Features of human roundworm. Life cycle of human roundworm

Question 1. Describe the structural features of roundworm. What is cuticle? What is its significance?

The digestive system begins with the mouth opening, surrounded by 3 lips (ridges). Semi-digested food by the host first enters the short pharynx, then into the midgut, where it is finally digested and absorbed. The midgut passes into the hindgut, ending in the anus.

Cuticle (from Latin cuticula - skin), in invertebrates - a derivative of cells of the single-layer integumentary epithelium. Performs mainly protective and support functions.

Question 2. What is the role of the body cavity in the roundworm?

The body cavity is the space between the internal organs and the skin-muscular sac, which is filled with cavity fluid. The cavity provides free placement of internal organs. The cavity fluid, under pressure above atmospheric pressure, gives elasticity to the body of the roundworm and performs the function of a hydroskeleton, and also transports nutrients and waste products (transport function).

Question 3. How does the nervous system of nematodes work?

The nervous system is formed by the peripharyngeal nerve ring surrounding the anterior part of the esophagus. Several short branches extend forward from the ring; Six trunks are directed back, and two of them, passing along the median dorsal and abdominal lines, are more powerful than the others. Both main nerve trunks are connected to each other by numerous jumpers, which look like thin half-rings encircling the body.

Question 4. What parts make up the digestive system of roundworms? What do you think is the biological significance of the appearance of the hindgut and anus?

The digestive system is represented by a straight tube starting from the mouth and ending at the anus. It consists of three sections: anterior, middle and posterior.

The appearance of the hind intestine and anus ensures the movement of food in one direction and its better absorption

Question 5. Describe the development of roundworm. What physical environmental factors determine the development of the larvae in the environment?

Male and female roundworms live in the human intestines for about a year. After fertilization, the female begins to lay approximately 250 thousand eggs every day. Together with feces, they enter the external environment (most often into the soil). If there is oxygen in the environment, a larva develops in the egg within 3-4 weeks, and the egg becomes infectious to humans. Eggs can enter a person's mouth with unwashed vegetables and fruits, through dirty hands. A larva emerges from the egg in the intestine. For further development, it needs an oxygen environment. Therefore, the larva pierces the intestinal villi and penetrates the blood vessels. Then it passes through the bloodstream into the liver, heart, lungs, and from them it rises through the trachea into the pharynx, from which it is swallowed and again enters the intestines. Such complex and lengthy (about two weeks) movements in the human body are necessary for the larva to grow and develop. Once again in the intestine, the grown larva turns into an adult.

Question 6. How can you become infected with roundworms? What is the geography of distribution of ascariasis?

Ascariasis is one of the most common diseases caused by helminths. This is explained by the fact that roundworm eggs, leaving the human intestines with feces, develop in the soil of the garden, vegetable garden, yard, i.e., in places visited by humans. Eggs retain the ability to develop further for up to 5 years or more. Therefore, in the absence of sewerage and hygiene skills, a person can easily become infected with ascariasis.

Question 7. What hygiene measures must be observed to prevent ascariasis? Why?

It is necessary to observe the rules of personal hygiene: clean hands, clean water, cleanly washed and well-cooked food. Do not eat unwashed fruits and vegetables. After playing with pets, be sure to wash your hands.

When the human roundworm develops, the structure must be examined. The fact is that roundworms are taking over increasingly larger territories. They can be found both on the ocean floor and at the North Pole. What is the structure of one of the most dangerous pests?

Roundworms have a specific appearance. Their body tapers at both ends; no members can be seen in a cross section. The cuticle covers the body from the outside; epithelial cells are located under it. Even deeper are the muscles that provide high mobility.

Ascaris can bend in different planes. The primary body cavity is formed by a skin-muscular sac. It is filled with liquid, which evenly distributes pressure on the walls of the body. The same liquid allows for the transfer of nutrients and the removal of waste decay products.

The mouth is located at the front end of the body. Their hydroskeleton maintains a level of pressure that does not allow them to swallow food. Their pharynx is formed by muscles that act as a pump. Food is pushed into the mouth, and then into the intestines, formed by muscular walls.

The intestine looks like a straight tube, but it does not play a special role in the process of digesting food. The human roundworm looks like an inflated, thickened thread. To ensure normal life, they need oxygen. Gas exchange is carried out due to glycogen - an organic substance. For the same reason, all decay products and nutrients are transported by the primary cavity.

