CESTODES
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此牌组中的学习卡（49）

  • What are the main parts of the cestode body plan?

    Answer
    • Scolex
    • Neck
    • Strobila / proglottids
    cestode morphology

  • What is the function of the tegument in cestodes?

    Answer
    • Nutrient absorption
    cestode tegument

  • What are microtriches in cestodes used for?

    Answer
    • Increase tegument surface area for absorption
    cestode microtriches

  • What notable feature describes cestode reproductive anatomy mentioned in the notes?

    Answer
    • Protandry
    cestode reproduction

  • Name two major groups of cestodes mentioned.

    Answer
    • Pseudophyllidean
    • Cyclophyllidean
    cestode classification

  • List the larval types of cestodes noted.

    Answer
    • Procercoid
    • Plerocercoid
    • Cysticercus
    • Hydatid
    cestode larvae

  • Give three key features of Diphyllobothrium latum from the summary.

    Answer
    • Fish-borne
    • Causes anemia
    • Produces operculated eggs
    diphyllobothrium epidemiology

  • What is the general body form of organisms in Cestoda (tapeworms)?

    Answer
    • Flat or ribbon-like appearance
    cestoda morphology

  • Which two major divisions belong to parasitic flatworms?

    Answer
    • Trematodes (flukes)
    • Cestodes (tapeworms)
    classification parasite

  • What is 'protandry' in cestodes?

    Answer
    • A microorganism begins life as a male and changes into a female
    reproduction cestoda

  • Which flatworms are exceptions to hermaphroditism?

    Answer
    • Schistosomes
    reproduction trematoda

  • Name the two orders of cestodes described and one distinguishing scolex feature for each.

    Answer
    • Order Pseudophyllidean: scolex with 2 opposing sucking organs
    • Order Cyclophyllidean: scolex with 4 suckers
    cestoda orders

  • How do cestodes obtain nutrition given they lack an alimentary tract?

    Answer
    • Food is absorbed through the tegument (integument) system
    physiology tegument

  • What are microtriches on cestodes?

    Answer
    • Highly specialized microvilli covering the tegument, fine hair-like filaments over the body
    tegument microtriches

  • List the main parts of a cestode body plan mentioned.

    Answer
    • Scolex: organ of attachment
    • Neck: region of growth and chain of developing proglottids
    anatomy cestoda

  • What strobila segment arrangements are described for cestodes?

    Answer
    • Craspedote: anterior proglottids overlap next exterior one
    • Acraspedote: proglottids do not overlap
    strobila morphology

  • Define 'apolytic' and 'anapolytic' in relation to proglottids.

    Answer
    • Apolytic: premature detachment or release of terminal gravid proglottids
    • Anapolytic: gravid proglottids are not shed; eggs released another way
    reproduction strobila

  • Where can the genital pore be located on a proglottid?

    Answer
    • Same side of proglottid
    • Bilateral
    • Ventral surface with uterine pore
    • Irregular alternate
    reproduction anatomy

  • Where do the vas deferens and vagina open when they share a common genital pore?

    Answer
    • Open on the ventral surface
    • Or open on the lateral margin
    reproduction genital

  • What are the main organs for attachment on a cestode scolex?

    Answer
    • Bothria: two elongated grooves
    • Sucking disks: cup-like
    • Rostellum: chitinous hooks
    morphology scolex

  • How does a proglottid develop and function in cestodes?

    Answer
    • Progressively matures and functions individually
    • Originates from the posterior neck region
    • Contains completely formed sexual organs
    proglottid reproduction

  • Describe the arrangement of genital pores in proglottids.

    Answer
    • Common genital pores: on the same side of each proglottid
    • Irregularly alternate
    • Bilateral
    proglottid genital

  • What are main features of the mature uterus in cestodes?

    Answer
    • Coiled
    • Saccular or lobulated
    • Tube: straight or branched
    female uterus

  • List the structures found in a gravid segment of a cestode.

