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Human Parasitology > Nematodes Introduction > Flashcards

Nematodes Introduction Flashcards

1
Q

How many species of nematodes have been described?

A

~25,000

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2
Q

In which kingdom are nematodes classified?

A

Animalia-Ecdysozoa

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3
Q

What do ecdysozoans have in common?

A

ecdysis (molting)

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4
Q

What are the 2 most abundant phyla in the Ecdysozoa?

A

Arthropoda (hard exoskeleton) & Nematoda (soft cuticle)

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5
Q

Explain what happens during molting.

A

growth for larger cuticle or exoskeleton: succession of molts, shed outer layer

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6
Q

Where are nematodes found?

A

found in all environments: aquatic and soil in particular

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7
Q

What types of nematodes are found in the soil?

A

bacterial-feeder, fungal feeders, predatory, parasitic

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8
Q

What is the impact of nematodes on plants?

A

parasitic nematodes destroy ~10% of all crops

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9
Q

How many people worldwide suffer from nematode infections?

A

> 3 billion

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10
Q

Why are nematodes called roundworms?

A

elongate, cylindrical, w both ends tapered

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11
Q

What are the 2 tubes which comprised the body of a nematode?

A

outer is body wall & inner is digestive tract

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12
Q

What are the 3 parts of the body wall?

A
  1. cuticle 2. hypodermis3. muscle layer: beneath hypodermis
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13
Q

Where is the cuticle found?

A

covers entired body surface & lines openings

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14
Q

What is the function of the hypodermis?

A

formation of cuticle during molting (cellular vs. syncytial)

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15
Q

What are the 3 major regions of the digestive tract?

A
  1. foregut 2. midgut 3. hindgut
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16
Q

Is the foregut lined with cuticle?

A

yes

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17
Q

What surrounds the mouth in some species?

A

lips - # varies among species

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18
Q

Is the buccal cavity found in all species?

A

no

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19
Q

Why is the buccal cavity useful for identification?

A

not present in all species: size & shape varies, may have teeth or cutting plates (thickening of cuticle)

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20
Q

What is the name of the junction between the esophagus and midgut?

A

esophago-intestinal value

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21
Q

Is the midgut lined with cuticle?

A

no

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22
Q

What type of cells are found in the midgut?

A

single layer of cells (for absorption): simple columnar & microvilli

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23
Q

What process occurs in the midgut?

A

absorption

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24
Q

Is the hindgut lined with cuticle?

A

yes

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25
Where is the pseudocoel and with what fluid is it filled?
between the body wall & digestive tract and filled with hemolymph
26
What are the major functions of the hemolymph?
1. transport nutrients 2. structural 3. hydrostatic skeleton
27
Explain how the hydrostatic skeleton functions in nematode locomotion.
1. 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
28
Are nematodes monoecious or dioecious?
dioecious - separate males and females
29
What does sexually dimorphic mean?
females are larger than males
30
Where is sperm produced in nematodes?
testes
31
How do nematode sperm differ from human sperm?
no flagella - use pseudopodia for locomotion
32
What is the function of the bursa?
hold female during mating in some species at posterior end
33
What is produced in the ovary?
oocytes
34
What stimulates the process of eggshell formation
sperm penetrates oocytes
35
What are the 3 layers found in the fully formed shell of most nematodes?
1. vitelline layer 2. chitnous layer 3. lipid layer
36
In some species there is a fourth layer in the eggshell called the
proteinaceous layer from uterine secretions.
37
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.
38
What are the 2 major commissures in a nematode?
1. circumesophageal commissre 2. rectal commissure
39
What nerve connects the 2 commissures?
ventral longitudinal nerve
40
What are the 4 types of sense organs we discussed?
1. labial papillae 2. cephalic papillae 3. amphids 4. phasmids
41
Where is the labial papillae located and what does it detect?
on lips w/ mechanoreceptors
42
Where is the cephalic papillae located and what does it detect?
posterior to lips w/ mechanoreceptors
43
Where are phasmids located and what does it detect?
near tail w/ chemo receptors (absence/presence = classification)
44
Where are amphids located and what does it detect?
same level as cephalic papillae (posterior to lips) w/ chemoreceptors
45
Which sense organ is most important in taxonomic classification?
phasmids
46
What neurotransmitter is released by excitatory nerve fibers?
acetylcholine
47
What happens to the muscle membrane and rate of APs when ACh is released?
depolarizes muscle membrane & increases rate of APs
48
What neurotransmitter is released by inhibitory nerve fibers?
GABA
49
What happens to the muscle membrane and the rate of APs when GABA is released?
muscle membrane is hyperpolarized & AP rate decreases
50
What are flaccid and spastic paralysis?
spastic paralysis - muscles rigid vs. flaccid - limp
51
How does piperazine function?
blocks ACh: muscle is hyperpolarized -> flaccid paralysis
52
How does ivermectin function?
stimulates GABA release -> flaccid paralysis
53
How does pyrantel function?
inhibits cholinesterase (enzyme that inactivates ACh) -> spastic paralysis
54
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
55
What are 2 classes of nematodes and how do they differ?
Adenophorea: cellular hypodermis & no phasmids vs. Secernentea: syncytial hypodermis & have phasmids
56
What are the 3 main routes of infection by nematodes?
1. oral 2. skin penetration 3. IH - vector
57
What is a vector?
actively transmits parasite
58
Is the life cycle of a nematode which infects by egg transmission a direct life cycle?
yes | one host
59
Is there amplification in the life cycle of a nematode which infects by egg transmission?
no
60
What is embryonation?
development of larva inside egg
61
How does molting occur?
1. larva excretes exsheathing fluid 2. cuticle detaches from hypodermis 3. hypodermis secretes new cuticle 4. old cuticle -> nematode exists old cuticle

Human Parasitology (22 decks)

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