Hypersensitivity
Hypersensitivity is an antigenic response that isn't normal; allergies are an example |
There are four types of hypersensitivity reactions: type 1 (anaphylactic), type 2 (cytotoxic), type 3 (immune complex), and type 4 (delayed cell-mediated, or delayed hypersensitivity) |
Type 1 reactions - anaphylactic reactions
Anaphylactic reactions occur within 2 to 30 minutes of coming into contact with an antigen |
IgE antibodies bind to mast cells or basophils; causes degranulation of mast cells or basophils, and causes the release of reactive substances like histamine |
There are two types of anaphylactic reactions: systemic anaphylaxis and localized anaphylaxis |
Systemic anaphylaxis is the result of an individual, who is sensitized to a particular antigen, is exposed to the particular antigen again. An example is an allergic reaction to penicillin |
Localized anaphylaxis is the result of someone ingesting (eating a food) inhaling (things like pollen) an antigen, and the symptoms depend on the way the antigen entered the body |
Sensitivity to an antigen is shown by a rapid inflammation reaction that causes swelling, redness, and itching at the inoculation site. The inoculation site is called a wheal |
Desensitization is one way to prevent anaphylactic reactions, and avoiding the antigens known to cause reactions is another way to prevent an anaphylactic reaction |
Desensitization involves increasing the dosages of the antigen, and carefully injecting the dosages beneath the skin |
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Microbial diseases of the skin
Caused by bacteria, viruses, and fungi/parasites |
Bacterial diseases of the skin
The bacteria that cause well known diseases are Staphylococci, Streptococci, Micrococci, Propionibacterium acnes, and Pseudomonas aeruginosa |
Viral diseases of the skin
The viruses that cause well known skin diseases are Morbillivirus, the mumps virus, Togaviruses, Papillomas coxsackievirus/entovirus, Smallpox, and Haemophilus influenzae |
Fungal and parasitic diseases of the skin
The fungi and parasites that cause well known diseases of the skin are ringworm, Candida albicans, and Sarcoptes scabiei mites* |
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Helminths
Most parasitic animals belong to one of two phyla: Platyhelminthes (flatworms) and Nematoda (roundworms) |
The Nematodes, aka the roundworms
The roundworms have cylindrical bodies and have a complete digestive system |
The roundworms are dioecious |
The males have spicules, which are used to take the sperm to the female's genital pore |
There are free-living and parasitic nematodes |
Some nematodes have eggs that are infective for humans |
The nematodes that have infective eggs are Ascaris lumbricoides (infects human intestines), Trichuris trichiura (whipworm transmitted by fecal-oral transmission or feces-contaminated food), and Enterobius vermicularis (pinworm that spends its life in a human host; adult pinworms are found in the host's large intestine) |
Some nematodes have larvae that infect humans |
The nematode larvae that infect humans are Strongyloides (there is a reemergence of Strongyloides infections; the larvae can travel to the intestine or the lungs), the hookworms (enter the skin and are carried to the intestines), and Dirofilaria immitis (causes heartworm and is spread by mosquitoes) |
The Protozoa
The protozoa are unicellular eukaryotes that inhabit water and soil |
The protozoans have complex life cycles and animal-like nutrition |
They require a large supply of water |
Some protozoa have a pellicle, which is an outer protective covering. The protozoa that have pellicles require specialized structures to take in food |
Protozoa's food is digested in vacuoles and wastes are eliminated through an anal pore |
There are some medically important protozoa: the Excavata, Amebae, Apicomplexa, and the Ciliates |
Amebae move by extending pseudopods* |
The amebae Entamoeba histolytica causes amebic dysentery |
The amebae Acanthamoeba infects the corneas and causes blindness |
The amebae Balamuthia causes granulomatous amebic encephalitis |
Apicomplexa are nonmotile, obligate intracellular parasites that have complex life cycles |
The apicomplexan parasite Plasmodium causes malaria, and it's transmitted by insect bites |
The apicomplexan paraside Babesia affects the red blood cells of its host. It causes fever and anemia of immunocompromised people. It's transmitted by an insect bite |
The apicomplexan parasite Toxoplasma gondii is transmitted by cats and causes fetal infections |
The apicomplexan parasite Cryptosporidium is transmitted by feces and causes waterbone illness |
Platyhelminths, aka the flatworms
There are two types of flatworms: trematodes, or flukes and the cestodes, or tapeworms |
The trematodes usually have flat, leaf-shaped bodies with a ventral sucker and an oral sucker |
The lung fluke (lung trematode) is a member of the Paragonimus species |
The Asian liver fluke (Asian liver trematode) is known as Clonorchis sinensis |
The blood flukes (blood trematode) are members of the Schistosoma species |
The trematodes are given common names according to the tissue of the definitive host that the adult trematodes live in |
The trematodes absorb food through their nonliving outer covering, which is called the cuticle |
Cestodes are intestinal parasites |
The head of cestodes is known as the scolex, and the body is made up of segments called proglottids |
Cestodes don't have a digestive system, so to obtain nutrients from the host's small intestine, they absorb food through their cuticle |
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Phylum Platyhelminthes (flatworms)
The trematodes are also known as the flukes |
The trematodes have a flat, leaf-shaped body. They also have an oral and ventral sucker |
The Paragonimus species is known as the lung fluke |
The Schistosoma species is known as the blood fluke |
The cestodes are known as the tapeworms |
The head is known as the scolex, and it has suckers for attachment |
The body segments of the cestodes are called proglottids; the proglottids have male and female reproductive organs |
The cestode Taenia solium uses humans as a definitive host |
The cestodes that use humans as a definitive host produce eggs in the human, the eggs hatch in to larvae, and the larvae bore into the intestinal wall |
The cestodes produce cysticerci in pigs |
When humans are the intermediate hosts for cestodes, humans ingest the eggs, and the eggs hatch in the intestine. The larvae migrate to the liver or the lungs of the host and form a hydatid cyst |
The cestode species Echinococcus granulosus uses humans as an intermediate host |
Characteristics of helminths
They might lack a digestive system |
They have a reduced nervous system |
Their means of moving (locomotion) are occasionally reduced or are completely lacking |
The reproductive system is usually complex |
Adult helminths life cycle can be dioecious or monoecious, or hermaphroditic |
Dioecious adult helminths have male reproductive organs in one individual, and female reproductive organs in another individual |
Monoecious adult helminths have male and female reproductive structures in the same individual |
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