The roundworm's excretory system has a specific appearance. It is formed by 2 lateral channels, which end with secretion holes on the front. Harmful substances are eliminated by the excretory system.

Roundworms do not have a nervous system as such. It is formed by nerve trunks that form annular bridges. It is from them that the path to the senses is paved. They are poorly developed. The bristles located on the front part are the organs of touch.

A person becomes infected with roundworm when he ingests eggs along with food or untreated water.

Eggs can remain on the surface of dirty fruits and vegetables for a long time. Many people use excrement for fertilizer, without following the banal rules of personal hygiene. A sexually mature female lays up to 200,000 eggs at a time.

Knowing the structure of roundworms, you can direct all your attention to preventing their subsequent development. If you notice the first symptoms of a helminthic infestation, you should immediately seek help from your doctor. The sooner you pay attention to the problem, the greater the chances of a quick recovery of the body.

Human roundworm

Structural features of the human roundworm

The outer layer of the roundworm is made up of hypodermis - its structure resembles epithelial cells, of which there are a significant number - ten layers, which play a protective role and prevent damage to the individual itself and digestion by intestinal enzymes. Under the hypodermis there is a layer of muscle fibers that allow the roundworm to actively move. Further under the muscle fibers there is a cavity that is filled with fluid. This structure allows the worms to maintain a constant body shape and elasticity.

The excretory system of the roundworm is represented by two lateral canals that run along the body and correspond to the length of the roundworm's body. Harmful undigested substances after the intestines enter the cavity filled with liquid, and then into these channels. Near the initial end of the roundworm's body, excretory openings open, which correspond to the excretory organs.

The nervous system of the human roundworm is represented by neural tubes, which are located on the sides of the body; they have connecting elements. This is how the innervation of the sense organs and other internal organs occurs. Sensitive organs are very poorly developed - they are represented by bristles, which are organs of touch.

The species of human roundworm that causes ascariasis is Ascaris lumbricoides, there may only be differences in the length of the individual between males and females.

Life cycle of the human roundworm

Ascaris has a very long life cycle, the peculiarity of which is the change in the location of the individual in the human body. The route of infection by worms from the class Nematodes is the fecal-oral route. The human roundworm belongs to geohelminths because one of its development cycles is in the ground. Thus, infection occurs during ingestion of roundworm eggs. The routes of infection may be the following:

1. dirty hands – children are at greater risk due to the fact that they constantly play in the sandbox and eggs can remain under the nails;
2. dirty, unwashed vegetables and fruits - during ripening, eggs from the ground can fall on vegetables and berries;
3. after animals that have roundworm eggs on their fur - they can be carriers;
4. with unboiled water that contains roundworm eggs;
5. poorly thermally processed food that does not kill roundworm eggs or larvae.

Diagnosis and differential diagnosis of human roundworm

Diagnosis should begin with a thorough history taking. Ascaris, being in the human body for a long time, contributes to the development of symptoms of intoxication, as well as dyspeptic disorders. Therefore, this disease will be accompanied by complaints of poor appetite, rumbling in the stomach, weight loss, and nausea in the morning. If it concerns children, then it is clear that the child is thin, small, pale. A characteristic sign of ascariasis, like any other helminthiasis, is teeth grinding at night while sleeping. If such symptoms have been observed for at least the last few months, then you should think about helminthiasis.

If the larvae of human roundworm enter the liver and lungs during migration, then nonspecific symptoms may occur with disruption of the intrahepatic outflow of bile. In this case, an informative method for identifying the cause of this pathology is an ultrasound examination. Ultrasound in the liver reveals anechoic foci that have clear edges and a round shape. Also, such changes can be detected in the lungs, which makes it possible to suspect the presence of roundworm larvae.

Many of the helminths can cause similar symptoms to those caused by roundworms, so differential diagnosis is necessary. First of all, it is necessary to differentiate between ascariasis and bovine tapeworm.

Although the principles of treatment for different types of helminthiases are similar, there are differences, so it is necessary to accurately differentiate the pathogen.

