Freshwater hydra structure of a sensitive cell. The structure of the freshwater hydra. Growth and ability to regenerate
Hydra is a genus of freshwater animals of the hydroid class of the intestinal type. Hydra was first described by A. Leeuwenhoek. In the reservoirs of Ukraine and Russia, the following species of this genus are common: common hydra, green, thin, long-stemmed. A typical representative of the genus looks like a single attached polyp 1 mm to 2 cm long.
Hydras live in fresh water bodies with stagnant water or a slow current. They lead an attached lifestyle. The substrate to which the hydra is attached is the bottom of the reservoir or aquatic plants.
The external structure of the hydra . The body has a cylindrical shape, on its upper edge there is a mouth opening surrounded by tentacles (from 5 to 12 in different species). In some forms, the body can be conditionally distinguished into a trunk and a stalk. At the posterior edge of the stalk there is a sole, thanks to which the organism is attached to the substrate, and sometimes moves. Characterized by radial symmetry.
The internal structure of the hydra . The body is a bag consisting of two layers of cells (ectoderm and endoderm). They are separated by a layer of connective tissue - mesoglea. There is a single intestinal (gastric) cavity, which forms outgrowths extending into each of the tentacles. The mouth opens into the intestinal cavity.
Food. It feeds on small invertebrates (cyclops, cladocerans - daphnia, oligochaetes). The poison of stinging cells paralyzes the prey, then, with the movements of the tentacles, the prey is absorbed through the mouth opening and enters the body cavity. At the initial stage, cavity digestion occurs in the intestinal cavity, then intracellular - inside the digestive vacuoles of endoderm cells. There is no excretory system, undigested food residues are removed through the mouth. The transport of nutrients from the endoderm to the ectoderm occurs through the formation of special outgrowths in the cells of both layers, tightly interconnected.
The vast majority of cells in the composition of hydra tissues are epithelial-muscular. They form the epithelial cover of the body. The processes of these ectoderm cells make up the longitudinal muscles of the hydra. In the endoderm, cells of this type carry flagella for mixing food in the intestinal cavity, and digestive vacuoles are also formed in them.
Hydra tissues also contain small interstitial progenitor cells that can, if necessary, transform into cells of any type. Characterized by specialized glandular cells in the endoderm, which secrete digestive enzymes into the gastric cavity. The function of the stinging cells of the ectoderm is the release of toxic substances to defeat the victim. In large numbers, these cells are concentrated on the tentacles.
The body of the animal also has a primitive diffuse nervous system. Nerve cells are scattered throughout the ectoderm, in the endoderm - single elements. Accumulations of nerve cells are noted in the area of the mouth, soles, and on the tentacles. Hydra can form simple reflexes, in particular, reactions to light, temperature, irritation, exposure to dissolved chemicals, etc. Breathing is carried out through the entire surface of the body.
reproduction . Hydra reproduction occurs both asexually (budding) and sexually. Most species of hydras are dioecious, rare forms are hermaphrodites. When the sex cells merge in the body of the hydra, zygotes are formed. Then the adults die, and the embryos hibernate at the gastrula stage. In spring, the embryo turns into a young individual. Thus, the development of the hydra is direct.
Hydras play an essential role in natural food chains. In science, in recent years, hydra has been a model object for studying the processes of regeneration and morphogenesis.
In lakes, rivers or ponds with clean, clear water, on duckweed roots, stems and leaves of other aquatic plants, animals are often found attached, similar to tousled twine. it Hydra. Externally, Hydras look like small translucent brownish or greenish stems, with a corolla tentacles at the free end of the body. Hydra is a freshwater polyp ("polyp" means "many-legged").
Hydras are radially symmetrical animals. Their body is in the form of a bag ranging in size from 1 to 3 cm (moreover, the body usually does not exceed 5-7 mm in length, but the tentacles can stretch several centimeters). At one end of the body is sole, which serves to attach to underwater objects, on the opposite - oral hole surrounded by long tentacles(5-12 tentacles). In our reservoirs, Hydra can be found from the beginning of June to the end of September.
