH for digestive enzymes
What are the digestive enzymes in saliva?
Lingual lipase and alpha amylase (denatured in the stomach)
Is saliva essential?
No
What does saliva aid in?
Talking, chewing and swallowing
How does saliva aid in chewing and swallowing?
Dissolves and lubricates food
What is saliva also involved in?
Hygiene and digestion
How does saliva help in hygiene?
Irrigation (removal of old food)
What is xerostomia?
Dry mouth from limited or absent saliva
How does saliva help in digestion?
Dissolves for allowing tasting
What dies lingual lipase break down?
Fats
What does alpha amylase break down?
Starch
What is saliva secretion regulated by?
Nervous system, autonomic nervous system
What is the nervous system activated by (saliva)?
Thought, smell, sight of food and the presence of food in the mouth
What does the parasympathetic nervous system do (saliva)?
Stimulates secretion of abundant quantities of fluid
What does the sympathetic nervous system do (saliva)?
Small volumes of viscous fluid
How much gastric secretion occurs in a day?
2-3L
What is the rate of gastric secretion between meals?
slow (15-30ml/h)
What secretes gastric fluid between meals?
Surface cells secrete mucus
What is the rate of gastric secretion when eating?
Superimposed on basal rate
What secretes gastric fluid when eating?
Mucous cells - mucus, parietal cells -150 ml/h HCl acid pH=0 and intrinsic factor, chief cells - pepsinogen
What is the function of mucus in gastric secretions?
Protection from abrasion and acid
What is the function of intrinsic factor in gastric secretions?
Absorption of vitamin B12 in the small intestine
What is pepsinogen?
The inactive form of pepsin
What type of enzyme is pepsin?
Gastric proteolytic
How is pepsinogen converted to its active form?
By acid
What does pepsin start digestion of?
Proteins
What is the function of gastric acid in gastric secretions?
Dilutes food, denatures protein, activates pepsinogen to pepsin, creates optimum pH for pepsin and protection
What is the source of acid (H+)?
Formation of H2CO3 (carbonic acid) by carbonic anhydrase (CO2 +H2O <>H2CO3) then dissociation of H2CO3 (H2CO3 <>H+ +HCO3-)
How is H+ secreted into the lumen?
By the H+K+ ATPase
Where is H+K+ ATPase found?
On the apical membrane of parietal cells