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Пищеварение. Часть 1. — Transcript

by Pavelum U · 2,509 words · 434 segments · language en · Watch on YouTube

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0:02So, the physiology of digestion. Ah,
0:08well, digestion is a very complex
0:10process that includes a number of
0:12functions. This includes a secretory
0:18function, when a large number of
0:19enzymes are released into the lumen of
0:21the gastrointestinal tract. A motor
0:28function, when chyme moves from one
0:30section to another in the digestive
0:32tract. This includes the absorption of
0:38hydrolysis products. An excretory
0:41function, when the gastrointestinal
0:43tract participates in the removal of
0:45harmful products, and other functions.
0:51Therefore, digestion is also divided
0:53into intracellular, intracellular, and,
0:56naturally, extracellular. Intracellular
1:04digestion occurs due to enzymes in
1:06lysomes, in the intracellular space, in
1:09the cytoplasm, when substances enter
1:11there, and extracellular digestion is
1:14divided into lumen digestion, due to
1:16enzymes secreted into the lumen of the
1:18gastrointestinal tract, and parietal
1:21digestion. Parietal digestion, which is
1:27provided by enzymes attached to the
1:29indigestible aqueous layer on the
1:35surface of gastrointestinal cells.
1:38There are a very large number of
1:40enzymes here that ensure extremely
1:42active hydrolysis processes and are
1:44also associated with this absorption
1:46process. This mechanism was discovered
1:49by Ugolov. Ugolov. Therefore, this type
1:54of digestion is also called Ugolov
1:56digestion. We will consider some
2:00processes throughout the
2:01gastrointestinal tract. It is also
2:10immediately noticeable that in the
2:12initial sections of the
2:13gastrointestinal tract, neural
2:15influences of regulation are more
2:17pronounced, more significant regulatory
2:19processes are due to the nervous system
2:21, and then the influence of humoral
2:23factors increases, starting in the
2:25small intestine. Humoral factors then
2:31play a very important role in
2:33regulation. The importance and
2:37complexity of neural influences is
2:39emphasized by the fact that the
2:41meta-sympathetic system is very
2:43pronounced in the gastrointestinal
2:45tract. It is represented by neurons of
2:49the Mesner and Auerbach plexuses, the
2:51intermuscular mucosal and submucosal
2:53nerve plexuses. The number of nerve
2:57cells in the gastrointestinal tract,
2:59well, almost corresponds to that in the
3:01brain, the central nervous system.
3:05That's why in English there is such a
3:07thing as "brain," or intestinal brain.
3:13The IC Brain, which very complexly
3:15coordinates and ensures the proper
3:18course of all digestive reactions, also
3:20plays a very important role. Humoral
3:28regulation is ensured by a huge number
3:30of hormones of the diffuse endocrine
3:32system, also called the Amin precursor
3:35decorboxation system. This includes a
3:39large number of, as I already mentioned
3:41, primarily peptide hormones. Secretin,
3:44bombesin, matilin, somatostatin, and
3:47others, which we'll discuss later, also
3:50ensure adequate digestion. The food
3:55that enters, and all processes are thus
3:57coordinated. So, let's begin our
4:02discussion in more detail with the
4:04digestive processes in the oral cavity
4:06and move further down the digestive
4:08conveyor belt. In the oral cavity, food
4:14is mechanically ground and chemical
4:17hydrolysis, the initial chemical
4:19breakdown, begins. Regarding saliva in
4:24the oral cavity. So, saliva contains
4:30lysozyme. Lysozyme is an antibacterial
4:35component. Well, not only lysozyme, but
4:38also immunoglobulins, secretory and
4:40other antibacterial substances.
4:42Nevertheless, the oral cavity contains
4:44a very large number of bacteria. This
4:46must be taken into account. In
4:49particular, wounds inflicted by bites,
4:54so-called bite wounds, take a long time
4:56to heal. In addition, there is amylase,
5:00salivary amylase, as it's called.
5:05Amylase. Amylase is an enzyme that
5:09breaks down bonds in large
5:11carbohydrates, such as starch.
