Eukaryotic cells have a nucleus (humans)

Prokaryotic cells have no nucleus (bacteria)

Humans beings are made of hundreds of billions of cells

Cells have very different shapes, sizes and functions

The diameter of most cells is between 0,5 and 25 ...

The average weight of a cell is 1 ng

Human cells are aerobic which means they obtein energy from oxygen

Tissue is made up of cells of a similar type that work together to carry out specific functions

Conective tissue supports, protects and connets other tissues. It is made by cells that secrete substances that form the intercellular matrix

Surrounds and connects organs and has a gel-like intercellular matrix

It stores lipids for protection and energy reserves

It supports the skeleton by forming cartilage. It has a solid, elastic intercellular matrix

It has a hard, solid extracellular matrix. It supports the body

It consists on a liquid intercellular matrix called plasma, red and white blood cells and platelets. It transports nutrients, hormons and waste

Muscle tissue fibres contract when they are stimulated producing movement

It is found in the hollow organs. Its contraction is responsible for the slow and involuntary movements of these organs

It only exists in the heart. Its contraction is fast and involuntary

It covers the skeleton. Its responsible for most fast and voluntary movements

Epithelial tissue cover both external and internal surfaces of the body acting as a barrier between distinct enviroments

It covers the outside of the body and also lines internal organs and cavities

It forms exocrine and endocrine glands which secrete substances for secretion and hormones to the blood respectively

It transmits nerve impulses to comunicate the body and the brain. It consists of neurons which are protected by neuroglia cells

Health is a state of complete physical, mental and social well-being and not only the absence of disease

• Pollution
• Weather
• Radiation
• Trauma
• Stress
• Pathogenic microorganisms

Illness occurs when one or more of the body's organs does not function correctly

These are only felt or experienced by the patient (pain, tiredness...)

These are objective indicators and can be seen by other people, detected in test or observed in examinations (temperature, rashes...)

It is caused by transmittable pathogens such as virus, bacteria, fungi and protozoa

It is not caused by pathogens so cannot be transmitted between human beings

Pathogens are transferred directly from the infected person (host) to another person via physical contact (touching, kissing) or through the air (airbone saliva droplets)

Pathogens are transferred via and intermediary from the host to another person (food. water, eating utensils)

External defenses are non-specific, meaning they react in the same way to all microorganisms

They are surfaces which separate the inside of the body from the outside.

Skin covers the outside of the body and mucous membranes cover digestive, respiratory and reproductive cavities

They are pathogen-blocking secretions

They include bacterial flora found on the skin and mucous membranes

They are good for us as they produce natural antibiotics that protect the body from other pathogens

• Body temperature increases to avoid the pathogen to multiply
• Blood vessels dilates and blood flow increases
• Chemical messengers are released to attract macrophages
• The skin becomes swollen and red

External defenses fail and the pathogen enters the body for the first time

White blood cells called phagocytes surround the microorganism using projections of their cell membrane called pseudopods and eliminate it in the form of pus

All cells of our body have the same membrane antigen

Phagocytes have a special receptor to detect our own membrane antigens and not attack our body cells

Phagocytes can detect foreign membrane antigens. In this case they phagocyte the pathogen

Phagocytes present the antigen of the pathogen to T lymphocyte and activate them

T lymphocyte activate B lymphocyte

T lymphocyte destroy damaged cells

B lymphocyte starts producing antibodies (it takes 4-5 days)

B lymphocyte release a large quantity of antibodies that destroy the pathogen

Some B lymphocyte become memory cells and stay in our body for years (immune memory)

External defenses fail again and the pathogen enters the body for the second time

All the processes mention before take place again but this time memory cells produce antibodies extremely fast and in a much larger quantity so the pathogen does not have time to cause any damage

Wash your hands frequently

Cover your mouth and use tissues when coughing and sneezing

Always wash and disinfect cuts

Thanks to vaccination you can improve immunity to certain pathogens and eradicate certain dangerous illneses

If enough people is vaccinated, the pathogen will not be able to be transferred and the illness may possibly be erradicated

They stop bacteria growing and multiplying

They cannot be used for treating other than bacteria

They kill or stop the growth of fungus

They are antibodies extracted from the blood of a previous infected animal

It is usually used to treat poisonous animal bites

They kill parasitic viruses. Few can be used as they can also damage our own cells