Digestion 2 saliva secretion

Mechanism of saliva secretion

  1. primary stage 2. modificarion stage

cAMP leads to protein (enzyme/mucus) secretion, while Ca2+ is the primary trigger for the water and electrolyte flow(the Cl– channels).

3. Driving Secondary Active Transport

This Na+ gradient is not just a byproduct; it is the energy source for other transporters. In the salivary glands, the most critical of these is the Na+/K+/2Cl− cotransporter (NKCC1).

  • Hitching a Ride: The NKCC1 transporter uses the energy of Na+ moving down its gradient to pull Cl− and K+into the cell against their own gradients.

  • Chloride Accumulation: This causes Cl− to accumulate inside the secretory cell far above its equilibrium point.

  • Secretion: Eventually, Cl− exits the apical membrane (facing the duct) through channels. Na+ and water then follow the Cl− into the duct to maintain electrical and osmotic neutrality, forming the initial saliva.

PRIMARY STAGE

. Parasympathetic Stimulation (The "Watery" Flow)

This is the dominant pathway for volume. It relies on the IP3/DAG pathway rather than cAMP to raise calcium.

  • Neurotransmitter: Acetylcholine (ACh).

  • Receptor: M3​ Muscarinic receptor.

Result: High Ca2+ opens apical Cl− channels

2. Sympathetic Stimulation (The "Protein" Flow)

This branch primarily uses the cAMP pathway, though it can cause modest increases in Ca2+.

  • Neurotransmitter: Norepinephrine (NE).

  • Receptor: β-Adrenergic receptor.

Mechanism:

  1. NE binds to the β receptor, activating Adenylyl Cyclase.

  2. Adenylyl Cyclase converts ATP into cAMP.

  3. cAMP activates Protein Kinase A (PKA).

it releases the proteins

Water follows this salt immediately via aquaporin-5 (AQP5) channels

300 mOsm/L

MODIFICATION STAGE

K= and HCO3- secretion is lesser thna reabsorption of Na+

the duct walls also not permeaable to water

tactile and taste stimuli from the oral tissues regulate and control salivation