Treatment and prevention of human roundworm infestation

Treatment of any helminthic infestation should be carried out only in combination with other means that prepare the gastrointestinal tract for deworming. Therefore, it is necessary to start with a diet that cleanses the intestines. It is necessary to completely limit sweet and starchy foods during treatment. It is necessary to eat cereals and cooked vegetables, which stimulate intestinal motility. After this, it is advisable to conduct a course of carrying therapy. To do this, it is necessary to conduct a single course with the use of laxatives. It is better to take herbal preparations with a carrying effect. These include “Senadexin” - a portable remedy based on the leaves of senna - a plant with a laxative effect. After this course of cleansing therapy, they move on to treating the helminthic infestation itself. Antihelminthic drugs are used.

1. Pirantel is an anthelmintic drug that acts against human roundworm by depolarizing the membranes of muscle cells of worms, which contributes to the death of mature forms of roundworm. The drug is available in the form of tablets and suspension. The dosage of the drug for children is 250 milligrams up to six years old, and over six years old – 500 milligrams. For adults in the treatment of roundworms, a dose of one gram is recommended, that is, four tablets per dose. Possible side effects from the digestive system in the form of diarrhea, abdominal pain, nausea, as well as changes in nervous activity in the form of dizziness, drowsiness, increased excitability, paresthesia.
2. Wormil is an anthelmintic drug whose main active ingredient is albendazole. The mechanism of action of the drug is to disrupt the metabolism of roundworm cells. The advantage of this remedy is that albendazole acts both on the intestinal form, that is, on the adult, and on larvae and eggs. The drug is available in the form of chewable tablets and suspension. The dosage of the drug is one tablet at a dose of 400 milligrams once a day, the course of treatment is three days. Possible side effects of the drug in the form of drowsiness, dizziness, decreased performance, as well as dyspeptic symptoms.

Prevention of infection with human roundworm can be specific and nonspecific. Specific prevention is the use of anthelmintic drugs that have activity against roundworms for prophylactic purposes. To do this, it is necessary to take anthelmintic drugs twice a year; for children, half the therapeutic doses can be recommended. You can use any anthelmintic drugs - mebendazole, albendazole, Pyrantel.

Nonspecific prophylaxis should be used by all people, especially children should be monitored. Before eating, be sure to wash your hands; fruits and vegetables should also be washed before eating. As for water and food, it is better for children not to drink water raw, but to allow food to undergo sufficient heat treatment. For good digestion and reducing the possibility of roundworm infestation, proper nutrition is necessary, which increases local immunity and the anthelmintic capabilities of the intestines.

Features of nematodes

External signs

The size of the helminth is from 20 to 45 cm. Males have an average body length of 15–20 cm, females reach 45 cm. Outside, the body of roundworms, like other roundworms, is covered with an impenetrable multilayered non-segmented shell. It has no cellular structure and is called the protein cuticle. Under the shell there is a single layer of epithelium and longitudinal fibers of the muscle layer.

Internal structure

Skeleton

The outer protein coat, the epithelial layer, and muscle fibers form the primary skin-muscle sac, filled with fluid under high pressure (more than atmospheric pressure). This makes it elastic, playing the role of a hydroskeleton. Cavity fluid ensures the delivery of nutrients and the removal of waste products.

Due to the contraction of muscle fibers and the movement of fluid throughout the body, roundworms actively move, resembling snake-like bends.

Digestive system

The digestive system is represented by a through tube, in which three main sections are distinguished: the foregut, middle and hind intestine.

On the body of roundworms in the neck area on the belly side there is an excretory opening, the so-called cervical gland. Lateral longitudinal channels open into this hole, into which harmful substances enter from the cavity fluid.

Reproductive system

This type of worm reproduces sexually. Female and male roundworms look different and differ in gender characteristics. Therefore, they say that roundworms are dioecious worms. The female has a uterus and vagina, two ovaries and an oviduct. The male individual has an apparatus for copulation, an ejaculatory duct, a testis, and a vas deferens. Fertilization in worms is internal, in the spermatheca.

The female lays more than 240,000 eggs per day.

Nervous system

Directly at the throat of the worm there is a nerve ganglion that performs the functions of the brain. Several longitudinal cords extend from it, interconnected by nerve bridges.

Ascaris has sensory organs. The worm has tactile and taste receptors. Adult worms have photosensitive organs that detect light beams; they look like microscopic eyes.

Respiratory system

The living conditions of roundworms in an oxygen-free environment evolutionarily determined the absence of respiratory organs. From the abundance of food that is in the human intestine, the worm receives a huge amount of glycogen or starch, which is necessary for energy. The amount of starch is so large that it accounts for about a third of the weight of the helminth. During its decay, a large proportion of the energy necessary for the life of worms is released.

