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Internal structure of medical leech

The medical leech has a powerful, well developed musculature. The muscles lie under the outer layer of the integumentary tissue, the cells of which reliably protect them from the harmful effects of the environment. The musculature, which is 70% of the total volume of the leech body, is heterogeneous in its structure. It is represented by several layers of specialized muscle beams. Internal structure of medical leech
Right under the skin are located the ring muscles. Their contraction in response to nerve impulses causes an increase in the length of the leech's body: it stretches. Under the layer of the ring pass the bundles of longitudinal muscles developed in the leech best.
The activity of these muscles causes a decrease in the length of the leech's body, causing it to contract. The medical leech also develops the spinal abdominal muscles.
The greatest interest for medicine and zoology is the digestive organs of the medical leech, since it is the characteristics of this physiological system that allow the leech to be used as a therapeutic agent. Leach is defined by scientists as a true hematophagous (haima-blood and phagos-devouring)
This definition is absolutely correct, because nothing but blood, medical leech does not feed. At the same time, it is able to absorb exclusively the blood of vertebrates, than it differs from other hirudins that have adapted to eating all kinds of aquatic and terrestrial invertebrates. Medical leech is adapted to the consumption of blood of any vertebrate, however its main host can become only a large mammal, including. human.
The digestive tract of the leech opens at the anterior end of the body with a mouth opening. In the depth of the mouth, just before the pharynx, there are three small white corpuscles in the form of a half lens. This jaw device leech. Two jaws are lateral, and the third is dorsal. Each of the jaws carries from 80 to 90 small denticles. The teeth of the medical leech are very sharp, which allows it to quickly bite through the thick skin of warm-blooded animals.
The pharynx near the leech is short, it is surrounded by thick beams of powerful muscles. This musculature compresses the pharyngeal walls and promotes active swallowing of the blood from the incised teeth. Following the pharynx is the esophagus, which passes into a multi-chamber stomach, also called the gastric gut. There is an intensive process of accumulation of blood, which is served by 10 pairs of segments that can expand.
The gastric gut is the most voluminous part of the digestive system of a medical leech. Segments of the stomach, called chambers, were formed by narrowing in several places the original straight tube of the food canal. Constrictions divided the tube into a number of partially isolated sections, the walls of each of them later became protruding. The lateral protrusion of the chambers led to the appearance of a bag similar to the shoots, increasing the volume of the segments of the stomach-gut.Reproduction of medical leeches
Throughout this part of the digestive canal, the size of the departments is different, A bag like protrusions are developed unequally. The largest segments are at the end of the stomach, closer to the throat they narrow. This structure of the stomach-gut, combined with its ability to stretch gives the leech the ability to suck (take away) the blood of the host.
Stocks of the stomach provide a full life leech for several months. At the same time, if you take into account the total volume of mammalian blood circulating in the body, the leech takes not much from the owner. The average leech, reaching a mass of 2 grams, sucks no more than 8 ml. Blood, although it can absorb up to 10-15 ml. those. Almost 8 times its own weight. The segments of the stomach of a healthy leech serve as a reliable storehouse of blood, which does not coagulate in them, does not become infected with microbes, and does not deteriorate for other reasons.
Previously, physicians forced leeches to regurgitate sucked blood to empty their stomach and force them to suck blood again. This allowed the use of leeches for a second time. The eructation occurs at immersing of a leech in vinegar, wine or a saline solution. Artificial eructation is also caused by squeezing the leech with your fingers. Now these techniques are not used, doctors do not force leeches to regurgitate, because with repeated regurgitate the medicinal qualities of the leech significantly decrease, their tender digestive system is injured. In natural conditions, healthy leeches never regurgitate with the exception of a difference in atmospheric pressure.
If the accumulation of blood occurs in the stomach of the leech, the process of digestion is carried out in the terminal intestine. It is very short, less than 1/4 of the length of the leech's body and resembles a thin straight tube. Blood enters this tube in small portions for digestion. The shortest part of the digestive canal is the anal gut. Here, the digested remains of blood form the feces, which are then evacuated through the anus (powder).
Emptying the bowels of leeches is carried out regularly, up to several times a day.Therefore, the water in the vessel where the leeches used are stored periodically. Frequent staining of water should not cause any concern, since it indicates only the health of leeches and the normal nature of their physiological dispatches. Occasional clogging of water does not cause any harm to leeches if the water is systematically changed.

