Helminthes- Trematode Intro Flashcards
What is the most common niche for helminthes in humans?
in the GI tract, as adults. They are one of the most prevalent forms of parasitic disease
By which two general means do helminthes do damage to the host?
through physical and chemical damage
What are the three groups of helminthes?
cestodes (tapeworms), trematodes (flukes), and nematodes (roundworms)
Which group of helminthes has proglottids that are each hemaphroditic?
cestodes
Which group of helminthes are all hemaphrodites with one exception?
all trematode species except schistosomes
Which group of helminthes are dioecious?
nematodes
Which groups’ bodies are covered by tegument?
cestodes and trematodes
Which group’s bodies are covered by cuticle?
nematodes
Which group lacks a digestive tubule?
cestodes
Which group’s digestive tubule ends in a cecum?
trematodes
Which group’s digestive tubule ends in an anus?
nematodes
How are digenetic trematodes classified?
by the organ that they invade
Where do blood flukes invade?
the vasculature of the GI or genitourinary systems
Where do intestinal flukes invade?
the lumen of the GIT
Where do live flukes invade?
the liver
Where do lung flukes invade?
lungs and sometimes other organs such as the CNS
What is a distinguishing feature of the trematode classification?
all trematodes are obligate parasites in all classes of vertebrates
What does digenetic mean?
the life cycle involves at least 2 hosts
What is the first intermediate host?
a mollusk, usually a snail
What is the definitive host?
a vertebrate
What is the name of the third host?
most trematodes have a second intermediate host
Where do the larval stages most often occur?
in the intermediate host(s)
Where do the adult stages most often occur?
in the definitive host
Where is the oral sucker located and what is its function?
at the anterior end of the trematode and is used for attachment and feeding
Define acetebulum
aka ventral sucker. located mid-ventral to oral sucker, has no internal opening, used for attachment only
What is the syntegument?
the outer layer of the tegument body covering. contains mitochondria, secretory bodies and occasional spines. covered by a chemical layer
What is cytotegument?
cells beneath syntegument that produce mucus. separated from syntegument by tegumental muscle and connected by cytoplasmic bridges
What are the functions of the tegument?
1) osmoregulation & excretion
2) synthesis & secretion of mucus
3) absorption of nutrients
Describe the trematode digestive tract
food enters mouth and passes into the esophagus, which separates into two long blind-ending cecum (no anus)
Define parenchyma
loosely arranged cells filling space between internal organs
What is the function of the excretory system?
removes excess water that has diffused into the worm
What are flame cells and how do they function?
cells with beating flagella that create hydrostatic pressure to draw water from parenchyma into the collecting duct.
The collecting ducts empty into the excretory bladder at the posterior end
Describe the nervous system of trematodes
Ladder-type system: anterior ganglion + lateral nerve trunks + connecting commissures. Sense organs in the tegument
Which two ways can hermaphroditic trematodes reproduce?
via auto-fertilization OR require another worm for cross-fertilization (even though they are hermaphroditic)
What are the components of the male reproductive system?
two testes -> sperm ducts (2 vas efferentia join to form vas deferens) -> cirrus sac
What are the components of the female reproductive system?
SINGLE ovary produces eggs -> oviduct -> ootype
Describe trematode eggs
well developed egg shells, usually operculate (having a lid) except in schistosomes (have spines)
When and what happens when the egg hatches?
release of operculum.
can happen when ingested or under certain environmental conditions
What distinguishing organ do most miracidium have?
cilia used for locomotion
What do the miracidium do?
free-swimming stage that either seeks the intermediate host OR, in a few cases, is not free-swimming and hatches in the intestine to invade mollusk tissues
What marks the transformation of the miracidium to mother sporocyst?
at the point of penetration where cilia, penetration glands and apical gland are lost
What is the sporocyst cell and what does it become?
a hollow fluid filled germinal sac containing germ cells.
the germ cells either multiply & develop into daughter sporocysts or into a second larval stage (redia)
How does the sporocyst obtain nutrients?
passage of soluble material across the tegument
Can a trematode have both a daughter sporocyst and redia stage?
NO! if there is a daughter sporocyst stage, there is no redia stage and vise versa
What are the distinguishing features of redia larvae?
more active form, has a simple gut (mouth + pharynx + simple intestine), may have a ridge-like collar
What is the ridge-like collar?
located behind the mouth. Below this, the birth canal opens and either a daughter redia or cercariae emerges
What can redia prey on?
sporocysts & redia of the same species or of other species
Describe the cercarial stage
infective stage. variations in structure depending on species. usually free-swimming form.
Has a brief free-living stage. At this point may penetrate the next host or be ingested.
What is the mesocercaria?
the stage where the cercaria enters a second intermediate host (3-host system)
What is the metacercaria?
encysted form where the mesocercaria’s second intermediate host is ingested by a third intermediate host
What are the potential final intermediate hosts?
a fish, an arthropod, another mollusc (usually an echinostome)
How does the cercaria/metacercaria enter the definitive host?
can be ingested with the intermediate host by a carnivore definitive host OR ingested in encysted form when on plants by a herbivore definitive host