5:17Typically, during the few dozen, maybe,
5:19well, seconds or tens of seconds that
5:22food is in the mouth, it doesn't have
5:24time to break down into glucose, of
5:26course, but hydrolysis of carbohydrates
5:28begins in the oral cavity. Saliva also
5:32contains other enzymes; there are more
5:34of them, but in much smaller quantities
5:37, lipases, and, in general, several
5:39dozen enzymes, but they play a lesser
5:42role. Nevertheless, saliva plays an
5:45important role; for example, for
5:47diagnostics, you can determine the
5:49levels of various hormones; you can
5:51even perform an ovulation test using
5:53saliva. So, diagnostics, that's the
5:56section of diagnostics. Then, mucus,
6:04mucus, uh, well, due to mucin, that is,
6:07whether it contains mucin. Mucin, mucus
6:11, a similar substance. This is
6:13necessary to ensure the formation of
6:15the food bolus. The food bolus, and
6:21without saliva, it could not be formed.
6:25And the regulation of salivation, then,
6:28is regulated by complex reflexes
6:30through conditioned and unconditioned
6:32reflexes. That's what "complex reflexes
6:35" means. Well, of course, reflexes are
6:38when food enters the mouth, the oral
6:40cavity, and acts on the receptors. And
6:44conditioned reflexes occur when,
6:46generally speaking, there's no food yet
6:48, but, for example, a person is
6:50thinking about food or, for example,
6:52reading a menu or remembering some
6:55delicious dishes. Or, for example,
6:58thinking about lemon—yes, lemon—and
7:01, in general, acid naturally promotes
7:04saliva secretion. So, these reflexes
7:07are primarily influenced by the
7:09sympathetic and parasympathetic systems
7:12. How do these two systems influence
7:13each other? One increases it, the other
7:15increases it. Here, we'll draw the
7:17basal secretion of saliva somewhere.
7:19Here, we'll draw the influence of the
7:20parasympathetic system. Well, and here,
7:22let's say, the sympathetic system. So,
7:24the parasympathetic system to a greater
7:26extent, the sympathetic to a lesser
7:28extent, but they both increase saliva
7:29secretion. However, the quality of
7:31saliva varies. The parasympathetic
7:34increases the secretion of enzyme-rich,
7:37mucus-poor saliva, while the
7:39sympathetic secretes mucin-rich,
7:41viscous saliva. Well, there aren't many
7:45enzymes there. How is saliva secreted?
7:48There are, uh, the major salivary
7:50glands. There are a large number of
7:53simple ones, which are disseminated
7:55throughout the oral cavity. Well, the
7:57major glands are the parotid,
7:58sublingual, and pelvic. They secrete
8:00different things, some serious, some
8:02mixed. Perhaps, well, uh, you can read
8:05about this in more detail. Then, this
8:15processed food forms a food bolus in
8:17the oral cavity, which then passes into
8:23the esophagus through the act of
8:25swallowing. Swallowing is a complex
8:28reflex action involving the muscles of
8:30the vena cava. Well, with the action of
8:35the food bolus, both boluses pass
8:37portionwise into the esophagus. Dry
8:42food stays there a little longer than
8:44liquid food. Liquid food, for example,
8:47spends maybe 2 seconds in the esophagus
8:49, 2-3 seconds. Dry digestion takes a
8:52little longer, maybe 5-8 seconds. Due
8:58to esophageal peristalsis, muscle
9:00contraction, the food bolus enters the
9:02stomach, where it's called chyme. Chyme
9:08. The cardiac sphincter between the
9:11esophagus and the stomach opens
9:13slightly, and the food bolus reaches
9:15the stomach. The stomach has a cardiac
9:21part, the cardia, a pylar part, a
9:24greater curvature, a lesser curvature
9:26of the stomach. There's the antral
9:30section. The antral section of the
9:33stomach. Oh, the antral section of the
9:35stomach and the cardiac, as already
9:37mentioned, the cardiac. And chyme stays
9:43in the stomach for quite a long time.
9:48It's about an hour for carbohydrate
9:50foods. The stomach passes through the
9:53chyme the fastest. Protein foods take
9:57several hours, 2-3 hours, and up to 5
10:00hours. Fatty foods accumulate for a
10:04long time. That's why patients with
10:09peptic ulcers, for example, consume
10:12dairy products at night, which contain
10:14a lot of fatty substances. Digestion in
10:21the stomach is ensured by gastric juice
10:23, which is secreted in quantities of
10:25several liters per day. That's about 2
10:28liters. By the way, we can also mention
10:31that the amount of saliva is quite
10:33large. It was also about one and a half
10:35to two liters of saliva per day. There
10:37is basal secretion, and there is
10:38induced secretion. We've already talked
10:40about this a little. So, gastric juice
10:44contains hydrochloric acid. What
10:51functions does hydrochloric acid
10:53perform? It ensures protein
10:55denaturation. The first function is
10:58protein denaturation. Protein
11:02denaturation. Third, the secondary and
11:05quaternary structures are destroyed,
11:07and proteins become more vulnerable to
11:10the action of pepsin. And by the way,
11:15the pH in the cardiac part varies by
11:17about one to two, very acidic. Here in
11:23the pylar part of the stomach, the
11:25acidity decreases slightly. And in
11:30addition to denaturation, hydrochloric
11:32acid activates pepsinogen. B.