Care of leeches is necessary. It is not only to periodically update the water in the vessel. Important for the content of leeches is the observance of normal light and temperature conditions. Leeches, however, are strictly forbidden to feed. For medical use only hungry leeches, capable of sucking blood of blood, are suitable.

In addition to sharp teeth and a powerful pharynx, the most important device for sucking blood is in the leech salivary glands. Strictly speaking, it is the function of these glands that determines the interest of physicians in leeches. Salivary glands of leeches are located around the pharynx, forming a large accumulation of negligible small whitish balls.
Each such ball is a body of the gland, consisting of a single cell. Inside this cell is a large nucleus, which has a small nucleolus with chromosomes and filled chromatin with grains. The rest of the inner space of the cell is filled with a special fluid - the cytoplasm, in which the grains that produce the secret of the salivary glands are suspended. This secret, i.e. The final product of biochemical synthesis, goes along the inferior duct and is mixed with the water in the body of the leech. As a result, saliva is formed, containing biologically active substances.
Each glandular cell is provided with a duct, which thus joins the jaws. The ducts gradually converge, as they approach the jaws, into bundles. These bundles pass inside the jaws, ending on their surface and opening with small holes between the teeth. From these holes, saliva enters the wound bitten by the leech.
Salivation, as experiments have shown, occurs continuously during the whole act of sucking. The active components of the secretion of the salivary glands and determine its biological and pharmacological properties.
In living cells, the flow of biochemical reactions is impossible, for the realization of which high temperatures or strong acids and alkalis are needed.
To cause the transformation of a variety of substances, the human body has a stock of some specific compounds called enzymes. They are active at normal body temperature and act as regulators inside and extracellular transformations of organic substances.
Since the process of digestion begins already during chewing, during the processing of food by saliva, it is here that the enzymes that split and transform nutrients contained in food enter the reaction for the first time. The same thing we see in leeches. The main enzyme of the salivary glands of the leech is hirudin, but some other enzymes play an important role: hyaluronidase, destabilase, orghelase, antistasin, decorzine, caleline, eagle. In total, in the leech saliva there are up to 20 active proteins.
Before, it was mainly spoken about enzymes that accelerate chemical transformations. These are catalysts, i.e. Activators of reactions. However, there are regulators of the reverse action, also contained in the secretion of the salivary glands of the leech. They are inhibitors, i.e. Suppress the activity of other enzymes and drown out certain reactions.
Hirudin and many other substances of the secretion of the salivary glands of the medical leech are both inhibitors that suppress the blood clotting reaction and catalysts that break down many of the proteins of our blood plasma. The chemical analysis of the medical leech tissues revealed a low content of hirudin in all parts of its digestive system.
In the terminal colon, hirudin is split by enzymes of a different type. Due to this, blood coagulation is possible here, clots of which are immediately digested by digestive juices into amino acids. This is how the blood is digested in the intestine of the leech.
Medical leech has a nervous system, built on a very special pattern, different from the nervous organization of the lower or, on the contrary, the highest representatives of the animal kingdom. More primitive jellyfish and hydra instead of the nervous system have a dense network of neurons (nerve cells) controlling the reactions of these creatures.
Of the special senses of the leech, only the eyes are present, although they are present in large numbers. Recall that the leech has 10 eyes. They are globular chambers that do not have a lens and carry 50 photoreceptors each.
Judging by the structure of the eyes, the leech does not perceive the whole image. But it responds well to many external influences, although it lacks organs of smell and touch. Irritations are detected by sensitive skin cells, which are either elements of sensory kidneys (receptors) or nervous leech bodies.
From the kidneys and other nerve cells of the skin stretch nerve fibers, gathering as they merge into the nodes of the neural chain. 