Circulatory system

Ascaris also lacks hematopoietic organs and blood vessels.

How long can roundworm reach?

Causes of ascariasis in children

It is quite difficult to determine that your child has roundworms in his body in the early stages of the disease. And it goes without saying that ascariasis is a serious disease that can lead to irreversible consequences, so the question of its treatment should arise as early as possible.

The fact is that any worms lay eggs at a certain time, outside of which it is almost impossible to determine their presence. Effective in this regard is a blood test that shows the presence of eosinophils in it as a percentage. If there are no other diseases, then an increase in the level of eosinophils indicates a foreign protein in the body, most often worms. In this case, special tests will be required.

Symptoms of ascariasis

It is almost impossible to protect children from ascariasis if they play in the sand or come into contact with animals. Frequent hand washing reduces the risk of infection, but young children often put their hands in their mouths in a way that even the most meticulous parents may miss the moment when the eggs enter the child's body. In addition, infection can occur through poorly washed fruits and vegetables; eggs can be carried by insects: flies, cockroaches.

As a result, the following symptoms appear one after another:

• restless sleep and grinding of teeth in sleep;
• decreased appetite;
• nausea, diarrhea;
• stomach ache;
• dry cough;
• sometimes a rash on the body and fever.

Why is treatment of ascariasis so important?

Roundworms are a type of roundworm. Roundworms, roundworms, enter the human body and go through several stages of development. The larva enters the intestine using the above methods. There it is freed from the shell of the egg and sticks to its wall. The structure of the larva contributes to this: in front it has a tooth-like formation. Once in the intestinal veins, the larva begins migrating throughout the body.

Grandmother's garlic expels those individuals that are currently directed towards the anus. But sometimes it happens that the roundworm “escaps” towards the respiratory tract and can cause suffocation. Therefore, treatment of ascariasis should be carried out under the supervision of a doctor. Walnuts, pumpkin seeds, St. John's wort, and carrots are indispensable for preventing infection with worms.

There are several types of roundworms, not all of which are so dangerous to humans. The most common human roundworm, but there is also the pork roundworm, which in appearance and structure is very similar to the human roundworm, but cannot live in the human body, and the horse roundworm. The human roundworm can easily live in the body of an animal, so the likelihood of infection through the meat of a sick animal is quite high.

Children most often become infected from pets, which often do not necessarily get sick themselves: they carry roundworm eggs on their fur and paws, and children get them into their bodies through contact with them.

Therefore, the hygiene of a dog or other pet is very important when it comes to families with small children. If ascariasis is still detected, take care to simultaneously treat the animals living in the house. Special preparations can be purchased at a veterinary pharmacy, but piperazine, which is sold at a regular pharmacy, will also work.

The first preventive step is to identify the source of infection. Since ascariasis reaches its peak in summer and early autumn, in child care institutions parents are forced to take three elementary stool tests to detect eggs in it.

In hotbeds of ascariasis, intensive deworming is carried out, and kindergartens are often closed for quarantine. It is very important to treat all family members, even if they are not bothered by the symptoms of ascariasis. Buy meat only in specialized stores, and during this period wash fruits and vegetables in running hot and then cold water. As for dogs and cats, try to dispose of their feces promptly so that children do not come into contact with them. Teach your child to protect himself: wash his hands often, do not contact other people's pets - then they will not become infected with worms.

Roundworms got their name from their typical worm-like body shape: spindle-shaped, always round in cross section; in some, the body is thread-like elongated, which is reflected in the Latin name of the type.

The phylum includes three-layered bilateral animals with an elongated body, round in cross section, the internal organs of which are protected by a skin-muscular sac consisting of a cuticle, hypodermis and longitudinal muscles; their digestive system includes the hindgut and ends at the anus; their most important feature is the primary body cavity. Species of this type are divided into several (six) classes, among which one covers the vast majority of species and is of greatest importance in theoretical, medical, veterinary and agricultural terms; This is the class of roundworms proper, or Nematoda - Nematoda, the only one studied in laboratory practice.

The structure of roundworms using the example of roundworms

Appearance of roundworm; macroscopic anatomy of roundworm:
body wall and primary cavity; digestive, sexual
and excretory system; microscopic anatomy

Work 1, Appearance of roundworm. The body of the roundworm is typically worm-shaped - elongated in length, narrowed at the ends, round in cross section. Its length varies: for a horse - up to 35 cm, y human - up to 25 cm; the color is white or pinkish.

