What blood does
Three functions, and the first of them is the one that makes blood a connective tissue rather than just a liquid.
Transport of substances
Blood tissue transports respiratory gases, nutrients, excretory substances and hormones to the relevant organs.
Protection
The white blood cells of blood tissue destroy germs, by phagocytosis and by producing antibodies, and so protect the body.
Maintaining homeostasis
Keeping the internal conditions of the body steady — temperature, water content, the concentration of dissolved substances — within the narrow range the cells can work in.
How a liquid connects anything
The function of a connective tissue is to maintain the connection between the organs of the body. Bone does that by holding parts rigidly together. Blood does it by carrying things between them: oxygen from the lungs to every cell, hormones from a gland to the organ they act on, waste from a cell to the kidney. The connection is real, and it is made of movement rather than of structure.
Blood is the reason an organ can be anywhere
An organ does not need to sit next to the organ it works with, because blood carries the message and the materials between them. The thyroid gland can be in the neck and still control processes in every tissue in the body. Without a transport tissue every body would have to be built with its parts touching.
Transport, protect, keep steady
Blood tissue transports gases, nutrients, waste and hormones, protects the body through the white cells, and helps maintain homeostasis. Its matrix is blood plasma, and it is the only matrix the tissue’s own cells do not secrete.