Almost every segment of the leech on the ventral side has such a node. The nodes are connected to each other, ensuring the reception and transmission of pulses in the nervous system.
Together, all this education is called the abdominal neural chain, performing in the leech the same functions as the central nervous system (brain and spinal cord) in humans. The largest nodes of the chain are the supra-pharyngeal and under the pharyngeal nodes located at the cephalic end. The supra-articular node is the largest. It is connected with under the pharyngeal special lintel, so that around the throat of the leech a ring is formed, which zoologists call the endocrine nerve node.
In importance it is like the human brain, although, of course, it is not equal to it and differs in structure. The "brain" of the leech is relatively simple. Its two constituent elements (the supra-pharyngeal and the pharyngeal nodes) mutually complement each other, since the action of one compensates and partially neutralizes the action of the other.
Despite the apparent primitiveness of the sensual perception of leeches, they are perfectly orientated in space. The sense of smell, taste and touch in the absence of appropriate sense organs are developed in them unusually, which contributes to their success in the search for a victim. First and foremost, leeches respond well to smells coming from objects immersed in water. Irritant smells cause the leech to hurry to move to another place. The leeches do not tolerate foul-smelling water.
From a variety of different smells - pleasant and unpleasant - animals with high accuracy recognize those that come from people and large mammals, i.e. Potential hosts. This proves simple, but cleverly delivered experiments that are easy to replicate at home. For example, 2 clean plugs are poured into the water. At the same time, one of them is necessarily lowered by a hand in the glove, another hand without a glove. As a result, most leeches invariably cram the plug, which is in contact with the human skin, and not with a glove. Leeches will become much more active if the smell of a person on the cork is strengthened (hold the palm between the forearm and the ribs in the armpit).
Of course, the scent of blood is more attractive for leeches. Their reaction to this stimulus is instantaneous. It is necessary to add a few drops of mammalian blood in a vessel with leeches, like leeches, if they are hungry and healthy, they quickly take a cunning "rack." They rise at the rear ends of the body, stretching out into a string, and begin to swing vigorously. The anterior end of the body produces movements that demonstrate attempts to leeches to attach to a potential victim.
Search for the future master parasites also lead by the fluctuation of water caused by any large animal. Noise in the water generates waves that leech catch easily and readily swim to the source of sounds. It has been proven by experience that even weak bursts attract dozens of leeches in densely populated with hirudinas.
Among other things, it is necessary to mention the presence of leeches in the so-called leeches. Thermal feeling. Thermoreceptors are present in a great number of living beings, but only in some highly organized bloodsuckers are they specialized. Temperature sensitive human skin receptors are adapted to distinguish the degree of heated surfaces of different objects in a large temperature range. Our skin, therefore, can signal only the danger of thermal damage to the skin - due to burns or frostbite.
Leeches, like South American vampires (bats), catch a slight difference in the heated surface. This has a certain biological meaning, because in the course of evolution, some worms developed thermotropism (the desire to move into the region with temperatures higher than normal).
Adhering to the skin, the leech does not immediately start to bite. She persistently searches around herself for the warmest patch of skin. The same instinct that controls the blood-sucking bats of the New World, tells the medical leech that the warmest areas of the skin are the most rich in blood. Capillaries are overcrowded here, intensive microcirculation in the tissues contributes to their greater warming and increases the power of the flow of infrared (thermal) radiation.
It is not desirable to mistake the leech in determining the body temperature of the victim. At all warm-blooded creatures at hit in cool water the narrowing of capillaries occurs, resulting in microcirculation of blood becomes slow. That's why the amount of blood taken away by the leech is strictly dependent on the point of the skin where it sucked. To take away more blood, the leech must find a zone with increased microcirculation, where the capillaries are narrowed slightly.
Reactions of leeches to smells, fluctuations in water and temperature of human skin have been thoroughly studied by zoologists in the last two centuries, and even earlier people managed to superficially study the sense of smell, touch and other feelings leech, based on personal observations. The findings are the basis for leech fever, leech breeding and bdellotechnics, and in particular the technique of setting medical leeches for patients.
At the same time, for practical needs, leech breeding is not at all of any importance for the research of the sexual system of the leech and the peculiarities of its reproduction. As it was said in the previous section, leeches are hermaphrodites, i.e. Have a dual sexual system, which includes both male and female genitalia.
Sexual maturity is reached only by leeches of 3 years of age, because they have already accumulated the necessary mass for the development of the body's sexual products - eggs and spermatozoa. Leech, breeding once a year, in the summer, for its life brings from 3 to 4 offspring.
As shown by laboratory studies, the average life expectancy of leech is 6 years. How many live wild animals, scientists do not know for sure, although it is possible that among the leeches there are their long-livers.

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