Immune System

the natural defense system, present in the body of a VERTEBRATE animal which helps to protect it against diseases caused by micro-organisms and parasites. There are two types of immunity provided by the immune system:

1) natural (known as innate)--this is present from birth and is wide ranging, operating against almost any foreign substance that threatens the body.

2) acquired immunity--this type of immunity occurs as a result of an attack by a particular foreign substance. The immune system builds up its defenses against that particular substance and uses them again in any future attack.

Taken from Dictionary of Science

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An immune system is a system of biological structures and processes within an organism that protects against disease by identifying and killing pathogens and tumour cells. It detects a wide variety of agents, from viruses to parasitic worms, and needs to distinguish them from the organism's own healthy cells and tissues in order to function properly. Detection is complicated as pathogens can evolve rapidly, producing adaptations that avoid the immune system and allow the pathogens to successfully infect their hosts.

To survive this challenge, multiple mechanisms evolved that recognize and neutralize pathogens. Even simple unicellular organisms such as bacteria possess enzyme systems that protect against viral infections. Other basic immune mechanisms evolved in ancient eukaryotes and remain in their modern descendants, such as plants and insects. These mechanisms include antimicrobial peptides called defensins, phagocytosis, and the complement system. Jawed vertebrates, including humans, have even more sophisticated defense mechanisms. The typical vertebrate immune system consists of many types of proteins, cells, organs, and tissues, which interact in an elaborate and dynamic network. As part of this more complex immune response, the human immune system adapts over time to recognize specific pathogens more efficiently. This adaptation process is referred to as "adaptive immunity" or "acquired immunity" and creates immunological memory. Immunological memory created from a primary response to a specific pathogen, provides an enhanced response to secondary encounters with that same, specific pathogen. This process of acquired immunity is the basis of vaccination.

Disorders in the immune system can result in disease. Immunodeficiency occurs when the immune system is less active than normal, resulting in recurring and life-threatening infections. Immunodeficiency can either be the result of a genetic disease, such as severe combined immunodeficiency, or be produced by pharmaceuticals or an infection, such as the acquired immune deficiency syndrome (AIDS) that is caused by the retrovirus HIV. In contrast, autoimmune diseases result from a hyperactive immune system attacking normal tissues as if they were foreign organisms. Common autoimmune diseases include Hashimoto's Thyroiditis, rheumatoid arthritis, diabetes mellitus type 1 and lupus erythematosus. Immunology covers the study of all aspects of the immune system which has significant relevance to human health and diseases. Further investigation in this field is expected to play a serious role in promotion of health and treatment of diseases.

Taken from Wikipedia

Jaundice

a condition characterized by the unusual presence of bile pigment circulating in the blood. Jaundice is caused by the bile produced in the liver, which should go into the intestines, passing instead into the circulation because of some obstruction. The symptoms of jaundice include a yellowing of the skin and the whites of the eyes.

Taken from Dictionary of Science

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Jaundice, also known as icterus (attributive adjective: icteric), is a yellowish discoloration of the skin, the conjunctival membranes over the sclerae (whites of the eyes), and other mucous membranes caused by hyperbilirubinemia (increased levels of bilirubin in the blood). This hyperbilirubinemia subsequently causes increased levels of bilirubin in the extracellular fluids. Typically, the concentration of bilirubin in the plasma must exceed 1.5 mg/dL, three times the usual value of approximately 0.5 mg/dL, for the coloration to be easily visible. Jaundice comes from the French word jaune, meaning yellow.

One of the first tissues to change color as bilirubin levels rise in jaundice is the conjunctiva of the eye, a condition sometimes referred to as scleral icterus. However, the sclera themselves are not "icteric" (stained with bile pigment) but rather the conjunctival membranes that overlie them. The yellowing of the "white of the eye" is thus more properly conjunctival icterus.

Taken from Wikipedia

Earthquake

the often violent movement of the earth along a fault or fault zone due to tectonic upheaval caused by the sudden release of stress that has built up over some time. The focus is the point at which the earthquake originates within the earth and earthquakes are classified by depth of focus: shallow -- less than 70 km; intermediate -- 70-300 km; deep -- more than 300 km. Attempts to predict earthquakes rely upon measurement of stress increases, but can so far be related only to an increasing risk of activity.

Taken from Dictionary of Science

Aberration

is what happens in physics when a lens (or curved mirror) does not produce a true image. It is caused by the light rays from any point on the object being viewed forming an image (focusing) at slightly different positions. In astronomy, aberration refers to the apparent change in position of a star. This is due to the fixed speed of light travelling from the star and the movement of the person looking at the star, because the Earth is moving in its orbit.

Taken from Dictionary of Science