Intro to Trematodes

Question 1

What is a trematode?

Answer 1

phylum platyhelminthes (flatworms - flukes) with bilateral symmetry (acoelomate) class trematoda subclass digenea (at least 2 hosts in life cycle). always snail in 1st IH

Question 2

What is important about the egg?

Answer 2

1. exists host to external environment 2. contains embryo (miracidium) 2. operculum - “escape hatch” that allows miracidium to hatch

Question 3

What causes hatching?

Answer 3

condition different from internal environment (e.g. light, temperature, osmolarity, pH)

Question 4

Describe the structure of a miracidium.

Answer 4

1. 100 um, non feeding, 2. cephalic ganglion (brain) 3. cilia 4. sensory endings: photoreceptors, georeceptors, chemoreceptors 5. glands 6. germinal cells

Question 5

What is primary miracidial behavior?

Answer 5

find and infect snail within 24 hours

Question 6

What are the 2 components of miracidial behavior?

Answer 6

1. host finding 2. infection of snail

Question 7

How does a miracidium find a host via host finding behavior?

Answer 7

1. environmental cues (+ or - to light, gravity, temperature) 2. similar to responses of snail hosts so parasite can go to same location 3. host cues (miraxone)

Question 8

What is miraxone?

Answer 8

substances of nail origin (amino acids, fatty acids, NH3)

Question 9

What is evidence that miracidium have host finding behaviors?

Answer 9

attraction measured by rate of change of direction (RCD) & swimming speed: 1. far from snail: low RCD & fast swimming -> moves to other spaces 2. close to snail: high RCD & slow swimming -> stays close to host

Question 10

What happens when a miracidium infects a snail?

Answer 10

respond to components of snail mucus: 1. wrong cues -> leave 2. correct cues -> penetrate snail 3. once inside -> metamorphosis

Question 11

What are the characteristics of a sporocyst?

Answer 11

1. loses cilia 2. forms new tegument (microvilli - increased surface area allows for absorption) 3. no mouth/digestive system 4 germinal sac - embryo -> daughter (secondary) sporocysts -> rediae -> cercariae

Question 12

What does redia do?

Answer 12

exit sporocyst & produce either daughter rediae or cercariae

Question 13

What is the effect of sporocysts & rediae on snail hosts?

Answer 13

parasitic castration: rediae move to reprodutive structures & feed on tissue & destory it, hormone manipulation

Question 14

What is parasitic castration?

Answer 14

snail not allocating resources to reproduction: resources go to growth

Question 15

What occurs during hormone manipulation?

Answer 15

schistosomin is snail peptide hormones involved in normal reproduction -> trematode larvae stimulate over production -> inhibits snail reproduction

Question 16

What behavior do cercariae exhibit?

Answer 16

exit snail via glands into external environment (1-3 days) swim or craw to encyst/infect host

Question 17

What is true about the metacercaria stage?

Answer 17

transmission stage (A & B strategies), inside DH it responds to complex stimuli to excyst and develop into adult worm

Question 18

Describe the structure of a metacercaria

Answer 18

no tail. multilayered cyst wall produced by cystogenous glands, A & B are thin & simple

Question 19

What is polyembryony?

Answer 19

asexual reproduction that results in multiple offspring from one embryo

Question 20

Where does species A encyst?

Answer 20

on plants: mucus from post acetabular glands & sheds tail

Question 21

How do species B & C find a suitable host?

Answer 21

via spatial location (gravity, light, temperature, host cues) & temporal location (circadian release - cercariae released from snail only at certain times of day that correlate to when the host is present)

Question 22

What happens when species B & C infect a host?

Answer 22

post-acetabular glands (mucus -> attachment), sheds tail, preacetabular glands produce enzymes -> allows for penetration

Question 23

What happens when species B & C is inside a host?

Answer 23

species B has cystogenous glands -> metacercaria in 2nd IH. species C inside DH - migrates in body & develops into adult worm

Question 24

What do bird schistasomes respond to?

Answer 24

respond to bird cues (ex: movement, warmth, shadow, chemical cues)

Question 25

What human cues do schistasomes respond to?

Answer 25

movement, warmth, shadow, chemical cues

Question 26

What happens if a bird cercaria infects a human?

Answer 26

wrong host -> parasite dies

Question 27

What is swimmers itch (cercarial dermatitis)?

Answer 27

human -> allergic rxn -> itchy rash

Question 28

Describe the morphology of an adult trematode.

Answer 28

acoelomate (no body cavity)/parenchyma (body is solid) w/ fixed cells & stem cells. collagen fibers provide support. lack circulatory, skeletal, & respiratory systems

Question 29

What are the functions of the morphology of adult trematodes (lack of body cavity)?

Answer 29

1. fills space between body wall & gut 2. attachment point for muscles 3. internal organs embedded 4. passage of materials

Question 30

How is respiration (diffusion) made easier for adult trematodes?

Answer 30

being flat makes this easy bc every cell is not too far from surface

Question 31

What are the components of the digestive tract of adult trematodes?

Answer 31

1. blind: have mouth but no anus 2. mouth for ingestion & expulsion of waste 3. muscular/mechanical pharynx that is glandular: enzymes (digestive, chemical) 4. esophagus 5. cecum: bifurcates, branched or unbranched

Question 32

What is the purpose of the ventral sucker in adult trematodes?

Answer 32

muscular allows for attachment

Question 33

What are the components of the NS of adult trematodes?

Answer 33

1. Platyhelminthes were 1st organism w/ clearly defined CNS 2. cerebral ganglion (“brain”) 3. sensory endings: chemoreceptors, tangoreceptors

Question 34

What are the two types of trematode reproduction?

Answer 34

1. sexual 2. monoecious - hermaphrodite (excpet schistosomes), self fertilization, cross fertilization

Question 35

What is a tegument?

Answer 35

outer surface of living tissue. syncytium - multinucleated tissue w/ no cell boundaries. lots of glucose uptake

Question 36

What is the outer surface of a tegument? What are some characteristics?

Answer 36

glycocayx: 1. muaginations inc SA & absorption 2. hydrolytic enzymes 3. defense - shield worm from antibodies & host enzymes

Question 37

What is the distal cytoplasm of a tegument?

Answer 37

anucleate w/ 2 membranous bodies that produce materials that maintain glycocalyx

Question 38

What are the 2 muscle layers of a tegument like?

Answer 38

circular & longitudinal

Question 39

What is in the proximal cytoplasm of a tegument? What happens here?

Answer 39

has nuclei & organelles. production of material that maintain distal cytoplasm

Question 40

What are cytoplasmic connective in a tegument?

Answer 40

channels between distal & proximal cytoplasm through muscle layer

Question 41

Where do adult schistosomes live? Why?

Answer 41

bloodstream of DH bc it is rich in glucose

Question 42

What are glucose transporter & what do they do?

Answer 42

integral membrane proteins in all organisms that move glucose molecules across hydrophobic membrane. carrier mediated diffusion = facilitated diffusion

Question 43

What are the 2 layers in schistosome teguments?

Answer 43

1. surrounded by lipid bilayer - external 2. basal membrane - internal

Question 44

What are the 2 schistosome GTPs synthesized by membranous bodies?

Answer 44

located only in tegument: 1. SGTP1 in basal membrane 2. SGTP4 in lipid bilayer

Question 45

Where do trematodes stay inside the DH?

Answer 45

depends on species: intestinal flukes vs. liver flukes vs. blood flukes vs. lung flukes

Question 46

What 3 place inside the DH can liver flukes stay?

Answer 46

1. liver 2. bile duct 3. gall bladder