Lifestyle. Hydras - predatory animals. They catch prey with the help of tentacles, on which there are a large number of stinging cells. When touching the tentacles, long threads containing strong toxins. Killed animals are pulled by tentacles to the mouth opening and swallowed. Hydra swallows small animals whole. If the victim is somewhat larger than the Hydra itself, it can also swallow it. At the same time, the mouth of the predator opens wide, and the walls of the body are strongly stretched. If the prey does not fit into the gastric cavity as a whole, the Hydra swallows only one end of it, pushing the victim deeper and deeper as it digests. Undigested food remains are also removed through the mouth opening. Hydras prefer daphnia (water fleas), but they can also eat other crustaceans, ciliates, various insect larvae, and even small tadpoles and fry. A moderate daily ration is one daphnia.
Hydras usually lead a stationary life, but can crawl from place to place, sliding on the soles or somersaulting over their heads. They always move in the direction of the light. When irritated, animals are able to shrink into a ball, which, perhaps, helps them with defecation.
Body structure. Hydra's body consists of two layers of cells. These are the so-called two-layer animals. The outer layer of cells is called ectoderm, and the inner layer endoderm (endoderm). Between the ectoderm and endoderm is a layer of structureless mass - mesoglea. Mesoglea in marine jellyfish is up to 80% of body weight, while in Hydra mesoglea is not large and is called supporting plate.
Rod Hydra - Hydra
Inside the Hydra's body is gastral cavity (intestinal cavity), opening outward with a single hole ( oral hole).
AT endoderm are located epithelial-muscular and glandular cells. These cells line the intestinal cavity. The main function of the endoderm is digestive. Epithelial-muscular cells, with the help of flagella facing the intestinal cavity, drive food particles, and with the help of pseudopods, they capture them and draw them in. These cells digest food. Glandular cells produce enzymes that break down proteins. The digestive juice of these cells enters the intestinal cavity, where digestion processes also take place. Thus, digestion in Hydra is of 2 types: intracavitary(extracellular), characteristic of other multicellular animals, and intracellular(characteristic of unicellular and lower multicellular).
In the ectoderm Hydra has epithelial-muscular, nerve, stinging and intermediate cells. Epithelial-muscular (integumentary) cells cover the body of the Hydra. Each of them has a long process extended parallel to the surface of the body, in the cytoplasm of which contractile fibers. The totality of such processes forms a layer of muscular formations. When the fibers of all epithelial-muscular cells contract, the Hydra's body contracts. If the fibers contract only on one side of the body, then the Hydra bends down in this direction. Thanks to the work of muscle fibers, Hydra can slowly move from place to place, alternately "stepping" either with the sole or with the tentacles.
Stinging or nettle cells there are especially many tentacles in the ectoderm. Within these cells is capsule with poisonous liquid and coiled tubular a thread. On the surface of stinging cells there is sensitive hair. These cells serve as Hydra's offensive and defensive weapons. When prey or an enemy touches a sensitive hair, the stinging capsule instantly throws the thread out. The poisonous liquid, getting into the thread, and then through the thread into the body of the animal, paralyzes it or kills it. Stinging cells after a single use die and are replaced by new ones formed by intermediate cells.
intermediate cells small, round, with large nuclei and a small amount of cytoplasm. When the body of the Hydra is damaged, they begin to grow and divide intensively. Intermediate cells can form epithelial-muscular, nerve, sex and other cells.
Nerve cells scattered under the integumentary epithelial-muscular cells, and they have a stellate shape. The processes of nerve cells communicate with each other, forming a nerve plexus, thickening around the mouth and on the sole.
Rod Hydra - Hydra
This type of nervous system is called diffuse- the most primitive in the animal kingdom. Part of the nerve processes approaches the skin-muscle cells. The processes are able to perceive various stimuli (light, heat, mechanical influences), as a result of which excitation develops in the nerve cells, which is transmitted through them to all parts of the body and the animal and causes an appropriate response.
Thus, Hydra and other coelenterates have real fabrics, although little differentiated - ectoderm and endoderm. The nervous system appears.
Hydra has no special respiratory organs. Oxygen dissolved in water penetrates into the hydra through the entire surface of the body. Hydra has no excretory organs either. Metabolic end products are excreted through the ectoderm. The sense organs are not developed. Touch is carried out by the entire surface of the body, the tentacles (sensitive hairs) are especially sensitive, throwing out stinging threads that kill or paralyze prey.
