Introduction – Upper Gastrointestinal Secretion

00:02 Hello! Today we’re going to talk about upper GI secretions.

00:07 For this particular lecture, we have a number of learning goals to obtain.

00:10 The first one is we will learn the constituents and the mechanisms of salivary secretions and how salivary glands are controlled and regulated.

00:19 Also, we will learn the constituents of gastric secretions.

00:24 Finally, we’ll be able to understand the mechanisms of hydrogen ion secretion from parietal cell, as well as the control and regulation of those parietal cells.

00:34 We will emphasize how this knowledge then is applied to pharmacology as we approach the task to reduce gastric acid secretion.

00:44 So let’s get right into it.

00:46 The first thing that we’re going to talk about is some of the functions of the GI system, and this helps us to regulate not only our functions now, but integrate that into what we’ve already covered.

01:00 We’re going to focus on the upper portion of the GI tract.

01:05 Particular here, we’re going to talk about the mouth, the salivary glands which will hydrolyze and lubricate food stuff.

01:15 And then finally, the stomach which will act as a blender.

01:19 But here, what will be more important will be the secretion of acid to sterilize the food stuff.

01:27 Again, we have the mouth, the salivary glands, and the stomach to talk about.

01:34 So, salivary secretions.

01:36 Why do we have salivary secretions? One of the first most important aspects is it helps protect the oral cavity.

01:45 So oral cavity protection is very important and we’ll go through which items do that in the constituents.

01:51 It also helps to lubricate food, helps in the digestion of food, especially carbohydrates and fats.

02:02 And what are salivary secretions and where do they come from? Well, the first thing that we need to think about is the parotid gland.

02:09 And this parotid gland secretes primarily serous secretions.

02:13 Serous secretion are watery secretions.

02:19 The sublingual and the submandibular glands have a mixture of mucous and serous secretions.

02:27 So altogether, the parotid gland provides mostly serous secretion.

02:33 The sublingual and submandibular have a mixture of serous and mucous secretions.

02:39 So, the serous secretions will help with hydrolyzing or getting water into the food stuff, and the mucous will provide the lubrication.

02:50 What other constituents are in the salivary glands? Well, probably, we should start off with talking about the ions.

02:58 There is a large amount of potassium in salivary secretions, and this primary function is so that you can reabsorb sodium and water, so you don’t lose as much salt and water.

03:09 You also have bicarb ions which help buffer hydrogen ions, or having a low PH.

03:16 You have two enzymes.

03:17 One is salivary amylase which aids in starch digestion, and lingual lipase which aids in lipid digestion.

03:26 The reason why I state that this aid in digestion is if the salivary glands are removed and you don’t produce salivary amylase or a lingual lipase, you won’t lose the ability to digest carbohydrates and fats.

03:40 It just won’t happen in the mouth.

03:42 They’ll only happen in the small intestine.

03:46 You also have some items that help do the oral cavity protection, such as muramidase which is a lysozyme.

03:54 You have lactoferrin which helps bind iron, and this prevents bacterial growth.

04:01 And you have some immune mediator such as IgA that are also released in the salivary gland secretions.

04:11 Now, the ions that are released with salivary secretions are released in a rate, depending upon how much salivary secretions there are.

04:21 So this can be diagrammed in this kind of format, where we have flow rate on the X axis and we have the concentration of the ion on the Y axis.

04:30 You have salivary secretions increasing the amount of sodium that is released in the salivary gland secretions, and then we compare it to the plasma value.

04:43 If it is below the level of the plasma value, you are reabsorbing that ion.

04:48 If it is above the level of the ion in the plasma, you are secreting it.

04:55 So in this case, you can see across flow rate, you’re always reabsorbing sodium.

04:59 But you do a better job at reabsorbing sodium at a lower flow rate than a higher flow rate.

05:06 Potassium, you secrete because the potassium amount in the blue line is above the plasma value in the blue bar.

05:18 Finally, chloride is reabsorbed, and this is done in a flow rate dependent fashion.

05:23 So, at low flow rates, you reabsorb more chloride than at fast flow rates.

05:29 And finally, we have bicarb which you secrete.

05:32 Again, you’re secreting it so you can help buffer acids, and you know it’s a secreted ion because it’s above the level of the plasma.

05:40 So you have to do something to make sure that happens.

05:44 So looking at all these ions, I talked a lot about how you either secrete them or reabsorb them.

05:50 But how in the world you go about doing that? We need to talk about transporters.