Arthropods (Doc Nikki)

• Arthropods are bilaterally symmetrical invertebrates with jointed appendages and exoskeletons
• Arthropods


  • Size: 1/250 -12 inches
  • May or may not be parasitic
  • Found everywhere; adaptable

  
• Arthropod exoskeleton


  • Chitinized, nitrogenous polysaccharide, waterproof
  • Appendages can be lost and regenerated
  • May have hairs, scales, or spines
  • Contains body fluids
• Metamorphosis


  Change in form/structure during period of development
• Types of metamorphosis


  • Gradual/incomplete: egg → nymph → adult
  • Complete: egg → larvae → pupa → adult
• There are ~740,000 species of arthropods
• Medically important classes of arthropods

  • Insecta
  • Arachnida
  • Chilopoda
  • Diplopoda
  • Crustacea
  • Pentastomida

  
• Class Insecta


  • Largest class (70% of phylum); Most medically important
• External anatomy of insects

  • Head
  • Thorax
  • Abdomen
• Insect eyes


  • Simple (ocelli): simple eye units/facets
  • Compound: very large, round/oval/kidney shaped, many facets
• Insect mouthpart types


  • Chewing
  • Sponging
  • Piercing-sucking
  • Chewing-lapping
• Insect thorax


  • Neck/cervix: membranous region connecting thorax to head
  • 3 segments: prothorax, mesothorax, metathorax
  • Pair of walking legs per segment
  • Wings on mesothorax and metathorax
• Insect wings


  • Membranous extension of body wall, upper and lower layer, reinforced by veins
• Insect legs


  • Division: coxa, trochanter, femur, tibia, tarsus, pretarsus
  • Tarsus has pulvilli (pair of claws) to walk on smooth surfaces
• Insect abdomen


  • Bears spiracles and external reproductive segments
  • 11 segments, 8th & 9th for external sex organs, 11th may have cerci
• Insect internal anatomy systems

  • Circulatory
  • Respiratory
  • Nervous
  • Digestive
  • Excretory
  • Reproductive
• Insect circulatory system


  Body cavity is hemocoel, blood is colorless hemolymph, flows through ostia (small valve-like openings)
• Insect respiratory system


  Direct gaseous exchange through spiracles (circular openings in cuticle) to trachea and tracheoles
• Insect nervous system


  Brain connected to spinal cord with ganglia at intervals, 1 ganglion per segment
• Insect excretory system


  Malpighian tubules filter and discharge waste products
• Insect reproductive system


  • Dioecious, oviparous or viviparous
  • Female: ovaries, oviduct, accessory glands
  • Male: testes, seminal vesicle, accessory glands, vas deferens, penis
• Insect senses


  Touch, taste, smell, hearing, sight, balance, orientation
• Medically important arthropod classes and orders

  • Class Insecta: Diptera, Siphonaptera, Hymenoptera, Lepidoptera, Hemiptera, Anoplura, Coleoptera
  • Class Crustacea: Copepoda, Decapoda
  • Class Arachnida: Scorpionida, Araneida, Acarina
  • Class Chilopoda
  • Class Diplopoda
  • Class Pentastomida

  
• Envenomization


  Process of acquiring injury from venoms produced by various animals including insects
• Arthropod venoms pose a threat when injected through the integument or upon contact with injured skin
• The severity of envenomization varies depending on the chemical composition and quantity of the injected venom
• Allergic reactions can develop with repeated exposure to venomous arthropods
• Arthropods


  • Conspicuous rings (not true segments)
  • Larval stage has true segments
  • Adult: at lungs or air passages of hosts
  • Larvae: free-living or encysted in viscera of other host

  
• Arthropods as Direct Causes of Injury
• Envenomization


  The process of acquiring injury from venoms produced by various animals including insects
• Orders and classes of arthropods capable of envenomization

  • Order Hymenoptera (Bees, Wasps, Ants)
  • Order Hemiptera
  • Order Lepidoptera
  • Class Chilopoda
  • Order Scorpionida
  • Order Araneida

  
• Order Hymenoptera (Bees, Wasps, Ants)


  • From the Greek word hymen meaning membrane and ptery meaning wing
  • Membranous-winged arthropods
  • Mouthparts have strong jaws, adapted for biting
  • Two pairs of wings, hind pair smaller than front
  • Wings folded back over abdomen at rest
  • Body divided into head, thorax, and abdomen
  • Abdomen further divided into 6-8 segments
  • Last abdominal segment is a modified ovipositor (stinging apparatus)
  • Stinging hymenopterans divided into two groups: kill prey by stinging, or paralyze prey by stinging
• Stinging/venom apparatus of hymenopterans

  Consists of three parts: the piercing apparatus, the lateral plate and appendages, and the poison sac and glands
• Honeybee


  • Ovipositor stinger stays in wound, stinger is barbed so insect dies when pulled out
  • Not capable of multiple stings, unlike hornets, wasps, and bumblebees
• Ants


  • Bite may be supplemented by sting
  • Formic acid of formicine ants may reach tissues only through wounds made by mandibles
  • Some ants bite and sting simultaneously, bite is necessary for inserting sting
  • Salivary secretions are not introduced
• Nature and action of bee venom

  • Contains histamine, mellitin, phospholipase A, and hyaluronidase
  • Causes local and general reactions like pain, inflammation, swelling, redness, and hemolysis of red blood cells
  • Can cause anaphylactic shock in sensitized individuals
• Order Hemiptera


  • Family Reduviidae (cone-nosed or assassin/cannibal bugs)
  • Subfamily Triatominae (kissing bugs) feed on vertebrate blood
  • Subfamily Haspactorinae inflict painful bites but not necessarily bloodsuckers
  • Triatoma rubrofasciata bite causes swelling, nausea, vomiting, irritation, and pain
  • Arilus (wheel bug) has a cog-like crest, attacks humans in defense, inflicts severe pain
• Order Lepidoptera (caterpillars)


  • Cylindrical, worm-like body divided into 12 segments
  • Well-developed head with biting mouthparts, unlike adults
  • Some species have spines or hairs containing toxins
  • Contact can cause burning sensation, redness, inflammation, urticarial wheals
• Class Chilopoda (centipedes)


  • Terrestrial, dorsoventrally flattened arthropods with one pair of legs per segment
  • Small types (2-5cm) have less developed fangs, amount of venom depends on size
  • Bite causes local pain, hardening of skin, papules, rash, swelling, purple patches
  • Large species (up to 25cm) are considered venomous
• Order Scorpionida (scorpions)


  • Body divided into cephalothorax and abdomen
  • Cephalothorax has unsegmented dorsal carapace
  • Abdomen has segmented tail with stinger at the end
  • Sting causes local pain, swelling, redness, and sometimes systemic effects