Salivary Glands: Structure and Functions – Upper Gastrointestinal Secretion

00:00 Let's now talk about saliva production.

00:04 This is a two step process.

00:06 The first step is producing the initial saliva and the second one is modifying it.

00:14 Let's begin by discussing the production of the initial saliva.

00:17 There are acinar cells, and ductal cells. In the acinar cells ions, mainly chloride ions, are secreted actively following these chloride ions.

00:29 Sodium via para cellular transport and water, among others, via aquaporins five.

00:36 Accompany them along with potassium and bicarbonate ions.

00:41 Water naturally follows these ions by osmosis, forming an initial saliva that is isotonic just as salty as our blood plasma.

00:51 Next, this initial saliva travels through ducts where duct cells refine it into its final form.

00:59 Here, the cells remove some salt.

01:02 Sodium is reabsorbed through apical sodium channels, or ENaC and sodium hydrogen exchangers.

01:10 while chloride is taken up via the cystic fibrosis transmembrane conductance regulator, CFTR, and chloride bicarbonate exchangers, which also secrete bicarbonate.

01:24 At the same time, ductal cells secrete potassium via potassium channels as well as extra bicarbonate using transporters such as Slc26a1 and MBC e1 But where does that bicarbonate come from? Duct cells don't just manufacture it out of thin air.

01:44 It enters from two sources.

01:47 First, bicarbonate is drawn into the cell from the blood by the sodium bicarbonate cotransporter known as NBC E1 B, which is located on the basal lateral membrane.

01:59 Think of it as a shuttle that uses sodium to carry bicarbonate from the blood plasma into the cell.

02:06 Second, bicarbonate is produced within the cell itself.

02:11 In this process, carbon dioxide and water combine to form carbonic acid, which quickly breaks down into hydrogen ions and bicarbonate with the enzyme carbonic anhydrase.

02:24 Speeding up the reaction, the hydrogen ions are then pumped out via the sodium hydrogen exchanger NHE1, leaving the bicarbonate behind.

02:37 As for the sodium that just entered, that one is moved via the sodium potassium ATPase out of the cell and into the interstitium.

02:48 The result is saliva that is less salty, hypertonic, and slightly basic.

02:58 Perfectly balanced to aid digestion and protect your mouth.