Reproduction. Hydra breeds like asexual, and sexual way. During the summer it reproduces asexually - budding. In the middle part of the body of the Hydra there is a budding belt, on which tubercles are formed ( kidneys). The kidney grows, a mouth and tentacles form on its top, after which the kidney thins at the base, separates from the body of the mother and begins to live independently. This is reminiscent of the development of a plant shoot from a bud - hence the name of this method of reproduction.
In autumn, with the approach of cold weather in the ectoderm of Hydra, germ cells are formed from intermediate cells - spermatozoa and eggs. stalked hydras separate sexes, and their fertilization cross. The egg cells are located closer to the base of the Hydra and look like an amoeba, while the spermatozoa are similar to flagellar protozoa and develop in tubercles located closer to the mouth opening. The spermatozoon has a long flagellum, with which it swims in the water and reaches the eggs, and then merges with them. Fertilization takes place inside the body of the mother. A fertilized egg begins to divide, becomes covered with a dense double shell, sinks to the bottom and hibernates there. In late autumn, Hydras die. And in the spring, a new generation develops from the overwintered eggs.
Regeneration. When the body is damaged, the cells located near the wound begin to grow and divide, and the wound quickly overgrows (heals). This process is called regeneration. Regeneration occurs in many animals, and humans also have it. But no animal can compare in this matter with the Hydra. Perhaps the hydra got its name precisely for this property (see the second feat of Hercules).
Lernaean Hydra (Second Labor of Hercules)
After the first feat, King Eurystheus sent Hercules to kill the Lernean hydra. It was a monster with the body of a snake and nine heads of a dragon. The hydra lived in a swamp near the city of Lerna and, crawling out of its lair, destroyed entire herds and devastated all the surroundings. The fight against the nine-headed hydra was dangerous because one of its heads was immortal. Hercules set out on his journey to Lerna with his friend Iolaus. Arriving at the swamp near the city of Lerna, Hercules left Iolaus with a chariot in a nearby grove, and he went to look for the hydra. He found her in a cave surrounded by a swamp. Having red-hot his arrows, Hercules began to let them go one by one into the hydra. The hydra was enraged by the arrows of Hercules. She crawled out, wriggling her body covered with shiny scales, from the darkness of the cave, rose menacingly on her huge tail and already wanted to rush at the hero, but the son of Zeus stepped on her body with his foot and crushed her to the ground. With its tail, the hydra wrapped itself around the legs of Hercules and tried to knock him down. Like an unshakable rock, the hero and with a wave of a heavy club knocked down the heads of the hydra one after another. Like a whirlwind, a club whistled through the air; the heads of the hydra flew off, but the hydra was still alive. Then Hercules noticed that in the hydra, two new ones grow in place of each knocked down head. The help of the hydra also appeared. A monstrous cancer crawled out of the swamp and dug its claws into Hercules' leg. Then the hero called for help Iolaus. Iolaus killed the monstrous cancer, set fire to a part of the nearby grove, and burned the necks of the hydra with burning tree trunks, from which Hercules knocked down their heads with his club. New heads have ceased to grow from the hydra. Weaker and weaker she resisted the son of Zeus. Finally, the immortal head flew off the hydra. The monstrous hydra was defeated and collapsed dead to the ground. The conqueror Hercules buried her immortal head deeply and piled a huge rock on it so that it could not come out into the light again.
If we talk about a real Hydra, then her ability to regenerate is even more incredible! A new animal is able to grow from 1/200 of the Hydra, in fact, a complete organism is restored from the gruel. Therefore, Hydra regeneration is often referred to as an additional method of reproduction.
Meaning. Hydras are a favorite object for studying regeneration processes. In nature, Hydra is an element of biological diversity. In the structure of the ecosystem, Hydra, as a predatory animal, acts as a consumer of the second order. Not a single animal simply wants to eat the Hydra itself.
Questions for self-control.
Name the systematic position of Hydra.
Where does the Hydra live?
What is the body structure of the Hydra?
How does Hydra eat?
How is the release of waste products from Hydra?
How does Hydra reproduce?
What is the significance of Hydra in nature?
Rod Hydra - Hydra
Rice. Hydra structure.
