Nematodes Introduction Flashcards
How many species of nematodes have been described?
~25,000
In which kingdom are nematodes classified?
Animalia-Ecdysozoa
What do ecdysozoans have in common?
ecdysis (molting)
What are the 2 most abundant phyla in the Ecdysozoa?
Arthropoda (hard exoskeleton) & Nematoda (soft cuticle)
Explain what happens during molting.
growth for larger cuticle or exoskeleton: succession of molts, shed outer layer
Where are nematodes found?
found in all environments: aquatic and soil in particular
What types of nematodes are found in the soil?
bacterial-feeder, fungal feeders, predatory, parasitic
What is the impact of nematodes on plants?
parasitic nematodes destroy ~10% of all crops
How many people worldwide suffer from nematode infections?
> 3 billion
Why are nematodes called roundworms?
elongate, cylindrical, w both ends tapered
What are the 2 tubes which comprised the body of a nematode?
outer is body wall & inner is digestive tract
What are the 3 parts of the body wall?
- cuticle 2. hypodermis3. muscle layer: beneath hypodermis
Where is the cuticle found?
covers entired body surface & lines openings
What is the function of the hypodermis?
formation of cuticle during molting (cellular vs. syncytial)
What are the 3 major regions of the digestive tract?
- foregut 2. midgut 3. hindgut
Is the foregut lined with cuticle?
yes
What surrounds the mouth in some species?
lips - # varies among species
Is the buccal cavity found in all species?
no
Why is the buccal cavity useful for identification?
not present in all species: size & shape varies, may have teeth or cutting plates (thickening of cuticle)
What is the name of the junction between the esophagus and midgut?
esophago-intestinal value
Is the midgut lined with cuticle?
no
What type of cells are found in the midgut?
single layer of cells (for absorption): simple columnar & microvilli
What process occurs in the midgut?
absorption
Is the hindgut lined with cuticle?
yes
Where is the pseudocoel and with what fluid is it filled?
between the body wall & digestive tract and filled with hemolymph
What are the major functions of the hemolymph?
- transport nutrients 2. structural 3. hydrostatic skeleton
Explain how the hydrostatic skeleton functions in nematode locomotion.
- muscles on one side contract 2. compress cuticle on that side 3. force of contraction transmits fluid to other side (hemolymph) 4. muscles on other side stretch 5. alternation of contraction & relaxation -> S shaped curves
Are nematodes monoecious or dioecious?
dioecious - separate males and females
What does sexually dimorphic mean?
females are larger than males
Where is sperm produced in nematodes?
testes
How do nematode sperm differ from human sperm?
no flagella - use pseudopodia for locomotion
What is the function of the bursa?
hold female during mating in some species at posterior end
What is produced in the ovary?
oocytes
What stimulates the process of eggshell formation
sperm penetrates oocytes
What are the 3 layers found in the fully formed shell of most nematodes?
- vitelline layer 2. chitnous layer 3. lipid layer
In some species there is a fourth layer in the eggshell called the
proteinaceous layer from uterine secretions.
What are the origins of the vitelline and chitinous layers and how are refringent bodies involved in the formation of the lipid layer?
The original oocyte PM, above the new PM, becomes vitelline layer and chitinous layer forms below the vitelline layer. Refringnet bodies from sperm migrate to periphery of oocytes and expell contents and fuse together to form lipid layer.
What are the 2 major commissures in a nematode?
- circumesophageal commissre 2. rectal commissure
What nerve connects the 2 commissures?
ventral longitudinal nerve
What are the 4 types of sense organs we discussed?
- labial papillae 2. cephalic papillae 3. amphids 4. phasmids
Where is the labial papillae located and what does it detect?
on lips w/ mechanoreceptors
Where is the cephalic papillae located and what does it detect?
posterior to lips w/ mechanoreceptors
Where are phasmids located and what does it detect?
near tail w/ chemo receptors (absence/presence = classification)
Where are amphids located and what does it detect?
same level as cephalic papillae (posterior to lips) w/ chemoreceptors
Which sense organ is most important in taxonomic classification?
phasmids
What neurotransmitter is released by excitatory nerve fibers?
acetylcholine
What happens to the muscle membrane and rate of APs when ACh is released?
depolarizes muscle membrane & increases rate of APs
What neurotransmitter is released by inhibitory nerve fibers?
GABA
What happens to the muscle membrane and the rate of APs when GABA is released?
muscle membrane is hyperpolarized & AP rate decreases
What are flaccid and spastic paralysis?
spastic paralysis - muscles rigid vs. flaccid - limp
How does piperazine function?
blocks ACh: muscle is hyperpolarized -> flaccid paralysis
How does ivermectin function?
stimulates GABA release -> flaccid paralysis
How does pyrantel function?
inhibits cholinesterase (enzyme that inactivates ACh) -> spastic paralysis
What is the mode of action of albendazole and mebendazole?
inhibit polymerization of tubulin into microtubules. the loss of cytoplasmic microtubules -> decreases uptake of glucose by parasites
What are 2 classes of nematodes and how do they differ?
Adenophorea: cellular hypodermis & no phasmids vs. Secernentea: syncytial hypodermis & have phasmids
What are the 3 main routes of infection by nematodes?
- oral 2. skin penetration 3. IH - vector
What is a vector?
actively transmits parasite
Is the life cycle of a nematode which infects by egg transmission a direct life cycle?
yes
one host
Is there amplification in the life cycle of a nematode which infects by egg transmission?
no
What is embryonation?
development of larva inside egg
How does molting occur?
- larva excretes exsheathing fluid 2. cuticle detaches from hypodermis 3. hypodermis secretes new cuticle 4. old cuticle -> nematode exists old cuticle
