(DON'T STUDY) NEMATODES L3 Flashcards
The main helminth groups:
- trematodes (flukes)
- cestodes (tapeworms)
- acanthocephalans (thorny-headed worms)
- nematodes (roundworms)
Nematodes are ____ organisms
moulting
Nematodes may be more closely related to ___ than other helminth groups since they ____.
they may be more closely related to arthropods since they moult
Nematodes developed in ____ environments
aquatic
Where did nematodes evolve in their environment?
evolved in the sludge present at the bottom of the sea – very similar conditions to the sludge in our guts
Nematodes can or cannot swim?
cannot swim so are not a parasitic of pelagic fish
Where do nematodes currently live now?
made it all the way to the land where they are one of the commonest lifeforms present in soil
all nematodes essentially need ____ to move around and feed in.
all nematodes essentially need liquid water to move around and feed in.
the nematodes are considered the most ____ species and their size is very ____
free living species that are very small
Most nematodes live for a ____ amount of time
short amount of time (days to weeks)
Nematodes are described as ____ unlike us
pseudocoelmates — so their organs hang free in the interior with no attachments other than at the termini
True or false: Nematodes have separate sexes?
TRUE
Nematodes can vary in length from ___ to ___?
micrometers to meters
Nematodes have a tubular ___ and ____
tubular gut and body
Nematodes have a ___outer cuticle thats composed of ____ and ____ growth
tough outer cuticle thats composed of collagen that limits growth
Nematodes organs such as the ___ and ___ float free in the anterior
guts and reproductive organs
What does psuedocoelom mean?
fluid filled body
The posture of nematodes with relaxed or paralysed muscles tends to be _____ – due to pressure in the ____.
The posture of nematodes with relaxed or paralysed muscles tends to be straight – due to pressure in the interior fluid.
The cuticle is a complex, highly variable, ____ structure that is secreted ___ by the underlying epidermis, unlike our own epidermis which is refreshed _____.
The cuticle is a complex, highly variable, collagenous structure that is secreted once by the underlying epidermis, unlike our own epidermis which is refreshed continuously.
Although ____, the cuticle does not allow much longitudinal stretch therefore to grow, nematodes must ____.
Although flexible, the cuticle does not allow much longitudinal stretch therefore to grow, nematodes must moult.
The cuticle can be describe as having ____ or _____ ridges
transverse ridges or longitudinal
What are the longitudinal ridges used for?
used by many small intestinal nematodes to grip the villi as the worms wrap themselves around them, allowing the worms to stay in place and resist being pushed along the gut by peristaltic contractions
The locomotion of nematodes is a _____ movement
muscles and the body fluid interact to produce a snake- like sinusoidal movement, with the worms flexing dorso-ventral
The anterior end of nematodes is for?
feeding
the posterior end of nematodes is for?
reproduction
What do free-living nematodes feed on?
Many free-living nematodes (including the free-living stages of many parasitic nematodes) feed on micro-organisms such as bacteria.
What do parasitic nematodes feed on?
Parasitic nematodes may feed on fluids (gut contents, mucus and other secretions, blood) or tissue.
In nematodes, the buccal capsule is made of ___ and considered ____.
chitin and considered rigid
The intestine is a ____ tube terminating at the ____. The lining is covered with _____ to increase absorptive area.
The intestine is a simple tube terminating at the anus. The lining is covered with microvilli to increase absorptive area.
A muscular ____ is needed at the anus to control the release of ____ and the anus is usually just behind the tip of the ____, on the ventral surface.
A muscular sphincter is needed at the anus to control the release of waste and the anus is usually just behind the tip of the tail, on the ventral surface.
The reproductive tracts are?
simple blind-ending tubes.
In female nematodes the reproductive and intestinal tracts have _____ openings. And sometimes the vulval opening may be protected by _____?
In female nematodes the reproductive and intestinal tracts have separate openings. And sometimes the vulval opening may be protected by a flap of cuticle.
Most female nematodes have how many uteruses?
Most female nematodes have more than one uterus – usually two.
Where is the vulval position?
Vulval position can vary anywhere from close to the tail to close to the mouth.
In the male, generally both the intestinal tract and testes open at the same point – _____ – close to the tip of the tail.
the cloaca
Most male’s have at least one, usually two protrusible structures called?
