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Physiology
[edit]Feeding and Nutrition
[edit]Developing Schistosoma mansoni worms that have infected their definitive hosts, prior to the sexual pairing of males and females, require a nutrient source in order to properly develop from cercariae to adults. The developing parasites lyse host red blood cells to gain access to nutrients; the hemoglobin and amino acids the blood cells contain can be used by the worm to form proteins.[1] While hemoglobin is digested intracellularly, initiated by salivary gland enzymes, iron waste products cannot be used by the worms, and are typically discarded via regurgitation.[2]
Kasschau et al. (1995) tested the effect of temperature and pH on the ability of developing S. mansoni to lyse red blood cells.[1] The researchers found that the parasites were best able to destroy red blood cells for their nutrients at a pH of 5.1 and a temperature of 37°C.[1]
Locomotion
[edit]S. mansoni is locomotive in primarily two stages of its life cycle: as cercariae swimming freely through a body of freshwater to locate the epidermis of their human hosts, and as developing and fully-fledged adults, migrating throughout their primary host upon infection.[2] Cercariae are attracted to the presence of fatty acids on the skin of their definitive host, and the parasite responds to changes in light and temperature in their freshwater medium to navigate towards the skin.[3] Ressurreicao et al. (2015) tested the roles of various protein kinases in the ability of the parasite to navigate its medium and locate a penetrable host surface.[3] Extracellular signal-regulated kinase and protein kinase C both respond to changes in medium temperature and light levels, and the stimulation of p38 mitogen-activated protein kinase, associated with recognition of parasite host surface, results in a glandular secretion that deteriorates the host epidermis, and allows the parasite to burrow into its host.
The parasite's nervous system contains bilobed ganglia and several nerve cords which splay out to every surface of the body; serotonin is a transmitter distributed widely throughout the nervous system and plays an important role in nervous reception, and stimulating mobility.[4] Locomotion is an important aspect of the parasite’s pathology, as worms in the host burrow through blood vessels to develop and find a mate for copulation.[2] Therefore, pharmacologists have targeted parasite muscles, means through which locomotion can occur, with various drugs to weaken the pathology of the organism on its host. Mendonca-Silva et al. (2006) found that voltage-operated calcium ion channels control the contraction of muscle fibers to an extent, and when introduced to dihydropirodine drugs, the activity of these channels is limited and muscle contraction may not occur.[5]
- ^ a b c Kasschau, Margaret R. et al. (1995). “Influence of pH and temperature on hemolysis by adult Schistosoma mansoni membranes.” Journal of Experimental Zoology 271(4): 315-322. DOI: 10.1002/jez.1402710409
- ^ a b c Wilmer, Pat, Graham Stone, and Ian Johnston (2005). Environmental Physiology of Animals. United Kingdom: Blackwell Publishing. pp. 677-692. ISBN: 9781405107242
- ^ a b Ressurreicao, Margarida et al. (2015). “Sensory Protein Kinase Signaling in Schistosoma mansoni Cercariae: Host Location and Invasion.” Journal of Infectious Diseases 212(11): 1787-1797. DOI: 10.1093/infdis/jiv464
- ^ Patocka, Nicholas et al. (Jan 2014). “Serotonin Signaling in Schistosoma mansoni: A Serotonin-Activated G Protein-Coupled Receptor Controls Parasite Movement.” PLoS Pathogens 10(1): e1003878. DOI:10.1371/journal.ppat.1003878
- ^ Mendonca-Silva, DL et al. (2006). “Role of calcium influx through voltage-operated calcium channels and of calcium mobilization in the physiology of Schistosoma mansoni muscle contractions.” Parasitology 133(1): 67-74. DOI:10.1017/S0031182006000023