Why do we consider blood as a connective tissue?

Connective tissues have cells scattered throughout an extra-cellular matrix. They connect different body systems. Blood is considered as a type of connective tissue because of two reasons.
 Like the other connective tissues, blood is mesodermal in origin.
 It connects the body systems, transports oxygen and nutrients to all the parts of the body, and removes the waste products. Blood has an extra-cellular matrix called plasma, with red blood cells, white blood cells, and platelets floating in it.

Blood is mesodermally derived; as other connective tissues. Blood serves the purpose of connecting the body systems; by transporting substances. Moreover, blood too has a matric; like other connective tissues. Hence, blood is considered as a connective tissue.

Connective tissue usually are involved in structure and support and derived from mesoderm. Blood is considered as a connective tissue because:

1. It has the same origin (mesodermal) as do the other connective tissues.

2. blood connects the body systems together bringing the needed oxygen, nutrients, hormones and other important molecules and removing the waste.

Blood is considered a connective tissue for two basic reasons: 

1. embryologically, it has the same origin (mesodermal) as do the other connective tissue types and 

2. Blood connects the body systems together bringing the needed oxygen, nutrients, hormones and other signaling molecules, and removing the wastes.