Rice. 58. Roundworms. A- numerous specimens of porcine roundworm in the small intestine of a pig; B- structure and location of the cuticular lips in the equine roundworm; the dorsal side is directed upward, the ventral side - downward.

Roundworms are dioecious animals, they are characterized by sexual dimorphism: males and females, in addition to the reproductive system, also differ in some external features, or secondary sexual characteristics. Males are much smaller than females, the rear end of their body is spirally twisted or hooked; in females in the front part of the body (in the horse roundworm at the end of the first quarter) there is a small depression that encircles the body of the roundworm in a ring.

At the anterior end there is a terminal oral opening surrounded by three cuticular swellings, or “lips” (Fig. 58). By compressing the lips, the roundworm pinches the host's intestinal mucosa. A little anterior to the posterior end lies an opening in the form of a small transverse slit (see description of the digestive system); the region lying posterior to it constitutes the tail, or caudal region.

The ventral side is found by the following features: on the mentioned ring-shaped depression in the female, in the middle of the ventral side, lies the genital opening, surrounded by a ring-shaped swelling; The male's tail end is bent to the ventral side. On the sides of the body there are two longitudinal light stripes; the same stripes run along the dorsal and ventral sides of the body; but they are narrower and less noticeable.

Progress. 1. Familiarize yourself with the appearance of the roundworm using a hand magnifying glass; find all the signs described above.

Draw a general view of the worm. 2. Examine and sketch the structure lips roundworms; Use a sharp scalpel to make a transverse incision behind the lips; Place the cut-off section on a glass slide in a drop of glycerol, with the cut plane facing the glass, and transfer it to the microscope stage at low magnification.

Work 2. Macroscopic anatomy of roundworm: body wall, primary cavity, digestive, reproductive and excretory systems. The internal organs of roundworms are studied in two ways: with the naked eye (sometimes using a hand-held magnifying glass) and microscopically. In the first case, the large anatomical features under observation will be as they are found on the dissected animal - the appearance of the organs and their topography, i.e., relative location, which can be called macroscopic anatomy; secondly, their fine microscopic structure (tissues and cells), which can be studied on microtome sections; this is microscopic anatomy.

The body wall (Fig. 59), surrounding the internal organs, is elastic. This property determines to a certain extent the elasticity of the entire body of the roundworm.

The space inward from the body wall is occupied primary cavity. All internal organs are located in it. The cavity is filled with aqueous liquid under some pressure; This pressure of the cavity fluid on the body wall, or turgor, further enhances the elasticity of the body. The cavity fluid concentrates decay products that must be removed from the body, as well as nutrients.

Digestive system stretches along the body of the roundworm in the form of a simple tube without branches, consisting of a number of sections. Immediately behind the oral opening begins the ectodermal, muscular, round cross-section, pharynx (about 1 cm length), which is often called the esophagus (Fig. 59). This is followed by the endodermal midgut; its anterior quarter is flattened dorsoventrally; throughout the rest of its length it retains a cylindrical shape. The ingested food juices of the host are finally processed and absorbed here.

The midgut passes inconspicuously into a short ectodermal hindgut; not reaching the posterior end of the body, in front of the “tail,” the hindgut opens outward on the ventral side of the body with the anus (anal) opening. In the male, the anus leads into a special extension, the cloaca, which in turn is connected to the external environment through the cloacal opening, located in the same way as the anus in the female (see Fig. 59).

Rice. 59. Internal organs of the horse roundworm. A - general view of the dissected female roundworm; B- male reproductive system; IN- longitudinal section through the posterior end of the male’s body (schematized); shows the connection between the digestive and reproductive systems, cloaca, anus and spicules:
1 -lips; 2 - body wall; 3- 7 --digestive tube (3 - place of the mouth opening, 4 - esophagus, 5 - midgut, 6 - hindgut, 7 - exit of the intestines into the cloaca in the male); 5 - anus in a female; 9 - 13 - female reproductive system (9 - ovary, 10 - oviduct, 11 - uterus, 12 - vagina, 13 - genital opening); 14-16 - male reproductive system (14 -testis, 15 - seed duct, 16 - seminal canal); 17 - 21 - cloaca- (17 - male genital opening, 18 - anus, 19 - spicules, 20 - cloaca cavity, 21 - external opening of the cloaca)

