Exam 3 Flashcards
Nematoda: Form and Function
- bilaterally symmetrical, posses a pseudocoel
- most are dioecious; considerable sexual dimorphism
- elongated, tapered at both ends; from < 1 mm to > 10 meters
- digestive tract usually complete; mouth at extreme anterior and anus near posterior tip
- noncellular cuticle that is secreted by an underlying hypodermis
- chitinous cuticle is shed 4 times during ontogeny (4 molts)
Nematoda: Form and Function
Bodv Wall
- nematode body wall consists of cuticle, hypodermis, and body wall musculature
- an important function of the hypodermis is secretion of cuticle.
- hypodermis is syncitial in adult worms; nuclei lie in 4 epidermal cords
- epidermal cords run longitudinally and divide body into 4 quadrants
- dorsal and ventral cords contain longitudinal nerve trunks
- lateral cords contain lateral canals of the excretory system in most species
Nematoda: Form and Function
Musculature
- muscles of the body wall are all longitudinally with no circular layer
- nematode muscles have a contractile portion and a noncontractile cell body (myocyton)
- muscle contraction occurs similar to vertebrate striated muscle with myosin & actin
- cuticle, hypodermis, somatic musculature, fluid filled pseudocoel functions as a hydrostatic skeleton
Nematoda: Form and Function
Pseudocoel and Hydrostatic Skeleton
- pseudocoel differs from a true coelom in that it has no peritoneal (mesodermal) lining
- pseudocoel is a fluid-filled cavity enclosed by body wall
- pseudocoelomic fluid in known as hemolymph
- pseudocoel functions as a hydrostatic skeleton that depends on:
(1) enclosed volume of non-compressible fluid
(2) ability of muscle contraction to apply pressure to that fluid
(3) transmission of the fluid pressure in all directions - alternation of contraction and relaxation in dorsal and ventral muscles produces the characteristic S-shaped motion seen in nematode locomotion
*water balloon *
Nematoda: Form and Function
Nervous System
- nervous system is relatively simple
- 2 main concentrations of nerve elements; connected by longitudinal nerve trunks
one in esophageal region
one in anal region - nematodes have a variety of sensilla (small sense organs)
- sensilla are most prominent in the cephalic and caudal regions
Nematoda: Form and Function
Digestive System and Acquisition of nutrients
- digestive system is complete; mouth, gut, and anus
- buccal muscles and anterior esophageal muscles contract to open mouth; suck in food
- hydrostatic pressure in pseudocoel closes the mouth and esophageal lumen
- food passes down the esophagus via muscle contractions until it reaches the intestine
- posterior bulb, one-way valve
- hydrostatic pressure pushes food posteriorly; newly ingested food & locomotor helps
- intestine constructed of a single layer of intestinal cells
- depressor ani (anal dialator muscles) contracts to open anus
- hydrostatic pressure causes defecation when the anus is opened
- food of nematodes include blood, tissue cells, fluids, and intestinal contents
Nematoda: Form and Function
Secretory-Excretory system
- most excretion occurs through the intestine
- no flame cells or nephridia
- 2 long canals in the lateral hypodermis connect near the anterior end
- secretory-excretory canal opens to the excretory pore
- ability to osmoregulate varies greatly; depends on habitat
Nematoda: Form and Function
Reproduction
- most are dioecious
- females generally larger; tail of males is more curled
- most nematodes are oviparous
- gonads of nematodes are solid cords of cells; germ cells move via rachis
- testes are generally paired, but some species only have one
- nematode spermatozoa use pseudopodium
- males have cloaca, ejaculatory duct opens into rectum
- the female reproductive system opens through a central vulva
- copulatory spicules of male are used in copulation
how young develop
-Oviparous: Animals that lay eggs, which hatch and develop outside of the parent’s body.
-Viviparous: Animals that give birth to live young after developing inside the parent’s body
-Ovoviviparous: Animals that produce eggs that hatch inside the parent’s body.
Nematoda: Trichuris trichiura
Whipworm
- tissue parasite
- 3 to 5 cm in length; adults live several years
- females produce 3,000 to 20,000 eggs per day
- embryonation, 21 days in moist and shady soil
- swallowed, hatch in small intestine, and enter intestinal crypts of large intestine
- slender anterior end embeds in gut mucosa; enlarged posterior portion in lumen
Nematoda: Trichuris trichiura
Pathology
- < 100 worms, often asymptomatic
- heavy burden may result in death; 200 to 1,000 in small children
- trauma to intestinal epithelium and underlying mucosa; chronic hemorrhage
- intense trichuriasis: dysentery, anemia, growth retardation, rectal prolapse, finger and toe clubbing, adversely affect cognitive function
Nematoda: Trichuris trichiura
Epidemiology
- poor standards of sanitation; night soil for fertilizer
- physical conditions for egg survival include: warm, high rainfall and humidity, moisture retaining soil, dense shade
- house flies can serve as mechanical vectors
- prevalence may reach 20-25% in small children in Southeastern US
- prevalence estimated at 795 million worldwide
layers of GI tract
-mucosa
-submucosa
-muscularis
-serosa
Nematoda: Trichinella spiralis
Porkworm
- smallest nematode parasite of human
- world’s largest intracellular parasite
- same individual host can be both intermediate and definitive host
- juveniles (J1) reside in “nurse cells” of skeletal muscle fibers of intermediate host
-increases angiogenesis factor (more blood cells grow) J1 gets fed - definitive host eats contaminated meat with nurse cells
- infective juveniles (J1) are released from nurse cells in stomach
- undergo 4 molts in small intestine, then copulation within mucosal epithelium
- adults are intramulticellular parasites in intestinal epithelium
- female gives birth (ovoviviparous) to thousands of juveniles over 4 months
- juveniles carried by hepatoportal system through liver, heart, lungs and arterial system
Nematoda: Trichinella spiralis
Pathology
Pathogenesis of trichinosis in 3 stages
(1) penetration of adult females into mucosa
- traumatic damage to host tissue
- host reacts to their waste products: nausea, vomiting, sweating & diarrhea
(2) migration of juveniles
- damage to blood vessels: localized edema
- wandering juveniles: pneumonia, encephalitis, meningitis, etc.
