Stomach: Anatomy – Digestive System Organs (Nursing)

00:02 The next major organ of the digestive system after the esophagus is the stomach.

00:09 The stomach is a temporary storage tank that also starts the chemical breakdown of protein.

00:17 Here in the stomach, we're now going to convert our food bolus into a paste like chyme.

00:25 An empty stomach is about 50 milliliters in volume.

00:29 However with food coming into the stomach the stomach can expand to 4 liters.

00:37 When empty the stomach mucosa has many folds in it known as rugae.

00:43 These are able to increase the surface area and also the ability of the stomach to distend when food comes into the stomach.

00:54 The mucosal layer of the stomach is modified a bit, it consists of a simple columnar epithelium entirely composed of mucous cells.

01:06 These are going to secrete a two-layer coat of alkaline mucus so that the surface layer traps bicarbonate rich fluid beneath it.

01:17 Then dotted throughout the mucosa, we have gastric pits.

01:22 These are going to lead into gastric glands.

01:26 These glands are responsible for producing the very acidic gastric juice.

01:35 So if we take a closer look at these glands, we find inside of the stomach, we find that they are going to include secretory cells such as parietal cells, into endocrine cells, mucus neck cells and chief cells.

01:52 Let's take a closer look at each of these glandular cells.

01:57 The parietal cells are going to be responsible for increasing the acidity of the stomach.

02:04 The secretions of the parietal cells include hydrochloric acid, which is there to denature protein as well as activate the enzyme that breaks down protein pepsin.

02:17 It also is able to break down plant cell walls and because of its extremely low PH kills many bacteria.

02:27 The parietal cells also are going to secrete intrinsic factor.

02:31 This is a very important glycoprotein that is required for the absorption of vitamin B12 in our small intestine.

02:42 The mucous neck cells are going to secrete a thin acidic mucus, but we not really sure what the purpose of that mucus is.

02:52 Next we have our chief cells our chief cells are going to secrete the enzyme that is going to be responsible for the breakdown of protein.

03:02 This includes pepsinogen.

03:04 Pepsinogen is an inactive enzyme that is activated to pepsin once it comes in contact with hydrochloric acid.

03:14 And the pepsin itself is going to also activate pepsinogen into becoming pepsin.

03:23 Also chief cells are going to release enzymes known as lipases, which are able to digest about 15% of lipids, which is a very small amount of our lipid digestion in our digestive system.

03:40 Lastly we have our enteroendocrine cells.

03:44 These are going to secrete chemical messengers into the lamina propria of the stomach that act as paracrines like serotonin and histamine.

03:54 And also these are going to secrete some hormones such as somatostatin which also can act as a paracrine and gastrin.

04:05 So now let's look at the mucosal barrier in the stomach.

04:09 Recall that the internal environment of the stomach is actually pretty harsh and it has a very low PH.

04:18 So because of these harsh digestive conditions the stomach area needs to be protected by a mucosal barrier.

04:27 The mucosal barrier contains a thick layer of bicarbonate rich mucus.

04:33 It also contains tight junctions between the epithelial cells found in the stomach, so these extremely acidic gastric juices do not seep underneath the tissue.

04:47 Stem cells that replace damaged epithelial cells are also going to be found in replace the surface cells in the stomach about every three to six days.

04:58 So each week the cells in your stomach are different than the cells in your stomach mean the previous week.