The reproductive system has a tubular structure (see Fig. 59). The reproductive tubes entwine the intestines on all sides. The female has a steam tube. It begins with a filiform ovary. Its loops are directed first forward and then backward; At the same time, the tubes gradually thicken and imperceptibly pass into the oviducts, which also form several loops. The distal ends of both tubes are much thicker, do not form loops, and are called the uterus; they are filled with fertilized eggs. Both uteruses merge into an unpaired short narrow canal - the vagina (vagina), which opens outwards with a single genital opening. The male's seminal fluid flows through the female's vagina into her uterus, where the eggs are fertilized. As the eggs mature

The male reproductive system is represented by an unpaired tube (see Fig. 59). The thinnest tubular testis imperceptibly passes into a canal of larger diameter - the seminal duct. The back-facing end of the seed tube goes into seminal duct, opening into the cloaca. Two curved, retractable cuticular needles also penetrate here; these are spicules - an auxiliary device that expands the female’s genital opening during copulation (see Fig. 59).

Excretory system peculiar. On the inner side of the body wall in the anterior part there are yellowish-brownish phagocytic cells, in quantity, up to four. Being in direct contact with the cavity fluid, phagocytic cells absorb insoluble excretory products and accumulate them in their body. According to some authors, these cells do not perform an excretory role, but participate in gas exchange (respiration).

In addition, excretory canals stretch along the body on the right and left, which from the outside look like light longitudinal stripes, visible during external examination of the roundworm. The posterior ends of the canals end blindly, and the anterior ones merge and open with an unpaired pore on the ventral side. This entire system of channels is the result of the growth of a single cell, so that the lumen of the tubes is intracellular (see Fig. 63). The excretory function of these channels is disputed, and their connection with phagocytic cells is not clear enough.

An idea of ​​the most general features of roundworms, characterizing the level of their organization, is given by the schematic figure. 60.

Progress. 1. For a macroscopic study of the internal organs, open the body of the roundworm, that is, cut the integument of its body. Place it in dissecting bath made of galvanized sheet with rectangular bottom 15×25 cm, deep 5 cm; the bottom is covered with a small layer of wax. Fill the animal with water.

When opening freshly fixed roundworms, the cavity fluid is sprayed out in a stream at the first incision; Due to its toxic properties, it causes temporary inflammation of human mucous membranes if it accidentally comes into contact with them. This can be avoided by opening the animal underwater.

Using two fingers of your left hand, press the roundworm to the bottom of the bath, and between them, on the dorsal side of the animal, make

small scalpel (2-3 cm. length) longitudinal section of the integument. Pull the edges of the cut to the sides and pin; stick the pins from the inside of the body wall at a certain angle to the bottom of the bath, and point the heads of the pins to the sides of the cut (so as not to interfere with further study of the material using a hand magnifying glass).

Rice. 60. Scheme of organization of roundworms; on the left - females, on the right - males:
1 - body wall; 2 - cavity, body; 3-8 - digestive tube (3 - mouth opening, 4 - esophagus, 5 -midgut, ( 6 - hindgut, 7 - exit of the intestines into the cloaca in the male, 8 - anus in a female); 9 -13 - female reproductive system (9 - ovary, 10 - oviduct, 11 - uterus, 12 - vagina, 13 - genital opening; 14 -16 - male reproductive system (14 - testis, 15 - seed duct, 16 - seminal canal); 17-21 - cloaca and male genital opening, 17 - genital opening, 18 - anus. 19 - spicula, 20 - cloaca cavity, 21 - external opening of the cloaca); 22 -23 -nervous system (22 - peripharyngeal ring, 23 - longitudinal trunks)

Holding the edge of the incision with tweezers, continue the incision (with scissors or a scalpel) forward and secure the edges with pins. Continue the cut all the way to the front and back ends of the body, after which a general view of the internal organs will open (see, Fig. 59). 2. Schematically depict the contours of the body of the dissected roundworm, mark the location of the primary cavity and its functions. 3. Examine with a hand magnifying glass and draw a contour drawing of the digestive system; indicate in the figure the names of its departments; pay special attention to the presence of the anus, noting its role in the body. 4. Familiarize yourself with the appearance of the reproductive system (female or male); without trying to completely unfold the loops of the reproductive tubes (they break off easily), find the organs of the reproductive system, sketch and note the functions of each. 5. Using a hand magnifying glass, find phagocytic cells and draw them into the same picture.