A - longitudinal section (1 - tentacles, 2 - ectoderm, 3 - endoderm, 4 - gastric cavity, 5 - mouth, 6 - testis, 7 - ovary and developing zygote).
B - cross section (1 - ectoderm, 2 - endoderm, 3 - gastric cavity, 4, 5 - stinging cells, 6 - nerve cell, 7 - glandular cell, 8 - supporting plate).
B - nervous system. G - epithelial-muscular cell. D - stinging cells (1 - at rest, 2 - with a thread thrown out; the nuclei are painted black).
Rod Hydra - Hydra
Rice. Hydra reproduction.
From left to right: Hydra with male gonads, Hydra with female gonads, Hydra during budding.
Rice. Hydra locomotion.
Hydras move, attaching to the substrate either with the sole or with a mouth cone with tentacles.
To the class hydroid include invertebrate aquatic cnidarians. In their life cycle, two forms are often present, replacing each other: a polyp and a jellyfish. Hydroids can gather in colonies, but single individuals are not uncommon. Traces of hydroids are found even in the Precambrian layers, however, due to the extreme fragility of their bodies, the search is very difficult.
A bright representative of hydroid - freshwater hydra, single polyp. Its body has a sole, a stalk, and long tentacles relative to the stalk. She moves like a rhythmic gymnast - with every step she makes a bridge and somersaults over her "head". Hydra is widely used in laboratory experiments, its ability to regenerate and high activity of stem cells, which provides "eternal youth" to the polyp, prompted German scientists to search for and study the "immortality gene".
Hydra cell types
1. Epithelial-muscular cells form the outer covers, that is, they are the basis ectoderm. The function of these cells is to shorten the body of the hydra or make it longer, for this they have a muscle fiber.
2. Digestive-muscular cells are located in endoderm. They are adapted to phagocytosis, capture and mix food particles that have entered the gastric cavity, for which each cell is equipped with several flagella. In general, flagella and pseudopods help food to penetrate from the intestinal cavity into the cytoplasm of hydra cells. Thus, her digestion goes in two ways: intracavitary (for this there is a set of enzymes) and intracellular.
3. stinging cells located primarily on the tentacles. They are multifunctional. Firstly, the hydra defends itself with their help - a fish that wants to eat the hydra is burned with poison and throws it away. Secondly, the hydra paralyzes the prey captured by the tentacles. The stinging cell contains a capsule with a poisonous stinging thread, a sensitive hair is located outside, which, after irritation, gives a signal to “shoot”. The life of a stinging cell is fleeting: after a “shot” with a thread, it dies.
4. Nerve cells, together with processes similar to stars, lie in ectoderm, under a layer of epithelial-muscular cells. Their greatest concentration is at the sole and tentacles. With any impact, the hydra reacts, which is an unconditioned reflex. The polyp also has such a property as irritability. Recall also that the “umbrella” of a jellyfish is bordered by a cluster of nerve cells, and ganglia are located in the body.
5. glandular cells secrete a sticky substance. They are located in endoderm and aid in the digestion of food.
6. intermediate cells- round, very small and undifferentiated - lie in ectoderm. These stem cells divide endlessly, are capable of transforming into any other, somatic (except epithelial-muscular) or sex cells, and ensure the regeneration of hydra. There are hydras that do not have intermediate cells (hence, stinging, nervous and sexual), capable of asexual reproduction.
7. sex cells develop in ectoderm. The egg cell of freshwater hydra is equipped with pseudopods, with which it captures neighboring cells along with their nutrients. Found among hydras hermaphroditism when eggs and sperm are formed in the same individual, but at different times.
Other features of freshwater hydra
1. Hydras do not have a respiratory system; they breathe the entire surface of the body.
2. The circulatory system is not formed.
3. Hydra feed on larvae of aquatic insects, various small invertebrates, crustaceans (daphnia, cyclops). Undigested food residues, like other coelenterates, are removed back through the mouth opening.
4. Hydra is capable of regeneration for which intermediate cells are responsible. Even cut into fragments, the hydra completes the necessary organs and turns into several new individuals.
Occur in the same cell. In the body of the hydra and all other multicellular animals, different groups of cells have different meanings, or, as they say, different functions.
