The main difference between a flat worm and other parasites is its complex structure. The structure of the liver flukes is represented by such organs and systems:
- The leaf form is 3-5 cm, flattened in the dorso-ventral direction.
- Developed fastening organs: oral and abdominal suckers with oral opening.
- Branched digestive system and absence of anus.
- Protonephridial excretory system.
- Undeveloped respiratory and circulatory system.
- Asexual reproduction and development with the change of carriers.
- Developed nervous system (okolglotochechnoe nerve ring, nerve strands along the body).
The cycle of helminth development passes with constant transformations. Each stage of development has its own structure.
Internal structure of the liver fluke
In humans, the fascioliasis can be both fasciola vulgaris and giant. Both have a specific and almost identical structure and functioning, which is due to their parasitic way of life. Consider the internal structure of the hepatic trematode:
- Oral sucker.
- Nerve ring.
- Abdominal sucker.
- The main branch of the intestine.
- Shellfish glands.
- Abdominal neural trunk.
- Swallow commissure.
The parasite has a leaf-shaped body, 2-7 cm in size and grayish-yellow in color. It lives in the bile ducts, liver and pancreas of vertebrates. With the help of the oral and abdominal suckers fastened and held on the walls of the ducts.
The basic systems of vital activity of the worm:
- Digestive - the oral opening is connected to a muscular pharynx (sucking apparatus). Behind the pharynx there is a branched esophagus and blindly terminating intestines.
- Nervous - is an oclo-pharyngeal nerve ring, from which three pairs of nerve trunks leave (lateral ones are most developed). Nerve trunks are connected by means of jumpers, which makes them look like a lattice.
- Excretory - developed protonephridia in the depth of the parenchyma. Thermal cells have channels with cilia, which select tissue tissue from the parenchyma and dissimilation products. Cilia propel the fluid through the canals and excretory pores, removing from the body.
- Sexual - helminth is a hermaphrodite. The male reproductive system consists of a pair of testes, two vas deferens that merge into the ejaculatory duct and cirrus. The female reproductive system is more complicated: the ovary, the vitellaria, the spermatheca, the ootype (in it fertilization and the formation of eggs take place), the uterus and the genital orifice. In some species, fertilization occurs in the seminal receptacle. In most cases, insemination is cross, but there are also cases of self-seeding.
The fluke is characterized by simplification and specialization in the structure of some organs. This is due to her parasitic way of life. As a specialization, suckers, thorns and other formations on the body of the worm, powerfully developed sexual organs and several complex life cycles act. Morphological simplification is expressed by the absence of sense organs in sexually mature individuals, which act as endoparasites.
Digestive system of the liver fluke
The structure of the digestive system of the baker's flukes is quite developed and consists of:
- Oral sucker.
- Abdominal sucker.
- Branching intestines.
The digestive tract, branched, and has two departments - front and middle. The anterior one is the pharynx and esophagus lined with ectoderm. The middle one is the endodermal bowel, two-branched, blind-closed. In some representatives of this class, the branches of the midgut have many blind processes. Parasites with a developed intestine have intestinal digestion of food, and helminths with rudimentary digestion absorb the digested food of the host through the tegument (integument of the body).
The parasite feeds on tissues and blood of its carrier with sucking movements of the pharynx. Undigested remains of food get to the outside through the mouth opening. Flat worms that infest fish have an anus, which is represented by a separate intestinal trunk and excretory vesicle.
Nervous system of the liver trematode
The central nervous system of the hepatic trematode is represented by such departments:
- Ocheloglonic ring.
- Nerve trunks: lateral, ventral.
The nervous system is located in the anterior third of the body at the pharyngeal level. It is an oclo-pharyngeal ring, from which three nerve trunks leave. The end sections of the trunks are ramified, and they enter the tegument. From the ganglion ganglion, two ventral, dorsal and lateral trunks extend, which extend to the posterior end of the body and merge, forming an arch. Longitudinal nerve trunks are connected by crosspieces - transverse commissures. Thanks to this, the nervous system resembles a lattice that surrounds the entire body.
Circulatory system of the liver trematode
Flat worms are parenchymatous, that is, are bespokostnymi animals. There is no circulatory system in the liver trematode. The space between its internal organs consists of a mesodermal-type connective tissue or a parenchyma with a multitude of cells. In this case, the parenchyma fills all the gaps between the organs. It serves as a store of nutrients and is responsible for the exchange processes.
