Cestodes

• Cestodes - a dorso ventrally flattened with bilateral symmetry.
• Cestodes - segmented, with a ribbon like appearance.
• Lack digestive tract and circulatory system
• Characteristics of cestodes

  • Flatworm (any of the phylum Platyhelminthes, a group of soft-bodied, usually much flattened invertebrates)
• Rostellum - a retractable, conelike structure that is located on the anterior end of the scolex.
• Hook - to penetrates the intestinal mucosa. to bind to the intestine of the host.
• General features:

  
  

  Scolex -  (head) functions as an anchoring organ that attaches to intestinal mucosa.  (usually covered with hooks or suckers)
• Scolex - is located at the anterior end equipped with a organs that function to maintain the position of the animal in the gut.
• Neck - it contains stem cell that evidently are responsible for giving rise to new proglottids.
• Scolices of tapeworms can be divided into three types:

  • Acetabula - cup an oval shape.
  • Bothria - a mobile shape. spoon, spatulate, or spindle shape with sucking grooves.
  • Bothridia - shallow pest / longer hooks.
  • Acetabulate – quadrate with 4 muscular suckers and rostellum (projection at the apex with hooks) 2
• Tegument - is the body covering of cestodes and trematodes that it is a living tissue with high metabolic activity.
• Microtriches - highly specialized microvilli covering the entire surface of the tegument. (enhance absorption)
•  Glycocalyx - is responsible for inhibition of the host digestive enzymes, absorption of cations and bile salts, and enhancement of the host amylase activity.
• Calcareous corpuscles - are found in excretory canals and consist of inorganic components.
• True or False

  The main excretory canals run the length of the strobila from the scolex to the posterior end.

  True
• Osmoregulation - is another function of the tegumental surface.
• Within each proglottid are male and female reproductive organs.
• Uterine pore - where the egg comes out.
• Apolysis - when mature proglottids detaches a passed intact out of the host.
• Pseudoapolysis / anopolysis - eggs released through gravid segment through uterine pore; segment detaches only when senile or exhausted.
• Hyperpolysis - segments shed while immature and lead independent existence.
• Tapeworms are monoecious with the exception of a few species from water birds and two from a stingray that are dioecious.
• Nearly every life cycle known for tapeworms requires two hosts for its completion.

  Human (primary host)

  Animals (secondary host)
• True or False

  Function of Calcareous capsules:

  mobilization of the inorganic compounds might be buffer the tissues of the worm against the large amounts of organic acids produced in its energy metabolism.

  • True

  Provide depots of ions or carbon dioxide use when such substances are present in insufficient quantity in the environment, such as on initial establishment in a host gut.

  • True

  Excretory product

  • True
• Stimuli in the small intestine cause it to excyst.
• Oncospheres - ingestion of the eggs by a susceptible intermediate host will allow the eggs to develop into larvae.
• Cysticerci - the oncospheres of T. saginata and T. solium further develop into encysted forms.
• Cysticercosis thus refers to the disease caused in cattle by cysticerci of T. saginata and to the disease caused by the larval stage of T. solium in pigs and humans.
• Basic theme of juvenile development:

  
  

  Embryogenesis within the egg to result in a larva, the oncosphere;

  
  

  Hatching of the oncosphere after or before being eaten by the next host, where it penetrates to a parenteral (extraintestinal) site;

  
  

  Metamorphosis of the larva in the parenteral site into a juvenile (metacestode) usually with a scolex; and

  
  

  Development of an adult from the metacestode in the intestine (enteral site) of the same or another host.
• Hexacanth - is the larval form of tapeworms in the family Hymenolepididae, such as Hymenolepis diminuta. The term ___ refers to the presence of six hooks on the larva.
• Coracidia - is the free-swimming, ciliated larval stage of tapeworms in the order Pseudophyllidea, such as Diphyllobothrium erinacei.
• Factors affecting strobilar development:

  • Size of the infecting juvenile
  • Species of the worm and host
  • Size and diet of the host
  • Presence of other worms
  • Immune and/or inflammatory state of the host
• Cyclophyllidea

  • Dipylidium caninum
  • Echinococcus spp.
  • Hymenolepis diminuta
  • Hymenolepis nana
  • Raililietina garrisoni
  • Taenia saginata
  • Taenia solium
• Pseudophyllidea

  
  

  • Diphyllobothrium latum
  • Spirometra sp.
• Monoecious - both having male and female reproductive organs in a single individual.
• Dioecious - each having either male and female reproductive organs.
• Neck -  unsegmented region with high regenerative capacity (where the proglottids develop)
• Strobila - it consists of a linear series of sets of reproductive organs of both sexes. (main body of cestodes) each sets is known as Genitalium (eggs, both M & F)
• • Hermaphroditic (adults only)
• • Intestine (Habitat)