Health: Definition, Factors, and Types of Diseases

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1. Human Beings and Health

The World Health Organization (WHO) defines health as 'the complete physical, mental and social well-being, not only the absence of disease'.

The Environment

Healthy surroundings should be free of biological, physical or chemical elements that are harmful to your health.

Personal Characteristics

Genetic factors, age and gender predispose people to suffer from certain types of illnesses.


Healthy habits and lifestyles are very important for staying healthy.


It is essential to have an efficient healthcare system to guarantee public health.

Vital Signs

Vital signs are physiological parameters that inform us of our state of health or the evolution.

Cause -> Organic Alteration -> Symptoms and Signs -> Cure

There are two types of treatments: curative and symptomatic.


Convalescence: a period of time to completely recover after it is cured.

2. Infectious Diseases

By Origin

Infectious-> They're caused by pathogenic microorganisms and most are contagious. An example is the measles; Non-infectious-> They include the rest of the diseases that can have different causes: degenerative, genetic or deficiency. They're not contagious. An example is anemia.

By Appearance and Duration

Acute-> They manifest quickly and last a long time. An example is arthritis; Chronic-> They manifest slowly and last a long time. An example is arthritis.

By Incidence in the Population

Sporadic-> They affect a few people in the population, such as heart attack; Epidemic-> They affect many people in a short period of time, such as cholera; Pandemic-> They affect many countries or even the entire planter, such as AIDS; Endemic-> They are common and exclusively to a specific region, such as malaria.


Virulence describes the capacity of an agent of infection to invade and damage our organism.


-By direct contact

The microorganism passes directly from an ill person to a healthy person, without an intermediary. For example, sexuality transmitted diseases.

-By touching inert objects

Any object or substance, such as a handkerchief, a glass, a fork, saliva, particles of earth, can act as a vehicle for transmitting microorganisms. For example, this is the case for a cold or the flu and infections in wounds, contaminated by microorganisms on the ground.

-By drinking water

Sometimes, water can be contaminated with pathogenic microorganisms and cause disease. For example, salmonellosis, caused by the Salmonella bacteria.

By the air

Sometimes microorganisms travel on duct particles or freely in the air. Tuberculosis is transmitted in this way.

-By animals

Some animals carry the pathogenic microorganism, but do not have the disease. For example, sleeping sickness is caused by a protozoan parasite Trypanosoma brucei and transmitted by the tsetse fly. Malaria is another example caused by protozoa from the genus Plasmodium.

Barriers to Infection


Barriers are the skin and mucous membranes that cover the body's external surface and line the digestive tract and respiratory airways. To prevent microorganisms from entering, it's essential that they're in a good state.


Barriers are saliva, tears and gastric juices. Some substances destroy most of the pathogens agents. The substances that the sebaceous glands secrete from the skin stop them from growing.


Barriers are movements that carry microorganisms that have entered our body and prevent them from attaching. These barriers are the cilia, small filaments that line our respiratory airways. When they move they eliminate mucus, which can contain microorganisms and other foreign elements.


Barriers are non-pathogenic microorganisms that exit on the external surface of our body and in the respiratory and digestive system. They compete with potential pathogenic microorganisms and stop them from developing. They are called ecological because this competition is similar to what takes place between two species in the same ecosystem.

The Immune System

The immune system comprises very effective internal defenses, based on the action of the leukocytes or white blood cells. These are found in the blood and many tissues.

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