What It contains
The blood contains erythrocytes ( red blood cells), leucocytes (white blood cells) and plasma. There are 3 different types of leucoytes , monocyte(macrophage), neutrophill and lynphocytes.
Erythrocytes are biconcave discs. They transport oxygen and carbon dioxide. Their shape means they have a relatively large surface area to volume ratio to speed up gas exchange. Their cytoplasm is packed with pigments of the protein haemoglobin. They have no nucleus which gives more room for haemoglobin inside them. They are small and flexible, so they can be flattened against capilary walls.
Neutrophils have small granules in the cytoplasm. These cells engulf microorganisms by phagocytosis. They have a lobed nucleus. some of the granules are lysosomes which contain emzymes that engulf and digest bacteria.
Lymphocytes have a large, darkly stained nucleus surrounded by a thin layer of clear cytoplasm. There are two kinds of lymphocytes B and T which look the same but have 2 different functions. Both are cells of the immune system. B lymphocytes produce antibodies. T lymphocytes have several functions, including cell destruction.
Monocytes are the largest type of leucocyte. They have a large bean shaped nucleus and clear cytoplasm.They spend 2-3 days in the circulatory system, then move into the tissues. Here they become macrophages engulfing microorganisms and other foreign materials
The blood transports substances
The blood transports many substances :
horemones - chemical messengers
hydration of cells
Defence against :
microbes ( either via antibodies or being engulfed)
Toxins ( by antitoxins - chemicals which nutralise toxins in your blood)