The parasite also lacks the respiratory system. Special organs of excretion - protonephridis, are found throughout the body. They represent a system of branching canals that end in the parenchyma in the form of star cells with cilia. With the help of special excretory (excretory) holes protonefridii contact with the external environment.
External structure of the hepatic trematode
The causative agent of fasciola has a dense body adapted to life in the bile ducts of the carrier. The external structure of the hepatic trematode is a multilayer cuticle that protects against digestion, antitoxins and secretory fluid of the primary host. Through the skin, gas exchange and release of nitrogen-containing substances occurs.
The outer part of the covers is a denuclearized cytoplasmic plate with mitochondria and vacuoles. With the help of cytoplasmic strands, this layer is connected to the areas of the cytoplasm (immersed in the parenchyma), in which the nuclei are located.
Helminth has a leaf-shaped body and can reach a size of 3-5 cm in length, up to 1.5 cm in width. The cephalic end of the body is covered with spinules, has an elongated proboscis, a head and abdominal suckers. Skin without cilia, but with a well developed muscular layer. Due to its structure and parasitic lifestyle, the worm is able to survive with a lack of oxygen.
The organs of fixation of the liver flukes
The adult helminth specimen has a leaf-shaped, flattened shape with a pointed posterior end. The organs of fixation of the liver fluke - suckers and thorns. With their help the parasite is fixed in the bile ducts, liver or pancreas of the host. Such a fixation method protects against flushing with a secretory fluid.
At the anterior (broad) end of the body there is a narrow protrusion with the oral sucker. Sexually mature individuals are well developed organs of fixation, digestive and reproductive systems. Having attached to live tissues, fluke does not change its location. It grows, feeds and lays eggs in the bile ducts. With the current of the bile, the eggs enter the intestine of the carrier and are excreted outward with excrement.
The sensory organs of the hepatic trematode
The causative agent of fasciola has poorly developed sense organs. The liver fluke, or rather its larvae, floating in the water, there are several pairs of small peepholes arranged in the manner of turbellarians. In rare cases, the appendages develop along the sides of the head end, resembling ears. Such growths are considered as sensory organs (tactile and chemical).
Sensils, that is, skin receptors, have an identical structure to the turbellarians, and an advantage is observed in the larval stage of the parasite. The nervous system has a more complex structure. It consists of an oclo-pharyngeal nerve ring, two ganglia and longitudinal nerve strings (innervate the sucker). From the nerve ring leaves 3 pairs of powerful longitudinal nerve trunks with well developed lateral nerves. They branch into numerous processes that run all over the body of the worm.
Organs of movement of the liver fluke
An important feature of the structure of the parasite is the organs of movement. In the hepatic trematode, they are represented by a skin-muscular sac. It consists of an outer cover (tegumen), fused with muscle threads. Actinic spines are located in the cytoplasm of the connecting bridges.
Fluke has an archaic structure of muscle tissue. The muscle cell is represented by the myocyte, from which the processes with contractile fibers depart. In this case, each of the myocytes from 2 to 10 shoots.
Under the solid external syncytial plate are the ring, diagonal and longitudinal muscles. The most pronounced muscular layers are in the locomotor department of the corpuscle corpuscle. The generative department of muscle fibers is smaller and they are disordered.
Egg of the liver fluke
Among the trematodes, the egg of the hepatic trematode is the largest. Its dimensions are 130-150x70-90 microns. Eggs are oval in color, ranging from yellowish to dark brown. Covered by a smooth, dense two-contour shell, on one side of which there is a small lid through which miracidium comes out. At the opposite pole, the shell is thickened and is a tubercle. The core content is fine-grained.
- From the ovary already formed eggs enter the ootype, where they are fertilized. The process of insemination takes place by the introduction of a copulatory organ into the uterus. Spermatozoa penetrate the spermatheca and into the ootype.
- The vitellaria and their ducts penetrate the ootype into the yolk cells and the cytoplasm with nutrient material. Such an environment is necessary for the normal development of each fertilized egg.
- Each egg is surrounded by a nutrient shell, around which a dense shell is formed. The outer shell consists of granules of the yolk cells.