Work 3. Microscopic anatomy of roundworm. The skin-muscular sac, which includes the integument and muscles, forms the body wall (Fig. 61).

The integument includes the cuticle and hypodermis.

The cuticle is multi-layered, transparent, and powerfully developed. It covers the body completely, almost without interruption. The previously noted elasticity of the body wall largely depends on the elasticity of the cuticle. For roundworms, as inhabitants of the intestines of animals and humans, the multilayer cuticle serves

Rice. 61. Cross section through the middle of the body of a female equine roundworm:
1 - 7 - skin-muscle bag ( 1 - cuticle, 2 - hypodermis, 3 - dorsal and 4 - ventral ridges of the hypodermis, 5 - lateral ridges of the hypodermis, 6 - longitudinal muscle fibers, contractile sections of muscle cells, 7 - plasmatic processes of muscle cells); 8 - 10 - primary body cavity (8 - body cavity at the border with the skin-muscle sac, 9 -on the border with the intestines, 10 - she is on the border of the uterus); 11 - dorsal nerve trunk; 12 - abdominal nerve trunk; 13 - 14 - intestines ( 13 - single-layer intestinal epithelium, 14 - intestinal lumen); 15 - channels of the “excretory” system, running in the lateral ridges of the hypodermis; 16 - 22 - female reproductive system (16 - wall of the uterus, 17 - eggs in the uterus, 18 - ovary in longitudinal section, 19 -ovary in transverse section, 20 -rachis in the ovary, 21 - oviduct in longitudinal section, 22 - oviduct in cross section)

Hypodermis, hidden under the cuticle layer, has a syncytial structure. This means that there are no boundaries between cells, the protoplasm has merged into a common granular protoplasmic layer in which cell nuclei are scattered. The hypodermal syncytium of roundworms was formed as a “modification of the typical integumentary epithelium, since in young animals the cells of the hypodermis are clearly distinguishable and only

later merge into syncytium. The thickness of the layer of the hypodermis is significantly inferior to the cuticle.

Four symmetrically located thickenings of the hypodermis stretch along the entire body and protrude into the body cavity, forming hypodermal rollers: two lateral, dorsal and ventral. The lateral ridges are the most powerfully developed, and this corresponds to the wider and more noticeable lateral stripes, or lateral lines, on the body of the roundworm (see p. 117). The channels of the excretory system run in the lateral ridges along their free edge. The walls of the canals are lined from the inside with a thin cuticle. Hypodermal ridges delimit the skin-muscular sac into four symmetrical sections: two on the dorsal side (right and left) and two on the abdominal side (see Fig. 61).

Cutaneous muscles adjacent directly to the hypodermis and formed by one layer of muscle cells, the fibers of which are located only longitudinally; There are no circular and diagonal (oblique) muscles. The muscle layer is not a mistake; hypodermal ridges divide it into four symmetrical bands, or muscle fields: two dorsal, bounded on one side by the dorsal ridge and on the other by one of the lateral ridges, two ventral - between the abdominal and lateral ridges; (see Fig. 61).

The muscle cells of roundworms (see Fig. 63) are complex; structure. Each of them consists of a contractile muscle fiber, a plasma sac, plasma muscle processes and a nucleus. Muscle fibers of a regular spindle-shaped shape are characterized by increased contractility and are located close to the hypodermis and to each other. From the middle of the fiber; the plasma sac comes off and hangs into the body cavity! and sending out long branching plasmatic processes from itself.

Primary body cavity(see Fig. 61) borders directly on the skin-muscle sac and the intestinal wall. There is no boundary structure between the cutaneous muscles and the body cavity; It is also not present between the hypodermis (its ridges) and the body cavity. This feature serves as a morphological sign of the primary nature of the body cavity.

Digestive system looks different on a microslide depending on which part of it the microphototomic section passed through. The pharynx is ectodermal and lined with cuticle; its function is reduced to sucking liquid food (Fig. 62). The intestine is lined with single-layer columnar epithelium of endodermal origin. In the anterior part, the lumen is compressed in the dorso-abdominal direction. In its middle part, the intestine is compressed by the organs located in the body cavity and acquires a folded structure (see Fig. 61). Outside

intestine (Coated with a thin structureless lining that covers the intestinal cells.

