Nematódeos - Brasil Escola

Summary

In this biology lesson, Professor Fred introduces the phylum Nematoda, also known as nematodes or roundworms. He explains their cylindrical, unsegmented bodies and their diverse habitats, including parasitic species that cause numerous human diseases. The lesson covers their anatomy, including a pseudocoelom, bilateral symmetry, and complete digestive system. Nematodes are dioecious, with distinct sexes, and reproduce via internal fertilization. Fred also discusses several diseases caused by nematodes, such as ascaridiasis, hookworm, and filariasis, and emphasizes the importance of studying them in relation to human health and sanitation.

Takeaways

• 😀 Nematodes (also called nematoda or nematiminos) are a diverse group of invertebrates, with some causing significant human diseases.
• 😀 Nematodes have cylindrical, elongated bodies, often described as vermiform (worm-like), and they lack limbs.
• 😀 These organisms can range in size from 1 mm to over 1 meter, with some parasitic species growing quite large.
• 😀 Nematodes are pseudocoelomates, meaning they have a false body cavity (pseudocoelom), which helps in nutrient transport but isn't entirely mesodermal.
• 😀 Nematodes exhibit bilateral symmetry, and their muscles are arranged longitudinally, enabling whip-like movements.
• 😀 They have a complete digestive system, with a mouth at one end and an anus at the other, aiding in efficient digestion.
• 😀 The nervous system of nematodes is partially centralized, with muscles branching to transmit contraction signals rather than nerves branching to muscles.
• 😀 Nematodes are dioecious, meaning they have separate sexes. Males are typically smaller and exhibit sexual dimorphism, with a curved tail for mating.
• 😀 Reproduction is internal in nematodes, with fertilization occurring inside the female. Development can be direct (from egg to adult) or indirect (passing through larval stages).
• 😀 Nematodes cause various diseases in humans, such as Ascaridiasis (caused by *Ascaris lumbricoides*), Ancylostomiasis (hookworm), Filariasis (elephantiasis), and Oxiurose (pinworm disease).
• 😀 Poor sanitation, inadequate hygiene, and contaminated water contribute to the spread of nematode-borne diseases, particularly in regions with poor infrastructure.

Q & A

What are nematodes and what are their common names?

Nematodes, also known as nematoda or nematodes, are a group of invertebrate animals characterized by their elongated, cylindrical bodies. Common names for these organisms include roundworms, and they can be found in both terrestrial and aquatic environments.

Why are nematodes important in the study of human health?

Nematodes are important because they are responsible for a number of diseases that affect humans. With over 50 species that can parasitize humans, they are directly related to health issues, including parasitic infections that are commonly studied in fields like parasitology.

What does the term 'nematode' mean and what are its key physical characteristics?

The term 'nematode' comes from the Greek word 'nema,' meaning 'fine thread.' These animals are characterized by their cylindrical, elongated, and thin bodies, which are often referred to as vermiform. They lack legs, and their body has pointed ends—one being sharper than the other.

How do nematodes differ in terms of size and habitat?

Nematodes vary greatly in size, ranging from just 1 mm to over 1 meter long, depending on the species. They can be found in a variety of environments, including soil, aquatic habitats, and within other organisms as parasites.

What is a pseudocoelom, and how does it function in nematodes?

A pseudocoelom is a body cavity that is not fully enclosed by mesodermal tissue, as is the case in true coelomates. In nematodes, the pseudocoelom serves to hold organs, facilitate the transport of substances, and provides structural support for the animal.

What is the significance of the nematode's digestive system?

Nematodes possess a complete digestive system, meaning they have both a mouth and an anus. This allows for more efficient digestion and processing of food. The digestive tract runs from the mouth through the intestines to the anus.

How is the nervous system of nematodes different from that of other invertebrates?

The nematode nervous system is partially centralized. It includes an annular nerve ring around the pharynx, from which nerve cords extend throughout the body. Interestingly, in nematodes, the muscle fibers branch out to the nervous system rather than the other way around, influencing their characteristic whip-like movement.

What are the reproductive characteristics of nematodes?

Nematodes are dioecious, meaning they have separate sexes—males and females. Dimorphism is often visible, with males being smaller and having a characteristic curved tail. They reproduce sexually with internal fertilization, and their eggs are typically microscopic.

What are some common diseases caused by nematodes?

Some well-known diseases caused by nematodes include ascaridiasis (lumbriga) from *Ascaris lumbricoides*, hookworm (ancylostomiasis) from *Ancylostoma* species, filariasis (elephantiasis) from *Wuchereria bancrofti*, and oxyuriasis (pinworm infection) caused by *Enterobius vermicularis*.

How do poor sanitation and hygiene contribute to the spread of nematode infections?

Nematode infections are often spread through contaminated food, water, or soil, particularly in areas with inadequate sanitation. Poor hygiene, such as not washing hands after using the restroom or consuming contaminated water, facilitates the transmission of nematode eggs and larvae, leading to widespread infections.