- The already formed egg enters the uterus and gradually moves to the exit. The fertilized egg (marita) exits the intestine of the carrier and must be introduced into the water for further development. In the aquatic environment, it turns into miracidia.
It is in this form that the helminth enters the human body or large cattle. In order to get infected, it is enough to drink unpeeled water or eat vegetables / fruits, washed in parasite-contaminated liquid.
Miracidia of the liver trematode
Larvae or miracidia of the liver fluke develop from marites, that is, fertilized eggs of a flat worm that have fallen into the water. The larva appears after 2-3 weeks of being in the aquatic environment. Their dimensions are very small - 0.02-0.34 millimeters. Life without water is 12-24 hours.
- Miracidia is an actively floating form, the body of which is covered with cilia. This skin provides rapid movement.
- The behavioral adaptive responses of the larvae of the first stage cause it to rise upward towards the light. Due to this, the future parasites gather on the surface film of water, where the ponders grow. Mycicides have a well developed chemical sensation, so they actively react to the mucus secreted by mollusks.
- The larva itself does not feed, but survives and develops due to the nutrients accumulated in the egg. It parasitizes in freshwater pond snails. Such a carrier is the gastropod (snail). Its main task is to find the next owner for further development.
Once the pond snake is found, the larva penetrates into its body with the help of special devices. At the anterior end of her body is a large gland, the ducts of which open on a muscular proboscis. The parasite is attached to the body of the mollusk by the proboscis and secrete the secret of the gland dissolving the tissue of the carrier. This process is carried out with the help of rhythmic muscle contractions and takes about 30 minutes. After this miracidium dumps the cilia, turning into a sporocyst.
Cercariae of the liver fluke
The larvae emerging from the body of the first host to search for the next one is the cercaria of the hepatic trematode. His body resembles an adult worm. Helminth has suckers, digestive, excretory systems and the brain are already formed, but do not act. The worm has eyes, it perceives chemical and mechanical irritation.
The main difference of this stage of fluke from an adult is the presence of a long tail with developed musculature at the posterior end of the body. Such a structure ensures free swimming and mobility of the larva. Leaving the body of the mollusk, the cercariae again enters the water. After a while, it crawls out onto the grass, throws off its tail and becomes covered with a cyst (a thick shell), inside which it maintains its viability.
Cysts of the liver fluke
Sporocyst is a form of development of a flat worm in which reproduction occurs. Cysts of the liver fluke or redia are in a large embryonic sac. Gradually they depart from the maternal sporocyst, which leads to a large increase in the number of embryos. The larvae gradually migrate to the liver of the mollusk.
- The cyst has a well-developed skin-muscular sac.
- The nervous system, like sensory organs, is poorly developed.
- At the posterior end of the body there are two motor outgrowths, and in the anterior part - the genital pore.
- The digestive system is a muscular pharynx and a sacciform sac. Redia feed on the tissues of the liver of a mollusc, absorbing nutrients throughout the surface of its body.
Cysts multiply in parteconomically (without fertilization). Germ cells in the worm's cavity give rise to the next generations and cercariae.
Adolescaria of the liver trematode
A fixed cyst, attached to plants or objects in a pond, is the adolescaria of the hepatic trematode. It is formed in the external environment from the cercariae, that is, the intermediate host. The process of transformation of free cercaria into adolescaria is a cystonia.
- The outer shell of the larva has an uneven, layered surface.
- The lower shell is fibrous and thin. It separates the outer shell from the cyst.
- The inner membrane lining the fluid-filled worm cavity.
Together with water or plant food Adolescaria gets to the final host, turning into a sexually mature parasitic individual - marita.
Adaptations to parasitism in the hepatic trematode
The causative agent of fasciola has adaptations to parasitism. In the hepatic trematode, they are associated with its body shape, dense protective shell, the presence of suckers and hermaphroditism.
Common adaptations to fluke parasitism:
- Cuticle (skin) protects against digestion of the host's juices.
- Many mounts to the carrier: suckers, spikes, hooks.
- Regressive development of the sense organs and the nervous system.
- Simple structure of the digestive system.
- High fertility.
- A complex cycle of development with alternation of ways of reproduction and change of hosts.
Huge fertility is associated with a parasitic way of life, since the chance to get into the body of the final host is minimal. To survive, the parasite lays many eggs with asexual reproduction (embryos repeatedly divide).