In the tissue known as marrow, found in the interior of bones, red blood cells are produced in the process called hematopoesis. They also produce lymphocytes, which are important to support the body's immune system. They are also called white blood cells. They include natural killer cells which are part of the immune response. They detect invaders that do not contain "self" markers and trigger lysis or apoptosis.
The pancreas is both an exocrine or digestive organ and endocrine gland at the same time. It makes the hormones insulin, glucagon, somatostatin and pancreatic polypeptide which are secreted into the bloodstream and sent to target organs. This makes it an endocrine gland as these chemicals do not travel through a duct, but in the circulating blood. It is an exocrine gland when it secretes digestive enzymes in the pancreatic juice. This aids in digestion in the small intestine.The pancreatic duct sends these substances to the upper part of the small intestine, where they mingle with the chyme and break down the carbohydrates, lipids and proteins to endproducts.
Aside from its most important function, to support the human body and give the muscles a platform to move against, the skeletal system is vital in supporting the immune system. Bones contain marrow, a porous material which creates both white and red blood cells. This replenishment of cells allows the body to fight and expel harmful bacteria, environmental toxins, and other foreign material. The white blood cells formed by the marrow are instrumental in isolating and destroying harmful particles (either on the site or in lymph nodes), or transporting them to the kidneys or bowels for excretion. Some people have marrow disorders which prevent their marrow from forming new cells; this is caused most often by cancer. Today, it is possible to transplant marrow from a healthy individual to a sick patient, and so help their bone marrow form new white and red blood cells to fight their sickness.