Digestion in roundworms is extracellular, cavity.

The microscopic structure of the reproductive system is different in its different parts. The beginning of the ovary is a tube of the smallest diameter, filled with small germ cells, loosely located. In the next segment of larger diameter, the cells (oocytes) are located radially; At one end they rest against the wall of the ovary, and at the other - against a special gelatinous rod, the so-called rachis, which stretches in the center of the tube, along its axis and serves as a source of nutrition for the eggs.

In the oviduct, the rachis disappears, the still unfertilized eggs - oocytes are located freely in the lumen of the tube; the tube is even wider. The uterus, the part of the tube with the largest diameter, contains numerous eggs in various stages of development; after meeting sperm and fertilization, they are covered with a multilayer membrane (Fig. 63). Unlike flukes and tapeworms, roundworm eggs are not follicular in structure and the zygote is not covered with yolk cells.

Progress. 1. Study of a cross section under a microscope at low magnification. Examine and sketch a cross section through the body of a female roundworm. Show in the figure: a) the structures of the skin-muscular sac (mark the cuticle, hypodermis, hypodermal ridges); b) muscles (note that the skin-muscle bag borders directly on the body cavity); .c) the structure of the intestinal wall; d) structure

Rice. 63. The most important types of roundworm cells. A- excretory cell that forms the channel of the excretory system; B- a muscle cell and two non-specialized areas - contractile and trophic; IN- egg. with multilayer shell

ovaries, oviducts and uterus, taking into account that the same tubular organ of the reproductive system, for example, the ovary or oviduct, is represented on the preparation by several sections, not only because it is paired, but also mainly because it forms several loops, directed either forward or backward; in this case, the cuts will be made in different directions - sometimes across (perpendicular to the main axis of the tube), sometimes along, sometimes obliquely. 2. Get acquainted with roundworm eggs under a microscope at low and high magnification, examine the shape, size, shells.

Prepare a temporary microslide for this: a piece of the uterus from the area adjacent to the vagina, split longitudinally with dissecting needles on a glass slide in a drop of glycerin, cover with a coverslip.

Habitat and external structure of the human roundworm

Figure: Human roundworm (male below)

Skin-muscle sac of human roundworm

The body of the roundworm is covered on the outside with a dense multilayer shell, under which there is a layer of muscles fused with it. These muscles are only longitudinal, so the roundworm can bend its body, but is not able to extend or shorten it.

Body cavity of a human roundworm

Figure: dissected human roundworm

Under the skin-muscle sac there is a body cavity. It does not have its own walls, that is, it is simply a space filled with liquid in which the digestive and reproductive organs are located. The liquid in the body cavity is under pressure, so the body of the roundworm is dense, constantly maintaining its shape. In addition, this liquid serves as an intermediary in the distribution of nutrients and in the removal of unnecessary processed substances.

Digestive organs of the human roundworm.

At the front end of the roundworm's body there is a mouth surrounded by three lips. From the mouth, through a muscular pharynx, which sucks food, food passes into the intestines - a thin straight tube. Undigested food remains are removed through anal, or anus, located at the posterior end of the roundworm's body.

Reproduction and development of the human roundworm

Roundworms are dioecious. The female has two ovaries, the males have one testis in the form of long thin convoluted tubes. The roundworm is extremely prolific: the female lays hundreds of thousands (up to 200,000) eggs every day, covered with a very dense shell. Eggs from the human intestine fall into the soil, where sufficient moisture and air access contribute to their development. After 2-3 weeks, larvae develop inside the eggs.
Eggs with larvae, together with poorly washed vegetables or with insufficiently clean hands, can get into a person’s mouth, and from there into the intestines. Here the larvae emerge from the eggs and burrow into the intestinal walls, and from there they enter the blood vessels. Together with the blood flow, they are carried into the lungs. Here the larvae penetrate through the walls of the alveoli (pulmonary vesicles) into the bronchi, trachea and oral cavity. Then, with phlegm or saliva, they return to the intestines, where they grow into adult worms. This journey of larvae through the human body lasts 1-2 weeks.

Harm of human roundworm

Although roundworms do not feed on human blood or intestinal cells, they poison the body with toxic secretions, causing intestinal disorders and headaches. When larvae burrow through the walls of the lung, they can cause pulmonary diseases. The main control measures are prevention and compliance with hygiene rules. If you become ill, you should consult a doctor.