Structure
The structure of the hydra can be different, due to the cells that perform different functions. Groups of cells that have the same structure and perform a specific function in the life of an animal are called tissues. In the body of the hydra, such tissues as integumentary, muscular and nervous are developed. However, these tissues do not form in its body those complex organs that other multicellular animals have. Thus, the hydra is the lowest, that is, the most simple multicellular animal in its structure.
In worms and other animals more complex than freshwater hydra, organs are formed from tissues. From organs that perform a common function in the life of an animal, organ systems are formed in the body of animals (for example, the nervous system, circulatory system, etc.). Hydra has no organ systems. Hydra reproduction occurs in two ways: sexual and asexual.
nettle cells
To understand why daphnia, touching the tentacles of freshwater hydra, are paralyzed, it is necessary to consider the structure of the tentacle under a microscope. The entire surface of the tentacle is covered with tiny knobby tubercles. These are special cells that look like bubbles. There are also such cells on the edges of the hydra's body, but most of them are on the tentacles. The bubbles contain thin threads with points at the ends sticking out. When the prey touches the body of the hydra, the threads, coiled in a calm state, are suddenly thrown out of their bubbles and, like arrows, pierce the body of the prey. At the same time, a drop of poison is poured from the bubble into the wound, paralyzing the victim. Hydra cannot hit the relatively thick skin of humans and large animals. But animals related to hydra live in the seas - sea jellyfish. Large jellyfish can cause severe burns to humans. They burn the skin like nettles. Therefore, these cells are called nettle cells, and the threads are called nettle threads. Hydra nettle cells are not only an organ of attack on prey, but also an organ of defense.
muscle cells
Some cells of the outer layer of the hydra body are continued on the inside by narrow muscular processes. These processes are located along the body of the hydra. They are able to shrink. The rapid contraction of the hydra into a small lump in response to irritation occurs precisely due to the contraction of these muscle processes. Cells with such processes are called integumentary-muscular. In the life of a hydra, they play the same role as muscles in humans. Thus, the hydra's outer cells protect it and help it move.
Nerve cells
Hydra perceives irritations by sensitive cells located in the ectoderm (outer layer). These irritations are transmitted through the nerve cells located in the integumentary layer, closer to the base of the integumentary muscle cells, on the supporting membrane, connecting with each other. Nerve cells form a neural network. This network is the beginning of the nervous system.
From sensitive cells, irritation (for example, from touching with a needle or stick) is transmitted to nerve cells and spreads throughout the nervous network of the hydra. From the nervous network, irritation passes to the integumentary muscle cells. Their processes are reduced, and accordingly the entire body of the hydra is reduced. This is how the hydra responds to external stimuli. Contraction of the hydra's body from touch has a protective value.
Digestive cells
The cells of the digestive layer are much larger than the cells of the integumentary layer. On their inner part, facing the intestinal cavity, these cells have long flagella. Moving, the flagella mix food particles that have fallen into the intestinal cavity. Digestive cells secrete juice that digests food. Digested food is absorbed by the cells of the digestive layer, and from them it enters all the cells of the body. Undigested food remains are thrown out through the mouth opening.
In ancient Greek myth, the Hydra was a multi-headed monster that grew two instead of a severed head. As it turned out, a real animal, named after this mythical beast, has biological immortality.
Freshwater hydras have a remarkable regenerative capacity. Instead of repairing damaged cells, they are constantly being replaced by stem cell division and, in part, differentiation.
Within five days, the hydra is almost completely renewed, which completely eliminates the aging process. The ability to replace even nerve cells is still considered unique in the animal kingdom.
Yet one feature freshwater hydra is that a new individual can grow from separate parts. That is, if the hydra is divided into parts, then 1/200 of the mass of an adult hydra is enough for a new individual to grow out of it.
What is hydra
The freshwater hydra (Hydra) is a genus of small freshwater animals of the phylum Cnidaria and the class Hydrozoa. It is, in fact, a solitary, sedentary freshwater polyp that lives in temperate and tropical regions.
There are at least 5 species of the genus in Europe, including:
- Hydra vulgaris (common freshwater species).
- Hydra viridissima (also called Chlorohydra viridissima or green hydra, the green coloration comes from chlorella algae).
