Ascaris - Life Cycle And Structure Of Human Roundworm

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Ascaris - Life Cycle And Structure Of Human Roundworm
Ascaris - Life Cycle And Structure Of Human Roundworm

Video: Ascaris - Life Cycle And Structure Of Human Roundworm

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Video: Ascaris lumbricoides Lifecycle ( English ) | Ascariasis | Round Worm 2023, February

Last updated 27 August 2017 at 12:29

Reading time: 4 minutes

Among the wide variety of helminths, the human roundworm or Ascaris lumbricoides is of great social importance.

The internal structure of the roundworm gives it the opportunity to carry out active life activities simultaneously in different human systems - in the digestive, respiratory, central nervous, blood circulation.

The parasite belongs to a variety of roundworms, which is ideally adapted to living in the internal environment of a person due to the uniqueness of its morphology, adaptation, physiology.

Unlike other representatives, such as the bovine tapeworm, they do not have attachment organs, so they have to move independently towards food. This feature also leads them to live mainly in the small intestine.


  • 1 External signs
  • 2 Morphology and physiology
  • 3 Body cavity
  • 4 Musculature and epithelial cover
  • 5 Digestion
  • 6 Nervous system
  • 7 Respiratory system
  • 8 Excretory system
  • 9 Reproductive system

    9.1 Related articles

External signs


The female worm at puberty reaches a length of about 40 cm, the male is much smaller, varying from 15 to 25 cm. Male representatives have morphological differences from female representatives by the presence of a bent posterior end to the abdominal wall.

The body shape of the nematode is spindle elongated. Coloring - pale light, light pink, translucent, sometimes with a gray tint. Both sexually mature individuals have three lips around the mouth opening. Branched genital tubes are visible through the thin wall of the female.

An adult worm is mobile, its behavior is active. The movement is carried out only in directions opposite to the central axis of movement, in a zigzag manner. This is due to the lack of transverse musculature. Muscle fibers are located along the trunk.

When one of the longitudinal muscles contracts, the worm wriggles in the appropriate direction.

Morphology and physiology


The structure of the ascaris worm has a number of characteristic features for nematodes and round helminths:

  1. dioeciousness of organisms;
  2. the presence of smooth transversely striated muscles;
  3. multilayer cuticle;
  4. the absence of a secondary cavity and the presence of a primary one;
  5. formed by the nervous system in the form of nerve trunks extending from the pharyngeal ring;
  6. atrophied respiratory and circulatory organs.

Body cavity


At both ends of the worm - anterior, posterior, narrowing occurs. On a cut, the body has a round profile, its cavity is represented by a gap between the internal organs and the wall. The cavity is filled with a colorless liquid.

The epithelial inner layer of the primary cavity is absent, which is a characteristic difference from the secondary. The digestive and genital organs are located in an internal confined space.

Cover functions

  • supporting, being the outer skeleton, creates a shell for the internal organs and fluid;
  • transportation of nutrients from the digestive system to the epithelial, muscle, reproductive;
  • transfer of metabolic products to the excretory organs.

Musculature and epithelial cover


The nematode epithelium forms a layer-by-layer flexible cuticle on the outside, otherwise called the hypodermis, which has 10 layers. The multilayer hypodermis produces a composition that prevents the intestinal enzymes from digesting the helminth. On a cut, the roundworm cuticle has a thin-walled shell that completely covers the parasite.

The hypodermis simultaneously has both flexible and durable properties, without interfering, thereby, active movement. Four cuticle ridges are located in the lateral, dorsal and abdominal parts. The organs of excretion are located in the rollers in the form of longitudinal channels. The canals are represented by depressions between the muscle frame and the hypodermis.

The muscle layer is formed by longitudinal fibers. The lining of the cavity is a layer of epithelial cells and muscle fibers, thus forming a skin - muscle bag or body wall.



The digestive structure is represented by an empty tube that forms the intestine with the main middle, as well as the front and back sections. The first two sections of ectodermal origin, the posterior one is formed from the endoderm.

The intestine is represented by a closed and very sinuous cavity located in the central part, passing through the entire parasite. The assimilation of the nutrient is carried out in the middle part of the intestine.

The relatively primitive structure of digestion is explained by the constant presence in the environment of the worm of food mass, which is processed for assimilation by the enzymes of the host's intestines.

Nervous system

It has a fairly simple structure. Formed by one ganglion node, in the form of a periopharyngeal ring, located in front of the parasite. From the pharyngeal ring along, six nerve dorsal and abdominal bundles depart. They are responsible for sensitivity and organize muscle control from the nerve plexuses during movement.

Receptors as such are absent, there are tactile tubercles in the form of papillomas, located mainly around the oral cavity.

Living in the intestinal digestive environment, in which there are no physical stimuli and natural enemies, the rest of the sensitive formations are atrophied.

Respiratory system


The worm's habitat is anaerobic, does not require the presence of oxygen, and therefore there is no need for respiratory organs - lungs, which are available in more developed objects. This natural adaptation of the human roundworm is associated with the lack of air in the human intestine.

Metabolism is provided by cellular respiration. It is carried out by glycolysis of glycogen stores in the cell cytoplasm. This is an anaerobic type, without the participation of oxygen, which is characteristic of anaerobic organisms.

Excretory system

Liquid metabolic products are removed through the excretory opening located at the front end of the parasite. Removal from the digestive tract is carried out through its own posterior anal passage.

Reproductive system


Nematodes are dioecious individuals. The reproductive organs are presented in the form of hollow convoluted tubes. In males, there is one testis that continues into the vas deferens into the hindgut. After mating, the death of the male occurs.

The female representatives have two ovaries that continue into the oviducts and pass into the uterus. They then form an unpaired vagina, which opens with an opening in the abdominal side. The female lays eggs released into the environment.

The human roundworm is a very dangerous representative in its class, which has adapted well to existence in the internal environment of a person.

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