Topic 6.3 Flashcards
3 types of secretors in the GI
- Exocrine glands (pancreas, salivary)
- Gland formed by the gut wall itself (Bruner, Lieb)
- Intestinal mucosa
2 main functions of GI secretion
Protection, and promotion of digestion + absorption
What are the 2 types of GI secretion?
Organic, inorganic
What are secretagogues?
Ligands which can act on secretory cells. Can be either endocrine or paracrine.
How much secretion / day?
9-10L day / secretion
Daily production of saliva
800-1500mL / day
7 main functions of saliva
- Disrupts the food into smaller particles
- Lubrication for swallowing and speaking
- Initiation of starch and lipid (kids) digestion
- Cleansing function
- Antimicrobial effect
- Neutralization of gastric content
- Calcium binding proteins for teeth
How does the saliva have an antimicrobial effect?
Contains IgA and lysozymes
What are the major salivary glands? (3)
Parotid, sublingual, submandibular
What are the minor salivary glands? (3)
Tongue, lips, palate
What is the general structure of the salivary glands?
Tubuloalveolar
What are the 2 types of acinar cells and their difference?
- Mucous : produce mucin
- Serous : have zymogen granules (amylase and lipase)
What type of gland is parotid?
Mostly serous
What type of gland is sublingual?
Mainly mucous / mixed
What type of gland is submandibular?
Mixed
What type of gland is buccal?
Mucous
4 proteins produced in the acinar cells?
- Amylase
- Ig
- Mucin
- R protein (haptocorin)
What is haptocorin useful for?
B12 absorption : protects it from acidity of the stomach
how is the primary secretion compared to the plasma?
Isoosmotic, with similar electrolyte concentration to blood plasma
What type of epithelium is the acinar epithelium?
leaky epithelium
What inhibits ENaC?
amiloride
What upregulates ENaC?
Aldosterone
How is the resulting saliva?
Hypoosmotic, and alkaline compared to its surroundings
How is salivary secretion regulated?
Mostly parasympathetic, neural regulation
What is VIP coupled to and what does it result in?
Gs coupled, causes “atropine resistant” vasodilation, which increases secretion
What is Ach couples to and what does it result in?
Gq coupled (M3) on acinar cells, causes exocytosis and constriction of acinar cells, which increases secretion
What effect does the sympathetic system have on salivary secretion? (2)
- B2 : increases mucin secretion
- A1 : constricts vessels
What is the external way of salivary secretion?
Unconditioned stimuli activates CN, for example : seeing food, smell…
What type of cells are in the midline of the gastric mucosa?
proliferative cells (regenerate the mucosa)
What do surface epithelial cells produce? (2)
mucin, bicarbonate
What do parietal cells secrete? (2)
the gastric acid + intrinsic factor through exocytosis
What do chief cells secrete?
digestive enzymes
Which cells of the gastric mucosa can be found everywhere in the stomach?
the surface epithelial cells
What is the daily production of gastric juice?
1-1.5L / day
How is the gastric juice osmotically?
isoosmotic
What are the 4 main constituents of gastric juice?
Water, electrolytes (H, Cl), bicarbonate, proteins (mucin, digestive enzymes)
What are the 3 functional regions of the stomach?
- Cardia / LES
- Fundus / body
- Antrum / pylorus
Which is the only region of the stomach to produce gastric juice / acid?
The fundus / body, the rest only secrete mucin and bicarbonate
What is the role of the cardia / LES?
prevent reflux, entry of food
What is the role of the fundus / body?
reservoir + secretion of gastric juice
What is the role of the antrum / pylorus?
mixing, grinding, regulation of emptying
Which cells secrete the intrinsic factor?
parietal cells
How do parietal cells increase their surface and energy?
With the canaliculi and the mitochondria
What are the 2 forms of the parietal cell?
- Resting / inactive
- Active / secreting (has canalicul)
Which drugs can inhibit the K+ / H+ pump? (2)
omeprazol, pantoprazol
What is the H+ source for gastric acid?
Parietal cell metabolism
How is the H+ gradient in parietal cell / lumen?
The gradient is a million-fold : 10^6 : from pH = 7.2 to pH = 1-2
What is the most important regulator of gastric acid secretion?
parasympathetic nervous system through vagal nerve stimulation
What are the 6 ways of activating G cells?
- Ach
- GRP (gastrin releasing peptide) : para sympathetic NT
- Mechanical stimuli : wall tension
- Alcohol, soda, cola
- Helicobacter pilori
- Sympathetic system : B2 receptor
What is the G cell inhibitor?
Somatostatin
How is the release of somatostatin triggered?
If GA secretion is too high, pH is too low, which activates the D cells - which produces somatostatin
What type of receptor is somatostatin coupled to?
Gi receptor
ON which cells can somatostatin act?
On g cells mostly, or directly on parietal cells
On which cells can gastrin act to regulate GA secretion?
On parietal cell directly or on ECL cells, which then release histamine to the parietal cells
What are the 2 phases of GA secretion?
Cephalic phase (smelling, tasting) Gastric phase (presence of protein breakdown product)
Which molecule can decrease GA secretion (on top of somatostatin)
prostaglandins
What produces prostaglandins?
COX enzymes
How do prostaglandins decrease GA?
Gi signaling, reduce cAMP signal and decrease secretion
How does GA composition change based on the rate of secretion?
- Basal secretion : ++ NaCl, low H+
- High secretion : ++ H+ and Cl
What can we use to measure the H+ content of GA?
- BAO (basal acid output)
- PAO (peak acid output)
What is the basal acid output?
1.5 - 2.5 mmol H+ / hour
What is the peak acid output?
Women : 25 mmol H+ / hour
Men : 35 mmol H+ / hour
What protects the gastric mucosa from high acidity?
2mm sticky mucin layer produced by surface epithelial cells
What can regulate Chief cell secretion? (4)
- Acetylcholine (vagus stimulation after meal)
- Gastrin, secretin, CCK