The structure of the hydra
Hydra has a tubular, radially symmetrical body up to 10 mm long, elongated, sticky leg at one end, called the basal disc. Omental cells in the basal disc secrete a sticky fluid that explains its adhesive properties.
At the other end is a mouth opening surrounded by one to twelve thin mobile tentacles. Every tentacle dressed in highly specialized stinging cells. Upon contact with prey, these cells release neurotoxins that paralyze the prey.
The body of freshwater hydra consists of three layers:
- "outer shell" (ectodermal epidermis);
- "inner shell" (endodermal gastroderma);
- a gelatinous support matrix, the so-called mesogloe, which is separated from the nerve cells.
The ectoderm and endoderm contain nerve cells. In the ectoderm, there are sensory or receptor cells that receive stimuli from the environment, such as the movement of water or chemical stimuli.
There are also ectodermal urticaria capsules that are ejected, releasing a paralyzing poison and, thus used to capture prey. These capsules do not regenerate, so they can only be dropped once. On each of the tentacles is from 2500 to 3500 nettle capsules.
Epithelial muscle cells form longitudinal muscle layers along the polypoid. By stimulating these cells, polyp can shrink quickly. There are also muscle cells in the endoderm, so named because of their function of absorbing nutrients. Unlike the muscle cells of the ectoderm, they are arranged in an annular pattern. This causes the polyp to stretch as the endoderm muscle cells contract.
The endodermal gastrodermis surrounds the so-called gastrointestinal cavity. Because the this cavity contains both the digestive tract and the vascular system, it is called the gastrovascular system. For this purpose, in addition to the muscle cells in the endoderm, there are specialized gland cells that secrete digestive secretions.
In addition, there are also replacement cells in the ectoderm, as well as endoderm, which can be transformed into other cells or produce, for example, sperm and eggs (most polyps are hermaphrodites).
Nervous system
The Hydra has a nerve network like all hollow animals (coelenterates), but it does not have focal points like the ganglia or the brain. Nonetheless accumulation sensory and nerve cells and their elongation on the mouths and stem. These animals respond to chemical, mechanical and electrical stimuli, as well as to light and temperature.
The hydra's nervous system is structurally simple compared to the more developed nervous systems of animals. neural networks connect sensory photoreceptors and touch-sensitive nerve cells located on the body wall and tentacles.
Respiration and excretion occur by diffusion throughout the epidermis.
Feeding
Hydras mainly feed on aquatic invertebrates. When feeding, they elongate their bodies to their maximum length and then slowly expand their tentacles. Despite their simple structure, tentacles are extraordinarily widened and can be up to five times their body length. Once fully extended, the tentacles slowly maneuver in anticipation of contact with a suitable prey animal. Upon contact, the stinging cells on the tentacle sting (the ejection process takes only about 3 microseconds), and the tentacles wrap around the prey.
Within a few minutes, the victim is drawn into the body cavity, after which digestion begins. Polyp can stretch a lot its body wall to digest prey more than twice the size of the hydra. After two or three days, the indigestible remains of the victim are expelled by contraction through the opening of the mouth.
The food of freshwater hydra consists of small crustaceans, water fleas, insect larvae, water moths, plankton and other small aquatic animals.
Traffic
Hydra moves from place to place, stretching its body and clinging to the object alternately with one or the other end of the body. Polyps migrate about 2 cm per day. By forming a gas bubble on the leg, which provides buoyancy, the hydra can also move to the surface.
reproduction and longevity.
Hydra can reproduce both asexually and in the form of germination of new polyps on the stem of the maternal polyp, by longitudinal and transverse division, and under certain circumstances. These circumstances are also have not been fully explored but nutritional deficiencies play an important role. These animals can be male, female, or even hermaphrodite. Sexual reproduction is initiated by the formation of germ cells in the wall of the animal.
Conclusion
The unlimited lifespan of the hydra attracts the attention of natural scientists. Hydra stem cells have the ability to perpetual self-renewal. The transcription factor has been identified as a critical factor in continuous self-renewal.
However, it appears that researchers still have a long way to go before they can understand how their work can be applied to reduce or eliminate human aging.
Application of these animals for needs Humans are limited by the fact that freshwater hydras cannot live in dirty water, so they are used as indicators of water pollution.