11:34Pepsinogen activation. Pepsinogen is a
11:44precursor to pepsin, a so-called
11:46proenzyme. This is important to prevent
11:50autolytic processes that cause gastric
11:52cells to self-digest. Many enzymes are
11:55activated directly in the stomach
11:57cavity. Another function of
12:06hydrochloric acid is its protective
12:12function. This protective function
12:14means it prevents the growth of a large
12:18number of bacteria. There's a species
12:22called Helicobacter pylori. This
12:26bacterium can live in very harsh
12:28conditions. It's associated with
12:33maintaining the ulcer process in the
12:34stomach and duodenum. It prevents
12:40ulcers from healing. However, many
12:43healthy people also have this condition
12:45, so a compromised immune system is key
12:47. Incidentally, under stress, we
12:54primarily see damage to the gastric and
12:56duodenal mucosa in patients. Another
13:06function of hydrochloric acid is to
13:08coordinate the passage of chyme from
13:10the stomach to the duodenum. The next
13:25component of gastric juice we'll
13:26discuss is pepsinogen, which is
13:28converted into pepsin. Pepsinogen. In
13:33fact, we don't have just one pepsin or
13:35one pepsinogen, but a whole group of
13:38these enzymes—pepsins of the first
13:40group, pepsins of the second group—
13:42and they have different optimal
13:43conditions. Some work in more acidic
13:46environments, others in more alkaline
13:48environments, and in more, er, alkaline
13:51, meaning less acidic environments. But
13:57they all break down bonds in proteins,
14:00and to form peptides, shorter chains
14:02are formed from long protein molecules.
14:09These factors are also part of gastric
14:12juice. Mucus is also part of gastric
14:16juice. Well, water, of course, and some
14:20other components may be present. For
14:23example, besides psinogen, it also
14:25contains other enzymes. For example,
14:28renin, which is involved in the
14:30curdling of dairy products, and other
14:32lipases. However, the pH here isn't
14:35optimal for them, so they're less
14:37significant. The main thing is the
14:39breakdown of protein bonds. This is
14:43what happens in the stomach. Gastric
14:45secretion is a very important issue. It
14:48is divided into several phases. The
14:52first phases, these phases were
14:54discovered by Ivan Petrovich Pavlov,
14:56and they are called as follows.
14:58According to Pavlov. So, the phases of
15:00gastric secretion according to Pavlov.
15:03The first phase of gastric secretion is
15:05called the complex reflex phase. The
15:08complex reflex phase. The phases of
15:13gastric secretion. This complex reflex
15:18phase, or the cerebral phase, as it is
15:20sometimes called, the complex reflex
15:24phase. It is conditioned by conditioned
15:27and unconditioned reflexes. Well,
15:30unconditioned reflexes are, for example
15:32, when certain foods act on receptors
15:35in the gastrointestinal tract, and
15:37conditioned reflexes are, say, reflexes
15:40that arise from smell, thoughts about
15:43food, or, say, time. For example, if a
15:46dog or a person is fed at a certain
15:48time, then this secretion can begin at
15:50that time. According to Ivan Petrovich
15:54Pavlov, approximately 50 ml is produced
15:57, and gastric juice, which Pavlov
15:59called "igniting juice" from the word "
16:02igniter." This igniting juice is not
16:08sufficient for digestion, but it is
16:10necessary to induce gastric secretion
16:12in the subsequent secretion phase. And,
16:22which is called the gastric phase. The
16:25gastric phase. The gastric phase is
16:29when the components of the chyme act on
16:31the receptors of the stomach and the
16:33production of juice corresponding to
16:35the components of the chyme is formed.
