Stomach: Gastric Secretion and Emptying – Digestive System Organs (Nursing)

00:02 So now let's look at the digestive process that is carried out by the stomach.

00:07 Recall that the stomach is going to break down food by way of chemical digestion.

00:13 It is also going to serve as a storage tank or holding area for food.

00:19 While it is holding food there, it is also delivering chyme to the small intestines, the next organ of the digestive tract.

00:30 Also, it is going to denature proteins by hydrochloric acid and as well, it's going to denature proteins by the enzyme pepsin which is going to carry out enzymatic digestion.

00:44 Also, there's a milk protein on his casein that is broken down by renin and infants but this is only found in infants and is not found in the adult stomach.

00:57 Also lipid-soluble alcohol as well as aspirin are actually able to be absorbed through the lining of the stomach.

01:06 So we normally don't consider the stomach and absorptive digestive organ, but some chemicals are able to be absorbed here.

01:17 The only stomach function that is essential to life is going to be the secretion of intrinsic factor.

01:24 This is necessary for vitamin B12 absorption.

01:29 B12 is absolutely necessary for our red blood cells to mature.

01:35 And if you have a lack of intrinsic factor, this can lead to a disease known as pernicious anemia.

01:42 And the way this is treated is by injecting B12 into the individual.

01:50 So looking at the gastric secretions, we find that the gastric mucosa secretes about 3 liters of gastric juice a day.

02:00 This is regulated by neural mechanisms such as vagus nerve stimulation which increases secretion of this gastric mucosa, and as well sympathetic stimulation, which will decrease the production of these gastric juices.

02:18 Also, we have hormonal mechanism such as the hormone gastrin which is going to stimulate enzymes as well as hydrochloric acid secretion.

02:30 Recall that hydrochloric acid is what makes the gastric juice very acidic.

02:37 Also, there are hormones that are referred to as gastrin antagonist, and these are secreted by the small intestine.

02:48 Secretion of our gastric juices is going to be regulated in three phases.

02:54 The first of these phases is the cephalic phase.

02:58 The cephalic phase happens prior to food entering the stomach and can be triggered by smell, taste, or even the sight of food.

03:09 These stimuli are going to activate neural centers in the cerebral cortex, the hypothalamus and the medulla oblongata that are going to stimulate the secretion of gastric juices as the stomach is prepared for the food that will eventually enter.

03:28 The cephalic phase can be inhibited by stimuli such as depression.

03:37 The second phase is going to be the gastric phase.

03:41 And this phase gastric juices are going to be released.

03:45 This is activated by stretch receptors and also chemical stimuli such as 1 chyme enters the stomach and increases the pH slightly then this chemical stimulus is going to activate the secretion of gastrin which then further activates the secretion or release of hydrochloric acid.

04:07 This phase can be inhibited by excessive acidity which is a negative feedback loop so that the stomach does not become too acidic.

04:17 And it also can be inhibited by emotional stress.

04:23 The final phase is the intestinal phase.

04:26 The intestinal phase involves partially digested food that enters into the small intestines.

04:34 This leads to a brief release of intestinal gastrin followed by inhibition of the release of gastric juices.

04:44 It is triggered, again, by the presence of partiallydigested food and the duodenum, which is the first section of the small intestine.

04:53 Or also the distention of the duodenum when the stomach begins to empty kind into the duodenal area.

05:03 After a brief gastrin release by the small intestines, there's an inhibition of gastric juices in the stomach.

05:12 This will then slow the exit of chyme from the stomach to the duodenum so that the duodenum does not become overwhelmed with food entering into the first part of the small intestine.

05:27 There are four main factors that are going to cause this inhibition of gastric secretions.

05:34 First, the distinction or stretch of the duodenum due to entry of kind is the first thing that's going to tell our stomach we need to stop making gastric juices.

05:46 Next the presence of this acidic chyme can be sensed by receptors and a duodenum again, sending signals back to the stomach to decrease gastric secretions.

06:00 As well, the presence of fatty chyme also has its effect and finally the presence of hypertonic or very salty kind can also have the effect of inhibiting gastric secretions.

06:15 These inhibitory effects are important because they protect our intestines from being overwhelmed by too much chyme or by too much acidity.

06:27 This inhibition is going to be achieved in two ways.

06:30 We have the enterogastric reflex, which involves the stretch receptors in the stomach the send nerve impulses to the brain turning on sympathetic stimulation in the stomach and slowing down gastric motility.

06:46 We also have enterogastrones which is a hormone that is secreted by the duodenum in response to high fat content, and also, slows our gastric motility.

07:01 So speaking of gastric motility peristaltic waves are going to move toward the pylorus or the end of the stomach at a rate of about 3 times per minute.

07:15 Basic electrical rhythm is set by enteric pacemaker cells.

07:21 These pacemaker cells are linked by gap junctions that caused the entire muscularis to contract.

07:30 Distension and gastrin release are going to force the motility of these peristaltic waves through the stomach.

07:41 Contractions are most vigorous and Powerful near the pylorus.

07:47 About 30 milliliters of chyme is produced and either delivered to the intestines and 3 milliliters spurts while the rest of the 27 milliliters are forced backward into the stomach.

08:03 Only liquids and small particles are allowed to pass through the pyloric valve without going through this process.

08:14 The duodenum can prevent overfilling by controlling how much chyme enters we have duodenal receptors that respond to both stretch as well as chemical signals.

08:27 Recall the enterogastric reflex as well as the enterogastrone-hormones inhibit gastric secretions, which further inhibit duodenal filling.

08:39 The stomach is able to empty its entire content in about four hours.

08:45 However, if there is a lot of fatty chyme, so if the content of the chyme has a large lipid content, then this time can be increased to about 6 hours.

08:57 The fastest moving kind moving from the stomach into the small intestine is going to be kind that is carbohydrate rich.