Blood cells are produced in which system?
a. circulatory system
b. immune system
c. skeletal system
d. endocrine system

Correct answer is c  - Blood cell are produced in the skeletal system.

Red blood cells are produced on a regular basis in the bone marrow. Bone marrow is a red spongy material found within the cavities of many of the large bones of the body.

Red blood cell start as immature cell in the bone marrow and after about seven days of maturation, they are released into the bloodstream, that is, the circulatory system where they circulate for about 120 days before being replaced with new ones.

thrombocytopenia, which is a deficiency in blood platelets, can cause bleeding and bruising in the dermis similar to senile purpura. other possible causes include: exposure to ultraviolet rays and aging skin are common causes of senile purpura. senile purpura may also be a sign of collagen loss in the skin and bones.