16:40And the third phase is the intestinal
16:42phase. The intestinal phase is when the
16:47food, when the chyme enters the
16:48intestine and gastric secretion is
16:50inhibited by the components of the
16:52chyme. Pavlov received the Nobel Prize
16:58in 1906 for the discovery of these
17:00phases. And it is also worth noting
17:10that, in general, so to speak,
17:19observing the stomach, the functions of
17:21the intestine, allowed Pavlov to
17:23further develop the concept of higher
17:26nervous activity, to an understanding
17:28of reflexology. That is, the
17:33functioning of the digestive system
17:35mirrors processes in the central
17:37nervous system. Which is understandable
17:41, given the complex internalization of
17:43this system. What allowed Pavlov to
17:46identify these secretory phases? Just a
17:48few words. These were operations on
17:52dogs using fistulas, the fistula
17:54technique. And before Pavlov, there
17:59were types of Heidenheind operations,
18:01for example, where a small ventricle
18:04was surgically formed, which, uh, could
18:06be examined using a fistula—that is,
18:09through a fistula, uh, to collect, say,
18:11the stomach, to collect, a tube like
18:14this, to collect gastric juice. But
18:17what did Pavlov do? He created this
18:21small ventricle, uh, and thus, uh,
18:23formed it so that the connection with
18:25the vagus was preserved. Thus, it
18:32became possible to regulate secretion
18:34in this small ventricle, which served
18:37as the foundation for Ivan Petrovich's
18:39discoveries. Well, now we need to talk
18:46about how this regulation is actually
18:48achieved. Well, here's the complex
18:51reflex phase. The main role here is,
18:54naturally, played by nervous regulation
18:57, which is ensured by the main
18:59parasympathetic nerve, the vagus, which
19:01innervates the stomach and, uh,
19:03secretes acystylcholine, which,
19:05accordingly, acts on the naimohali
19:07receptors, which triggers gastric
19:09secretion. So, the vagus nerve
19:16innervates the stomach. But the next
19:20mechanism we'll now consider concerns
19:22the fact that, uh, gastrin plays an
19:24important role. Let's, uh, now consider
19:29the gastric mucosa and the cells
19:31located there. Well, let's designate
19:34the parietal cells or parietal cells.
19:37Parietal or parietal cells secrete
19:39hydrochloric acid. Well, more precisely
19:42, protons and chloride anions. This is
19:45where the proton pump is located. And
19:49this proton pump can be blocked with
19:51drugs, proton pump inhibitors. For
19:54example, Amez, one of them with many
19:57trade names: Prozol, Parit. And then
20:05next to it are the chief cells that
20:07secrete pepsinogen. Pepsinogen is the
20:11chief cell of the stomach. The chief
20:14cells. Also located here may be some,
20:17so to speak, accessory cells, mucin,
20:21mucus. And, of course, we'll also
20:24designate G cells. G cells belong to
20:28that very same opportunistic system we
20:30already mentioned. G cells produce the
20:33hormone gastrin, which is secreted into
20:35the body's internal environment.
20:40Gastrin, and it acts on mast cells,
20:43that is, tissue basophils, mast cells
20:45whose granules contain histamine,
20:47heparin, and other bioactive substances
20:50. In particular, histamine acts on
20:56histamine receptors of the second type
20:58on the surface of parietal cells, that
21:00is, parital cells. Stimulation of these
21:05histamine receptors of the second type
21:07by histamine leads to increased proton
21:09secretion. Well, uh, that means
21:13pharmacologists use it. You can block,
21:16for example, these H2 histamine
21:18receptors, like ranitidine, and reduce
21:21gastric acid secretion. It's not a very
21:24good drug; they can become addictive,
21:26which is why proton pump inhibitors are
21:28now used. But these H2 receptor
21:31blockers are selective for the
21:33treatment of allergies. There are other
21:36antihistamines, H1 receptor blockers,
21:39like Vigil, Dimidrol, and others. So,
21:44this mechanism ensures, uh, increased
21:46secretion. And what does gastrin
21:51secretion depend on? It depends on the
21:53components of the chyme. I've already
21:55talked about this. If, say, there's a
21:58lot of protein in the diet, then
22:00secretion increases accordingly. It's
22:09also possible to use gastrin analogs,
22:11for example, pentogestrin, a
22:13pharmacological drug for stimulating
22:15gastric secretion. Well, then, when,
22:23for example, gastric intubation needs
22:26to be studied, secretion needs to be
22:28stimulated to obtain gastric juice.
22:33Cabbage extract, broths, and, by the
22:35way, alcohol are also good secretion
22:38stimulants. So, we'll probably stop
22:44here for the first part, and then we'll
22:46continue.

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