Question

Name the two types of diseases one caused by some external agents and other due to some internal disorder of the body. Mention any two causative agents.

Answer 1

Hint:- When the functioning of one or more organs or systems of the body is disabled or malfunctioned, characterised by various signs and symptoms, we say, that we are not healthy, i.e., we have a disease. A wide range of organisms could cause disease in man. They are called pathogens.

Complete answer:
When a disease is caused by any agent such as virus, bacteria or protozoa it is said to be caused by an external agent. For example
Malaria:
Malaria is a protozoan disease which is caused by Pathogen: Malaria is caused by Plasmodium, a tiny protozoan. Different species of Plasmodium which attack humans are Pvivax, P. malariae, P. ovale and P. falciparum.
Mode of transmission: Malarial parasite (Plasmodium) requires two hosts to complete its life cycle Human, and Mosquito (female Anopheles) which is the vector/transmitting agent too. Plasmodium eget
pierce in the human body as sporozoites (infectious form) through the bite of infected female Anopheles.
Life-history: When an infected female Anopheles bites a human to suck blood, it also injects the malarial parasites into the human blood with its saliva.
The stage of Plasmodium that causes infection is a minute sickle-shaped sporozoite. Sporozoites are grouped in thousands into the human blood. In about half an hour the sporozoites disappear from the bloodstream and enter the parenchymatous cells of the liver to escape from phagocytic white blood corpuscles and multiply their own number.
Schizogony: Each sporozoite grows in the liver cell to form a large and rounded schizont, which divides to form about 1,000 small spindle-shaped merozoites.
The multiple fission is called schizogony. The schizont ruptures and merozoites are liberated into liver venous passages (sinusoids). This phase of reproduction is termed as the pre-erythrocytic phase and in this the merozoites are also called cryptozoites, they are immune to medicines and also to the resistance of the host.
When a disease is caused by malfunctioning of the internal system it is said to be caused due to internal agents. For example
Cancer:-
It is one of the most dreaded diseases of human beings and is a major cause of death all over the world. More than a million Indians suffer from cancer and a large number of them die annually. In our body, cell growth and differentiation is a highly controlled and regulated process. But in cancer cells, there is an abnormal and uncontrolled division of cells due to breakdown of these regulatory mechanisms.
Normal cells exhibit a property called contact inhibition, in which the cells which are dividing when in contact with other cells, stop their uncontrolled growth but cancer cells do not have this property.
Therefore, cancerous cells continue to divide giving rise to mass of cells called neoplasm or tumors.
Types of Tumors:
Benign Tumors: It remains confined to their original location and do not spread to other parts of the body and hence causes little damage
Malignant Tumors: It is a tumor when neoplastic or tumor cells divide and grow very rapidly, invading and damaging surrounding normal tissues, starving the normal cells by competing for vital nutrients. Cells that suffer from such tumors reach the different and distant site through blood and whenever they get lodged in the body. they start a new tumor formation. This property is named as metastasis and is the most scared property of malignant tumors

Note:- Plasmodium, the causative agent of malaria, was discovered by Charles Laveran in 1880. Lancisi first suspected a relationship between mosquito and malaria. Ronald Ross (1897) discovered a (confirmed) relationship between malaria and mosquito. In 1897 Ross discovered oocytes of Plasmodium in the stomach of mosquitoes.