    Answer
    • Reticulate with ova in capsules
    • Lateral branches
    • Vagina
    • Seminal receptacle
    • Ovary
    • Oviduct joined to spermatic duct
    • Ootype: egg formation
    • Vitellaria: nourishment of the eggs
    gravid reproduction

  • What is the function of vitellaria in cestodes?

    Answer
    • Provide nourishment for the eggs
    vitellaria female

  • What is the cirrus in cestodes and where is it found?

    Answer
    • Cirrus: muscular male copulatory organ that opens to the vagina
    • Found in Hymenolepis spp and Taenia spp
    male cirrus

  • What type of excretory cell system do cestodes have?

    Answer
    • Flame cell (protonephridium)
    excretory physiology

  • Define heteroxenous and homoxenous life cycles for cestodes.

    Answer
    • Heteroxenous: one or more intermediate hosts
    • Homoxenous: one intermediate host
    life-cycle hosts

  • Where do cestodes typically inhabit in the host and what is their metabolism?

    Answer
    • Habitat: intestinal lumen (ileum, jejunum, colon)
    • Metabolism: anaerobic; absorption by tegument; causes Vitamin B decrease/starvation
    habitat metabolism

  • Describe cestode reproduction modes and typical lifespan detail given.

    Answer
    • Hermaphroditism: self and cross fertilization
    • Asexual: in intermediate host
    • Life span: generally short-lived; Taenia may last 20–25 years
    reproduction lifespan

  • Name the two larval types classified as 'solid' in cestodes and a key feature of each.

    Answer
    • Procercoid: no scolex; with oncospiral hooks
    • Plerocercoid: elongated, infective stage with developing scolex & strobila
    larva solid

  • What are the vesicular (bladder) larval forms and key characteristics?

    Answer
    • Cysticercus: true bladder with enlarged central cavity
    • Cysticercoid: slightly developed bladder with scolex at apex
    • Variations: coenurus (multiple scolices), echinococcus/hydatid (daughter cysts, brood capsules)
    larva vesicular

  • Use the diagram to recall female reproductive organs visible in a cestode cross-section.

    Answer

    female reproductive organs - Visible structures: uterus, testes, ovary, genital pore

    diagram female

  • What are key external features of a scolex described in the notes?

    Answer
    • 2 suctorial grooves
    • 4 muscular suckers (may have spines or hooks)
    morphology scolex

  • Where is the genital pore located on a pseudophyllidean proglottid?

    Answer
    • Center of the proglottid (center of segment)
    reproduction proglottid

  • Where are uterine pores located in the described proglottids?

    Answer
    • At the margins of the proglottid; may be absent
    reproduction uterus

  • Give three morphological facts about adult Diphyllobothrium yonagoensis from the notes.

    Answer
    • Ivory white
    • Length: 3–10 meters
    • About 4000 proglottids
    diphyllobothrium morphology

  • How is the uterus described in the midterm notes for pseudophyllideans?

    Answer
    • Coiled; sac-like branched; may contain eggs in capsule
    uterus morphology

  • What are the characteristics of ova listed for pseudophyllideans?

    Answer
    • Operculated
    • Immature (if found in feces)
    ova pseudophyllidean

  • What is the oncosphere (onco larva) stage called and its feature?

    Answer
    • Coracidium: ciliated
    larva coracidium

  • List the main differences between Pseudophyllidean and Cyclophyllidean eggs/larvae as given.

    Answer
    • Pseudophyllidean: operculated; immature when laid; coracidium; ciliated
    • Cyclophyllidean: non-operculated; mature when laid; hexacanth embryo; non-ciliated with 3 pairs of hooks
    comparison life-cycle

  • What is the diagnostic and infective stage of Diphyllobothrium latum?

    Answer
    • Diagnostic stage: embryonated egg
    • Infective stage: procercoid larva
    diphyllobothrium life-cycle

  • How is Diphyllobothrium latum transmitted to humans?