- death can result from myocarditis
(3) penetration and nurse cell formation
- intense muscular pain, difficulty breathing or swallowing
- heavy infection suppresses muscle contractibility
Nematoda: Trichinella spiralis
Epidemiology
- zoonotic disease: humans not important for life cycle
- eating infected pork is most common source of infection
- solid meat is safe when all traces of pink have disappeared
- well known in Mexico, parts of South America, Africa, southern Asia, & Middle East
Nematoda: Ascaris lumbricoides
- females up to 49 cm long
- unembryonated develop into J3s in 13 days
- juveniles molt twice to become infective J3 inside egg
- infection occurs when unhatched juveniles are swallowed
- hatch in duodenum and penetrate small intestine and enter venules
- enter pulmonary circulation and break out of capillaries
- juveniles usually molt once in lungs, migrate up trachea and swallowed (must molt to J4 or they’ll be killed by gastric juices)
- pass through stomach and mature in small intestine
Nematoda: Ascaris lumbricoides
Pathology
- many worms get lost and cause acute tissue reactions, inflammatory response
- breaking out of lung capillaries causes a small hemorrhage at each site
- small pools of blood accumulate in lungs causing edema, clogging air spaces
- lung can become diseased and result in bacterial infection, death
- massive infections can cause fatal intestinal blockage
Nematoda: Ascaris lumbricoides
Epidemiology
- contamination is the typical means of infection
- eggs infective after 10 years in soil
- cockroaches can be mechanical vectors
- dogs are reservoir host
- one quarter of world population infected
Nematoda: Strongyloides stercoralis
Threadworm
- parasitic females burrow into submucosa of small intestine
- parthenogenic females release eggs in mucosa, hatch and migrate to lumen
- J1s are passed in feces and become either:
•non-infective rhabditiform in soil that give rise to free-living adults in soil
•infective filariform J3s in soil - both free-living and parasitic females can produce free-living and parasitic juveniles (ambient temperature <34C then free-living)
- infective filariform J3s continue development after they penetrate skin
- migrate to small intestine usually via lungs, coughed up and swallowed
- autoinfection may occur if juveniles molt twice before exiting in feces
Nematoda: Strongyloides stercoralis
Pathology
-Strongyloidiasis can be described in 3 stages:
(1) invasive: intense itching at site of entry, slight hemorrhage & swelling
(2) pulmonary: burning sensation in chest, nonproductive cough, and possible bronchial pneumonia
(3) intestinal: worms migrate randomly through mucosa, intense localized burning sensation in abdomen, intestinal ulceration and septicemia
Nematoda: Strongyloides stercoralis
Epidemiology
- contacting filariform juveniles in contaminated soil
- transmammary infection in dogs, and presumably humans
- present under conditions of low sanitation standards
- cats and dogs serve as reservoir hosts
Nematoda: Onchocerca volvulus
- females up to 50 cm long; males up to 42 cm long
- adult worms located under the skin; become encapsulated by host (onchocercomas)
- encapsulated nodules are located at site of black fly (Simulium spp.) bite
- adult females produce microfilariae (ovoviviparous)
- microfilariae concentrate in skin where black flies bite
- black fly becomes infected when it takes tissue fluid / blood meal
- microfilariae penetrate fly midgut and molt twice in black fly thoracic muscles
- infective filariform J3s move to fly mouth parts to infect new host
Nematoda: Onchocerca volvulus
Pathology
- River Blindness; not fatal, but does cause disfigurement and blindness
- most middle-aged people and older are blind in some communities
- adult worms stimulate the growth of benign subcutaneous nodules (onchocercomas)
- onchocercomas consist of collagen fibers surrounding up to several adult worms
- pruritus and severe dermatitis occurs because of degenerating juveniles in skin
- degenerating juveniles in eyes resulting in sclerosing keratitis
- true elephantiasis may occur and also hanging groin
Nematoda: Onchocerca volvulus
Epidemiology
- significant public health problem in Africa and South America
- black fly larval stages only in clear, fast-running streams
- adult flies survive in high humidity and plenty of streamside vegetation