Spicules
What do spicules do?
that can be pushed through the cloaca into the female body and direct the flow of sperm
Which group of nematodes have a large claw like spicule?
the whipworms
The copulatory bursa is an extension of the ___ and what is it comprised of?
cuticle and comprised of two lateral lobes and one dorsal lobe
which group of nematodes has a grasping structure called _____ that is used to grip the female?
the ascarid nematodes have a grasping structure called the copulatory bursa
Do nematodes use oxygen?
some do some do not and this can change in the nematode lifecycle
egg development in nematodes is usually anaerobic or aerobic?
aerobic
the free-living stages of nematodes are typically anaerobic or aerobic?
aerobic
Large adult nematodes that live in the lumen of the gut are anaerobic or aerobic
anaerobic
Nematodes lack a ____system
circulatory
Many of the bigger nematodes are too big for oxygen to diffuse into their tissues and hence they respire anaerobically or aerobically?
anaerobically
Slender nematodes living close to, sometimes in, the mucosal surface will have access to lower or higher levels of oxygen concentrations
higher
Many nematodes produce their own _____ like molecules to help them access what little oxygen might be present, but some anaerobic worms use these to keep O2 away from their biochemical processes.
hemoglobin
TRUE OR FALSE: The development of eggs doesn’t require O2
FALSE – it does require o2
you can’t get energy from lipids, the main nutrient stored in eggs, anaerobically - and this is one reason why very few nematodes can complete their lifecycle inside the one host – once released into the luminal fluid of the gut, the eggs cannot develop until the eggs exit the host.
it is generally accepted that all nematode lifecycles involve?
adults themselves, an egg, and four immature, larval stages
Nematodes get bigger by?
moulting
The L4s show the beginnings of some sexual maturation, but reproduction is only carried out by?
adults
For most nematodes, the eggs are laid by females in an early stage of development, not yet ready to hatch, but for a minority what happens?
they may already be close to hatching when released by the females and in a very small number of cases, the eggs will hatch inside the uterus (larviparous)
In many lifecycles the ___ hatches out of the egg, but sometimes the nematodes will develop all the way to the ___ stage before hatching.
L3; L3
What shapes can the eggs be?
elliptical, near spherical, even lemon shaped
What is one very important consequence of nematode mounting behavior?
Each parasitic stage (L3, L4, and adult) may be antigenically different
The lifecycle of nematodes ____ generally be completed in ___ host
cannot; one
for most nematode parasites, adults and later larval stages are in the?
definitive host
Eggs and larvae that are shed in the feces represent what stage?
dispersal stage
Development in the environment or in the intermediate hosts is what stage?
infective
What stages of the larvae hatch out of the egg?
L1, L2, or L3
Hatching of the eggs may be?
spontaneous or triggered
Eggs can hatch spontaneously, just because they’ve finished developing, or a trigger may be needed to stimulate hatching, in which case the stimulus for hatching is often exposure to the internal conditions of a new host
What happens if the larvae hatch right away?
- more vulnerable
- can feed less investment by adult in egg (more eggs laid)
- can move and get out go feces onto pasture
What happens if the larvae stay in the egg and decide NOT to hatch?
- greater protection in the egg
- cannot feed so any development must be sustained by nutrients in the egg (less eggs laid)
- cannot actively move
Free-wriggling larval stages can also do things like move ____ from feeces – enhancing the likelihood that they’ll get ______?
away; picked up by new hosts
after a period of feeding, they become less ___?
mobile—making them lethargus
Describe the moulting in nematodes:
After feeding and growing as much as the stage can before its cuticle becomes too restrictive – the nematode will become inactive for a while. It will then split off the old cuticle from the underlying epidermis, but won’t get rid of the old one until the new one has been secreted. Finally the old cuticle will be split, usually by the action of enzymes and the next stage emerges. Initially the same size (or slightly smaller) as the previous stage it can then start expanding and growing further.
Can ensheathed larvae feed?
no they cannot feed and must rely on internal stores
for many parasitic nematodes, moult from ___ to ____ is incomplete
L2 to L3
When moulting is incomplete, ____ is delayed and old cuticle is _____ as an extra ____ layer.
- Ecydsis is delayed
- old cuticle is retained as an extra protective layer
When is larvae ensheathed in nematodes?
L3
When do nematode species have a defined infective stage for the definitive host?
This is most often the L3 in various forms and in various locations, but occasionally the earlier L1 or L2 may be infective.
TRUE OR FALSE: Once the infective stage is reached, the lifecycle cannot progress any further until a new host is found.
true
List the ways the infective stage can be acquired in nematodes:
- ingesting the infective stage in food or water (ORAL INFECTION)
- ingesting the infective stage in mother’s milk (TRANSMAMMARY INFECTION)
- ingesting the infective stage in intermediate or paramedic host
- percutaneous infection (infective stage penetrating the skin)
- Prenatal infection (infective stage crossing the placenta)
- biting insect or arthropods (vector) transmits the infective stage to the host as it feeds