    Answer
    • By ingestion of raw or undercooked freshwater fish
    transmission diphyllobothrium

  • What clinical effect related to vitamins is associated with Diphyllobothrium latum?

    Answer
    • Causes anemia by interfering with intrinsic factor and vitamin B12 absorption
    clinical anemia

  • Provide key facts about Diphyllobothrium latum size, longevity, and common name.

    Answer
    • Largest human tapeworm: up to 10 meters
    • Can live up to 25 years
    • Common name: Fish tapeworm (Broad tapeworm)
    diphyllobothrium epidemiology

  • What are the described features of Diphyllobothrium latum proglottids and uterus?

    Answer
    • Proglottids broader (2–4 mm long × 10–12 mm wide)
    • Male and female organs present; uterus coiled (rosette)
    proglottid morphology

  • List the ovum characteristics for Diphyllobothrium latum given in the notes.

    Answer
    • Size: 30–50 μm
    • Posterior part thickened; yellowish to yellow-brown
    • May be immature if found in feces; ~100,000 eggs/day
    ova diagnosis

  • Which regions are listed as endemic areas for Diphyllobothrium latum?

    Answer
    • Great Lakes, Scandinavia, Western Europe, Japan, South America
    epidemiology diphyllobothrium

  • Show an illustrative image of Diphyllobothrium latum scolex and gravid proglottid.

    Answer
    • Image: Scolex and gravid proglottid of Diphyllobothrium latum
    • Caption: Scolex and gravid proglottid (illustration only)
    image diphyllobothrium
学习笔记

Clinical Parasitology — Cestodes (Tapeworms) — Study Notes

Quick facts

  • Platyhelminths = flatworms; most are hermaphroditic (both sexes in one individual); exception: schistosomes (dioecious).
  • Two main groups: Trematodes (flukes) and Cestodes (tapeworms).

Cestode (Tapeworm) overview

  • Body: long, flattened strobila made of segments (proglottids).
  • No digestive tract; nutrients are absorbed through the tegument.
  • Surface specialized by microtriches (fine microvilli) to increase absorption.
  • Reproductive strategy: protandry (segments mature male first, then female) and usually hermaphroditic; some species self- or cross-fertilize.

Main body regions

  • Scolex: attachment organ (varies by species: bothria, suckers, rostellum with hooks).
  • Neck: proliferative zone producing new proglottids.
  • Proglottids: individual segments containing complete sexual organs; mature sequentially from neck outward.

Proglottid types and strobila features

  • Craspedote: anterior proglottids overlap next exterior one.
  • Acraspedote: proglottids do not overlap.
  • Apolytic: terminal gravid proglottids detach to release eggs.
  • Anapolytic: gravid proglottids remain; eggs released by other means.

Tegument and excretory systems

  • Tegument: syncytial covering; site of nutrient uptake and immune interaction.
  • Flame cells / protonephridia: excretory/osmoregulatory units.

Reproductive anatomy (key structures)

Female structures (ventral side of proglottid)

  • Uterus: may be coiled, sac-like, lobulated or branched (forms a rosette in some species).
  • Ootype: site of egg formation.
  • Vitellaria: yolk glands that supply nutrients to eggs.
  • Seminal receptacle, ovary, oviduct: typical components in mature proglottid.

Male structures (dorsal part of proglottid)

  • Testes and small ducts (vasa efferentia) lead to vas deferens.
  • Cirrus: muscular copulatory organ (present in genera such as Hymenolepis and Taenia).

Microscopic view showing uterus, testes and genital pore

Genital pore positions

  • Can be unilateral (same side), bilateral, ventral central, or alternating irregularly.
  • Vas deferens and vagina can share a common genital pore that opens on the ventral or lateral margin.

