10. Nematodes intro Flashcards
nematodes make up what fraction of the multicellular animals on earth?
4/5
how many species of nematodes have been described?
500,000
what is a non-parasitic nematode that is used for research and development?
Caenorhabditis elegans (C. elegans)
what is the most common human parasitic nematode worldwide?
Acaris lumbricoides
what is the most common human parasitic nematode in US/Canada?
Enterobius vermicularis
in most species _____ reproduction by adult nematodes is the norm and occurs within an infective definitive host
sexual
what are the ways in which the larval stages may be passed?
- within the egg
- free living in soil
- parasitic in an intermediate host
- parasitic in the definitive host
what is the basic life cycle of nematodes
- egg
- four larval stages (L1, L2, L3, and L4)
- two adult stages comprising separate males and females
what is L5?
another name for sexually immature adults
what are the two phases of the life cycle of nematodes?
- pre-parasitic
- parasitic
what stages are part of the pre-parasitic phase?
- L1, L2 and L3
- the parasite must pass through these stages before the nematode is again infective for another host
what stages are part of the parasitic phase?
- L3 and onward
- will undergo a migration within the body of the definitive host
which nematodes have infectious eggs?
- ascaris (ex: ascaris lumbricoides)
- pinworm (ex: enterobius vermicularis)
which nematode is up to 30 cm in length and lives in the intestines of humans, horses, and pigs?
Ascaris
which nematode spends the entire lifecycle in or on the human host?
pinworm/Enterobius vermicularis
which parasite lays eggs in the perianal region causing itch?
pinworm/Enterobius vermicularis
which nematodes have infectious larvae?
- adult hookworm (Necator americanus)
- trichina worm (Trichinella spiralis)
how do the larvae of the hookworm enter the human host?
by penetrating skin
describe the path in the body which is taken by the hookworm?
they penetrate the skin, enter the blood stream to travel to the lungs and are coughed up and swallowed in the sputum
what is the best way to avoid getting hookworm?
wearing shoes
what is the largest nematode and in what animal is it found?
- Placentonema gigantisma
- 9-13m long
- found in sperm whales
is the body of a nematode segmented or non segmented? flat or round?
- non-segmented
- round (roundworm) and tapered at both ends
what does the nematode body wall consist of?
- an outermost cuticle
- an underlying hypodermis that secretes the cuticle
what is the cuticle made of?
- the syncytial hypodermis secretes the thick outer layer of collagen
- it is proteinaceous (not callagen) with outer lipid laters
what are the characteristics of the collagenous cuticle?
- tough
- flexible
does a nematodes cuticle have cilia?
no
how often is the cuticle molted/shed?
usually four times in the life of the nematode, as it goes through the life stages
with which other groups does the nematode share the characteristics of a molted cuticle and the lack of cilia?
- arthropods
- ecdysozoans
what constrains the growth of the parasite between life stages?
the cuticle
what are the two steps of molting?
- SYNTHESIS of a new cuticle by the hypodermis
- EXSHEATHMENT - a process by which the old cuticle is loosened and ruptured followed by the larva wriggling out of the casing
what does exsheathment initiate?
infection
the process of exsheathment during infection is not only _______ but is also _______ within the host
- host-specific
- site-specific
what kind of muscle lies below the hypodermis?
longitudinal muscle (NO circular muscle, meaning the worm cannot shorten and lengthen as do earthworms)
movement of the parasite is due to _________ caused by contraction of the longitudinal muscles
undulating motion
what type of motion is observed with longitudinal muscle?
dorsoventral flexion, which allows for the characteristic sinusoidal undulating motion
what is another name for the body cavity?
pseudocoelom
why is it a pseudocoelom and not a coelom?
it is not lined internally with cilia
what fills the pseudocoelom?
pseudocoelomic fluid
where are reproductive organs found?
suspended in the pseudocoelom
what are the two functions of the pseudocoelomic fluid?
- gives the body rigidity
- transports materials from cell to cell
is the digestive tract complete or incomplete?
complete
what are the parts of the digestive tract in order?
mouth –> pharynx –> oesophagus –> intestine –> anus
what is found in the intestine to increase absorption?
microvilli
who does most of the digestion, the host or the nematode?
the host, the nematode mostly just absorbed the digested food of the host
what does the nervous system of the nematode consist of?
- a ganglian nervous system
- with an anterior neural ring,
- and 2 or 4 longitudinal nerve truncs extending the length of the nematode
what is another name for the anterial neural ring?
circumesophageal ring
where is the excretory pore of the nematode?
near the mouth
what are the characteristics of the excretory system?
- simple and tubular
- one or 2 one-celled renette glands and excretory ducts
- excretory pore is anterior
- NO flame cells*
does the nematode have a respiratory system?
no
how does gas exchange occur in nematode?
diffusion
all nematodes are ______ (reproductive anatomy)
dioecious (separate male and female organisms)
what does the reproductive system consist of?
tubular organs lying in the pseudocoelom
what do all nematodes release?
eggs
which are smaller, male or female nematodes?
male
what is particular about the posterior end of a male nematode?
it is curved
what does the male reproductive system consist of?
a single tubules starting with one testis and ending with a terminal cloaca and copulatory spicules
what is different in the female reproductive system?
the organs are doubled
what are the components of the female reproductive system?
- 2 threadlike ovaries
- 2 oviducts
- 2 uterus
- single genital pore at mid-body
what is common about the male and female reproductive organs?
they are both tubular and continuous, and increase in diameter as they extend to the genital opening
