Directly The immune system is designed to defend the body against foreign or dangerous invaders. Such invaders include
Microorganisms (commonly called germs, such as bacteria, viruses, and fungi)
Parasites (such as worms)
Cancer cells
Transplanted organs and tissues
To defend the body against these invaders, the immune system must be able to distinguish between
What belongs in the body (self)
What does not (nonself or foreign) normal immune response consists of the following:
Recognizing a potentially harmful foreign antigen
Activating and mobilizing forces to defend against it
Attacking it
Controlling and ending the attack
If the immune system malfunctions and mistakes self for nonself, it may attack the body’s own tissues, causing an autoimmune disorder, such as rheumatoid arthritis, Hashimoto thyroiditis, or systemic lupus erythematosus (lupus).
They are capable of dividing and renewing for Long periods of time They are unspecialized and they can give rise to speacialized cell types
A BMI of 18.88 would be pretty normal for a 13 year old if not a bit on the lower side already. Usually we consider a BMI between around 18/19 and around 25 to be that of a normal weight person. If it is below theis, we would recommend to eat more, if ti above this we would recommend to eat less. Considering that we're talking about a 13 year old, perhaps it would be better if he/she ate a bit more to supply his body with the necessary nutritional needs.