Life cycles & hosts

  • Heteroxenous: requires one or more intermediate hosts.
  • Homoxenous: requires only definitive host (rare among cestodes).
  • Typical cycle: egg → larva (in intermediate host) → adult (definitive host).
  • Larval forms vary by species (see next section).

Larval types / metacestodes

  • Solid (no big bladder): e.g., procercoid (no scolex initially, often in copepods), plerocercoid (elongated, infective, developing scolex).
  • Vesicular (bladder): e.g., cysticercus (single scolex within bladder), cysticercoid (small bladder with apex scolex), coenurus (many scolices), hydatid cyst (Echinococcus with daughter cysts).

Key differences: Pseudophyllidean vs Cyclophyllidean

  • Pseudophyllidean
  • Eggs operculated, often passed as immature in feces.
  • Coracidium (ciliated) hatches; typically aquatic life cycle with copepod first intermediate host.
  • Scolex with bothria (two longitudinal grooves).
  • Cyclophyllidean
  • Eggs non-operculated, mature when shed; embryo = hexacanth (six hooks), non-ciliated.
  • Scolex usually with four suckers ± rostellum/hooks; vitellaria condensed near ovary.
Feature Pseudophyllidean Cyclophyllidean
Egg shell Operculated Non-operculated
Embryo Coracidium (ciliated) Hexacanth (6 hooks, non-ciliated)
Scolex Bothria (grooves) 4 suckers ± hooks

Physiology (clinical relevance)

  • Habitat: adult cestodes inhabit the intestinal lumen (ileum, jejunum, colon).
  • Metabolism: anaerobic; absorb nutrients across tegument; can cause vitamin deficiencies (notably vitamin B12).
  • Reproduction: high egg output; some species live many years (e.g., Taenia up to \(20\text{–}25\) years).
  • Pathogenicity: usually mild intestinal irritation; more serious disease from larval/cystic forms (tissue invasion), and nutrient/vitamin depletion.

Laboratory diagnosis (general)

  • Stool microscopy: detection of eggs (operculated vs non-operculated), proglottids, or segments.
  • Identification based on egg morphology, proglottid shape, and scolex features when available.

Diphyllobothrium latum — "Fish (broad) tapeworm" (Pseudophyllidean)

  • Epidemiology: associated with ingestion of raw/undercooked freshwater fish; regions: Great Lakes, Scandinavia, W. Europe, Japan, South America.
  • Size & longevity: can reach large size; humans may harbor worms up to about \(10\ \text{m}\) and survive \(\sim25\) years.
  • Clinical: often asymptomatic in light infections; may cause megaloblastic (Diphyllobothrium) anemia by interfering with intrinsic factor and vitamin B\(_{12}\) absorption.
  • Diagnostic stage: embryonated egg in feces.
  • Infective stage: procercoid (in copepod) → plerocercoid (in fish) → adult in human.
  • Proglottid: broader than long (typical proglottid size ~\(2\text{–}4\ \text{mm}\) long by \(10\text{–}12\ \text{mm}\) wide), hermaphroditic with coiled (rosette) uterus.
  • Egg: \(30\text{–}50\ \mu\text{m}\), yellow-brown, operculated; heavy egg production (~\(100{,}000\) eggs/day).

Diphyllobothrium latum scolex and gravid proglottid

Clinical & public health points to remember

  • Prevent infection by cooking fish thoroughly or proper freezing where indicated.
  • Consider D. latum in patients with unexplained vitamin B\(_{12}\) deficiency and history of eating raw freshwater fish.
  • Identify eggs/proglottids in stool for diagnosis; imaging/serology needed for larval (tissue) forms.

High-yield summary

  • Cestodes: segmented, tegumental absorption, complex life cycles.
  • Distinguish Pseudophyllidean vs Cyclophyllidean by egg type, embryonic form, and scolex.
  • Larval (metacestode) forms determine tissue disease; adult worms mainly cause nutrient loss and mechanical irritation.